Co-reporter:Xiaoli Zhao, Weiwei Gao, Weiquan Yao, Yanqiu Jiang, Zhen Xu, and Chao Gao
ACS Nano October 24, 2017 Volume 11(Issue 10) pp:9663-9663
Publication Date(Web):August 29, 2017
DOI:10.1021/acsnano.7b03480
The layer-by-layer (LbL) assembly approach has been widely used to fabricate multilayer coatings on substrates with multiple cycles, whereas it is hard to access thick films efficiently. Here, we developed an ion diffusion-directed assembly (IDDA) strategy to rapidly make multilayer thick coatings in one step on arbitrary substrates. To achieve multifunctional coatings, graphene oxide (GO) and metallic ions were selected as the typical building blocks and diffusion director in IDDA, respectively. With diffusion of metallic ions from substrate to negatively charged GO dispersion spontaneously (i.e., from high-concentration region to low-concentration region), GO was assembled onto the substrate sheet-by-sheet via sol–gel transformation. Because metallic ions with size of subnanometers can diffuse directionally and freely in the aqueous dispersion, GO was coated on the substrate efficiently, giving rise to films with desired thickness up to 10 μm per cycle. The IDDA approach shows three main merits: (1) high efficiency with a μm-scale coating rate; (2) controllability over thickness and evenness; and (3) generality for substrates of plastics, metals and ceramics with any shapes and morphologies. With these merits, IDDA strategy was utilized in the efficient fabrication of functional graphene coatings that exhibit outstanding performance as supercapacitors, electromagnetic interference shielding textiles, and anticorrosion coatings. This IDDA approach can be extended to other building blocks including polymers and colloidal nanoparticles, promising for the scalable production and application of multifunctional coatings.Keywords: assembly; coating; graphene oxide; ion diffusion; thick multilayer;
Co-reporter:Zheng Li, Tieqi Huang, Weiwei Gao, Zhen Xu, Dan Chang, Chunxiao Zhang, and Chao Gao
ACS Nano November 28, 2017 Volume 11(Issue 11) pp:11056-11056
Publication Date(Web):October 16, 2017
DOI:10.1021/acsnano.7b05092
Carbon textiles are promising electrode materials for wearable energy storage devices owing to their conductive, flexible, and lightweight features. However, there still lacks a perfect choice for high-performance carbon textile electrodes with sufficient electrochemical activity. Graphene fiber fabrics (GFFs) are newly discovered carbon textiles, exhibiting various attractive properties, especially a large variability on the microstructure. Here we report the fabrication of hierarchical GFFs with significantly enlarged specific surface area using a hydrothermal activation strategy. By carefully optimize the activation process, the hydrothermally activated graphene fiber fabrics (HAGFFs) could achieve an areal capacitance of 1060 mF cm–2 in a very thin thickness (150 μm) and the capacitance is easily magnified by overlaying several layers of HAGFFs, even up to a record value of 7398 mF cm–2. Meanwhile, a good rate capability and a long cycle life are also attained. As compared with other carbon textiles, including the commercial carbon fiber cloths, our HAGFFs present much better capacitive performance. Therefore, the mechanically stable, flexible, conductive, and highly active HAGFFs have provided an option for high-performance textile electrodes.Keywords: areal capacitance; graphene fiber fabrics; hierarchical structure; hydrothermal activation; supercapacitors; textile electrodes;
Co-reporter:Youhua Xiao, Zhen Xu, Yingjun Liu, Li Peng, Jiabin Xi, Bo Fang, Fan Guo, Peng Li, and Chao Gao
ACS Nano August 22, 2017 Volume 11(Issue 8) pp:8092-8092
Publication Date(Web):August 4, 2017
DOI:10.1021/acsnano.7b02915
Understanding and modulating the conformation of graphene are pivotal in designing graphene macroscopic materials. Here, we revealed the sheet collapsing behavior of graphene oxide (GO) sheets by poor solvents in an analogy with linear macromolecules. Triggered by poor solvents, extended GO sheets in good solvents can collapse to hierarchically wrinkled conformations. The collapsing behavior of GO enabled the fabrication of amorphous self-standing GO and graphene papers with rich hierarchical wrinkles and folds over mutliple size scales. The collapsed GO and graphene papers had a rubber-like mechanical behavior with viscoelasticity. By our collapsing method, GO and graphene self-standing papers were designed to be stiff with high modulus or to become soft with low modulus of 100 MPa at a remarkably large breakage elongation up to 23%. Our philosophy of treating graphene as a 2D polymer enables the efficient control of molecular conformations of graphene and other 2D polymers and the design of macroscopic materials of 2D nanomaterials as in the polymer industry.Keywords: graphene paper; rubber-like; sheet collapsing; viscoelasticity; wrinkles;
Co-reporter:Xiaoli Zhao, Zhen Xu, Yang Xie, Bingna Zheng, Liang Kou, and Chao Gao
Langmuir April 8, 2014 Volume 30(Issue 13) pp:3715-3722
Publication Date(Web):March 20, 2014
DOI:10.1021/la500553v
Stabilization of colloids is of great significance in nanoscience for their fundamental research and practical applications. Electrostatic repulsion-stabilized anisotropic colloids, such as graphene oxide (GO), can form stable liquid crystals (LCs). However, the electrostatic field would be screened by ions. To stabilize colloidal LCs against electrolyte is an unsolved challenge. Here, an effective strategy is proposed to stabilize GO LCs under harsh conditions by association of polyelectrolytes onto GO sheets. Using sodium poly(styrene sulfonate) (PSS) and poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PMEDSAH), a kind of polyzwitterion, GO LCs were well-maintained in the presence of NaCl (from 0 M to saturated), extreme pH (from 1 to 13), and serum. Moreover, PSS- or PMEDSAH-coated chemically reduced GO (rGO) also showed stability against electrolyte.
