Co-reporter:Zhihui Zeng, Mingji Chen, Yongmao Pei, Seyed Ismail Seyed Shahabadi, Boyang Che, Peiyu Wang, and Xuehong Lu
ACS Applied Materials & Interfaces September 20, 2017 Volume 9(Issue 37) pp:32211-32211
Publication Date(Web):August 28, 2017
DOI:10.1021/acsami.7b07643
Flexible waterborne polyurethane (WPU)/silver nanowire (AgNW) nanocomposites with unidirectionally aligned micrometer-sized pores are fabricated using a facile freeze-drying process, and their dimensions, densities, and AgNW contents are easily controllable. The high-aspect-ratio AgNWs are well-dispersed in the nanocomposite cell walls, giving the nanocomposites good compression strength and excellent electrical conductivity even at very low densities. The large conductivity mismatch between the AgNWs and WPU also induces substantial interfacial polarization that benefits the absorption of electromagnetic (EM) waves, whereas the aligned cell walls promote multireflections of the waves in the porous architectures, further facilitating the absorption. The synergistic actions of the AgNWs, WPU, and unidirectionally aligned pores lead to ultrahigh EM shielding performance. The X-band shielding effectiveness (SE) of the nanocomposites is 64 and 20 dB at the densities of merely 45 and 8 mg/cm3, respectively, and ultrahigh surface specific SE of ∼1087 dB cm3/(g mm) is achieved with only 0.027 vol % AgNWs, demonstrating that they are promising ultralight, flexible, mechanically robust, high-performance EM shielding materials.Keywords: electromagnetic interference shielding; lightweight; nanocomposites; porous; silver nanowires;
Co-reporter:Seyed Ismail Seyed Shahabadi, Junhua Kong, and Xuehong Lu
ACS Sustainable Chemistry & Engineering April 3, 2017 Volume 5(Issue 4) pp:3148-3148
Publication Date(Web):February 15, 2017
DOI:10.1021/acssuschemeng.6b02941
Lignin is an undervalued sustainable commodity with many potential applications. In this work, we used lignin to produce noncovalently modified graphene from pristine graphite. Lignin-modified graphene (LMG) was added to waterborne polyurethane (WPU) to produce nanocomposites through a facile, aqueous-only route. Dynamic mechanical analysis shows increased storage modulus, i.e., as high as 171%, for WPU/LMG nanocomposites. Unlike unloaded WPU, WPU/LMG nanocomposite coatings show complete self-healing after only 150 s of infrared (IR) irradiation because of entropic and enthalpic contributions of LMG to self-healing. Moreover, it is revealed for the first time that although the nanocomposite coatings display two-dimensional healing behavior, at each phase the healing progresses uniaxially, which can be attributed to the interplay among viscoelastic recovery response, surface-tension-driven viscoelastic restoration, and polymer diffusion. Furthermore, WPU/LMG nanocomposites exhibit substantial improvement in UV stability owing to LMG’s preventive antioxidant activities such as UV absorption and gas impermeability, its radical scavenging properties, as well as the synergy between lignin and LMG. Finally, WPU/LMG shows decent conductance, up to 0.276 S/m, which means that our self-healable, UV-resistant films can find applications as durable corrosion-preventive or antistatic coatings.Keywords: Conductive coatings; Graphene; lignin; Multifunctional; Nanocomposites; Self-healing; UV resistance; Waterborne polyurethane;
Co-reporter:Yuliang Dong, Noreen L. Thomas, Xuehong Lu
Materials & Design 2017 Volume 134(Volume 134) pp:
Publication Date(Web):15 November 2017
DOI:10.1016/j.matdes.2017.08.033
•Zinc oxide nanoparticles are covalently bonded onto poly(vinylidene fluoride) mats as durable antibacterial agent.•The hybrid mats are combined with hydrophilic polyacrylonitrile mats to facilitate moisture transport via push-pull effect.•This is a novel, useful strategy for design of multi-functional sports textiles.The fast growing demand for advanced sportswear suitable for tropical countries has led to research on fabrics with both moisture wicking and anti-bacterial properties. In this work, to improve the water transport behaviour, dual-layer nanofibrous nonwoven mats composed of a hydrophilic polyacrylonitrile (PAN) outer layer and a hydrophobic poly(vinylidene fluoride) (PVDF) inner layer are fabricated by electrospinning. The distinct difference in surface hydrophobicity between the inner and outer layers induces a push-pull effect to transport water from the inner to the outer surface efficiently. To render an antibacterial property, zinc oxide (ZnO) nanoparticles are covalently attached to the PVDF nanofibers. The good anti-wash properties and anti-bacterial function of the ZnO-PDVF/PAN dual layer mats are demonstrated.Download high-res image (284KB)Download full-size image
Co-reporter:Huiqing Wu, Yuejun Liu, Long Mao, Chunhai Jiang, Jiaming Ang, Xuehong Lu
Journal of Membrane Science 2017 Volume 532(Volume 532) pp:
Publication Date(Web):15 June 2017
DOI:10.1016/j.memsci.2017.03.010
•TiO2-PDA was prepared using PDA as adhesive substrate and free-radical scavenger.•Hybrid membrane with 0.8 wt% TiO2-PDA possesses the optimal performance.•TiO2-PDA/PSf presents good self-cleaning and self-protection properties under UV.To prepare an ultrafiltration membrane with simultaneous self-cleaning and self-protection abilities, TiO2-polydopamine (PDA) nanohybrid are facilely prepared and used to functionalize polysulfone (PSf) membrane matrix. In the TiO2-PDA nanohybrid, PDA spheres acts as an adhesive substrate to hold densely covered photocatalytic TiO2 nanoparticles, and also serves as a free-radical scavenger to protect PSf membrane against the damage by free radicals produced by TiO2 during UV exposure treatment. The spherical-shaped TiO2-PDA can be easily doped into PSf membrane via phase inversion method, which allows the hydrophilic TiO2-PDA spheres migrating to the hydrophobic PSf surface and benefiting the antifouling ability. As a result, the TiO2-PDA/PSf hybrid membrane exhibits excellent overall performances in separation efficiency, remarkable self-cleaning property and performance stability under UV irradiation, in comparison with PSf and TiO2/PSf membrane. The influence of TiO2-PDA content on the membrane properties is also investigated, and it is found the hybrid membrane with 0.8 wt% TiO2-PDA possesses the optimal performance.Download high-res image (356KB)Download full-size image
Co-reporter:Zhihui Zeng;Seyed Ismail Seyed Shahabadi;Boyang Che;Youfang Zhang;Chenyang Zhao
Nanoscale (2009-Present) 2017 vol. 9(Issue 44) pp:17396-17404
Publication Date(Web):2017/11/16
DOI:10.1039/C7NR05106A
Nanocomposite strain sensors composed of compressed honeycomb-like reduced-graphene-oxide (RGO) foam embedded in polydimethylsiloxane are facilely fabricated via unidirectional freeze-drying and simple mechanical compression. The microstructural characteristics of the nanocomposites endow the sensors with excellent flexibility, high stretchability and sensing sensitivity, as well as anisotropic mechanical and sensing performance when stretched along directions vertical and parallel to the aligned RGO cell walls (defined as transverse and longitudinal directions, respectively). In particular, the compression of the aligned RGO foam into a thinner film results in more conductive pathways, greatly increasing the sensing sensitivity of the nanocomposite sensors. The sensors stretched along the transverse direction show an outstanding combination of high stretchability over 120%, wide linear sensing region of 0–110% and high strain sensing sensitivity with a gauge factor of around 7.2, while even higher strain sensitivity and lower sensing strain are exhibited along the longitudinal direction. Sensitive and reliable detection of human motions is also successfully demonstrated using these light-weight thin-film nanocomposite sensors.
Co-reporter:Dan Zhou;Boyang Che
Journal of Materials Chemistry C 2017 vol. 5(Issue 7) pp:1758-1766
Publication Date(Web):2017/02/16
DOI:10.1039/C6TC05216A
In this article, we report, for the first time, the preparation of polyaniline/manganese dioxide (PANI/MnO2) hybrid electrochromic films via one-pot potentiostatically anodic electrodeposition from an aqueous solution containing aniline and manganese sulfate. In the one-pot deposition process, electropolymerization of aniline and electrodeposition of MnO2 occur simultaneously, while some of the resultant MnO2 can act as an oxidizer to further initiate chemical polymerization of aniline, facilitating rapid growth of the hybrid films. This unique deposition mechanism gives rise to significant differences between the hybrid and neat PANI films in morphology, structures, electrochemical and electrochromic properties. Compared with neat PANI films, the hybrid film with optimal MnO2 content shows much higher optical contrast, coloration efficiency, and cycling stability. The excellent performance of the hybrid film can be attributed to its unique porous morphology with interconnected small nanoparticles, and donor–acceptor interactions between PANI and MnO2.
Co-reporter:Junhua Kong, Seyed Ismail Seyed Shahabadi and Xuehong Lu
Nanoscale 2016 vol. 8(Issue 4) pp:1770-1788
Publication Date(Web):22 Dec 2015
DOI:10.1039/C5NR06711A
Polydopamine (PDA), a mussel adhesive-inspired biomimetic polymer, has attracted tremendous attention owing to its extremely versatile adhesion properties, facile aqueous coating process, capability of self-assembly to form nanostructures, and abundant surface functional groups for secondary modification. PDA is also a fantastic carbon source because it gives nitrogen (N)-doped graphite-like carbon in high yield, and the carbonized PDA (C-PDA) thin coatings have similar properties to those of N-doped multilayered graphene, i.e., they exhibit high electrical conductivity, and good electrochemical and mechanical properties. In comparison with other carbon sources, an outstanding feature of PDA lies in its ease of integration with inorganic nanostructures and capability for easy tailoring the structure and morphology of the resultant composite nanostructures. In this article, different routes for the preparation of C-PDA-based composite nanostructures, such as carbon/metal oxide and carbon/Si hollow, mesoporous, core–shell, yolk–shell nanostructures, are introduced with typical examples. The structures, morphologies and properties of the C-PDA-based composite nanostructures are also reviewed, and their potential applications in various engineering fields, such as energy storage, solar water splitting, flexible electronics, catalysis, sensing and environmental engineering, are highlighted. Finally a future outlook for this fascinating composite-nanostructure enabler is also presented.
Co-reporter:Chenyang Zhao, Xu Wang, Junhua Kong, Jia Ming Ang, Pooi See Lee, Zhaolin Liu, and Xuehong Lu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 3) pp:2372
Publication Date(Web):January 8, 2016
DOI:10.1021/acsami.5b11492
In this article, a simple self-assembly strategy for fabricating van der Waals heterostructures from isolated two-dimensional atomic crystals is presented. Specifically, dopamine (DOPA), an excellent self-assembly agent and carbon precursor, was adsorbed on exfoliated MoS2 monolayers through electrostatic interaction, and the surface-modified monolayers self-assembled spontaneously into DOPA-intercalated MoS2. The subsequent in situ conversion of DOPA to highly conductive nitrogen-doped graphene (NDG) in the interlayer space of MoS2 led to the formation of a novel NDG/MoS2 nanocomposite with well-defined alternating structure. The NDG/MoS2 was then studied as an anode for lithium-ion batteries (LIBs). The results show that alternating arrangement of NDG and MoS2 triggers synergistic effect between the two components. The kinetics and cycle life of the anode are greatly improved due to the enhanced electron and Li+ transport as well as the effective immobilization of soluble polysulfide by NDG. A reversible capacity of more than 460 mAh/g could be delivered even at 5 A/g. Moreover, the abundant voids created at the MoS2–NDG interface also accommodate the volume change during cycling and provide additional active sites for Li+ storage. These endow the NDG/MoS2 heterostructure with low charge-transfer resistance, high sulfur reservation, and structural robustness, rendering it an advanced anode material for LIBs.Keywords: dopamine; heterostructure; lithium-ion batteries; molybdenum disulfide (MoS2); self-assembly
Co-reporter:Han Ling, Guoqiang Ding, Daniel Mandler, Pooi See Lee, Jianwei Xu and Xuehong Lu
Chemical Communications 2016 vol. 52(Issue 60) pp:9379-9382
Publication Date(Web):21 Jun 2016
DOI:10.1039/C6CC03813A
An aqueous suspension of WO3/poly(4-(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid) (PEDTS) hybrid nanoparticles (NPs) is prepared by air-assisted oxidative polymerization and simultaneous attachment of PEDTS on WO3-NPs, and used for electrochromic (EC) film fabrication via air-brush spraying. The hybrid EC device exhibits enhanced EC properties compared to the ones based on WO3-NP or PEDTS alone.
Co-reporter:Fenggui Chen, Wanshuang Liu, Seyed Ismail Seyed Shahabadi, Jianwei Xu, and Xuehong Lu
ACS Sustainable Chemistry & Engineering 2016 Volume 4(Issue 9) pp:4997
Publication Date(Web):July 26, 2016
DOI:10.1021/acssuschemeng.6b01369
Lignin is an attractive renewable reinforcing agent for polyolefins and also a promising low-cost antioxidant for polymers. It, however, exhibits poor compatibility with nonpolar polymers. In this work, alkali lignin was freeze-dried to achieve sheet-like morphology and then incorporated into polypropylene (PP) by melt compounding. Owing to the significantly increased interfacial area and improved dispersion, with the addition of only 2 wt % freeze-dried lignin, the PP/lignin composites show much enhanced tensile mechanical properties, including a moderately improved Young’s modulus and almost doubled elongation at break compared with those of neat PP. The enhancements brought by the sheet-like lignin are far more impressive than those achieved with the same amount of as-received lignin. The composites with the freeze-dried lignin also have rough fractured surfaces with fiber pull-out near the interface, revealing a significant toughening effect of the lignin, which can be attributed to the crazing near the interface, and enhanced relaxation in PP-lignin interphase as evidenced by the reduced Tg. Furthermore, the large interfacial area also drastically improves the antioxidant effect of lignin, greatly slowing the UV-induced and thermo-oxidative degradation of PP. After 2 weeks of intense UV exposure, neat PP becomes very brittle with its yield strain reduced to about 37% of its original value, whereas the yield strain of the composite with 2 wt % sheet-like lignin is almost unchanged, demonstrating the excellent free-radical scavenger effect of the lignin.Keywords: Antioxidant; Freeze-drying; Lignin; Polypropylene; Sheet-like; Toughness
Co-reporter:Jia Ming Ang, Yonghua Du, Boon Ying Tay, Chenyang Zhao, Junhua Kong, Ludger Paul Stubbs, and Xuehong Lu
Langmuir 2016 Volume 32(Issue 36) pp:9265-9275
Publication Date(Web):August 22, 2016
DOI:10.1021/acs.langmuir.6b02331
We report one-pot synthesis of Fe(III)–polydopamine (PDA) complex nanospheres, their structures, morphology evolution, and underlying mechanism. The complex nanospheres were synthesized by introducing ferric ions into the reaction mixture used for polymerization of dopamine. It is verified that both the oxidative polymerization of dopamine and Fe(III)–PDA complexation contribute to the “polymerization” process, in which the ferric ions form coordination bonds with both oxygen and nitrogen, as indicated by X-ray absorption fine-structure spectroscopy. In the “polymerization” process, the morphology of the complex nanostructures is gradually transformed from sheetlike to spherical at the feed Fe(III)/dopamine molar ratio of 1/3. The final size of the complex spheres is much smaller than its neat PDA counterpart. At higher feed Fe(III)/dopamine molar ratios, the final morphology of the “polymerization” products is sheetlike. The results suggest that the formation of spherical morphology is likely to be driven by covalent polymerization-induced decrease of hydrophilic functional groups, which causes reself-assembly of the PDA oligomers to reduce surface area. We also demonstrate that this one-pot synthesis route for hybrid nanospheres enables the facile construction of carbonized PDA (C-PDA) nanospheres uniformly embedded with Fe3O4 nanoparticles of only 3–5 nm in size. The C-PDA/Fe3O4 nanospheres exhibit catalytic activity toward oxygen reduction reaction and deliver a stable discharge voltage for over 200 h when utilized as the cathode in a primary Zn–air battery and are also good recyclable catalyst supports.