Co-reporter:Yingjun Liu, Hui Liang, Zhen Xu, Jiabin Xi, Genfu Chen, Weiwei Gao, Mianqi Xue, and Chao Gao
ACS Nano April 25, 2017 Volume 11(Issue 4) pp:4301-4301
Publication Date(Web):March 29, 2017
DOI:10.1021/acsnano.7b01491
Superconductors are important materials in the field of low-temperature magnet applications and long-distance electrical power transmission systems. Besides metal-based superconducting materials, carbon-based superconductors have attracted considerable attention in recent years. Up to now, five allotropes of carbon, including diamond, graphite, C60, CNTs, and graphene, have been reported to show superconducting behavior. However, most of the carbon-based superconductors are limited to small size and discontinuous phases, which inevitably hinders further application in macroscopic form. Therefore, it raises a question of whether continuously carbon-based superconducting wires could be accessed, which is of vital importance from viewpoints of fundamental research and practical application. Here, inspired by superconducting graphene, we successfully fabricated flexible graphene-based superconducting fibers via a well-established calcium (Ca) intercalation strategy. The resultant Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition at ∼11 K, which is almost 2 orders of magnitude higher than that of early reported alkali metal intercalated graphite and comparable to that of commercial superconducting NbTi wire. The combination of lightness and easy scalability makes Ca-GF highly promising as a lightweight superconducting wire.Keywords: Ca intercalation; carbon-based superconductor; graphene; graphene fiber; superconducting wire; wet-spinning;
Co-reporter:Li Peng;Zhen Xu;Zheng Liu;Yan Guo;Peng Li
Advanced Materials 2017 Volume 29(Issue 27) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/adma.201700589
Electrical devices generate heat at work. The heat should be transferred away immediately by a thermal manager to keep proper functions, especially for high-frequency apparatuses. Besides high thermal conductivity (K), the thermal manager material requires good foldability for the next generation flexible electronics. Unfortunately, metals have satisfactory ductility but inferior K (≤429 W m−1 K−1), and highly thermal-conductive nonmetallic materials are generally brittle. Therefore, fabricating a foldable macroscopic material with a prominent K is still under challenge. This study solves the problem by folding atomic thin graphene into microfolds. The debris-free giant graphene sheets endow graphene film (GF) with a high K of 1940 ± 113 W m−1 K−1. Simultaneously, the microfolds render GF superflexible with a high fracture elongation up to 16%, enabling it more than 6000 cycles of ultimate folding. The large-area multifunctional GFs can be easily integrated into high-power flexible devices for highly efficient thermal management.
Co-reporter:Hao Chen;Chen Chen;Yingjun Liu;Xiaoli Zhao;Nimrodh Ananth;Bingna Zheng;Li Peng;Tieqi Huang;Weiwei Gao
Advanced Energy Materials 2017 Volume 7(Issue 17) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/aenm.201700051
Poor quality and insufficient productivity are two main obstacles for the practical application of graphene in electrochemical energy storage. Here, high-quality crumpled graphene microflower (GmF) for high-performance electrodes is designed. The GmF possesses four advantages simultaneously: highly crystallized defect-free graphene layers, low stacking degree, sub-millimeter continuous surface, and large productivity with low cost. When utilized as carbon host for sulfur cathode, the GmF-sulfur hybrid delivers decent areal capacities of 5.2 mAh cm−2 at 0.1 C and 3.8 mAh cm−2 at 0.5 C. When utilized as cathode of Al-ion battery, the GmF affords a high capacity of 100 mAh g−1 with 100% capacity retention after 5000 cycles and excellent rate capability from 0.1 to 20 A g−1. This facile and large-scale producible GmF represents a meaningful high-quality graphene powder for practical energy storage technology. Meanwhile, this unique high-quality graphene design provides an effective route to improve electrochemical properties of graphene-based electrodes.
Co-reporter:Xiaoli Zhao;Weiquan Yao;Weiwei Gao;Hao Chen
Advanced Materials 2017 Volume 29(Issue 35) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adma.201701482
Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high-performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost-effective scalable fabrication and miniaturization with group effect. This study shows millimeter-scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core–shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure-elastic and adsorbing materials. The GS shows a press-fly behavior with an extremely high jump velocity up to 1.2 m s−1. For the first time, both free and oil-adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties.
Co-reporter:Zhen Xu, Li Peng, Yingjun Liu, Zheng Liu, Haiyan Sun, Weiwei Gao, and Chao Gao
Chemistry of Materials 2017 Volume 29(Issue 1) pp:
Publication Date(Web):September 12, 2016
DOI:10.1021/acs.chemmater.6b02882
Graphene macroscopic materials have attracted tremendous attention for their fascinating performance and rich functionalities. Here, we provide an elaborate description of techniques in the fabrication of graphene macroscopic materials, focusing on the wet-spinning of 1D fibers and wet-spinning of continuous 2D films and 3D ultraflyweight aerogels. The thread of the research concepts is discussed to offer an overview of graphene macroscopic assembly. We summarize the fabrication system of wet-spinning of fiber and films, which extends to the chemistry of solvated graphene, the formation of graphene LCs, and the chemical/thermal reduction of graphene materials. The experimental details of graphene ultraflyweight aerogel are also been described. We hope that this paper can act as an experimental guidance for researchers, and become suggestive for forthcoming advances in graphene macroscopic materials.
Co-reporter:Liang Kou;Yingjun Liu;Cheng Zhang;Le Shao;Zhanyuan Tian
Nano-Micro Letters 2017 Volume 9( Issue 4) pp:51
Publication Date(Web):16 August 2017
DOI:10.1007/s40820-017-0151-7
Nanocarbon-based materials, such as carbon nanotubes (CNTs) and graphene have been attached much attention by scientific and industrial community. As two representative nanocarbon materials, one-dimensional CNTs and two-dimensional graphene both possess remarkable mechanical properties. In the past years, a large amount of work have been done by using CNTs or graphene as building blocks for constructing novel, macroscopic, mechanically strong fibrous materials. In this review, we summarize the assembly approaches of CNT-based fibers and graphene-based fibers in chronological order, respectively. The mechanical performances of these fibrous materials are compared, and the critical influences on the mechanical properties are discussed. Personal perspectives on the fabrication methods of CNT- and graphene-based fibers are further presented.