Co-reporter:Rui Zhou, Wanshuang Liu, Xiayin Yao, Yew Wei Leong and Xuehong Lu
Journal of Materials Chemistry A 2015 vol. 3(Issue 31) pp:16040-16049
Publication Date(Web):30 Jun 2015
DOI:10.1039/C5TA02154E
In this article, it is demonstrated that the electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF–HFP)) nanofibrous mat functionalized with (3-aminopropyl)triethoxysilane is a versatile platform for the fabrication of hybrid nanofibrous mats by covalently attaching various types of inorganic oxide nanoparticles on the nanofiber surface via a sol–gel process. In particular, SiO2-on-P(VDF–HFP) nanofibrous mats synthesized using this method is an excellent ionic liquid (IL) host for electrolyte applications. The IL-based electrolytes in the form of free-standing mats are obtained by immersing SiO2-on-P(VDF–HFP) mats in two types of liquid electrolytes, namely LiClO4/1-butyl-3-methylimidazolium tetrafluoroborate and bis(trifluoromethane)sulfonimide lithium salt/1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. It is found that the surface attached SiO2 nanoparticles can effectively serve as salt dissociation promoters by interacting with the anions of both ILs and lithium salts through Lewis acid–base interactions. They dramatically enhance the ionic conductivity and lithium transference number of the electrolytes. In addition, better compatibility of the electrolytes with lithium electrodes is also observed in the presence of surface-attached SiO2. Using IL-loaded SiO2-on-P(VDF–HFP) nanofibrous mats as the electrolytes, electrochromic devices display higher transmittance contrast, while Li/LiCoO2 batteries show significantly improved C-rate performance and cycling stability. This class of novel non-volatile electrolytes with high ionic conductivity also has the potential to be used in other electrochemical devices.
Co-reporter:Wanshuang Liu, Chenyang Zhao, Rui Zhou, Dan Zhou, Zhaolin Liu and Xuehong Lu
Nanoscale 2015 vol. 7(Issue 21) pp:9919-9926
Publication Date(Web):30 Apr 2015
DOI:10.1039/C5NR01891A
In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 ± 0.08 mg mL−1, which is much higher than the typical reported concentrations (<1.0 mg mL−1) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved electrochemical performance compared with the pristine MoS2 mineral because of the enhanced ion and electron transfer kinetics. This facile, scalable and eco-friendly aqueous-based process in combination with renewable and ultra-low-cost lignin opens up possibilities for large-scale fabrication of MoS2-based nanocomposites and devices. Moreover, herein we demonstrate that AL is also an excellent surfactant for exfoliation of many other types of layered materials, including graphene, tungsten disulfide and boron nitride, in water, providing rich opportunities for a wider range of applications.
Co-reporter:Dan Zhou, Liping Yang, Linghui Yu, Junhua Kong, Xiayin Yao, Wanshuang Liu, Zhichuan Xu and Xuehong Lu
Nanoscale 2015 vol. 7(Issue 4) pp:1501-1509
Publication Date(Web):03 Dec 2014
DOI:10.1039/C4NR06366J
In this work, a series of hollow carbon nanospheres simultaneously doped with N and Fe-containing species are prepared by Fe3+-mediated polymerization of dopamine on SiO2 nanospheres, carbonization and subsequent KOH etching of the SiO2 template. The electrochemical properties of the hollow nanospheres as nonprecious-metal electrocatalysts for oxygen reduction reaction (ORR) are characterized. The results show that the hollow nanospheres with mesoporous N-doped carbon shells of ∼10 nm thickness and well-dispersed Fe3O4 nanoparticles prepared by annealing at 750 °C (Fe/N/C HNSs-750) exhibit remarkable ORR catalytic activity comparable to that of a commercial 20 wt% Pt/C catalyst, and high selectivity towards 4-electron reduction of O2 to H2O. Moreover, it displays better electrochemical durability and tolerance to methanol crossover effect in an alkaline medium than the Pt/C. The excellent catalytic performance of Fe/N/C HNSs-750 towards ORR can be ascribed to their high specific surface area, mesoporous morphology, homogeneous distribution of abundant active sites, high pyridinic nitrogen content, graphitic nitrogen and graphitic carbon, as well as the synergistic effect of nitrogen and iron species for catalyzing ORR.
Co-reporter:Junhua Kong, Chenyang Zhao, Yuefan Wei, and Xuehong Lu
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 43) pp:24279
Publication Date(Web):October 13, 2015
DOI:10.1021/acsami.5b07950
In this work, solid, hollow, and porous carbon nanofibers (SNFs, HNFs, and PNFs) were used as hosts to grow MoS2 nanosheets hydrothermally. The results show that the nanosheets on the surface of SNFs and HNFs are comprised of a few grains stacked together, giving direct carbon–MoS2 contact for the first grain and indirect contact for the rest. In contrast, the nanosheets inside of PNFs are of single-grain size and are distributed evenly in the mesopores of PNFs, providing efficient MoS2–carbon contact. Furthermore, the nanosheets grown on the polydopamine-derived carbon surface of HNFs and PNFs have larger interlayer spacing than those grown on polyacrylonitrile-derived carbon surface. As a result, the MoS2 nanosheets in PNFs possess the lowest charge-transfer resistance, the most accessible active sites for lithiation/delithiation, and can effectively buffer the volume variation of MoS2, leading to its best electrochemical performance as a lithium-ion battery anode among the three. The normalized reversible capacity of the MoS2 nanosheets in PNFs is about 1210 mAh g–1 at 100 mA g–1, showing the effective utilization of the electrochemical activity of MoS2.Keywords: carbon nanofibers; electrospinning; lithium-ion batteries; MoS2; polydopamine
Co-reporter:Rui Zhou, Wanshuang Liu, Yew Wei Leong, Jianwei Xu, and Xuehong Lu
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 30) pp:16548
Publication Date(Web):July 13, 2015
DOI:10.1021/acsami.5b04034
Electrospun polymer nanofibrous mats loaded with ionic liquids (ILs) are promising nonvolatile electrolytes with high ionic conductivity. The large cations of ILs are, however, difficult to diffuse into solid electrodes, making them unappealing for application in some electrochemical devices. To address this issue, a new strategy is used to introduce proton conduction into an IL-based electrolyte. Poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) copolymer is functionalized with sulfonic acid through covalent attachment of taurine. The sulfonic acid-grafted P(VDF-HFP) electrospun mats consist of interconnected nanofibers, leading to remarkable improvement in dimensional stability of the mats. IL-based polymer electrolytes are prepared by immersing the modified mats in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4–). It is found that the SO3– groups can have Lewis acid–base interactions with the cations (BMIM+) of IL to promote the dissociation of ILs, and provide additional proton conduction, resulting in significantly improved ionic conductivity. Using this novel electrolyte, polyaniline-based electrochromic devices show higher transmittance contrast and faster switching behavior. Furthermore, the sulfonic acid-grafted P(VDF-HFP) electrospun mats can also be lithiated, giving additional lithium ion conduction for the IL-based electrolyte, with which Li/LiCoO2 batteries display enhanced C-rate performance.Keywords: electrochromic device; electrolyte; ionic liquid; lithium-ion battery; sulfonic acid
Co-reporter:Wanshuang Liu, Rui Zhou, Dan Zhou, Guoqiang Ding, Jie Miin Soah, Chee Yoon Yue, Xuehong Lu
Carbon 2015 Volume 83() pp:188-197
Publication Date(Web):March 2015
DOI:10.1016/j.carbon.2014.11.036
In this work, graphene is facilely prepared by direct exfoliation of graphite in aqueous media with the assistance of alkali lignin (AL). The graphite is successfully exfoliated into single- and multi-layer graphene, with about 20% monolayer ones, and the concentration of graphene in the aqueous dispersions can reach 0.65 ± 0.03 mg mL−1. The nanosheets are stabilized in the dispersions owing to π–π interaction between the graphene and AL, and the electrostatic repulsion between negative charged AL, as verified by fluorescence and zeta-potential measurements. The results also show that there are very few defects in the basil-plane of the graphene so that the free-standing graphene films prepared from the dispersions exhibit good electrical conductivity. Finally, the addition of only 0.1 wt% such graphene sheets to an epoxy resin gives 15%, 49%, and 97% enhancement in tensile strength, critical stress intensity factor and critical strain energy release rate, respectively.
Co-reporter:Han Ling, Liang Liu, Pooi See Lee, Daniel Mandler, Xuehong Lu
Electrochimica Acta 2015 Volume 174() pp:57-65
Publication Date(Web):20 August 2015
DOI:10.1016/j.electacta.2015.05.147
Layer-by-layer assembly method is employed to fabricate multilayer hybrid films based on poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) and tungsten oxide nanoparticles (WO3 NPs). Polyethylenimine (PEI) is deposited in between to introduce electrostatic force between the components. In the hybrid films, randomly oriented disk-like WO3 NPs are homogeneously distributed in the polymers and form an interdigitated structure. This very rough surface morphology hinders the formation of a continuous PEI layer between the electrochromic layers. Owing to the efficient charge transfer between the two active components and complementary electrical conductivity of the two components in the redox switching process, the coloration efficiency of the hybrid film is significantly improved to 117.7 cm2/C at wavelength of 633 nm. The underlying mechanism for the enhancement is verified by scanning electrochemical microscopic studies through probing the conductivity changes of PEDOT:PSS, WO3-NP and hybrid films under various applied potentials.Remarkably enhanced coloration efficiency is achieved in PEDOT:PSS/WO3-NPs LBL hybrid films compared with single component LBL films, owing to the efficient charge transfer process studied through probing the conductivity change of PEDOT:PSS, WO3-NP and hybrid films in redox switching process by scanning electrochemical microscopy.
Co-reporter:Junhua Kong, Xiayin Yao, Yuefan Wei, Chenyang Zhao, Jia Ming Ang and Xuehong Lu
RSC Advances 2015 vol. 5(Issue 18) pp:13315-13323
Publication Date(Web):19 Jan 2015
DOI:10.1039/C4RA16460A
In this work, highly mesoporous carbon nanofibers in free-standing mat form are successfully fabricated by single-spinneret electrospinning of polystyrene (PS) followed by coating the porous PS nanofibers via in situ polymerization of dopamine and subsequent annealing. The pores inside the nanofibers are mainly in the range of 10–50 nm and interconnected to each other, forming nanochannels. ZnFe2O4 crystals can then be grown from the nanofibers via a solution route. Strikingly, ZnFe2O4 nanoneedles are formed, which have diameter and length of about 8 nm and 70 nm, respectively, and are located evenly not only on the surface of the nanofibers but also inside the nanochannels. The ZnFe2O4/carbon composite nanofibers exhibit excellent cyclability and rate performance as anodes of lithium ion batteries (LIBs), in which the ZnFe2O4 nanoneedles are the major active component with normalized capacity of 1000–1700 mA h g−1 at 0.1 A g−1 and 560 mA h g−1 at 5 A g−1, respectively. The excellent properties can be ascribed to the very small diameter of the nanoneedles that ensures complete conversion reactions and alloying/de-alloying between Zn and lithium, the good contact of the nanoneedles with polydopamine-derived N-doped graphitic carbon that offer efficient electrical conduction, and the nanochannels that allow facile transport of the electrolyte and lithium ions.
Co-reporter:Ching Mui Cho;Wei Teng Neo;Dr. Qun Ye; Xuehong Lu;Dr. Jianwei Xu
ChemPlusChem 2015 Volume 80( Issue 8) pp:1306-1311
Publication Date(Web):
DOI:10.1002/cplu.201500192
Abstract
A series of dithienothiophene-based electrochromic polymers are synthesized by a Stille coupling reaction of 2,6-bis(trimethylstannyl)dithieno[3,2-b:2′,3′-d]thiophene, 2,5-dibromo-3,4-bis(dodecyloxy)thiophene, and tris(4-bromophenylamine). The resulting polymers have high molecular weights in the range of 59 200 to 81 300 g mol−1, and good solubility in common organic solvents. The polymer films are purple/red in neutral states and gradually become gray when oxidized to an intermediate state and blue when fully oxidized. Incorporation of triphenylamine into the polymer chains has resulted in a significant increase in the redox stability, which renders this a potential method to create high-performance electrochromic polymers.
Co-reporter:Junhua Kong, Chenyang Zhao, Yuefan Wei, Si Lei Phua, Yuliang Dong and Xuehong Lu
Journal of Materials Chemistry A 2014 vol. 2(Issue 36) pp:15191-15199
Publication Date(Web):17 Jul 2014
DOI:10.1039/C4TA02813A
In this work, unique carbonaceous nanocups, densely attached on a free-standing hollow microfibrous mat, were prepared via a mussel-inspired biomimetic polydopamine (PDA)-coating process using electrospun porous microfibers as the templates, followed by annealing. Electron microscopic studies show that the diameters and depths of the ellipsoid-shaped nanocups are in the range of a few hundred nanometers, and they have small openings of less than 100 nm, allowing the cups to act as nano-chambers to host other functional materials as well as nano-reactors for the synthesis of embedded nanostructures. To demonstrate the functions of such a unique hollow structure, the nanocups were used to host a MoS2 precursor, and through hydrothermal treatment, MoS2 nanosheets were effectively trapped in the nanocups. The MoS2-in-nanocups were used as an anode in lithium ion batteries. Good cyclability and excellent rate capacity (around 520 mA h g−1 at 2 A g−1) were achieved owing to the efficient charge transport provided by the good contact of the MoS2 nanosheets with the conductive nanocups and surrounding electrolyte. The nanocups could also act as buffering chambers to effectively accommodate the volume expansion of MoS2 during cycling.
Co-reporter:Junhua Kong, Yuefan Wei, Chenyang Zhao, Meng Yew Toh, Wu Aik Yee, Dan Zhou, Si Lei Phua, Yuliang Dong and Xuehong Lu
Nanoscale 2014 vol. 6(Issue 8) pp:4352-4360
Publication Date(Web):06 Feb 2014
DOI:10.1039/C3NR04308H
In this work, bundles of rutile TiO2 nanoneedles/nanorods are hydrothermally grown on carbon nanofibers (CNFs), forming free-standing mats consisting of three dimensional hierarchical nanostructures (TiO2-on-CNFs). Morphologies and structures of the TiO2-on-CNFs are studied using a field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and thermogravimetric analyzer (TGA). Their electrochemical properties as electrodes in lithium ion batteries (LIBs) are investigated and correlated with the morphologies and structures. It is shown that the lateral size of the TiO2 nanoneedles/nanorods ranges from a few nanometers to tens of nanometers, and increases with the hydrothermal temperature. Small interspaces are observed between individual nanoneedles/nanorods, which are due to the diverging arrangement of nanoneedles/nanorods induced by growing on the convex surface of nanocylinders. It is found that the growth process can be divided into two stages: initial growth on the CNF surface and further growth upon re-nucleation on the TiO2 bundles formed in the initial growth stage. In order to achieve good electrochemical performance in LIBs, the size of the TiO2 nanostructures needs to be small enough to ensure complete alloying and fast charge transport, while the further growth stage has to be avoided to realize direct attachment of TiO2 nanostructures on the CNFs, facilitating electron transport. The sample obtained after hydrothermal treatment at 130 °C for 2 h (TiO2-130-2) shows the above features and hence exhibits the best cyclability and rate capacity among all samples; the cyclability and rate capacity of TiO2-130-2 are also superior to those of other rutile TiO2-based LIB electrodes.
Co-reporter:Yuliang Dong, Junhua Kong, Si Lei Phua, Chenyang Zhao, Noreen L. Thomas, and Xuehong Lu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 16) pp:14087
Publication Date(Web):July 14, 2014
DOI:10.1021/am503417w
In this article, liquid moisture transport behaviors of dual-layer electrospun nanofibrous mats are reported for the first time. The dual-layer mats consist of a thick layer of hydrophilic polyacrylonitrile (PAN) nanofibers with a thin layer of hydrophobic polystyrene (PS) nanofibers with and without interpenetrating nanopores, respectively. The mats are coated with polydopamine (PDOPA) to different extents to tailor the water wettability of the PS layer. It is found that with a large quantity of nanochannels, the porous PS nanofibers exhibit a stronger capillary effect than the solid PS nanofibers. The capillary motion in the porous PS nanofibers can be further enhanced by slight surface modification with PDOPA while retaining the large hydrophobicity difference between the two layers, inducing a strong push–pull effect to transport water from the PS to the PAN layer.Keywords: capillary motion; electrospinning; moisture transport; porous nanofibers; push−pull; wetting
Co-reporter:Chenyang Zhao, Junhua Kong, Xiayin Yao, Xiaosheng Tang, Yuliang Dong, Si Lei Phua, and Xuehong Lu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 9) pp:6392
Publication Date(Web):April 4, 2014
DOI:10.1021/am4058088
In this work, highly flexible MoS2-based lithium-ion battery anodes composed of disordered thin MoS2 nanoflakes encapsulated in amorphous carbon nanofibrous mats were fabricated for the first time through hydrothermal synthesis of graphene-like MoS2, followed by electrospinning and carbonization. X-ray diffraction as well as scanning and transmission electron microscopic studies show that the as-synthesized MoS2 nanoflakes have a thickness of about 5 nm with an expanded interlayer spacing, and their structure and morphology are well-retained after the electrospinning and carbonization. At relatively low MoS2 contents, the nanoflakes are dispersed and well-embedded in the carbon nanofibers. Consequently, excellent electrochemical performance, including good cyclability and high rate capacity, was achieved with the hybrid nanofibrous mat at the MoS2 content of 47%, which may be attributed to the fine thickness and multilayered structure of the MoS2 sheets with an expanded interlayer spacing, the good charge conduction provided by the high-aspect-ratio carbon nanofibers, and the robustness of the nanofibrous mat.Keywords: carbon nanofibers; electrospinning; flexible anode; hydrothermal; lithium-ion battery; molybdenum disulfide (MoS2);
Co-reporter:Wanshuang Liu, Rui Zhou, Hwee Li Sally Goh, Shu Huang, and Xuehong Lu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 8) pp:5810
Publication Date(Web):March 24, 2014
DOI:10.1021/am500642n
A novel approach to toughen epoxy resin with lignin, a common waste material from the pulp and paper industry, is presented in this article. First, carboxylic acid-functionalized alkali lignin (AL-COOH) was prepared and subsequently incorporated into anhydride-cured epoxy networks via a one-pot method. The results of mechanical tests show that covalent incorporation of rigid AL-COOH into epoxy networks can significantly toughen the epoxy matrix without deteriorating its tensile strength and modulus. The addition of 1.0 wt % AL-COOH gives increases of 68 and 164% in the critical stress intensity factor (KIC) and critical strain energy release rate (GIC), respectively, relative to that of neat epoxy. This article opens up the possibility of utilizing low-cost and renewable lignin feedstocks as effective toughening agents for thermoset polymers.Keywords: epoxy resin; lignin; polymer additive; toughening;
Co-reporter:Xiayin Yao, Chenyang Zhao, Junhua Kong, Huiqing Wu, Dan Zhou and Xuehong Lu
Chemical Communications 2014 vol. 50(Issue 93) pp:14597-14600
Publication Date(Web):30 Sep 2014
DOI:10.1039/C4CC07350A
Polydopamine-derived carbon (C-PDA) nanospheres embedded with zinc ferrite (ZnFe2O4) are synthesized by in situ polymerization of dopamine with zinc and iron species followed by carbonization. The composite nanospheres contain ZnFe2O4 nanoparticles ∼8 nm in size well dispersed in porous C-PDA. The unique structure and morphology endow the nanospheres with excellent rate capability and cycling stability for use as anodes in lithium-ion batteries.
Co-reporter:Chenyang Zhao, Junhua Kong, Liping Yang, Xiayin Yao, Si Lei Phua and Xuehong Lu
Chemical Communications 2014 vol. 50(Issue 68) pp:9672-9675
Publication Date(Web):30 Jun 2014
DOI:10.1039/C4CC04099F
Single-layer MoS2–carbon nanocomposites (SLMoS2/C) are facilely prepared via a dopamine (DOPA)–MoVI complexation-assisted approach. The large interlayer spacing, sandwich structure and crumpled nanosheet morphology of SLMoS2/C render it excellent electrochemical performances as a lithium-ion battery anode, showing a reversible capacity of 500 mA h g−1 at a discharge rate of 5 A g−1.
Co-reporter:Guoqiang Ding, Hui Zhou, Jianwei Xu and Xuehong Lu
Chemical Communications 2014 vol. 50(Issue 6) pp:655-657
Publication Date(Web):07 Nov 2013
DOI:10.1039/C3CC47732K
Selective detection of cyanide anions is realized via electrofluorochromism of a benzothiadiazole-containing conjugated copolymer because oxidative fluorescence quenching induced by positive potentials can be significantly weakened by interaction between nucleophilic cyanide and electron-deficient benzothiadiazole.
Co-reporter:Xiaosheng Tang, Xiayin Yao, Yu Chen, Bohang Song, Dan Zhou, Junhua Kong, Chenyang Zhao, Xuehong Lu
Journal of Power Sources 2014 Volume 257() pp:90-95
Publication Date(Web):1 July 2014
DOI:10.1016/j.jpowsour.2014.01.107
•CuInZnS-decorated graphene nanosheets were used as LIB anode materials for the first time.•It was demonstrated that CuInZnS has multiple alloying reactions with lithium ions.•The CuInZnS-decorated graphene anode showed enhanced rate capability and cycling stability.CuInZnS-decorated graphene (CIZS@graphene) is prepared via a hydrothermal process and investigated as an anode material for lithium-ion batteries. CIZS@graphene exhibits an initial discharge capacity of 1623 mA.h g−1 at 100 mA g−1, and at a high rate of 2000 mA g−1 its reversible capacity is steadily increased from 389 mA h g−1 to 494 mA h g−1 in 480 cycles, demonstrating promising stable cycling performance at high rates. Electrochemical impedance spectroscopic studies show that charge-transfer resistances of CIZS@graphene reduces after cycling at high rates, justifying the excellent high-rate performance and stability of the CIZS@graphene anode.
Co-reporter:Xiayin Yao, Junhua Kong, Dan Zhou, Chenyang Zhao, Rui Zhou, Xuehong Lu
Carbon 2014 Volume 79() pp:493-499
Publication Date(Web):November 2014
DOI:10.1016/j.carbon.2014.08.007
Mesoporous zinc ferrite (ZnFe2O4)/graphene composites are synthesized using a facile ambient-pressure method, i.e., co-precipitation of metal cations onto graphene oxide followed by solid state reaction to yield ZnFe2O4 nanoparticles anchored on reduced graphene oxide. The resultant ZnFe2O4/graphene composites have large specific surface area with mesopores, and the size of the ZnFe2O4 nanoparticles is less than 20 nm. When the composites are employed as an anode material for lithium-ion batteries, it exhibits superior electrochemical performances in term of high reversible capacity, good cyclic performance and excellent rate capability. Its reversible discharge capacities can be maintained at 870 mAh/g at 1.0 A/g for 100 cycles and consecutively 713 mAh/g at 2.0 A/g for another 100 cycles. Moreover, other graphene-based composites containing ferrites, such as cobalt ferrite and nickel ferrite, are also synthesized with this generic strategy which is promising for large-scale production of lithium-ion battery anode materials.
Co-reporter:Rui Zhou, Kumari Pallathadka Pramoda, Wanshuang Liu, Dan Zhou, Guoqiang Ding, Chaobin He, Yew Wei Leong, Xuehong Lu
Electrochimica Acta 2014 Volume 146() pp:224-230
Publication Date(Web):10 November 2014
DOI:10.1016/j.electacta.2014.09.065
•The well dispersed POSS-OH promotes the dissociation of both LiClO4 and BMIM+BF4−.•POSS-OH significantly increases the ionic conductivity and lithium transference number.•POSS-OH containing electrolyte improves the optical contrast of electrochromic device.Electrospun polymer nanofibrous mats loaded with ionic liquids (ILs) and lithium salts are promising non-volatile electrolytes owing to their high ionic conductivities. However, the large cations of ILs are difficult to diffuse into solid electrodes, whereas the lithium ions in ILs tend to form anionic complexes with the IL anions, reducing the number of free lithium ions. To address these issues, octa(3-hydroxy-3-methylbutyldimethylsiloxy) polyhedral oligomeric silsesquioxane (POSS-OH), which has large specific surface area and functionality number, is incorporated into electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) nanofibrous mats, and the mats are used to host LiClO4/1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4−). It is found that POSS-OH can significantly increase both ionic conductivity and lithium transference number of the electrolytes owing to the Lewis acid-base interactions of POSS-OH with ClO4− and BF4−. The electrochromic device using the hybrid mat (with 5 wt% POSS-OH) loaded with LiClO4/BMIM+BF4− as the electrolyte shows significantly improved transmittance contrast and switching time, as a result of increased number of free lithium ions.
Co-reporter:Xiayin Yao, Junhua Kong, Chenyang Zhao, Dan Zhou, Rui Zhou, Xuehong Lu
Electrochimica Acta 2014 Volume 146() pp:464-471
Publication Date(Web):10 November 2014
DOI:10.1016/j.electacta.2014.08.144
Zinc ferrite (ZnFe2O4) nanorods are synthesized using a facile and scalable method, i.e., decomposition of oxalate precursors which are obtained through a polyvinyl alcohol-assisted aqueous precipitation reaction. The ZnFe2O4 nanorods are further coated with carbon by self-polymerization of dopamine on the surfaces of the ZnFe2O4 nanorods followed by carbonization. The carbon layer on the ZnFe2O4 nanorods is homogeneous with the thickness of 3 to 5 nm. The polydopamine-derived carbon coating greatly improves the electrochemical performances of the ZnFe2O4 nanorods, especially rate capability and cycling stability. When galvanostatic diacharging/charging at 0.5 and 2 A/g, the ZnFe2O4/carbon nanorod anode can deliver reversible capacities of 805 and 504 mAh/g, respectively, whereas the ZnFe2O4 nanorod anode only delivers the capacities of 616 and 154 mAh/g, respectively. Besides, the ZnFe2O4/carbon nanorod anode shows excellent cycling stability; no obvious capacity fading is observed at the current density of 1 A/g for 100 cycles. The improved electrochemical performances could be attributed to the enhanced electron conductivity of the ZnFe2O4 nanorods with the carbon layer, which is confirmed by electrochemical impedance spectroscopy measurements and scanning electron microscopic studies of the cycled electrodes.
Co-reporter:Shu Huang, Cher Ling Toh, Liping Yang, Silei Phua, Rui Zhou, Aravind Dasari, Xuehong Lu
Composites Science and Technology 2014 Volume 93() pp:30-37
Publication Date(Web):18 March 2014
DOI:10.1016/j.compscitech.2013.12.015
This article reports the preparation of nylon 6/stacked-cup carbon nanofiber (CNF) nanocomposites via in situ anionic ring-opening polymerization partially initiated from caprolactam-functionalized CNFs. As a result of the successful functionalization of CNF surface, good dispersion of the CNFs was observed by transmission electron microscopy (TEM). Moreover, with the addition of a very small amount of CNFs, significant enhancements in tensile modulus and yield strength were achieved together with slightly improved impact resistance. The enhanced stiffness may be attributed to effective filler–matrix stress transfer induced by interfacial covalent bonds. On the other hand, SEM micrographs provided evidence for the possible unraveling of the stacked-cup CNF, which may allow the CNFs to bridge the matrix during crack propagation, hence resulting in the toughening of the nanocomposites.
Co-reporter:Xiayin Yao, Chenyang Zhao, Junhua Kong, Dan Zhou and Xuehong Lu
RSC Advances 2014 vol. 4(Issue 71) pp:37928-37933
Publication Date(Web):15 Aug 2014
DOI:10.1039/C4RA06816E
Hollow NiCo2O4 nanospheres with the outer diameter of about 60 nm and inner diameter of around 40 nm are prepared using monodisperse polydopamine spheres as the templates followed by a calcination process. The shell of the obtained NiCo2O4 is composed of nanoparticles with inter-particle spaces of below 10 nm. When they are employed as an anode in lithium-ion batteries, the hollow NiCo2O4 nanospheres with mesoporous shells exhibit superior electrochemical performances in terms of high reversible capacity, excellent rate capability and cycling stability. When galvanostatic discharging/charging at 0.2, 0.6, 1.0 and 2.0 A g−1, the anode can deliver discharge capacities as high as 1210, 1053, 923 and 659 mA h g−1, respectively. Moreover, the reversible capacity could be maintained at 695 mA h g−1 under the current density of 2.0 A g−1 for 200 cycles. These make the hollow NiCo2O4 nanospheres promising candidates for anode materials in high-energy and high-power lithium ion batteries.
Co-reporter:Si Lei Phua, Liping Yang, Shu Huang, Guoqiang Ding, Rui Zhou, Jun Heng Lew, Soo Khim Lau, Xiaowen Yuan, Xuehong Lu
European Polymer Journal 2014 Volume 57() pp:11-21
Publication Date(Web):August 2014
DOI:10.1016/j.eurpolymj.2014.04.019
•Polydopamine-modified layered double hydroxides (D-LDHs) have been synthesized.•Superior shape memory properties are achieved by incorporation of 2 wt.% D-LDH.•D-LDH interacts strongly with hard segments, promoting phase separation in PU.•The addition of D-LDH enhances the crystallization of both hard and soft segments.Two different sizes of polydopamine-coated layered double hydroxides (D-LDHs) are incorporated into polycaprolactone-based polyurethane (PU) to enhance the mechanical and shape memory properties of the PU. The results show that D-LDH interacts strongly with hard segments and hence enhancing phase separation between hard and soft segments. It is found that the tensile moduli of the PU/D-LDH nanocomposites are much higher than that of neat PU at 60 °C. In comparison with neat PU, the nanocomposite with 2 wt% of small D-LDH exhibits a 60% increase in recovery stress while shape fixity and strain recovery ratio are also improved simultaneously. This is because at low filler loading, most small D-LDH nanosheets interact with hard domains and they are not large enough to connect neighbor hard domains. They can hence reinforce the hard domains without sacrificing the elasticity of the system. Two-dimensional X-ray diffraction studies indicate that most small D-LDH nanosheets are able to rotate back from aligned state to original random state in shape recovery process, justifying the improved strain recovery ratio.Graphical abstract
Co-reporter:Xiayin Yao, Junhua Kong, Xiaosheng Tang, Dan Zhou, Chenyang Zhao, Rui Zhou and Xuehong Lu
RSC Advances 2014 vol. 4(Issue 52) pp:27488-27492
Publication Date(Web):09 Jun 2014
DOI:10.1039/C4RA02835J
Porous CoFe2O4 nanosheets, having the thickness of 30–60 nm and lateral size of several microns with numerous penetrating pores, are synthesized via thermal decomposition of (CoFe2)1/3C2O4·2H2O nanosheets, which are facilely prepared through a poly(vinyl alcohol)-assisted precipitation-cum-self-assembly process in an aqueous medium. The obtained porous CoFe2O4 nanosheets are employed as anodes in lithium-ion batteries (LIBs). The anode exhibits excellent rate capability and cycling stability. When discharging–charging at 1 A g−1 and 2 A g−1, it can deliver discharge capacities as high as 806 mA h g−1 and 648 mA h g−1, respectively, each for 200 cycles. This makes the porous CoFe2O4 nanosheets promising candidates for anode materials in high-energy and high-power LIBs.
Co-reporter:Dr. Liping Yang;Dr. Junhua Kong;Dr. Dan Zhou;Jia Ming Ang;Dr. Si Lei Phua;Dr. Wu Aik Yee;Hai Liu; Yizhong Huang; Xuehong Lu
Chemistry - A European Journal 2014 Volume 20( Issue 25) pp:7776-7783
Publication Date(Web):
DOI:10.1002/chem.201402241
Abstract
Inspired by the high transition-metal-ion content in mussel glues, and the cross-linking and mechanical reinforcement effects of some transition-metal ions in mussel threads, high concentrations of nickel(II), cobalt(II), and manganese(II) ions have been purposely introduced into the reaction system for dopamine polymerization. Kinetics studies were conducted for the Ni2+–dopamine system to investigate the polymerization mechanism. The results show that the Ni2+ ions could accelerate the assembly of dopamine oligomers in the polymerization process. Spectroscopic and electron microscopic studies reveal that the Ni2+ ions are chelated with polydopamine (PDA) units, forming homogeneous Ni2+–PDA complexes. This facile one-pot approach is utilized to construct transition-metal-ion–PDA complex thin coatings on graphene oxide, which can be carbonized to produce robust hybrid nanosheets with well-dispersed metallic nickel/metallic cobalt/manganese(II) oxide nanoparticles embedded in PDA-derived thin graphitic carbon layers. The nickel–graphene hybrid prepared by using this approach shows good catalytic properties and recyclability for the reduction of p-nitrophenol.