Co-reporter:Jiabin Xi, Erzhen Zhou, Yingjun Liu, Weiwei Gao, Ji Ying, Zichen Chen, Chao Gao
Carbon 2017 Volume 124(Volume 124) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.carbon.2017.07.088
Microwave absorption (MA) materials have gained wide range of applications including satellite communications, radar detections, etc. Here, for the first time we designed high-performance porous biomass-pyrolized carbon (PBPC) based on natural wood. The PBPC with orderly parallel channel structure is on the top among all MA materials, showing excellent MA performance with maximum reflection loss (RL) of −68.3 dB and absorption bandwidth (RL ≤ −10 dB) up to 7.63 GHz. Furthermore, we predict the reflection loss by calculation and point out regulation of electrical conductivity would maximize MA performance. The combination of renewability, easy mass production and simple fabrication provides PBPC practical application value, and the strategy of channel structure design followed by permittivity adjustment casts a light for accessing new high-performance MA materials.Download high-res image (258KB)Download full-size image
Co-reporter:Bo Fang;Jiabin Xi;Yingjun Liu;Fan Guo;Zhen Xu;Weiwei Gao;Daoyou Guo;Peigang Li
Nanoscale (2009-Present) 2017 vol. 9(Issue 33) pp:12178-12188
Publication Date(Web):2017/08/24
DOI:10.1039/C7NR04175F
The interfacial adhesion between graphene and metals is poor, as metals tend to generate superlubricity on smooth graphene surface. This problem renders the free assembly of graphene and metals to be a big challenge, and therefore, some desired conducting properties (e.g., stable metal-like conductivities in air, lightweight yet flexible conductors, and ultralow temperature coefficient of resistance, TCR) likely being realized by integrating the merits of graphene and metals remains at a theoretical level. This work proposes a wrinkle-stabilized approach to address the poor adhesion between graphene surface and metals. Cyclic voltammetry (CV) tests and theoretical analysis by Scharifker–Hills models demonstrate that multiscale wrinkles effectively induce nucleation of metal particles, locking in metal nuclei and guiding the continuous growth of metal islands in an instantaneous model on rough graphene surface. The universality and practicability of the wrinkle-stabilized approach is verified by our investigation through the electrodeposition of nine kinds of metals on graphene fibers (GF). The strong interface bonding permits metal-graphene hybrid fibers to show metal-level conductivities (up to 2.2 × 107 S m−1, a record high value for GF in air), reliable weatherability and favorable flexibility. Due to the negative TCR of graphene and positive TCR of metals, the TCR of Cu- and Au-coated GFs reaches zero at a wide temperature range (15 K–300 K). For this layered model, the quantitative analysis by classical theories demonstrates the suitable thickness ratio of graphene layer and metal layer to achieve zero TCR to be 0.2, agreeing well with our experimental results. This wrinkle-stabilized approach and our theoretical analysis of zero-TCR behavior of the graphene-metal system are conducive to the design of high-performance conducting materials based on graphene and metals.
Co-reporter:Erzhen Zhou;Jiabin Xi;Yingjun Liu;Zhen Xu;Yan Guo;Li Peng;Weiwei Gao;Ji Ying;Zichen Chen
Nanoscale (2009-Present) 2017 vol. 9(Issue 47) pp:18613-18618
Publication Date(Web):2017/12/07
DOI:10.1039/C7NR07030F
As promising carbonaceous films, graphene films (GF) have exhibited many remarkable mechanical and electrical/thermal properties of great potential for wide functional applications. However, the electrical conductivity of GF still needs to be improved and the limitation lies in the low carrier density of pure graphene. Here, we presented a post-doping method for large-area potassium doped graphene films (GF-K) and promoted the electrical conductivity of GF approaching benchmark metals. The macroscopic-assembled GF-K shows a similar color to graphite intercalation compounds. The potassium doping increased the carrier density of the GF without undermining the electronic quality of the graphene unit. The doping concentration was optimized to prepare stage-2 GF-K (C24K) with the highest electrical conductivity (1.49 × 107 S m−1), holding merits of low density (1.63 g cm−3), and high flexibility. Doped GF with better specific electrical conductivity than copper showed outstanding electromagnetic interference shielding performance. Shielding effectiveness (SE) increased from 70–85 dB for graphene film (GF) to over 130 dB for GF-K only at 31 μm thickness, which is among the best SEs in previous reports. The combination of high specific conductivity, mechanical flexibility, high EMI SE, light weight, and facile productivity enables GF-K to be promising in many high-end EMI applications such as aerospace and wearable devices.
Co-reporter:Qishi Tian;Zhen Xu;Yingjun Liu;Bo Fang;Li Peng;Jiabin Xi;Zheng Li
Nanoscale (2009-Present) 2017 vol. 9(Issue 34) pp:12335-12342
Publication Date(Web):2017/08/31
DOI:10.1039/C7NR03895J
Graphene fiber (GF) has emerged as a new carbonaceous fiber species since graphene-based liquid crystals were discovered. The growing performances of GFs in terms of their mechanical performance and their functionalities have assured their extensive applications in structural materials and functional textiles. To date, many spinning strategies utilizing coagulation baths have been applied in GF, which necessitates a complicated washing process. Dry spinning is a more convenient and green method for use with fibers in the chemical fiber industry, and should be a good option for GFs; however, this technique has never been used in a system of GF. In this research, first the dry spinning technique was used to fabricate continuous GFs and the dry spun GFs showed good toughness and flexibility. The dry spinnability of graphene oxide liquid crystals was achieved by choosing dispersive solvents with low surface tension and high volatility. The dry spun neat GFs possessed high toughness up to 19.12 MJ m−3, outperforming the wet spun neat GFs. This dry spinning methodology facilitates the green fabrication of fibers of graphene and graphene-beyond two-dimensional nanomaterials, and it may also be extended to other printing technologies for complex graphene architectures.
Co-reporter:Qiuyan Yang;Zhen Xu;Bo Fang;Tieqi Huang;Shengying Cai;Hao Chen;Yingjun Liu;Karthikeyan Gopalsamy;Weiwei Gao
Journal of Materials Chemistry A 2017 vol. 5(Issue 42) pp:22113-22119
Publication Date(Web):2017/10/31
DOI:10.1039/C7TA07999K
Two dimensional MXene materials have demonstrated attractive electrical and electrochemical properties for various applications, particularly in energy storage, benefiting from their intrinsic 2D atomic thick topological structures. However, assembling MXene into macroscopic fibers with regular alignment still remains a huge challenge, inherently due to the insufficient interlaminar interaction between MXene sheets and the lack of well-developed assembling techniques. Herein, we report a wet-spinning assembly strategy for the continuous fabrication of MXene-based fibers through a synergistic effect between graphene oxides liquid crystals and MXene sheets. MXene sheets are orderly aligned between graphene oxides liquid crystalline templates and assembled into hybrid fibers with the highest MXene mass ratio achieving 95 w/w%. An excellent overall fiber electrical conductivity (2.9 × 104 S m−1) and superior volumetric capacitance (586.4 F cm−3) of the integrated fiber-constructed supercapacitor exceeding those of neat reduced graphene fibers were achieved.
Co-reporter:Tieqi Huang;Shengying Cai;Hao Chen;Yanqiu Jiang;Siyao Wang
Journal of Materials Chemistry A 2017 vol. 5(Issue 18) pp:8255-8260
Publication Date(Web):2017/05/10
DOI:10.1039/C7TA01921A
A meter-length, graphene-confined polypyrrole (GP) film was fabricated by a scalable wet-spinning technology. The GP film-assembled supercapacitors had an extremely high cycling stability (115% retention after 50 000 cycles) due to the delicate graphene-confined polypyrrole-layered structures. Highly flexible supercapacitors with different sizes were further assembled with a gel electrolyte.
Co-reporter:Shengying Cai;Tieqi Huang;Hao Chen;Muhammad Salman;Karthikeyan Gopalsamy
Journal of Materials Chemistry A 2017 vol. 5(Issue 43) pp:22489-22494
Publication Date(Web):2017/11/07
DOI:10.1039/C7TA07937K
Graphene/CNTs/35% PEDOT:PSS@CMC (GCP-35@CMC) ternary coaxial fibers were continuously prepared through coaxial wet-spinning technology. The GCP-35@CMC-assembled flexible fiber-shaped supercapacitors (FSCs) exhibited an advanced area specific capacitance (396.7 mF cm−2 at 0.1 mA cm−2) and energy density (13.8 μW h cm−2). This performance was ascribed to the synergistic effect of the well-designed ternary system and its special microstructures.
Co-reporter:Zhen Xu;Yingjun Liu;Xiaoli Zhao;Li Peng;Haiyan Sun;Yang Xu;Xibiao Ren;Chuanhong Jin;Peng Xu;Miao Wang
Advanced Materials 2016 Volume 28( Issue 30) pp:6449-6456
Publication Date(Web):
DOI:10.1002/adma.201506426
Co-reporter:Jia Yang;Haiyan Sun;Haiyi Liang;Hengxing Ji;Li Song;Hangxun Xu
Advanced Materials 2016 Volume 28( Issue 23) pp:4606-4613
Publication Date(Web):
DOI:10.1002/adma.201505855
Co-reporter:Bingna Zheng, Zhen Xu and Chao Gao
Nanoscale 2016 vol. 8(Issue 3) pp:1413-1420
Publication Date(Web):26 Nov 2015
DOI:10.1039/C5NR07067H
The output of graphene nanoscrolls (GNSs) has been greatly enhanced to the gram-level by using an improved spray-freeze-drying method without damaging the high transforming efficiency (>92%). The lowest bulk density of GNS foam reaches 0.10 mg cm−3. Due to the unique morphology and high specific surface area (386.4 m2 g−1), the specific capacitances of the GNSs (90–100 F g−1 at 1 A g−1) are all superior to those of multiwalled carbon nanotubes meanwhile maintaining excellent rate capabilities (60–80% retention at 50 A g−1). For the first time, all-graphene-based films (AGFs) are fabricated via the intercalation of GNSs into graphene layers. The AGF exhibits a capacitance of 166.8 F g−1 at 1 A g−1 and rate capability (83.9% retention at 50 A g−1) better than those of pure reduced graphene oxide (RGO) films and carbon nanotubes/graphene hybrid films (CGFs).
Co-reporter:Chen Chen, Zhen Xu, Yi Han, Haiyan Sun, and Chao Gao
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 12) pp:8000
Publication Date(Web):March 4, 2016
DOI:10.1021/acsami.6b00126
As a sort of scalable precursor of graphene, single-layer graphene oxide (GO) has received widespread attention. However, producing dried GO powder which can redisperse in solvents on a molecular level is still under challenge. Here, we have developed a strategy to obtain flower-shaped GO powder (fGO) via a low-temperature spray-drying method. Such GO powder can be redissolved in various solvents including water, with a concentration higher than 3 wt %. The excellent solubility of fGO is totally preserved even after being compressed into a high-density disk (1.26 g/cm3). The aqueous solution of fGO can form liquid crystals, which can be assembled into macroscopic graphene papers. By tracking the dissolution process of fGO, we reveal a “swelling–dissociation–stretching” behavior of the GO particles. For the first time, nuclear magnetic resonance (NMR) solution relaxation is applied to in situ monitor the degree of unfolding (DU) of fGO during dissolution. We discover that the classic polymer dissolution mechanism of linear polymer can extend to GO, a two-dimensional macromolecule. Our findings not only provide a solution for the problems in the transportation, storage and applications of GO, but also open a new way to adjust the microstructure of crumpled GO in large scale.Keywords: crumple; graphene oxide; high density; powder; redissolution; unfold
Co-reporter:Xiaozhen Hu;Sangeetha Rajendran;Yuansi Yao;Zheng Liu
Nano Research 2016 Volume 9( Issue 3) pp:735-744
Publication Date(Web):2016 March
DOI:10.1007/s12274-015-0952-2
Nacre is a lightweight, strong, stiff, and tough material, which makes it a mimicking object for material design. Many attempts to mimic nacre by various methods resulted in the synthesis of artificial nacre with excellent properties. However, the fabrication procedure was very laborious and time-consuming due to the sequential steps, and only limited-sized materials could be obtained. Hence, a novel design enabling scalable production of high-performance artificial nacre with uniform layered structures is urgently needed. We developed a novel wet-spinning assembly technique to rapidly manufacture continuous nacremimic graphene oxide (GO, brick)-sodium alginate (SA, mortar) films and fibers with excellent mechanical properties. At high concentrations, the GO-SA mixtures spontaneously produced liquid crystals (LCs) due to the template effect of GO, and continuous, 6 m long nacre-like GO-SA films were wet-spun from the obtained GO-SA liquid crystalline (LC) dope with a speed of up to 1.5 m/min. The assembled macroscopic GO-SA composites inherited the alignment of the GO sheets from the LC phase, and their mechanical properties were investigated by a joint experimental-computational study. The tensile tests revealed that the maximum strength (σ) and Young’s modulus (E) of the obtained films reached 239.6 MPa and 22.4 GPa, while the maximum values of σ and E for the fibers were 784.9 MPa and 58 GPa, respectively. The described wet-spinning assembly method is applicable for a large-scale and fast production of high-performance continuous artificial nacre.