Co-reporter:Guoqiang Ding;Dr. TingTing Lin;Rui Zhou;Yuliang Dong;Dr. Jianwei Xu; Xuehong Lu
Chemistry - A European Journal 2014 Volume 20( Issue 41) pp:13226-13233
Publication Date(Web):
DOI:10.1002/chem.201403133
Abstract
An electrofluorochromic (EFC) conjugated copolymer (PEFC) containing carbazole and benzothiadiazole (BTD) moieties is synthesized through Suzuki coupling followed by electrochemical polymerization, resulting in a nanoporous EFC polymer electrode. The electrode exhibits high sensitivity and selectivity in the EFC detection of cyanide anions (CN−) in largely aqueous electrolyte (67 vol % water) because electrochemical oxidation of PEFC leads to significant fluorescence quenching, and the presence of different concentrations (1 to 100 μM) of CN− in the electrolyte can weaken the oxidative quenching to substantially different extents. Although PEFC is hydrophobic in the neutral state, it is converted to radical cation/dication states upon oxidation, rendering the PEFC some hydrophilicity. Moreover, its nanoporous morphology provides a large surface area and short diffusion distance, facilitating the movement of CN− in the electrolyte into the PEFC film to interact with receptors. Density functional theory calculations show that the noncovalent interaction between electron-deficient BTD and nucleophilic CN− is energy favorable in the oxidized states in both aqueous and organic media, suggesting that the specific π−–π+ interaction plays the main role in the CN− detection.
Co-reporter:Rui Zhou, Wanshuang Liu, Junhua Kong, Dan Zhou, Guoqiang Ding, Yew Wei Leong, Pramoda Kumari Pallathadka, Xuehong Lu
Polymer 2014 Volume 55(Issue 6) pp:1520-1526
Publication Date(Web):24 March 2014
DOI:10.1016/j.polymer.2014.01.047
In this work, ultrathin free-standing electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) nanofibrous mats are realized through the use of 1,3-diaminopropane as the chemical cross-linking agent. The cross-linking reaction occurs within the nanofibers as well as between the nanofibers that are in touch, forming relatively strong inter-fiber junctions and hence resulting in remarkable improvement in structural integrity of the electrospun mats with very small thickness. The chemically cross-linked electrospun mats are used as the host for 1-butyl-3-methylimidazolium tetrafluoroborate to prepare ionic liquid (IL)-based polymer electrolytes, and the effects of cross-linking on swelling and crystallization behaviors of the mats are studied. The results show that with a low degree of cross-linking, a high ionic conductivity of 2.6 mS/cm can be achieved, which is mainly due to the presence of a significant amount of free ILs in the interpenetrating pores of the mats. An electrochromic device is fabricated using this electrolyte to demonstrate the potential of the mat as IL host, especially its capability to greatly reduce IL consumption.
Co-reporter:Yuefan Wei, Junhua Kong, Liping Yang, Lin Ke, Hui Ru Tan, Hai Liu, Yizhong Huang, Xiao Wei Sun, Xuehong Lu and Hejun Du
Journal of Materials Chemistry A 2013 vol. 1(Issue 16) pp:5045-5052
Publication Date(Web):12 Feb 2013
DOI:10.1039/C3TA10499K
The modification of zinc oxide (ZnO) with silver (Ag) has proven to be an effective strategy to enhance the optical and electrical properties, in which the interactions between ZnO and Ag are critically determined by the structure and morphology of the ZnO–Ag hybrids. In order to achieve homogeneous and controllable distribution, polydopamine (PDA) was introduced via in situpolymerization to assist the decoration of ZnO nanorods (NRs) with Ag nanoparticles (NPs). Compared with pristine ZnO NRs, the light absorption is significantly enhanced for the PDA assisted Ag-decorated ZnO, which is attributed to the Ag NPs as well as the carbonized PDA thin film. Ag NPs of small size enhance the multiple/high-angle scattering from localized plasmonic effect, which increases the light path length hence traps more light. The carbonized PDA film is further beneficial to the absorption of the visible light. The Ag-decorated ZnO NRs on fluorine-doped tin oxide (FTO) coated glasses were then used as photoanodes of the photoelectrochemical (PEC) cell. The short circuit current density (JSC, 1.8 mA cm−2), maximum photo current conversion efficiency (PCE, 3.9%) and lifetime (3.07 mA cm−2 at 500 seconds) are achieved with an optimized loading of Ag nanoparticles derived from 0.01 M silver nitrate (AgNO3), which are found to be much higher than those of pristine ZnO NRs and other reported Ag–ZnO-based photoanodes. The overall PEC performance improvement is attributed to the localized plasmonic effect enhanced light harvesting as well as the facilitated charge transport and inhibition of recombination of electrons and holes from both Ag nanoparticles that act as an electron acceptor and carbonized PDA film as stabilizer and separator.
Co-reporter:Junhua Kong, Wu Aik Yee, Yuefan Wei, Liping Yang, Jia Ming Ang, Si Lei Phua, Siew Yee Wong, Rui Zhou, Yuliang Dong, Xu Li and Xuehong Lu
Nanoscale 2013 vol. 5(Issue 7) pp:2967-2973
Publication Date(Web):06 Feb 2013
DOI:10.1039/C3NR34024D
Silicon (Si) is a promising material for lithium ion battery (LIB) anodes due to its high specific capacity. To overcome its shortcomings such as insulation property and large volume change during the charge–discharge process, a novel hybrid system, Si nanoparticles encapsulated in hollow graphitized carbon nanofibers, is studied. First, electrospun polyacrylonitrile (PAN)–Si hybrid nanofibers were obtained using water as the collector. The loose nanofiber lumps suspended in water have large inter-fiber distance, allowing in situ coating of a thin layer of polydopamine (PDA), the source for graphitized carbon, uniformly throughout the system. The designed morphology and structure were then realized by etching and calcination, and the morphology and structure were subsequently verified by various analytical techniques. Electrochemical measurements show that the resulting hollow hybrid nanofibers (C-PDA–Si NFs) exhibit much better cycling stability and rate capacity than conventional C/Si nanofibers derived by electrospinning of PAN–Si followed by calcination. For instance, the capacity of C-PDA–Si NFs is as high as 72.6% of the theoretical capacity after 50 cycles, and a high capacity of 500 mA h g−1 can be delivered at a current density of 5 A g−1. The significantly improved electrochemical properties of C-PDA–Si NFs are due to the excellent electrical conductivity of the carbonized PDA (C-PDA) shell that compensates for the insulation property of Si, the high electrochemical activity of C-PDA, which has a layered structure and is N-doped, the hollow nature of the nanofibers and small size of Si nanoparticles that ensure smooth insertion–extraction of lithium ions and more complete alloying with them, as well as the buffering effect of the remaining PAN-derived carbon around the Si nanoparticles, which stabilizes the structure.
Co-reporter:Si Lei Phua, Liping Yang, Cher Ling Toh, Ding Guoqiang, Soo Khim Lau, Aravind Dasari, and Xuehong Lu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 4) pp:1302
Publication Date(Web):January 29, 2013
DOI:10.1021/am3024405
Inspired by the radical scavenging function of melanin-like materials and versatile adhesive ability of mussel-adhesion proteins, dopamine-modified clay (D-clay) was successfully incorporated into polypropylene (PP) using an amine-terminated PP oligomer as the compatibilizer. Although the PP/D-clay nanocomposites exhibit intercalated morphology, the incorporation of D-clay greatly improves the thermo-oxidative stability and UV resistance of PP owing to the strong radical scavenging ability of polydopamine (PDA) and large contact area between PP and the PDA coating on clay mineral. Moreover, the reinforcement effect brought by D-clay is fairly significant at very low clay loadings probably owing to the strong interfacial interactions between the layered silicates and the compatibilizer as well as that between the compatibilizer and the PP matrix. The work demonstrates that D-clay is a type of promising nanofiller for thermoplastics used for outdoor applications since it stabilizes and reinforces the polymers simultaneously.Keywords: clay; mechanical properties; polydopamine; polypropylene; UV resistance;
Co-reporter:Chuanxiang Chen, Guoqiang Ding, Dan Zhou, Xuehong Lu
Electrochimica Acta 2013 Volume 97() pp:112-119
Publication Date(Web):1 May 2013
DOI:10.1016/j.electacta.2013.02.138
•Poly(aniline-co-3-amino-4-hydroxybenzoic acid) (PAAHBA) was prepared.•Morphology and electrochemical activity of PAAHBA were studied.•PAAHBA film shows a nanostructured network of mass interwoven fibers.•PAAHBA film exhibits improved electrochemical properties under highly basic conditions.Poly(aniline-co-3-amino-4-hydroxybenzoic acid) was synthesized using cyclic voltammetry. The monomer concentration ratio and applied potential strongly affect the copolymerization rate and electrochemical properties of the copolymer. The results from the infrared spectrum (IR) and X-ray photoelectron spectroscopy (XPS) of the copolymer demonstrate that 3-amino-4-hydroxybenzoic acid units are incorporated into the copolymer chain and that SO42− ions can be doped into the copolymer film during the electrochemical copolymerization. The scanning electron microscopy (SEM) micrograph proves that the copolymer film has a nanostructured network of mass interwoven fibers with a diameter of 10–50 nm. The copolymer obtained at the optimum conditions exhibits excellent redox activity in a 0.30 M Na2SO4 aqueous solution (pH 11.0), which is superior to that of polyaniline itself. The improvement can be attributed to the synergistic effect of the COOH and OH functional groups in the copolymer chain.
Co-reporter:Guoqiang Ding, Ching Mui Cho, Chuanxiang Chen, Dan Zhou, Xiaobai Wang, Angeline Yan Xuan Tan, Jianwei Xu, Xuehong Lu
Organic Electronics 2013 Volume 14(Issue 11) pp:2748-2755
Publication Date(Web):November 2013
DOI:10.1016/j.orgel.2013.07.037
•Azulene–carbazole–2,1,3-benzothiadiazole conjugated terpolymers are synthesized.•Electrochemical and electrochromic properties of the terpolymers are studied.•The terpolymers exhibit high electrochromic contrast and fast switching speed.•A black-to-transmissive complementary electrochromic device is demonstrated.A series of azulene–carbazole–2,1,3-benzothiadiazole (BTD) conjugated terpolymers were synthesized and their electrochemical and electrochromic properties were studied. The terpolymer containing a small amount of BTD units exhibits significantly higher electrochromic contrast and faster switching speed than azulene–carbazole alternating copolymer under low potentials because the BTD units act as electron acceptors, facilitating electron removal from azulene and carbazole units (electron donors) upon oxidation and hence leading to a lower oxidation potential. A complementary electrochromic device (ECD) was fabricated using the terpolymer as the anodically coloring layer and poly(4-styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as the cathodically coloring layer. The ECD exhibits black-to-transmissive electrochromism as the absorption bands of the two polymers are complementary to each other in covering the whole visible region and they can be switched simultaneously under relatively low potentials.Graphical abstract
Co-reporter:Yu Bai;Liping Yang;Cher Ling Toh;Chaobin He
Macromolecular Chemistry and Physics 2013 Volume 214( Issue 3) pp:396-404
Publication Date(Web):
DOI:10.1002/macp.201200578
Abstract
Novel temperature and pH dual-responsive dendritic polyoligomeric silsesquioxane (POSS)–poly(N-isopropylacrylamide) (PNIPAm)–poly(2-hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (Tc) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter-molecular interactions and enhanced intra-molecular hydrogen bonding, whereas the Tc exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated.
Co-reporter:Cher Ling Toh;Liping Yang;Kumari Pallathadka Pramoda;Soo Khim Lau
Polymer International 2013 Volume 62( Issue 10) pp:1492-1499
Publication Date(Web):
DOI:10.1002/pi.4448
Abstract
This paper presents a new approach for the preparation of poly(ethylene terephthalate) (PET)/clay nanocomposites using surfactant-free clay (sodium montmorillonite, Na-MMT) with trisilanolphenyl polyhedral oligomeric silsesquioxane (Tsp-POSS) as dispersant. The dispersion of clay in the PET/Na-MMT/Tsp-POSS nanocomposites is enhanced over that in PET/Na-MMT by using a very small amount of Tsp-POSS, which acts as functional spacer to keep clay platelets apart and pull monomers in, and, at the same time, acts as a PET chain extender. As a result, thermomechanical properties and thermo-oxidative stability of PET/Na-MMT/Tsp-POSS are improved simultaneously compared with those of PET/organoclay nanocomposites. © 2013 Society of Chemical Industry
Co-reporter:Shu Huang, Liping Yang, Ming Liu, Si Lei Phua, Wu Aik Yee, Wanshuang Liu, Rui Zhou, and Xuehong Lu
Langmuir 2013 Volume 29(Issue 4) pp:1238-1244
Publication Date(Web):January 6, 2013
DOI:10.1021/la303855t
Clay-based functional hydrogels were facilely prepared via a bioinspired approach. Montmorillonite (clay) was exfoliated into single layers in water and then coated with a thin layer of polydopamine (PDOPA) via in situ polymerization of dopamine under basic aqueous conditions. When a small amount of ferric salt was added into aqueous suspensions of the polydopamine-coated clay (D-clay), D-clay and Fe3+ ions could rapidly self-assemble into three-dimensional networks through the formation of coordination bonds. Consequently, supramolecular hydrogels were formed at very low D-clay contents. Rheological measurements show that the D-clay/Fe3+ hydrogels exhibit fairly elastic response in low stain range, and have self-healing capability upon removal of applied large stress. More importantly, the hydrogels can be used as adsorbents to effectively remove Rhodamine 6G (Rh6G), an organic pollutant, from water. UV–vis absorption spectra of the Rh6G-loaded hydrogels show bands related to π–π stacking interactions between the aromatic moieties of PDOPA and Rh6G, confirming the formation of PDOPA/Rh6G complex on the surface of D-clay.
Co-reporter:Dan Zhou, Rui Zhou, Chuanxiang Chen, Wu-Aik Yee, Junhua Kong, Guoqiang Ding, and Xuehong Lu
The Journal of Physical Chemistry B 2013 Volume 117(Issue 25) pp:7783-7789
Publication Date(Web):June 6, 2013
DOI:10.1021/jp4021678
A series of solvent-free ionic liquid (IL)-based polymer electrolytes composed of amorphous and biodegradable poly(propylene carbonate) (PPC) host, LiClO4, and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4–) were prepared and characterized for the first time. FTIR studies reveal that the interaction between PPC chains and imidazolium cations weakens the complexation between PPC chains and Li+ ions. Thermal analysis (DSC and TGA) results show that the incorporation of BMIM+BF4– into PPC/LiClO4 remarkably decreases the glass transition temperature and improves the thermal stability of the electrolytes. AC impedance results show that the ionic conductivities of the electrolytes are significantly increased with the increase of BMIM+BF4– amount, the ambient ionic conductivity of the electrolyte at a PPC/LiClO4/BMIM+BF4– weight ratio of 1/0.2/3 is 1.5 mS/cm, and the ionic transport behavior follows the Arrhenius equation. Both PPC/LiClO4/BMIM+BF4– and PPC/BMIM+BF4– electrolytes were applied in electrochromic devices with polyaniline as the electrochromic layer. The PPC/LiClO4/BMIM+BF4–-based device exhibits much better electrochromic performance in terms of optical contrast and switching time due to the presence of much smaller cations.
Co-reporter:Junhua Kong, Yuefan Wei, Liping Yang, Wu Aik Yee, Yuliang Dong, Rui Zhou, Siew Yee Wong, Lin Ke, Xiao Wei Sun, Hejun Du, Xu Li, and Xuehong Lu
The Journal of Physical Chemistry C 2013 Volume 117(Issue 19) pp:10106-10113
Publication Date(Web):April 17, 2013
DOI:10.1021/jp3125395
Highly porous three-dimensional (3D) hierarchical nanostructures suspended in aqueous media were facilely prepared via electrospinning of polyacrylonitrile (PAN)/indium tin oxide (ITO) nanofibers and collection of the hybrid nanofibers by water, followed by hydrothermally growing ZnO nanorods from the nanofibers. The large interfiber distances facilitated the uniform growth of the ZnO nanorods throughout the whole system. The suspended PAN/ITO nanofibers process excellent light trapping capability due to their centimeter-sized dimensions and hence large light penetration path. This significantly increases the probability of multiple-reflections, leading to high absorption with almost zero transmission when the size of the sample reaches 10 mm in the direction parallel to incident light. High photocurrent was generated when the nanorods-on-nanofibers was used as a photoanode. The high photocurrent density generated by the anode can be attributed to its excellent light-trapping capability brought by the large amount of interaction sites between the ZnO nanorods and light, its large contact area with electrolyte, as well as the conduction path constructed by high-content ITO nanoparticles.