Co-reporter:Zheng Li, Zheng Liu, Haiyan Sun, and Chao Gao
Chemical Reviews 2015 Volume 115(Issue 15) pp:7046
Publication Date(Web):July 13, 2015
DOI:10.1021/acs.chemrev.5b00102
Co-reporter:Yaochen Zheng, Sipei Li, Zhulin Weng and Chao Gao
Chemical Society Reviews 2015 vol. 44(Issue 12) pp:4091-4130
Publication Date(Web):23 Apr 2015
DOI:10.1039/C4CS00528G
Hyperbranched polymers (HPs) are highly branched three-dimensional (3D) macromolecules. Their globular and dendritic architectures endow them with unique structures and properties such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. HPs can be facilely synthesized via a one-pot polymerization of traditional small molecular monomers or emerging macromonomers. The great development in synthetic strategies, from click polymerization (i.e., copper-catalyzed azide–alkyne cycloaddition, metal-free azide–alkyne cycloaddition, strain-promoted azide–alkyne cycloaddition, thiol–ene/yne addition, Diels–Alder cycloaddition, Menschutkin reaction, and aza-Michael addition) to recently reported multicomponent reactions, gives rise to diverse HPs with desirable functional/hetero-functional groups and topologies such as segmented or sequential ones. Benefiting from tailorable structures and correspondingly special properties, the achieved HPs have been widely applied in various fields such as light-emitting materials, nanoscience and technology, supramolecular chemistry, biomaterials, hybrid materials and composites, coatings, adhesives, and modifiers. In this review, we mainly focus on the progress in the structural control, synthesis, functionalization, and potential applications of both conventional and segmented HPs reported over the last decade.
Co-reporter:Zhen Xu, Chao Gao
Materials Today 2015 Volume 18(Issue 9) pp:480-492
Publication Date(Web):November 2015
DOI:10.1016/j.mattod.2015.06.009
New fibers with increased strength and rich functionalities have been untiringly pursued by materials researchers. In recent years, graphene fiber has arisen as a new carbonaceous fiber with high expectations in terms of mechanical and functional performance. In this review, we elucidated the concept of sprouted graphene fibers, including strategies for their fabrication and their basic structural attributes. We examine the rapid advances in the promotion of mechanical/functional properties of graphene fibers, and summarize their versatile applications as multifunctional textiles. Finally, a tentative prospect is presented. We hope this review will lead to further work on this new fiber species.
Co-reporter:Li Peng, Yaochen Zheng, Jiachen Li, Yu Jin, and Chao Gao
ACS Catalysis 2015 Volume 5(Issue 6) pp:3387
Publication Date(Web):April 22, 2015
DOI:10.1021/acscatal.5b00233
Graphene oxide (GO) is highly attractive for catalysis because of its large specific surface area and rich chemical structures. However, it has generally been used as a catalyst carrier. Here, we designed a three-dimensional monolith of neat GO aerogel as a fixed-bed carbocatalyst used in the reaction of S → O acetyl migration for the synthesis of thiol compounds, showing the merits of ultrafast catalytic speed (5–8 h), high selectivity (100%), high yields (near 100%), easy isolation of products, and long-life recyclability (>18 times). Particularly, we achieved for the first time thiol compounds containing functional groups of halogen and hydroxyl, which cannot be synthesized using other currently reported catalysts. Control experiments demonstrated that the efficient catalysis mechanism is mainly attributed to the protonic functional groups, ultralarge size, and unpaired electrons of GO, as well as the “cage effect” at nanoscale confined spaces of aerogel cells.Keywords: acetyl migration; aerogel; carbocatalyst; fixed-bed; graphene oxide; thiol compound
Co-reporter:Tieqi Huang, Bingna Zheng, Zheng Liu, Liang Kou and Chao Gao
Journal of Materials Chemistry A 2015 vol. 3(Issue 5) pp:1890-1895
Publication Date(Web):08 Dec 2014
DOI:10.1039/C4TA06533F
We fabricated continuous wrinkle-structured graphene film electrodes by a wet-spinning method. The assembled supercapacitors showed an excellent rate performance (79% retention from 1 to 100 A g−1) with a high specific capacitance (177 F g−1 at 1 A g−1). When further functionalized with polyaniline, the electrodes maintained their wrinkled structure and showed an improved rate capability (90% retention from 1 to 100 A g−1) with a superior capacitance as high as 505 F g−1 (1 A g−1).
Co-reporter:Xiaoli Zhao, Bingna Zheng, Tieqi Huang and Chao Gao
Nanoscale 2015 vol. 7(Issue 21) pp:9399-9404
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5NR01737H
A novel all graphene coaxial fiber supercapacitor (GCS) was fabricated, consisting of a continuously wet-spun core graphene fiber and facilely dip-coated graphene sheath. GCS is flexible, lightweight and strong, and is also accompanied by a high specific capacitance of 205 mF cm−2 (182 F g−1) and high energy density of 17.5 μW h cm−2 (15.5 W h kg−1). The energy density was further improved to 104 μW h cm−2, when an organic ion liquid electrolyte was used.
Co-reporter:Liang Kou, Zheng Liu, Tieqi Huang, Bingna Zheng, Zhanyuan Tian, Zengshe Deng and Chao Gao
Nanoscale 2015 vol. 7(Issue 9) pp:4080-4087
Publication Date(Web):26 Jan 2015
DOI:10.1039/C4NR07038K
Supercapacitors with porous electrodes of graphene macroscopic assembly are supposed to have high energy storage capacity. However, a great number of “close pores” in porous graphene electrodes are invalid because electrolyte ions cannot infiltrate. A quick method to prepare porous graphene electrodes with reduced “close pores” is essential for higher energy storage. Here we propose a wet-spinning assembly approach based on the liquid crystal behavior of graphene oxide to continuously spin orientational graphene hydrogel films with “open pores”, which are used directly as binder-free supercapacitor electrodes. The resulting supercapacitor electrodes show better electrochemical performance than those with disordered graphene sheets. Furthermore, three reduction methods including hydrothermal treatment, hydrazine and hydroiodic acid reduction are used to evaluate the specific capacitances of the graphene hydrogel film. Hydrazine-reduced graphene hydrogel film shows the highest capacitance of 203 F g−1 at 1 A g−1 and maintains 67.1% specific capacitance (140 F g−1) at 50 A g−1. The combination of scalable wet-spinning technology and orientational structure makes graphene hydrogel films an ideal electrode material for supercapacitors.