Co-reporter:Wanshuang Liu, Kwang Liang Koh, Jinlin Lu, Liping Yang, Silei Phua, Junhua Kong, Zhong Chen and Xuehong Lu
Journal of Materials Chemistry A 2012 vol. 22(Issue 35) pp:18395-18402
Publication Date(Web):09 Jul 2012
DOI:10.1039/C2JM32708B
In this study, an imidazole-functionalized graphene (G-IMD) was prepared from graphene oxide by a facile one-pot method. The functionalized graphene not only showed improved organic compatibility but also could simultaneously play the roles of a cure accelerator and reinforcement for anhydride-cured epoxies. Our results showed that G-IMD could successfully catalyze the curing reaction without the addition of any routine accelerator. Thermal and mechanical properties of the epoxy–G-IMD nanocomposites were systematically studied at different filler loadings. Compared with neat epoxy resin, tensile strength and Young's modulus of the nanocomposites were enhanced by 97% and 12%, respectively, at only 0.4 wt% G-IMD loading. Dynamic mechanical analysis and electron microscopic results revealed that the drastic improvements in mechanical properties could be attributed to the homogeneous dispersion of G-IMD and covalent bonding at the interface, which effectively improved the efficiency of load transfer between the matrix and graphene.
Co-reporter:Liping Yang, Junhua Kong, Wu Aik Yee, Wanshuang Liu, Si Lei Phua, Cher Ling Toh, Shu Huang and Xuehong Lu
Nanoscale 2012 vol. 4(Issue 16) pp:4968-4971
Publication Date(Web):20 Jun 2012
DOI:10.1039/C2NR31258A
Polydopamine-coated graphene oxide (DGO) films exhibit electrical conductivities of 11000 S m−1 and 30000 S m−1 upon vacuum annealing at 130 °C and 180 °C, respectively. Conductive poly(vinyl alcohol)/graphene and epoxy/graphene nanocomposites show low percolation thresholds due to the excellent dispersibility of the DGO sheets and their effective in situ reduction.
Co-reporter:Junhua Kong, Zhaolin Liu, Zhengchun Yang, Hui Ru Tan, Shanxin Xiong, Siew Yee Wong, Xu Li and Xuehong Lu
Nanoscale 2012 vol. 4(Issue 2) pp:525-530
Publication Date(Web):29 Nov 2011
DOI:10.1039/C1NR10962F
A carbon/SnO2/carbon core/shell/shell hybrid nanofibrous mat was successfully prepared via single-spinneret electrospinning followed by carbonization and hydrothermal treatment. The morphology and structure of carbon/SnO2/carbon hybrid nanofibers were characterized by field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, wide-angle X-ray diffraction and X-ray photoelectron spectroscopy, and their electrochemical properties were studied as an anode in lithium ion batteries (LIBs). It is shown that the designed hybrid nanofibrous mat exhibits excellent electrochemical properties, including high reversible capacity with high columbic efficiency and impressive rate capacity. The greatly enhanced electrochemical performance is mainly due to the morphological stability and reduced diffusion resistance, which are induced by both the carbon core and deposited carbon skin. Furthermore, the embedded and de-aggregated SnO2 nanoparticles in the carbon phase, which are less than 10 nm in size, provide large numbers of reaction sites for lithium ions and ensure complete alloying with them.
Co-reporter:Junhua Kong, Wu Aik Yee, Liping Yang, Yuefan Wei, Si Lei Phua, Hock Guan Ong, Jia Ming Ang, Xu Li and Xuehong Lu
Chemical Communications 2012 vol. 48(Issue 83) pp:10316-10318
Publication Date(Web):24 Aug 2012
DOI:10.1039/C2CC35284B
Thin carbonized polydopamine (C-PDA) coatings are found to have similar structures and electrical conductivities to those of multilayered graphene doped with heteroatoms. Greatly enhanced electrochemical properties are achieved with C-PDA-coated SnO2 nanoparticles where the coating functions as a mechanical buffer layer and conducting bridge.
Co-reporter:Si Lei Phua, Liping Yang, Cher Ling Toh, Shu Huang, Zviad Tsakadze, Soo Khim Lau, Yiu-Wing Mai, and Xuehong Lu
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 9) pp:4571
Publication Date(Web):August 29, 2012
DOI:10.1021/am300947b
Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures.Keywords: clay; hydrogen bonds; interface; polydopamine; polyurethane;
Co-reporter:Shanxin Xiong, Fan Yang, Hao Jiang, Jan Ma, Xuehong Lu
Electrochimica Acta 2012 Volume 85() pp:235-242
Publication Date(Web):15 December 2012
DOI:10.1016/j.electacta.2012.08.056
In this article, we report a novel fullerene–polyaniline emeraldine base (C60–PANI-EB) hybrid synthesized through covalent bonding of polyaniline (PANI) onto para-phenylenediamine (PPD)-functionalized fullerene and its capacity properties. C60–PANI-EB exhibits a unique coral-like porous morphology with PANI particles interconnected by nanofibers. In comparison with polyaniline emeraldine base (PANI-EB), C60–PANI-EB shows significantly higher specific capacitance, specific power and specific energy, and better cycling stability. The specific capacitance of C60–PANI-EB and PANI-EB are 776 F g−1 and 492 F g−1 at current density of 1 mA cm−2, respectively. The specific capacitance of C60–PANI-EB has 37% enhancement over that of PANI-EB even at high current density of 100 mA cm−2. The specific energy of C60–PANI-EB is 64 Wh kg−1 at 1 mA cm−2 and the specific power is 36,595 W kg−1 at current density of 100 mA cm−2. The greatly enhanced capacity performance can be attributed to the increased ionic conductivity induced by the loose molecular packing structure and porous morphology as well as the increased electrical conductivity caused by the coral-like interconnected morphology and the strong electron-withdrawing function of the fullerene through its covalent bonding to PANI.
Co-reporter:Shanxin Xiong, Fan Yang, Guoqiang Ding, K. Yi Mya, Jan Ma, Xuehong Lu
Electrochimica Acta 2012 Volume 67() pp:194-200
Publication Date(Web):15 April 2012
DOI:10.1016/j.electacta.2012.02.026
In this article, fullerene covalently bonded with multiple polyaniline (PANI) arms (C60-PANI) was readily synthesized via copolymerization of aniline with p-phenylenediamine (PPD) functionalized fullerene in the presence of poly(styrene sulfonate) (PSS) dopant agent in an aqueous medium to produce a water-processable electrochromic material. The PSS-doped C60-PANI (C60-PANI:PSS) film possesses finer morphology in comparison with PSS-doped PANI (PANI:PSS) film. Owing to the electron acceptor characteristic and high conductivity of fullerene as well as the loose morphology of C60-PANI:PSS, the synthesized hybrids exhibit simultaneously enhanced electrical and ionic conductivities, resulting in improvement of electrochromic performance. In particular, the electrochromic device with C60-PANI:PSS as the active layer shows significant enhancement in optical contrast and electrochemical stability over the PANI:PSS-based device.Water-soluble and branched C60-PANI hybrids are readily synthesized. The enhanced ionic conductivity and the electron withdrawing function of C60 lead to improved contrast and switch kinetics of the C60-PANI-based electrochromic device. The electrochemical stability of the device is also significantly improved owing to the donor-acceptor interactions in the C60-PANI hybrids.
Co-reporter:Jinlin Lu, Wanshuang Liu, Han Ling, Junhua Kong, Guoqiang Ding, Dan Zhou and Xuehong Lu
RSC Advances 2012 vol. 2(Issue 28) pp:10537-10543
Publication Date(Web):11 Sep 2012
DOI:10.1039/C2RA21579A
In this article, we report the facile synthesis of sulfonic acid-grafted reduced graphene oxide (S-rGO) using a one-pot method under mild conditions, and layer-by-layer (LbL) assembly and electrochromic properties of S-rGO/polyaniline (S-rGO/PANI) nanocomposite thin films. It was found that the multilayer films of S-rGO/PANI exhibit much faster electrochromic switching kinetics than that of corresponding spin-coated PANI thin films. The enhancement can be attributed to the drastically increased electrical and ionic conductivities of the S-rGO/PANI films brought by the graphitic structure of the S-rGO sheets and the sulfonic acid groups attached to S-rGO, which lead to non-diffusion-controlled redox processes of PANI.
Co-reporter:Liping Yang, Wu Aik Yee, Si Lei Phua, Junhua Kong, Hui Ding, Jun Wei Cheah and Xuehong Lu
RSC Advances 2012 vol. 2(Issue 6) pp:2208-2210
Publication Date(Web):27 Jan 2012
DOI:10.1039/C2RA00798C
Highly conductive graphene sheets were prepared by coating graphene oxide with polydopamine (PDA) followed by reduction with hydrazine. Polyacrylonitrile/graphene nanocomposites prepared via solution blending exhibit high electrical conductivities at very low graphene loadings owing to the good exfoliation and relatively planar conformation of the PDA-coated graphene in the polymer matrix.
Co-reporter:Yu Bai;Jia Wei;Liping Yang;Chaobin He
Colloid and Polymer Science 2012 Volume 290( Issue 6) pp:507-515
Publication Date(Web):2012 April
DOI:10.1007/s00396-011-2562-1
Poly(acrylic acid-block-N-isopropylacrylamide) (PAAc-b-PNIPAm)-tethered octafunctional polyhedral oligomeric silsesquioxane (POSS) were synthesized via POSS-initialized atom transfer radical polymerization. When very short PAAc blocks are placed between the POSS core and PNIPAm short chains, the critical temperature (Tc) of POSS-PAAc-b-PNIPAm determined by cloud point measurements varies in a wide temperature range with pH, and its Tc is even lower than that of POSS-PNIPAm with similar chain length at pH = 5.0, indicating a synergic effect between high local chain density and intramolecular interaction between PAAc and PNIPAm. When the PAAc blocks are relatively long, the pH response of POSS-PAAc-b-PNIPAm diminishes owing to the reduced local PNIPAm chain density.
Co-reporter:Jia Wei, Shanxin Xiong, Yu Bai, Pengtao Jia, Jan Ma, Xuehong Lu
Solar Energy Materials and Solar Cells 2012 99() pp: 141-147
Publication Date(Web):
DOI:10.1016/j.solmat.2011.05.016
Co-reporter:Wu Aik Yee, Junhua Kong, Chao Zhang, Tianxi Liu, Masaya Kotaki, Xuehong Lu
Polymer 2012 Volume 53(Issue 22) pp:5097-5102
Publication Date(Web):12 October 2012
DOI:10.1016/j.polymer.2012.08.044
In this work, the effects of single-walled carbon nanotubes (SWCNT) surface chemistry on the polymorphism behaviors of electrospun poly(vinylidene difluoride) (PVDF) nanofibers collected under high extensional force and subsequently treated with supercritical carbon dioxide (SCCO2) are investigated via X-ray diffraction, infrared and Raman spectroscopy. It is found that the SWCNTs with hydroxyl groups (h-SWCNTs) interact with PVDF chains more intensively than the ones with ester groups, and the interaction in couple with the high extensional force promotes the formation of β-form extended-chain crystallites (ECCs). With the SCCO2 treatment, the growth of the β-form ECCs is further promoted in the PVDF/h-SWCNT nanofibers owing to the synergistic effect of the strong confinement effect of h-SWCNT for stabilizing the nuclei of the β-form ECCs and the high pressure applied.Graphical abstract
Co-reporter:Junhua Kong, Siew Yee Wong, Yu Zhang, Hui Ru Tan, Xu Li and Xuehong Lu
Journal of Materials Chemistry A 2011 vol. 21(Issue 40) pp:15928-15934
Publication Date(Web):2011/09/07
DOI:10.1039/C1JM12492G
Carbon–SnO2 hybrid nanofibers with tunable morphology were prepared from polyacrylonitrile (PAN) and tin compounds via single-spinneret electrospinning and subsequent carbonization. Different tin compounds, including tin acetate (Sn(CH3COO)2), tin chloride dihydrate (SnCl2·2H2O), tin sulfate (SnSO4) and tin sulfide (SnS), were chosen as precursors of SnO2 to tune the morphology of carbon–SnO2 nanofibers. Morphology of the obtained nanofibers was studied using a field emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM), and their structures were characterized by thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). A carbon–SnO2 core–shell morphology is formed during carbonization when Sn(CH3COO)2 and SnCl2·2H2O are used as precursors of SnO2, while uniform distribution of Sn compounds in a carbon matrix is observed with SnSO4 or SnS as the precursor. Our study demonstrates that the Kirkendall effect, which is responsible for the formation of the core–shell morphology during carbonization, is strongly dependent on melting points and decomposition behaviours of the precursors. SnO2 nanofibers and nanotubes with a high aspect ratio were produced upon burning out carbon, and their morphology is dependent on that of the corresponding hybrid nanofibers. TEM studies show that the SnO2 nanofibers/nanotubes are constituted of SnO2 single crystals, yet the grain size and facet varies with the precursor. The Brunauer–Emmett–Teller (BET) study verifies that the nanofibers/nanotubes have a large surface area, which also varies with the precursors used.
Co-reporter:Liping Yang, Si Lei Phua, Jun Kai Herman Teo, Cher Ling Toh, Soo Khim Lau, Jan Ma, and Xuehong Lu
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 8) pp:3026
Publication Date(Web):July 5, 2011
DOI:10.1021/am200532j
A facile biomimetic method was developed to enhance the interfacial interaction in polymer-layered silicate nanocomposites. By mimicking mussel adhesive proteins, a monolayer of polydopamine was constructed on clay surface by a controllable coating method. The modified clay (D-clay) was incorporated into an epoxy resin, it is found that the strong interfacial interactions brought by the polydopamine benefits not only the dispersion of the D-clay in the epoxy but also the effective interfacial stress transfer, leading to greatly improved thermomechanical properties at very low inorganic loadings. Rheological and infrared spectroscopic studies show that the interfacial interactions between the D-clay and epoxy are dominated by the hydrogen bonds between the catechol-enriched polydopamine and the epoxy.Keywords: biomimetics; clay; dopamine; interface; nanocomposite;
Co-reporter:Jia Wei, Beng H. Tan, Yu Bai, Jan Ma, and Xuehong Lu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 9) pp:1929-1935
Publication Date(Web):February 15, 2011
DOI:10.1021/jp1078168
The strong ability of polyhedral oligomeric silsesquioxane (POSS) to aggregate in nonsolvents makes it interesting to study the self-assembly behaviors of polymer-POSS hybrids. Telechelic poly(styrene-ran-sodium styrenesulfonate) with POSS as the end groups was prepared via end-capping of anionic living polystyrene chains with POSS followed by a mild sulfonation. The morphology and association properties of this new amphiphilic hybrid in an aqueous solution were investigated by dynamic and static light scattering, transmission electron microscopy and atomic force microscopy. The studies reveal that the strong aggregation propensity of POSS leads to a low critical micelle concentration and induces the aggregation of micelles. Hollow supermicellar structures can be observed at a low concentration of 1 mg/mL.
Co-reporter:Jun Kai Herman Teo, Cher Ling Toh, Xuehong Lu
Polymer 2011 Volume 52(Issue 9) pp:1975-1982
Publication Date(Web):19 April 2011
DOI:10.1016/j.polymer.2011.02.034
In this article, we report novel epoxy-based hybrids prepared via incorporating 1,2-dimethyl-3-(benzyl-heptaisobutyl-POSS) imidazolium chloride (POSS-IMC) and POSS-IMC-modified clay (POSS-MMT) into the resin based on 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ECHM) and hexahydrophthalic anhydride (HHPA). We demonstrate that both POSS-IMC and POSS-MMT can reduce the cure temperature of the epoxy/anhydride system, and the catalyzing effect involves chemical reactions between POSS-IMC and ECHM/HHPA, which may lead to the attachment of POSS cages at chain ends. The incorporation of the POSS-IMC, free and ionically bonded in clay, gives rise to dissimilar morphologies that affect the thermo–mechanical properties of the hybrids. The ECHM/HHPA/POSS-IMC resin exhibits a slight improvement in glassy modulus as compared with the neat ECHM/HHPA resin, which is attributed to the formation of sub-micron and nano-sized POSS domains that act as physical cross-link points hindering polymer chain motions. The much enhanced reinforcing effect of POSS-MMT is ascribed to the effective stress transfer between the matrix and clay layers that may originate from the strong interactions between the pendent POSS in the network and POSS attached to the clay surfaces. Reduction in coefficient of thermal expansion (CTE) was also found for the hybrids.