Co-reporter:Yi Han, Yanqiu Jiang, and Chao Gao
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 15) pp:8147
Publication Date(Web):April 2, 2015
DOI:10.1021/acsami.5b00986
A sort of novel high-flux nanofiltration membrane was fabricated by synergistic assembling of graphene and multiwalled carbon nanotubes (MWNTs), in which graphene played the role of molecular sieving and MWNTs expanded the interlayer space between neighbored graphene sheets. The MWNT-intercalated graphene nanofiltration membrane (G-CNTm) showed a water flux up to 11.3 L m–2 h–1 bar–1, more than 2 times that of the neat graphene nanofiltration membrane (GNm), while keeping high dye rejection (>99% for Direct Yellow and >96% Methyl Orange). The G-CNTm also showed good rejection ratio for salt ions (i.e., 83.5% for Na2SO4, 51.4% for NaCl). We also explored the antifouling performance of G-CNTm and GNm with bovine serum albumin (BSA), sodium alginate (SA) and humic acid (HA). Both G-CNTm and GNm possessed excellent antifouling performance for SA and HA but inferior for BSA because of the strong interaction between protein and graphene sheets.Keywords: antifouling; carbon nanotubes; graphene membrane; high-flux; nanofiltration;
Co-reporter:Yu Jin, Jiachen Li, Li Peng and Chao Gao
Chemical Communications 2015 vol. 51(Issue 84) pp:15390-15393
Publication Date(Web):26 Aug 2015
DOI:10.1039/C5CC05396J
Silica gel, widely used in chromatography separation and as a catalyst carrier, was employed here for the first time as a fixed-bed catalyst for the S → O acetyl migration to synthesize thiol compounds under mild conditions, showing the merits of high efficiency, high selectivity, long-life recyclability, low cost and scalable availability.
Co-reporter:Bo Zhao, Yaochen Zheng, Zhulin Weng, Shengying Cai and Chao Gao
Polymer Chemistry 2015 vol. 6(Issue 20) pp:3747-3753
Publication Date(Web):24 Mar 2015
DOI:10.1039/C5PY00307E
This paper firstly revealed the electrophilic effect of thiol groups on thiol–yne polymerization. For this, we designed and synthesized five kinds of α-thiol-ω-alkynyl AB2 type intermediates with thiols with different electrophilicities. The thiol electrophilic effect can be assessed by chemical shift (δ) and measured directly by nuclear magnetic resonance (NMR) spectroscopy. As the evidence from gel permeation chromatography (GPC) and NMR tracking measurements shows, the polymerization rate and molecular weight (MW) were significantly enhanced as the thiol electrophilic effect reduced. On the contrary, with increasing electrophilicity of the thiol, the resultant degrees of branching (DBs) increased. The semiquantitative relation between reactive rate constant (k) and δ (or electrophilicity of thiol) can be expressed by k = 2.41–1.34δ. Therefore, important features of thiol–yne polymerization and HPTEs, such as rate constant (k), MW, DB, etc., can be roughly estimated in advance by the NMR measurement of the thiol's electrophilic effect.
Co-reporter:Bo Fang, Li Peng, Zhen Xu, and Chao Gao
ACS Nano 2015 Volume 9(Issue 5) pp:5214
Publication Date(Web):April 20, 2015
DOI:10.1021/acsnano.5b00616
All-inorganic fibers composed of neat 2D crystals possessing fascinating performance (e.g., alternately stacking layers, high mechanical strength, favorable electrical conductivity, and fire-resistance) are discussed in detail. We developed a wet-spinning assmebly strategy to achieve continuous all-inorganic fibers of montmorillonite (MMT) nanoplatelets by incorporation of a graphene oxide (GO) liquid crystal (LC) template at a rate of 9 cm/s, and the templating role of GO LC is confirmed by in situ confocal laser scanning microscopy and polarized optical microscopy inspections. After protofibers underwent thermal reduction, the obtained binary complex fibers composed of neat 2D crystals integrate the outstanding fire-retardance of MMT nanoplatelets and the excellent conductivity of graphene nanosheets. High-resolution transmission electron microscopy and scanning electron microscope observations reveal the microstructures of fibers with compactly stacking layers. MMT-graphene fibers show increaing tensile strengths (88–270 MPa) and electrical conductivities (130–10500 S/m) with increasing graphene fraction. MMT-graphene (10/90) fibers are used as fire-resistant (bearing temperature in air: 600–700 °C), lightweight (ρ < 1.62 g/cm3) conductors (conductivity: up to 1.04 × 104 S/m) in view of their superior performance in high-temperature air beyond commercial T700 carbon fibers. We attribute the fire-resistance of MMT-graphene fibers to the armor-like protection of MMT layers, which could shield graphene layers from the action of oxidative etching. The composite fibers worked well as fire-resistant conductors when being heated to glowing red by an alcohol lamp. Our GO LC-templating wet-spinning strategy may also inspire the continuous assembly of other layered crystals into high-performance composite fibers.Keywords: 2D crystals; conductor; fire-resistance; lightweight; liquid crystal; self-templating; wet-spinning;
Co-reporter:Zhen Xu and Chao Gao
Accounts of Chemical Research 2014 Volume 47(Issue 4) pp:1267
Publication Date(Web):February 20, 2014
DOI:10.1021/ar4002813
In nanotechnology, the creation of new nanoparticles consistently feeds back into efforts to design and fabricate new macroscopic materials with specific properties. As a two-dimensional (2D) building block of new materials, graphene has received widespread attention due to its exceptional mechanical, electrical, and thermal properties. But harnessing these attributes into new materials requires developing methods to assemble single-atom-thick carbon flakes into macroscopically ordered structures. Because the melt processing of carbon materials is impossible, fluid assembly is the only viable approach for meeting this challenge. But in the meantime, researchers need to solve two fundamental problems: creating orientational ordering in fluids and the subsequent phase-transformation from ordered fluids into ordered solid materials. To address these problems, this Account highlights our graphene chemistry methods that take advantage of liquid crystals to produce graphene fibers.We have successfully synthesized graphene oxide (GO) from graphite in a scalable manner. Using the size of graphite particles and post fractionation, we successfully tuned the lateral size of GO from submicron sizes to dozens of microns. Based on the rich chemistry of GO, we developed reliable methods for chemical or physical functionalization of graphene and produced a series of functionalized, highly soluble graphene derivatives that behave as single layers even at high concentrations.In the dispersive system of GO and functionalized graphenes, rich liquid crystals (LCs) formed spontaneously. Some of these liquid crystals had a conventional nematic phase with orientational order; others had a lamellar phase. Importantly, we observed a new chiral mesophase featuring a helical-lamellar structural model with frustrated disinclinations. The graphene-based LCs show ordered assembly behaviors in the fluid state of 2D colloids and lay a foundation for the design of ordered materials with optimal performances.Using the wet-spinning assembly approach, we transformed prealigned liquid crystalline dopes into graphene fibers (GFs) with highly ordered structures. We extended the wet-spinning assembly strategy to polymer-grafted or mixed graphene LCs to obtain hierarchically assembled, continuous nacre-mimetic fibers and hybridized graphene fibers. Both the neat GFs and the composite fibers are strong, flexible, electrically conductive, and chemically resistive. Multifunctional fibers that are both flexible and modular could be a key for applying atomically thin graphene in real-world materials and devices such as supercapacitors and solar cells.Therefore, we have opened a brand-new avenue for transforming mineral graphite into high performance, multifunctional GFs and offered an alternative strategy for the fabrication of carbon fibers. We hope that this Account and further efforts in the field will guide researchers toward the macroscopic assembly of graphene and its real-world applications.