Co-reporter:Pengtao Jia, Wu Aik Yee, Jianwei Xu, Cher Ling Toh, Jan Ma, Xuehong Lu
Journal of Membrane Science 2011 376(1–2) pp: 283-289
Publication Date(Web):
DOI:10.1016/j.memsci.2011.04.040
Co-reporter:Chee Leng Lay;Hui Ru Tan; Xuehong Lu;Dr. Ye Liu
Chemistry - A European Journal 2011 Volume 17( Issue 8) pp:2504-2509
Publication Date(Web):
DOI:10.1002/chem.201001403
Abstract
Poly(methacrylic acid)-grafted hollow silica vesicles (PMAA-g-hollow silica vesicles) were obtained through a grafting-from approach. PMAA brushes were formed by performing atom-transfer radical polymerisation of sodium methacrylate with an initiator attached to the hollow silica spheres. PMAA-g-hollow silica vesicles were characterised by using TEM, thermogravimetric analysis (TGA) and FTIR spectroscopy. pH-dependent ξ potential and 1H NMR spectra of PMAA-g-hollow silica vesicles were measured, and the results indicated that MAA brushes in PMAA-g-hollow silica vesicles had a lower ionisation degree and low solubility in acidic aqueous solution, for example, pH 3.4, but a higher ionisation degree and high solubility when the pH was higher than 7. Also it was demonstrated that calcein blue and fluorescein isothiocyanate (FITC) labelled dextran (Mn: 10 kDa) could be encapsulated in the interiors of the PMAA-g-hollow silica vesicles with a negligible amount in PMAA brushes at pH 2, and pH-triggered release of calcein blue and FITC-labelled dextran from PMAA-g-hollow silica vesicles was observed at pH 7.4.
Co-reporter:Shanxin Xiong, Si Lei Phua, Bruce S. Dunn, Jan Ma and Xuehong Lu
Chemistry of Materials 2010 Volume 22(Issue 1) pp:255
Publication Date(Web):December 10, 2009
DOI:10.1021/cm903058c
In this article, we report the synthesis, structures, morphologies, and electrochromic properties of covalently bonded polyaniline (PANI)−TiO2 hybrids. The hybrids were synthesized via a sol−gel process, followed by oxidative polymerization, using a bifunctional compound to bridge the two phases. In comparison with PANI, the hybrids show significant enhancement in optical contrast and coloration efficiency. Furthermore, when covalently bonded to PANI, the TiO2 nanodomains can act as electron acceptors, reducing the oxidation potential and band gap of PANI, and improving the long-term electrochromic stability.
Co-reporter:Pengtao Jia, Avni A. Argun, Jianwei Xu, Shanxin Xiong, Jan Ma, Paula T. Hammond, and Xuehong Lu
Chemistry of Materials 2010 Volume 22(Issue 22) pp:6085
Publication Date(Web):October 20, 2010
DOI:10.1021/cm101683c
In this Article, we report the layer-by-layer (LbL) assembly and electrochromic properties of polyaniline-tethered cubic polyhedral oligomeric silsesquioxane (POSS-PANI)/sulfonated polyaniline (SPANI) multilayer thin films. The interaction between POSS-PANI and SPANI is characterized using X-ray photoelectron spectroscopy (XPS), ultraviolet−visible-near-infrared spectroscopy, and four-point probe conductivity. We show that the inclusion of SPANI during LbL assembly effectively dopes the underlying POSS-PANI layer and extends the conjugation length, as evidenced by probing the surface layers with XPS. We also demonstrate that the POSS-PANI/SPANI multilayer films have more electroactive units, lower band gap energies, and higher electrical conductivity values compared to those of POSS-PANI/poly(2-acrylamido-methane-2-propanesulfonic acid) (PAMPS) and spin-coated SPANI films. Under constant applied potentials, a 50 bilayer film of POSS-PANI/SPANI, (POSS-PANI/SPANI)50, shows significant enhancement in optical contrast compared with (POSS-PANI/PAMPS)50. Furthermore, the switching kinetics of (POSS-PANI/SPANI)50 are much faster than that of the spin-coated SPANI. The improvement in electrochromic contrast under dynamic switching conditions is attributed to the presence of a larger number of electrochromic units in POSS-PANI/SPANI, the loose packing structure of POSS-PANI brought by its starlike molecular architecture, and the unique morphology created by the LbL assembly.
Co-reporter:Junhua Kong, Hui Ru Tan, Sze Yu Tan, Fengji Li, Siew Yee Wong, Xu Li and Xuehong Lu
Chemical Communications 2010 vol. 46(Issue 46) pp:8773-8775
Publication Date(Web):20 Oct 2010
DOI:10.1039/C0CC03006F
Carbon–SnO2 core–shell hybrid nanofibers were prepared via single-spinneret electrospinning and subsequent heat treatment. The Kirkendall effect during the heat treatment is found to be responsible for the formation of core–shell morphology. The route is proven to be generic for fabrication of carbon–metal oxide or carbon–metal core–shell nanofibers, and corresponding nanotubes.
Co-reporter:Wu Aik Yee;Shanxin Xiong;Guoqiang Ding;Chien Anh Nguyen;Pooi See Lee;Jan Ma;Masaya Kotaki;Ye Liu
Macromolecular Rapid Communications 2010 Volume 31( Issue 20) pp:1779-1784
Publication Date(Web):
DOI:10.1002/marc.201000201
Co-reporter:Wu Aik Yee;Shanxin Xiong;Guoqiang Ding;Chien Anh Nguyen;Pooi See Lee;Jan Ma;Masaya Kotaki;Ye Liu
Macromolecular Rapid Communications 2010 Volume 31( Issue 20) pp:
Publication Date(Web):
DOI:10.1002/marc.201090055
Co-reporter:Cher Ling Toh, Lifei Xi, Soo Khim Lau, Kumari Pallathadka Pramoda, Yang Choo Chua and Xuehong Lu
The Journal of Physical Chemistry B 2010 Volume 114(Issue 1) pp:207-214
Publication Date(Web):November 25, 2009
DOI:10.1021/jp908276a
This paper reports the packing structures of two types of polyhedral oligomeric silsesquioxane (POSS)-imidazolium surfactants with different molecular rigidity in the intergalleries of montmorillonite clay. Wide-angle X-ray scattering (WAXS) and molecular modeling studies suggest that the POSS-imidazolium cations have a bilayer packing structure in clay with the long axes of the molecules largely tilted with respect to the basal plane. Direct evidence for the bilayer structure is provided by transmission electron microscopy (TEM). WAXS and differential scanning calorimetry (DSC) results indicate that the relatively flexible POSS-imidazolium cation is able to form a two-dimensionally ordered structure in the clay intergalleries, while the relatively rigid one exhibits a disordered structure in clay. Furthermore, with reducing surfactant loading, the clay modified with the rigid surfactant exhibits increased interlayer d-spacings probably because the surfactant is able to take more extended conformation at lower loadings. With its low organic content and disordered surfactant packing structure, the clay modified with the rigid surfactant also exhibits excellent thermal and thermo-oxidative stabilities.
Co-reporter:Chao Zhang, Tianxi Liu, Xuehong Lu
Polymer 2010 Volume 51(Issue 16) pp:3715-3721
Publication Date(Web):22 July 2010
DOI:10.1016/j.polymer.2010.06.021
In this paper, a novel method for fabrication of core-shell nanospheres with polystyrene (PS) as the core and multi-walled carbon nanotubes (MWNTs) as the shell via hydrogen-bonding self-assembly is introduced. The PS nanospheres with carboxyl acid groups on the surface (PS–COOH nanospheres) were prepared by typical soap-free emulsion copolymerization with acrylic acid as comonomer. The MWNTs were grafted with poly(vinyl pyrrolidone) (PVP), in which the carbonyl oxygen can act as proton acceptors to form hydrogen bonds with the carboxyl acid groups. The results show that the functionalized MWNTs can self-assemble onto the surface of PS–COOH nanospheres rapidly via hydrogen bonding interaction, and the process is reversible and can be well controlled by adjusting pH value of the system. These core-shell nanospheres have the potential to be used as conductive and synergistic reinforcement fillers in fabricating high-performance and functional nanocomposites.
Co-reporter:Yang Xiao;Xinhai Zhang;Chaobin He
Journal of Nanoparticle Research 2010 Volume 12( Issue 8) pp:2787-2798
Publication Date(Web):2010 October
DOI:10.1007/s11051-010-9857-x
This article reports the synthesis and characterization of a quantum-confined luminescent dot with size 2–3 nm using well-defined m-octa(bromophenyl) silsesquioxane (m-OBPS) as core. The highly regioselective bromination of octaphenylsilsesquioxane (OPS), which is an electron-deficient nanometer-sized molecule, has been synthesized using combined catalyst of iodine and zinc chloride at room temperature in dichloromethane solvent. Based on m-OBPS, a hybrid luminescent dot with well-defined structure was synthesized. UV absorption and PL spectra of this light-emitting dot remain same in dilute solution, condensed state, and solid solution. Furthermore, time-resolved PL study indicates that the exciton decay time of the light-emitting dot remains similar regardless in dilute solution, condensed state, or blended with other polymers, suggesting that the charge carriers are well confined within the individual light-emitting dot due to the unique star-like structure and shielding alkyl chain layer. The light-emitting nano-particles can be considered as isolated chromophores as both inter- and intra- molecular aggregation are prohibited.
Co-reporter:Pengtao Jia, Avni A. Argun, Jianwei Xu, Shanxin Xiong, Jan Ma, Paula T. Hammond and Xuehong Lu
Chemistry of Materials 2009 Volume 21(Issue 19) pp:4434
Publication Date(Web):September 18, 2009
DOI:10.1021/cm9009817
Polyaniline (PANI)-tethered cubic polyhedral oligomeric silsesquioxane (POSS) in emeraldine base (EB) form is synthesized via oxidative copolymerization of octa(aminophenyl) silsesquioxane and aniline in the presence of HCl followed by the treatment with triethylamine. The chemical structures of POSS-PANI-EB are elucidated by Fourier transform infrared spectroscopy and elemental analysis. POSS-PANI/poly(2-acrylamido-methane-2-propanesulfonic acid) (PAMPS) multilayer thin films are successfully fabricated via layer-by-layer (LBL) assembly. Cyclic voltammetry studies show that the redox reactions in the thin film containing 50 POSS-PANI/PAMPS bilayers ((POSS-PANI/PAMPS)50) are close to non-diffusion-controlled processes in the studied scan-rate range of 10−100 mV/s, and the reactions are also more reversible than that in the linear counterpart (PANI/PAMPS)50. Under a dynamic switching condition of 40 s per cycle, the electrochromic contrast of (POSS-PANI/PAMPS)50 is increased by more than 30% over that of (PANI/PAMPS)50 and the switching time of (POSS-PANI/PAMPS)50 is also significantly shorter than that of (PANI/PAMPS)50. In addition to the better control of film thickness and morphology, the electrochromic performance of the POSS-PANI/PAMPS multilayer films is also superior to the previously studied spin-coated thin films of POSS-PANI/polymeric acid complexes. The improvements can be attributed to the unique morphology brought by the synergistic combination of the starlike structure of POSS-PANI and the LBL assembly method, which allows for more favorable interactions between PANI chains and polymeric dopants as well as faster ion transport during the redox switching.
Co-reporter:Pengtao Jia, Jianwei Xu, Jan Ma, Xuehong Lu
European Polymer Journal 2009 Volume 45(Issue 3) pp:772-778
Publication Date(Web):March 2009
DOI:10.1016/j.eurpolymj.2008.12.001
A new series of electrochromic polymers are synthesized via oxidative emulsion copolymerization of hexa(4-aminophenoxy)cyclotriphosphazene (HACP) and aniline in the presence of dodecylbenzene sulfonic acid. The structures of the copolymers are characterized using nuclear magnetic resonance spectroscopy, size exclusion chromatography, wide angle X-ray diffraction, scanning and transmission electron microscopy. The results reveal that the copolymer containing 4.0 mol % HACP (4.0% HACP–PANI) possesses a large number of nanometer-sized crystallites due to the unique molecular architecture of HACP–PANI. Spectro-electrochemical studies show that 4.0% HACP–PANI exhibits a significant enhancement in electrochromic contrast as compared with homopolyaniline (PANI). The contrast enhancement can be attributed to the easier diffusion of cations into nanometer-sized crystals, which is evidenced by a significant increase in ionic conductivity. At lower HACP concentrations, the copolymers induce the crystallization of linear PANI as substantial amounts of PANI may form during the polymerization, resulting in increased crystal size, and hence low electrochromic contrasts.
Co-reporter:Yang Xiao;Li-Wei Tan;K.S. Ong;Chaobin He
Journal of Polymer Science Part A: Polymer Chemistry 2009 Volume 47( Issue 21) pp:5661-5670
Publication Date(Web):
DOI:10.1002/pola.23608
Abstract
Hyperbranched organic–inorganic hybrid conjugated polymers P1 and P2 were prepared via FeCl3-oxiditive polymerization of 4,7-bis(3-ethylhexyl-2-thienyl)-2,1,3-benzothiadiazole (A) and octa(3-ethylhexyl-2-thienyl-phenyl)polyhedral oligomeric silsesquioxane (POSS) (B) at different POSS concentrations. Compared to linear polymer PM derived from A, P1, and P2 exhibit much higher PL quantum efficiency (ϕPL-f) in condensed state with improved thermal stability. ϕPL-f of P1 and P2 increased by 80% and 400%, and the thermal degradation temperatures of P1 and P2 are increased by 35 °C and 46 °C, respectively. Light-emitting diodes were fabricated using P1, P2, and PM. While the electroluminescent spectra of both P1 and PM show λmax at 660 nm, P1 exhibits a much narrower EL spectrum and higher electroluminescence (∼500%) compared with PM at a same voltage and film thickness. The maximum current efficiency of P1 is more than seven times of that of PM. The turn-on voltages of the LEDs are in the order of P2 > PM > P1. LED prepared by blending P1 with MEH-PPV shows a maximum luminescence of 2.6 × 103 cd/m2 and a current efficiency of 1.40 cd/A, which are more than twice (1.1 × 103 cd/m2) and five times (0.27 cd/A) of LED of PM/MEH-PPV blend, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5661–5670, 2009
Co-reporter:Yang Choo Chua, Ling Chen, Xuehong Lu
Composites Part A: Applied Science and Manufacturing 2009 Volume 40(Issue 4) pp:423-430
Publication Date(Web):April 2009
DOI:10.1016/j.compositesa.2009.01.005
The hierarchical structure developed in an injection-molded poly(ethylene naphthalate) (PEN)/clay nanocomposite, and its impact on the reinforcement of the nanocomposite are investigated. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) show that the clay sheets tend to orient parallel to the largest face of the molded sample. SAXS further provides evidence that upon annealing, this preferred orientation of clay induces an anisotropic crystalline morphology in the PEN matrix, where there are more secondary lamellae aligned parallel to the clay basal planes. Such lamellar organization of PEN works synergistically with the oriented clay phase in stiffening the material along the flow direction, as confirmed by dynamic mechanical analysis (DMA) and nanoindentation.
Co-reporter:Liying Zhang, Shanxin Xiong, Jan Ma, Xuehong Lu
Solar Energy Materials and Solar Cells 2009 93(5) pp: 625-629
Publication Date(Web):
DOI:10.1016/j.solmat.2008.12.021
Co-reporter:Shanxin Xiong, Jan Ma, Xuehong Lu
Solar Energy Materials and Solar Cells 2009 93(12) pp: 2113-2117
Publication Date(Web):
DOI:10.1016/j.solmat.2009.06.006
Co-reporter:Shanxin Xiong, Pengtao Jia, K. Yi Mya, Jan Ma, Freddy Boey, Xuehong Lu
Electrochimica Acta 2008 Volume 53(Issue 9) pp:3523-3530
Publication Date(Web):20 March 2008
DOI:10.1016/j.electacta.2007.12.034
We report the structures, electrochemical and electrochromic properties of organic–inorganic hybrid polymers prepared via copolymerization of octa(aminophenyl) silsesquioxane and aniline. Compared with homopolyaniline (PANI), this class of novel materials exhibits much greater thermodynamic penetrability in solution, as detected using static and dynamic light scattering, suggesting that they have a star-like molecular geometry. Due to their star-like geometry, in solid state the copolymers (POSS–PANI) exhibit a loosely packed structure with relatively low crystallinity, as evidenced by X-ray and TEM characterization, and hence relatively high ionic conductivity. Cyclic voltammetric studies show that POSS–PANI undergoes similar electrochemical reactions to that of PANI but its loosely packed structure allows slightly faster cation diffusion. Spectro-electrochemical studies show a ∼40% enhancement in electrochromic contrast brought by tethering PANI onto POSS, which can be attributed to more accessible doping sites in POSS–PANI. Furthermore, the electrochemical stability of POSS–PANI is also significantly improved over that of PANI. Infrared spectroscopic measurements indicate that the formation of electrochemically inactive quinonediimine is retarded in POSS–PANI possibly due to the increased conformation freedom of the dopant anions.