Co-reporter:Xinxiang Lei ; Zhen Xu ; Han Sun ; Shun Wang ; Christian Griesinger ; Li Peng ; Chao Gao ;Ren X. Tan
Journal of the American Chemical Society 2014 Volume 136(Issue 32) pp:11280-11283
Publication Date(Web):July 30, 2014
DOI:10.1021/ja506074a
Residual dipolar couplings (RDCs) have proven to be an invaluable anisotropic NMR parameter for the structural elucidation of complex biopolymers and organic molecules. However, a remaining bottleneck limiting its wider use by organic and natural product chemists is the lack of a range of easily applicable aligning media for diverse organic solvents. In this study, graphene oxide (GO) liquid crystals (LCs) were developed to induce partial orientation of organic molecules to allow RDC measurements. These LCs were determined to be maintainable at very low concentrations (as low as 1 mg/mL, corresponding to quadrupolar 2H splittings ranging from 2.8 to 30 Hz and maximum 13C–1H dipolar couplings of 20 Hz for camphor in a CH3COCH3/water system) and to be remarkably stable and broadly compatible with aqueous and organic solvents such as dimethyl sulfoxide, CH3COCH3, and CH3CN. Moreover, compared with those for other alignment media, very clean and high-quality NMR spectra were acquired with the GO molecules in solution because of their rigidity and high molecular weight. The developed medium offers a versatile and robust method for RDC measurements that may routinize the RDC-based structure determination of organic molecules.
Co-reporter:Zhen Xu, Bingna Zheng, Jiewei Chen, and Chao Gao
Chemistry of Materials 2014 Volume 26(Issue 23) pp:6811
Publication Date(Web):November 3, 2014
DOI:10.1021/cm503418h
Graphene nanoscroll (GNS) is an important one-dimensional tubular form of graphitic carbon with characteristic open topology. It has been predicted to possess extraordinary properties that are significantly different from the analogical multiwalled carbon nanotubes. However, comprehensive experimental investigations on its properties and applications are still hindered by the lack of its reliable synthesis in high yield. To efficiently transform the scalable graphene oxide sheets into GNSs, here, we proposed a well-controlled lyophilization that comprises four sequential steps: chemical reduction of giant GO, freezing isolation of reduced graphene sheets, freeze-drying, and thermal annealing. The combined method has an extremely high efficiency, up to the record 92%. Systemic control experiments and cryo-SEM inspections revealed that the topological transformation from 2D sheet to 1D scroll is the sublimation-induced scrolling of individually confined graphene sheets in ice, which was controlled by chemical reduction, feed concentration, and freezing rate. GNSs exhibited high structural integration and were solution-processed into macroscopic forms. We also revealed the spontaneous swelling behavior of GNS in a reversible manner for the first time, verifying the featured open topology of GNS. Through this combined protocol, GNS can be scalably synthesized from massive graphene oxide with high efficiency, which should promote comprehensive research and massive applications in the real world.
Co-reporter:Zheng Liu, Zheng Li, Zhen Xu, Zhixiang Xia, Xiaozhen Hu, Liang Kou, Li Peng, Yangyang Wei, and Chao Gao
Chemistry of Materials 2014 Volume 26(Issue 23) pp:6786
Publication Date(Web):October 24, 2014
DOI:10.1021/cm5033089
Macroscopic assembled, self-standing graphene and graphene oxide (GO) films have been demonstrated as promising materials in many emerging fields, such as Li ion battery electrodes, supercapacitors, heat spreaders, gas separation, and water desalination. Such films were mainly available on centimeter-scale via the time- and energy-consuming vacuum-filtration method, which seriously impedes their progress and large-scale applications. Due to the incompatibility between large-scale and ordered assembly structures, it remains a big challenge to access large-area assembled graphene thick films. Here, we report for the first time a fast wet-spinning assembly strategy to produce continuous GO and graphene thick films. A 20 m long, 5 cm wide, well-defined GO film was readily achieved at a speed of 1 m min–1. The continuous, strong GO films were easily woven into bamboo-mat-like fabrics and scrolled into highly flexible continuous fibers. The reduced graphene films with high thermal and moderate electrical conductivities were directly used as fast-response deicing electrothermal mats. The fast yet controllable wet-spinning assembly approach paves the way for industrial-scale utilization of graphene.
Co-reporter:Karthikeyan Gopalsamy, Zhen Xu, Bingna Zheng, Tieqi Huang, Liang Kou, Xiaoli Zhao and Chao Gao
Nanoscale 2014 vol. 6(Issue 15) pp:8595-8600
Publication Date(Web):06 Jun 2014
DOI:10.1039/C4NR02615B
Graphene–bismuth oxide nanotube fiber as electrode material for constituting flexible supercapacitors using a PVA/H3PO4 gel electrolyte is reported with a high specific capacitance (Ca) of 69.3 mF cm−2 (for a single electrode) and 17.3 mF cm−2 (for the whole device) at 0.1 mA cm−2, respectively. Our approach opens the door to metal oxide–graphene hybrid fibers and high-performance flexible electronics.
Co-reporter:Bingna Zheng, Tieqi Huang, Liang Kou, Xiaoli Zhao, Karthikeyan Gopalsamy and Chao Gao
Journal of Materials Chemistry A 2014 vol. 2(Issue 25) pp:9736-9743
Publication Date(Web):28 Apr 2014
DOI:10.1039/C4TA01868K
Fiber-based micro-supercapacitors (F-mSCs) are new members of the energy storage family, which facilitate SCs with flexibility and expand their application to fields such as tiny, flexible and wearable devices. One of the biggest challenges for F-SCs is to enhance the energy density (E) and keep the flexibility at the same time. Here, for the first time we assembled a type of fiber-based asymmetric micro-supercapacitors (F-asym-mSCs) with two different graphene fiber-based electrodes. The excellent electrochemical performances (59.2 mF cm−2 and 32.6 mF cm−2) of both electrodes offered a chance to achieve high performance two-ply F-asym-mSCs. The potential window of F-asym-mSCs was expanded to 1.6 V, and both the area energy density (EA: 11.9 μW h cm−2) and the volume energy density (EV: 11.9 mW h cm−3) are the highest E ever reported in F-SCs. The F-asym-mSCs exhibit good cycling stability with a 92.7% initial capacitance retention after 8000 cycles and can be integrated into a fiber-like device to realize the flexibility of fibers.