Co-reporter:Shu Huang, Wu Aik Yee, Wuiwui Chauhari Tjiu, Ye Liu, Masaya Kotaki, Yin Chiang Freddy Boey, Jan Ma, Tianxi Liu and Xuehong Lu
Langmuir 2008 Volume 24(Issue 23) pp:13621-13626
Publication Date(Web):October 28, 2008
DOI:10.1021/la8024183
Polyvinylidene difluoride (PVDF) solutions containing a very low concentration of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) of similar surface chemistry, respectively, were electrospun, and the nanofibers formed were collected using a modified rotating disk collector. The polymorphic behavior and crystal orientation of the nanofibers were studied using wide-angle X-ray diffraction and infrared spectroscopy, while the nanotube alignment and interfacial interactions in the nanofibers were probed by transmission electron microscopy and Raman spectroscopy. It is shown that the interfacial interaction between the SWCNTs and PVDF and the extensional force experienced by the nanofibers in the electrospinning and collection processes can work synergistically to induce highly oriented β-form crystallites extensively. In contrast, the MWCNTs could not be well aligned along the nanofiber axis, which leads to a lower degree of crystal orientation.
Co-reporter:Jan Ma;Yang Xiao;Liying Zhang;Shanxin Xiong
Macromolecular Rapid Communications 2007 Volume 28(Issue 3) pp:281-285
Publication Date(Web):30 JAN 2007
DOI:10.1002/marc.200600717
Copolymerization of aniline with octa(aminophenyl) silsesquioxane (OAPS) was performed, which resulted in polyaniline-tethered, polyhedral oligomeric silsesquioxane (POSS-PANI), with star-like molecular geometry. The spectro-electrochemical studies show that the electrochromic contrast of POSS-PANI is much higher than that of polyaniline (PANI). The great improvement can be attributed to the more accessible doping sites and the facile ion movement during the redox switching, brought by the loose packing of the PANI chains. This was evidenced by a drastic increase in ionic conductivity, a decrease in the electrical conductivity, and a decrease in the crystallinity and crystal size, with the increase of the OAPS concentration in the POSS-PANI.
Co-reporter:Jiyuan Hao;Songlin Liu;Soo Khim Lau;Yang Choo Chua
Journal of Applied Polymer Science 2006 Volume 101(Issue 2) pp:1057-1064
Publication Date(Web):25 APR 2006
DOI:10.1002/app.23585
A poly(ethylene terephthalate)/clay nanocomposite (PET/clay) was prepared via in situ polymerization, in which the clay was modified with 12-aminododecanoic acid (ADA). A compatibilizer containing an amino and an ester group was introduced into the PET/ADA-clay system, which can attach to ADA-clay through ionic interaction and be incorporated into PET chains through transesterification. The compatibilizer-modified ADA-clay was first formed in a pretreatment process and then participated in polymerization. The compatibilizer, as an intermedium between organoclay and polymer, improved clay dispersion in PET matrix. The PET/clay nanocomposite prepared by this novel method possesses significantly higher storage modulus than does neat PET. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1057–1064, 2006
Co-reporter:Xuehong Lu, Jianwei Xu, Limin Wong
Synthetic Metals 2006 Volume 156(2–4) pp:117-123
Publication Date(Web):1 February 2006
DOI:10.1016/j.synthmet.2005.10.022
This paper describes the effects of polyimide (PI) structure on electrical conductivity of blends of dodecylbenzene sulfonic acid-doped polyaniline (PANI-DBSA) and PI, as well as its thermal degradation behavior. Four types of PIs with different molecular architecture were synthesized and subsequently solution blended with PANI-DBSA. Of the four types of PIs, 4-4′-diaminodiphenyl sulfone (DADPS)-based PI provides the highest conductivity to the blends. It is attributed to the rigid nature of DADPS, which may induce more extended conformation of PANI chains, and hence result in a more ordered structure. The conductivity of the blends has significant higher thermal stability than that of PANI-DBSA. The thermal stability is, however, independent on the polyimide structure. TGA studies show that the PI matrix may have hindered the thermo-oxidative degradation and evaporation of the dopants and thus slowed down the process of thermal degradation of the conductivity.
Co-reporter:Yang Choo Chua;Tong Wan
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 7) pp:1040-1049
Publication Date(Web):15 FEB 2006
DOI:10.1002/polb.20754
Thermally stable organically modified clays based on 1,3-didecyl-2-methylimidazolium (IM2C10) and 1-hexadecyl-2,3-dimethyl-imidazolium (IMC16) were used to prepare poly(ethylene naphthalate) (PEN)/clay nanocomposites via a melt intercalation process. The clay dispersion in the resulting hybrids was studied by a combination of X-ray diffraction, polarizing optical microscopy, and transmission electron microscopy. It was found that IMC16 provided better compatibility between the PEN matrix and the clay than IM2C10, as evidenced by some intercalation of polymer achieved in the PEN/IMC16-MMT hybrid. The effects of clay on the crystal structure of PEN were investigated. It was found that both pristine MMT and imidazolium-treated MMT enhanced the formation of the β-crystal phase under melt crystallization at 200 °C. At 180 °C, however, the imidazolium-treated MMT was found to favor the α-crystal form instead. The difference in clay-induced polymorphism behavior was attributed to conformational changes experienced by the clay modifiers as the crystallization temperature changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1040–1049, 2006
Co-reporter:Hsiao Yen Ng;Soo Khim Lau
Polymer Composites 2005 Volume 26(Issue 6) pp:778-790
Publication Date(Web):9 NOV 2005
DOI:10.1002/pc.20151
The thermal conductivity of boron nitride (BN)-filled poly(butylene terephthalate) (PBT) was investigated as a function of particle size, aspect ratio, surface area, surface chemistry, and concentration of BN as well as composite processing methods and conditions. In the low filler concentration region, a larger BN surface area resulted in lower thermal conductivity of the composites as a result of phonon scattering at interfaces. In the high filler concentration region the ease in forming filler networks, as reflected by the aspect ratio of BN, played a more dominant role. A percolation-like behavior was observed when BN networks were formed while the thermal conductivity at close vicinity of the percolation threshold was not completely governed by the scaling law of classic percolation theory. High shear force employed in extrusion was effective in dispersing BN agglomerates into fine platelets while also inducing PBT degradation. When a low screw speed was used in extrusion followed by injection molding, the samples exhibited significantly lower thermal conductivity, which may be attributed to flow-induced orientation of BN platelets in the direction perpendicular to the heat flow, relatively low concentration of filler at sample surfaces (skin-core effect), and agglomeration of the BN platelets. POLYM. COMPOS. 26:778–790, 2005. © 2005 Society of Plastics Engineers
Co-reporter:Hsiao Yen Ng;Soo Khim Lau
Polymer Composites 2005 Volume 26(Issue 1) pp:66-73
Publication Date(Web):30 DEC 2004
DOI:10.1002/pc.20076
Hybrid composites consisting of boron nitride (BN) platelets and carbon fibers (CF) in a polybutylene terephthalate (PBT) matrix were melt-compounded, and their thermal and electrical conductivity, tensile, and rheological properties were investigated. While it does not lead to an enhancement in thermal conductivity with respect to PBT/BN composites, the results indicate that a combination of BN and CF in PBT can significantly reduce electrical conductivity of the composites compared to that of PBT/CF composites. The relative low thermal conductivity of the hybrid composites is attributed to CF breakage that occurred during the extrusion and alignment of CF in melt flow direction, which is normal to the heat flow encountered during the thermal conductivity tests induced by injection molding. The hybrid composites were, however, found to have better tensile properties and processibility than PBT/BN composites at the same total filler content. POLYM. COMPOS., 26:66–73, 2005. © 2004 Society of Plastics Engineers
Co-reporter:Wei Zhao;Jian Wei Xu;Yu Chen;Jianhong Zhao
Journal of Applied Polymer Science 2004 Volume 92(Issue 2) pp:960-969
Publication Date(Web):17 FEB 2004
DOI:10.1002/app.20000
Two liquid-crystalline polyesters (LCPs) with different chain rigidities were synthesized and melt-blended with polycarbonate (PC) at an LCP concentration of 2 wt %. The first LCP (LCP1) was based on hydroxybenzoic acid (HBA), hydroquinone (HQ), sebacic acid (SEA), and suberic acid (SUA) and contained a relatively high concentration of flexible units (SEA and SUA). The other one (LCP2) was based on HBA, hydroxynaphthoic acid, HQ, and SEA and contained a lower concentration of flexible units. LCP2 had a much lower melting point, a higher clearing temperature, and a lower shear viscosity than LCP1. The blending was carried out at 265, 280, and 300°C for both systems. The extent of the viscosity reduction induced by the addition of LCP1 depended on the compounding temperature, and the lowest viscosity was achieved with blending at 280°C. This was attributed to the large interfacial area and interactions between the flexible segments of LCP1 and PC chains at the interface. For PC/LCP2, the viscosity reduction was not significantly dependent on the compounding temperature, and when it was compounded at 280°C, its viscosity was significantly higher than that of PC/LCP1 at high shear rates, even though LCP2 had lower viscosity. A scanning electron microscopy study revealed that, with compounding at 265 and 280°C, LCP2 was poorly dispersed in the PC matrix in comparison with LCP1, and the glass-transition-temperature depression caused by the addition of LCP2 was relatively small. This indicated that interfacial interactions in PC/LCP2 were weaker, thereby explaining their different rheological behavior in comparison with PC/LCP1. With compounding at 300°C, the compatibility of both systems improved because of transesterification reactions, but this did not lead to a lower viscosity because of the lack of physical interfacial interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 960–969, 2004
Co-reporter:Tong Wan;Ling Chen;Yang Choo Chua
Journal of Applied Polymer Science 2004 Volume 94(Issue 4) pp:1381-1388
Publication Date(Web):13 SEP 2004
DOI:10.1002/app.20975
A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod-shaped and later exhibited three-dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide-angle X-ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1381–1388, 2004
Co-reporter:Wenge Zheng;Cher Ling Toh;Tong Hua Zheng;Chaobin He
Journal of Polymer Science Part B: Polymer Physics 2004 Volume 42(Issue 10) pp:1810-1816
Publication Date(Web):2 APR 2004
DOI:10.1002/polb.20043
The effects of clay on polymorphism of polypropylene (PP) in PP/clay nanocomposites (PPCNs) under various thermomechanical conditions were studied. In extruded PP and PPCN pellet samples, only α-phase crystallites existed, as they were prepared by rapidly cooling the melt extrudates to room temperature. Under compression, β-phase crystallites can develop in neat PP under various thermal conditions, of which isothermal crystallizing at 120 °C gave the highest content of β-phase crystallites. In contrast, no β-phase crystallite was detected in the PPCN samples prepared under the same conditions. This indicated that clay significantly inhibits the formation of β-phase crystallites. The likely reason is that the presence of clay in PPCNs greatly sped up the crystallization process of the α phase, whereas it had an insignificant effect on the crystallization rates of the β phase. The results also showed that clay may slightly promote the formation of γ-phase PP crystallites in PPCNs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1810–1816, 2004
Co-reporter:Yang Choo Chua;Wei Zhao
Journal of Applied Polymer Science 2003 Volume 90(Issue 11) pp:3051-3058
Publication Date(Web):9 OCT 2003
DOI:10.1002/app.13033
A liquid-crystalline polyester based on hydroxybenzoic acid, hydroquinone, sebacic acid, and suberic acid (named as BQSESU) was melt blended with polycarbonate (PC) at the BQSESU concentration of 2 wt %. It was found that the extent of viscosity reduction induced by the addition of BQSESU depends on the compounding temperature and the relation between them is not monotonic. The lowest viscosity was achieved by blending at 280°C. GPC measurements indicate that molecular weight reduction induced by the compounding is not a major contributor to the viscosity reduction. SEM study shows that when compounded at 280°C the blend is partially miscible with particle size at the submicron level. At the same time a large Tg depression was observed, which indicates strong interactions between the flexible segments of BQSESU and PC in the interfacial regions. The lowest viscosity achieved by blending at 280°C is thus proposed as an interfacial phenomenon. When compounded at 265°C, BQSESU particle size is larger, which gives a small interfacial area and hence less viscosity reduction. When compounded at 300°C a nearly miscible morphology was achieved, which also leads to less viscosity reduction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3051–3058, 2003
Co-reporter:Xuehong Lu, Chiang Yang Tan, Jianwei Xu, Chaobin He
Synthetic Metals 2003 Volume 138(Issue 3) pp:429-440
Publication Date(Web):4 July 2003
DOI:10.1016/S0379-6779(02)00471-X
This paper describes the effect of molecular weight of dopants on thermal degradation behaviour of electrical conductivity of polyacrylic acid (PAA) doped polyaniline (PANI). Two PAA with weight-average molecular weight (Mw) of 5000 and 250,000, respectively, were used as dopants to synthesise PANI–PAA complexes by in situ oxidative polymerisation. PANI doped with the low Mw PAA has lower electrical conductivity, which is attributed to its smaller size of crystal islands due to the end group effect. When annealed at 180 °C, within a period of 2 h the conductivity of PANI doped with the high Mw PAA decreases continuously with the annealing time following law, while the one doped with the low Mw PAA obeys this law only within 1 h of annealing. This indicates that the decrease of conducting island size is responsible for the thermal degradation of the conductivity of the complexes in a certain period and the length of this period depends on Mw of the dopants. TGA study shows that at 180 °C weight loss rates of the low and high Mw PAA doped PANI are about the same, which implies that the faster reduction of the conductivity in the low Mw PAA doped PANI is mainly due to its smaller initial crystal size. FT-IR study shows that annealing leads to de-doping, but it is less pronounced in the high Mw PAA doped PANI.
Co-reporter:Xuehong Lu, Hsiao Yen Ng, Jianwei Xu, Chaobin He
Synthetic Metals 2002 Volume 128(Issue 2) pp:167-178
Publication Date(Web):30 April 2002
DOI:10.1016/S0379-6779(01)00668-3
Polyaniline (PANI) doped with dodecylbenzene sulphonic acid (DBSA) and methylbenzene sulphonic acid (MBSA) were used as model compounds to investigate thermal degradation mechanisms of electrical conductivity of PANI salts. The effects of high temperature annealing on the conductivity, thermal stability and morphology of the doped PANI were studied. Within a period of 2 h, the conductivity of the two PANI salts decreases continuously with the annealing time. The conductivity reduction also increases significantly with the annealing temperature. Both polymers show significant weight loss during the annealing, especially at 200 °C. The weight loss of PANI–MBSA is more pronounced than that of PANI–DBSA, while the conductivity reduction shows an opposite trend. Scanning electronic microscopy (SEM) study reveals a significant morphology change caused by the annealing. Fourier transformed infrared (FT-IR) results indicate that some dopants are converted to free acids due to the annealing. It is, therefore, suggested that in addition to cross-linking of PANI and evaporation and degradation of the dopants, the segregation of the dopants from the polymers is also an important mechanism responsible for the conductivity degradation observed.
Co-reporter:Xuehong Lu, Lau Soo Khim
Journal of Materials Processing Technology 2001 Volume 113(1–3) pp:189-195
Publication Date(Web):15 June 2001
DOI:10.1016/S0924-0136(01)00606-9
In the injection molding of plastic optical lenses, the processing conditions have critical effects on the quality of the molded lenses. Since there are many process parameters involved in an injection molding process, and more importantly, an optical lens needs precisely controlled surface contours, determination of the processing conditions for lens molding is very complicated. The objective of this work is to investigate experimentally some effects of the molding conditions on the surface contours of injection molded lenses. A spherical lens was molded using polycarbonate. The surface profiles of the lenses molded under different processing conditions were measured using a laser interferometer. The birefringence of the lenses was measured using a specially designed polarimeter to characterize the residual stress in the lenses. Statistical methods were employed in the experimental studies in order to systematically analyze the effects of various process parameters on the lens contour errors. The process parameters studied include injection speed, holding pressure and mold temperature, etc. The contour errors were correlated to the mold shrinkage and the residual stress in the molded lenses. The study shows that in addition to the mold shrinkage the stress also plays a vital role in determining the lens surface contours.
Co-reporter:Pengfei Wang, Wanshuang Liu, Xin Zhang, Xuehong Lu, Jinglei Yang
Engineering Fracture Mechanics (November 2015) Volume 148() pp:73-81
Publication Date(Web):1 November 2015
DOI:10.1016/j.engfracmech.2015.09.010
The fracture toughness of carbon fiber reinforced plastic laminates was investigated in term of modifying the epoxy matrix with the pristine and functionalized stacked-cup carbon nanofibers. The results showed that the highest enhancements in Mode I (13.6%) and Mode II (45.3%) fracture toughness were achieved by adding 0.5 wt% and 1.0 wt% functionalized nanofibers, respectively. The toughening mechanism was analyzed based on the morphology evaluations of the fracture surfaces. The evidence of bridging, pull-out, peeling-off and unravelling of nanofibers were clearly observed, which contributed to dissipating more energy for crack propagation, resulting in the improvement of fracture toughness.
Co-reporter:Wanshuang Liu, Yiru Wang, Pengfei Wang, Yan Li, Qiuran Jiang, Xiaoyu Hu, Yi Wei, Yiping Qiu, Seyed Ismail Seyed Shahabadi, Xuehong Lu
Composites Part B: Engineering (15 March 2017) Volume 113() pp:
Publication Date(Web):15 March 2017
DOI:10.1016/j.compositesb.2017.01.040
In this work, the surface of stacked-cup carbon nanofibers (CNFs) was coated with polydopamine (PDA) via a facile biomimetic method based on catecholic chemistry. The modified CNFs (D-CNFs) were incorporated into an epoxy resin in a solvent-free manner. In addition to hydrogen bonding, covalent bonding is also present between amino groups in PDA and epoxy, as verified by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Owing to the strong interfacial interactions brought by PDA, D-CNFs show significantly improved dispersibility in epoxy matrix. Consequently, the reinforcing effects of D-CNFs clearly outperform those of pristine CNFs (P-CNFs), especially in terms of fracture toughness. Dynamic thermo-mechanical studies show that the addition of D-CNFs can increase storage modulus more effectively without deteriorating the thermal stability of epoxy matrix. This study confirms that enhancing interfacial interactions in polymer composites by coating nanofillers with PDA is a useful strategy to obtain simultaneous stiffening and toughening in rigid thermoset polymers.
Co-reporter:Dan Zhou, Boyang Che, Junhua Kong and Xuehong Lu
Journal of Materials Chemistry A 2016 - vol. 4(Issue 34) pp:NaN8051-8051
Publication Date(Web):2016/08/08
DOI:10.1039/C6TC03194C
In order to enhance the electrochromic performance of sol–gel derived WO3 coatings, especially the electrochemical cycling stability, a small amount of dopamine (DA) is introduced into a peroxotungstic acid (PTA) precursor sol to form complexes with tungsten on the surface of PTA colloidal nanoparticles. The DA molecules act as a precursor stabilizer, giving the sol a very long shelf life, which is crucial for practical applications, and also play the role of a structure-directing agent, providing a nanocrystal-embedded amorphous WO3 coating by annealing at 300 °C. Compared with the corresponding neat WO3 coating, the modified WO3 coating prepared from the complex sol gives much higher optical contrast, a faster switching speed and a higher coloration efficiency. It also shows excellent long-term cycling stability (maintaining a stable high contrast up to 35000 cycles), which is far superior to not only the reference neat WO3 coating but also WO3 coatings prepared via other wet chemical routes. The excellent cycling stability may be attributed to the buffering effect of the nanocrystal-embedded amorphous regions, which accommodate the volume change of the nanocrystals induced by ion insertion/extraction. The uniform distribution of the nanometer-sized amorphous and crystal regions may help to reduce stress concentration and hence suppress erosion caused by local stress.
Co-reporter:Yuefan Wei, Junhua Kong, Liping Yang, Lin Ke, Hui Ru Tan, Hai Liu, Yizhong Huang, Xiao Wei Sun, Xuehong Lu and Hejun Du
Journal of Materials Chemistry A 2013 - vol. 1(Issue 16) pp:NaN5052-5052
Publication Date(Web):2013/02/12
DOI:10.1039/C3TA10499K
The modification of zinc oxide (ZnO) with silver (Ag) has proven to be an effective strategy to enhance the optical and electrical properties, in which the interactions between ZnO and Ag are critically determined by the structure and morphology of the ZnO–Ag hybrids. In order to achieve homogeneous and controllable distribution, polydopamine (PDA) was introduced via in situpolymerization to assist the decoration of ZnO nanorods (NRs) with Ag nanoparticles (NPs). Compared with pristine ZnO NRs, the light absorption is significantly enhanced for the PDA assisted Ag-decorated ZnO, which is attributed to the Ag NPs as well as the carbonized PDA thin film. Ag NPs of small size enhance the multiple/high-angle scattering from localized plasmonic effect, which increases the light path length hence traps more light. The carbonized PDA film is further beneficial to the absorption of the visible light. The Ag-decorated ZnO NRs on fluorine-doped tin oxide (FTO) coated glasses were then used as photoanodes of the photoelectrochemical (PEC) cell. The short circuit current density (JSC, 1.8 mA cm−2), maximum photo current conversion efficiency (PCE, 3.9%) and lifetime (3.07 mA cm−2 at 500 seconds) are achieved with an optimized loading of Ag nanoparticles derived from 0.01 M silver nitrate (AgNO3), which are found to be much higher than those of pristine ZnO NRs and other reported Ag–ZnO-based photoanodes. The overall PEC performance improvement is attributed to the localized plasmonic effect enhanced light harvesting as well as the facilitated charge transport and inhibition of recombination of electrons and holes from both Ag nanoparticles that act as an electron acceptor and carbonized PDA film as stabilizer and separator.
Co-reporter:Junhua Kong, Chenyang Zhao, Yuefan Wei, Si Lei Phua, Yuliang Dong and Xuehong Lu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 36) pp:NaN15199-15199
Publication Date(Web):2014/07/17
DOI:10.1039/C4TA02813A
In this work, unique carbonaceous nanocups, densely attached on a free-standing hollow microfibrous mat, were prepared via a mussel-inspired biomimetic polydopamine (PDA)-coating process using electrospun porous microfibers as the templates, followed by annealing. Electron microscopic studies show that the diameters and depths of the ellipsoid-shaped nanocups are in the range of a few hundred nanometers, and they have small openings of less than 100 nm, allowing the cups to act as nano-chambers to host other functional materials as well as nano-reactors for the synthesis of embedded nanostructures. To demonstrate the functions of such a unique hollow structure, the nanocups were used to host a MoS2 precursor, and through hydrothermal treatment, MoS2 nanosheets were effectively trapped in the nanocups. The MoS2-in-nanocups were used as an anode in lithium ion batteries. Good cyclability and excellent rate capacity (around 520 mA h g−1 at 2 A g−1) were achieved owing to the efficient charge transport provided by the good contact of the MoS2 nanosheets with the conductive nanocups and surrounding electrolyte. The nanocups could also act as buffering chambers to effectively accommodate the volume expansion of MoS2 during cycling.
Co-reporter:Junhua Kong, Hui Ru Tan, Sze Yu Tan, Fengji Li, Siew Yee Wong, Xu Li and Xuehong Lu
Chemical Communications 2010 - vol. 46(Issue 46) pp:NaN8775-8775
Publication Date(Web):2010/10/20
DOI:10.1039/C0CC03006F
Carbon–SnO2 core–shell hybrid nanofibers were prepared via single-spinneret electrospinning and subsequent heat treatment. The Kirkendall effect during the heat treatment is found to be responsible for the formation of core–shell morphology. The route is proven to be generic for fabrication of carbon–metal oxide or carbon–metal core–shell nanofibers, and corresponding nanotubes.
Co-reporter:Xiayin Yao, Chenyang Zhao, Junhua Kong, Huiqing Wu, Dan Zhou and Xuehong Lu
Chemical Communications 2014 - vol. 50(Issue 93) pp:NaN14600-14600
Publication Date(Web):2014/09/30
DOI:10.1039/C4CC07350A
Polydopamine-derived carbon (C-PDA) nanospheres embedded with zinc ferrite (ZnFe2O4) are synthesized by in situ polymerization of dopamine with zinc and iron species followed by carbonization. The composite nanospheres contain ZnFe2O4 nanoparticles ∼8 nm in size well dispersed in porous C-PDA. The unique structure and morphology endow the nanospheres with excellent rate capability and cycling stability for use as anodes in lithium-ion batteries.
Co-reporter:Han Ling, Guoqiang Ding, Daniel Mandler, Pooi See Lee, Jianwei Xu and Xuehong Lu
Chemical Communications 2016 - vol. 52(Issue 60) pp:NaN9382-9382
Publication Date(Web):2016/06/21
DOI:10.1039/C6CC03813A
An aqueous suspension of WO3/poly(4-(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid) (PEDTS) hybrid nanoparticles (NPs) is prepared by air-assisted oxidative polymerization and simultaneous attachment of PEDTS on WO3-NPs, and used for electrochromic (EC) film fabrication via air-brush spraying. The hybrid EC device exhibits enhanced EC properties compared to the ones based on WO3-NP or PEDTS alone.
Co-reporter:Dan Zhou, Boyang Che and Xuehong Lu
Journal of Materials Chemistry A 2017 - vol. 5(Issue 7) pp:NaN1766-1766
Publication Date(Web):2017/01/16
DOI:10.1039/C6TC05216A
In this article, we report, for the first time, the preparation of polyaniline/manganese dioxide (PANI/MnO2) hybrid electrochromic films via one-pot potentiostatically anodic electrodeposition from an aqueous solution containing aniline and manganese sulfate. In the one-pot deposition process, electropolymerization of aniline and electrodeposition of MnO2 occur simultaneously, while some of the resultant MnO2 can act as an oxidizer to further initiate chemical polymerization of aniline, facilitating rapid growth of the hybrid films. This unique deposition mechanism gives rise to significant differences between the hybrid and neat PANI films in morphology, structures, electrochemical and electrochromic properties. Compared with neat PANI films, the hybrid film with optimal MnO2 content shows much higher optical contrast, coloration efficiency, and cycling stability. The excellent performance of the hybrid film can be attributed to its unique porous morphology with interconnected small nanoparticles, and donor–acceptor interactions between PANI and MnO2.
Co-reporter:Chenyang Zhao, Junhua Kong, Liping Yang, Xiayin Yao, Si Lei Phua and Xuehong Lu
Chemical Communications 2014 - vol. 50(Issue 68) pp:NaN9675-9675
Publication Date(Web):2014/06/30
DOI:10.1039/C4CC04099F
Single-layer MoS2–carbon nanocomposites (SLMoS2/C) are facilely prepared via a dopamine (DOPA)–MoVI complexation-assisted approach. The large interlayer spacing, sandwich structure and crumpled nanosheet morphology of SLMoS2/C render it excellent electrochemical performances as a lithium-ion battery anode, showing a reversible capacity of 500 mA h g−1 at a discharge rate of 5 A g−1.
Co-reporter:Guoqiang Ding, Hui Zhou, Jianwei Xu and Xuehong Lu
Chemical Communications 2014 - vol. 50(Issue 6) pp:NaN657-657
Publication Date(Web):2013/11/07
DOI:10.1039/C3CC47732K
Selective detection of cyanide anions is realized via electrofluorochromism of a benzothiadiazole-containing conjugated copolymer because oxidative fluorescence quenching induced by positive potentials can be significantly weakened by interaction between nucleophilic cyanide and electron-deficient benzothiadiazole.
Co-reporter:Junhua Kong, Wu Aik Yee, Liping Yang, Yuefan Wei, Si Lei Phua, Hock Guan Ong, Jia Ming Ang, Xu Li and Xuehong Lu
Chemical Communications 2012 - vol. 48(Issue 83) pp:NaN10318-10318
Publication Date(Web):2012/08/24
DOI:10.1039/C2CC35284B
Thin carbonized polydopamine (C-PDA) coatings are found to have similar structures and electrical conductivities to those of multilayered graphene doped with heteroatoms. Greatly enhanced electrochemical properties are achieved with C-PDA-coated SnO2 nanoparticles where the coating functions as a mechanical buffer layer and conducting bridge.
Co-reporter:Rui Zhou, Wanshuang Liu, Xiayin Yao, Yew Wei Leong and Xuehong Lu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 31) pp:NaN16049-16049
Publication Date(Web):2015/06/30
DOI:10.1039/C5TA02154E
In this article, it is demonstrated that the electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF–HFP)) nanofibrous mat functionalized with (3-aminopropyl)triethoxysilane is a versatile platform for the fabrication of hybrid nanofibrous mats by covalently attaching various types of inorganic oxide nanoparticles on the nanofiber surface via a sol–gel process. In particular, SiO2-on-P(VDF–HFP) nanofibrous mats synthesized using this method is an excellent ionic liquid (IL) host for electrolyte applications. The IL-based electrolytes in the form of free-standing mats are obtained by immersing SiO2-on-P(VDF–HFP) mats in two types of liquid electrolytes, namely LiClO4/1-butyl-3-methylimidazolium tetrafluoroborate and bis(trifluoromethane)sulfonimide lithium salt/1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. It is found that the surface attached SiO2 nanoparticles can effectively serve as salt dissociation promoters by interacting with the anions of both ILs and lithium salts through Lewis acid–base interactions. They dramatically enhance the ionic conductivity and lithium transference number of the electrolytes. In addition, better compatibility of the electrolytes with lithium electrodes is also observed in the presence of surface-attached SiO2. Using IL-loaded SiO2-on-P(VDF–HFP) nanofibrous mats as the electrolytes, electrochromic devices display higher transmittance contrast, while Li/LiCoO2 batteries show significantly improved C-rate performance and cycling stability. This class of novel non-volatile electrolytes with high ionic conductivity also has the potential to be used in other electrochemical devices.
Co-reporter:Junhua Kong, Siew Yee Wong, Yu Zhang, Hui Ru Tan, Xu Li and Xuehong Lu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 40) pp:NaN15934-15934
Publication Date(Web):2011/09/07
DOI:10.1039/C1JM12492G
Carbon–SnO2 hybrid nanofibers with tunable morphology were prepared from polyacrylonitrile (PAN) and tin compounds via single-spinneret electrospinning and subsequent carbonization. Different tin compounds, including tin acetate (Sn(CH3COO)2), tin chloride dihydrate (SnCl2·2H2O), tin sulfate (SnSO4) and tin sulfide (SnS), were chosen as precursors of SnO2 to tune the morphology of carbon–SnO2 nanofibers. Morphology of the obtained nanofibers was studied using a field emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM), and their structures were characterized by thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). A carbon–SnO2 core–shell morphology is formed during carbonization when Sn(CH3COO)2 and SnCl2·2H2O are used as precursors of SnO2, while uniform distribution of Sn compounds in a carbon matrix is observed with SnSO4 or SnS as the precursor. Our study demonstrates that the Kirkendall effect, which is responsible for the formation of the core–shell morphology during carbonization, is strongly dependent on melting points and decomposition behaviours of the precursors. SnO2 nanofibers and nanotubes with a high aspect ratio were produced upon burning out carbon, and their morphology is dependent on that of the corresponding hybrid nanofibers. TEM studies show that the SnO2 nanofibers/nanotubes are constituted of SnO2 single crystals, yet the grain size and facet varies with the precursor. The Brunauer–Emmett–Teller (BET) study verifies that the nanofibers/nanotubes have a large surface area, which also varies with the precursors used.
Co-reporter:Wanshuang Liu, Kwang Liang Koh, Jinlin Lu, Liping Yang, Silei Phua, Junhua Kong, Zhong Chen and Xuehong Lu
Journal of Materials Chemistry A 2012 - vol. 22(Issue 35) pp:
Publication Date(Web):
DOI:10.1039/C2JM32708B