Co-reporter:Jin Han, Yaochen Zheng, Shuai Zheng, Sipei Li, Tiannan Hu, Aijin Tang and Chao Gao
Chemical Communications 2014 vol. 50(Issue 63) pp:8712-8714
Publication Date(Web):19 May 2014
DOI:10.1039/C4CC01956C
A series of water soluble octa-functionalized POSSs were facilely synthesized via thiol–ene and Menschutkin click chemistry. Among them, octa-alkynyl POSS further reacted with azide-terminal alkyl long chains, resulting in a well-defined, amphiphilic octopus-like POSS. For the first time it was used for host–guest encapsulation and it exhibited an ultrahigh loading capability.
Co-reporter:ZhuLin Weng;Zhen Xu
Science China Chemistry 2014 Volume 57( Issue 4) pp:605-614
Publication Date(Web):2014 April
DOI:10.1007/s11426-013-5060-0
We prepared hyper-oxidized graphene (HOG) as a form of graphene derivative by additional oxidation of graphene oxide (GO) sheets. HOG, which formed more functional groups and isolated conjugated clusters on the sheets, accordingly showed high solubility in water and alcohols, high transmittance and film transparence, longer fluorescence decay constant time, and enhanced fluorescence in states of solution and solid. By contrast, GO has much weaker fluorescence in solution and its fluorescence is totally quenched in solid. The influences of concentration, metallic ions, and pH on HOG fluorescence in aqueous solution were also investigated in detail. Due to HOG’s strong fluorescence, direct visualization was realized on substrates and in solution. In addition, direct 3D fluorescence visualizations of HOG phase in polymer composites were achieved. These results show the great potential of HOG in a broad range of applications, from biological labeling, probes, and drug carriers to high-performance composites and nanomanipulation.
Co-reporter:Xiaoli Zhao, Zhen Xu, Yang Xie, Bingna Zheng, Liang Kou, and Chao Gao
Langmuir 2014 Volume 30(Issue 13) pp:3715-3722
Publication Date(Web):March 20, 2014
DOI:10.1021/la500553v
Stabilization of colloids is of great significance in nanoscience for their fundamental research and practical applications. Electrostatic repulsion-stabilized anisotropic colloids, such as graphene oxide (GO), can form stable liquid crystals (LCs). However, the electrostatic field would be screened by ions. To stabilize colloidal LCs against electrolyte is an unsolved challenge. Here, an effective strategy is proposed to stabilize GO LCs under harsh conditions by association of polyelectrolytes onto GO sheets. Using sodium poly(styrene sulfonate) (PSS) and poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PMEDSAH), a kind of polyzwitterion, GO LCs were well-maintained in the presence of NaCl (from 0 M to saturated), extreme pH (from 1 to 13), and serum. Moreover, PSS- or PMEDSAH-coated chemically reduced GO (rGO) also showed stability against electrolyte.
Co-reporter:Haiyan Sun;Zhen Xu
Advanced Materials 2013 Volume 25( Issue 18) pp:2554-2560
Publication Date(Web):
DOI:10.1002/adma.201204576
Co-reporter:Haiyan Sun;Zhen Xu
Advanced Materials 2013 Volume 25( Issue 18) pp:
Publication Date(Web):
DOI:10.1002/adma.201370116
Co-reporter:Zhen Xu;Haiyan Sun;Xiaoli Zhao
Advanced Materials 2013 Volume 25( Issue 2) pp:
Publication Date(Web):
DOI:10.1002/adma.201370013
Co-reporter:Zhen Xu;Zheng Liu;Haiyan Sun
Advanced Materials 2013 Volume 25( Issue 23) pp:3249-3253
Publication Date(Web):
DOI:10.1002/adma.201300774
Co-reporter:Zhen Xu;Haiyan Sun;Xiaoli Zhao
Advanced Materials 2013 Volume 25( Issue 2) pp:188-193
Publication Date(Web):
DOI:10.1002/adma.201203448
Co-reporter:Yi Han;Zhen Xu
Advanced Functional Materials 2013 Volume 23( Issue 29) pp:3693-3700
Publication Date(Web):
DOI:10.1002/adfm.201202601
Abstract
A method of fabricating ultrathin (≈22–53 nm thick) graphene nanofiltration membranes (uGNMs) on microporous substrates is presented for efficient water purification using chemically converted graphene (CCG). The prepared uGNMs show well packed layer structure formed by CCG sheets, as characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The performance of the uGNMs for water treatment was evaluated on a dead end filtration device and the pure water flux of uGNMs was high (21.8 L m−2 h−1 bar−1). The uGNMs show high retention (>99%) for organic dyes and moderate retention (≈20–60%) for ion salts. The rejection mechanism of this kind of negatively charged membranes is intensively studied, and the results reveal that physical sieving and electrostatic interaction dominate the rejection process. Because of the ultrathin nature of uGNMs, 34 mg of CCG is sufficient for making a square meter of nanofiltration membrane, indicating that this new generation graphene-based nanofiltration technology would be resource saving and cost-effective. The integration of high performance, low cost, and simple solution-based fabrication process promises uGNMs great potential application in practical water purification.
Co-reporter:Liang Kou and Chao Gao
Nanoscale 2013 vol. 5(Issue 10) pp:4370-4378
Publication Date(Web):12 Mar 2013
DOI:10.1039/C3NR00455D
Nacre is characterized by its excellent mechanical performance due to the well-recognized “brick and mortar” structure. Many efforts have been applied to make nacre-mimicking materials, but it is still a big challenge to realize their continuous production. Here, we prepared sandwich-like building blocks of poly(vinyl alcohol) (PVA)-coated graphene, and achieved high-nanofiller-content kilometers-long fibers by continuous wet-spinning assembly technology. The fibers have a strict “brick and mortar” layered structure, with graphene sheet as rigid brick and PVA as soft mortar. The mortar thickness can be precisely tuned from 2.01 to 3.31 nm by the weight feed ratio of PVA to graphene, as demonstrated by both atomic force microscopy and X-ray diffraction measurements. The mechanical strength of the nacre-mimicking fibers increases with increasing the content of PVA, and it rises gradually from 81 MPa for the fiber with 53.1 wt% PVA to 161 MPa for the fiber with 65.8 wt% PVA. The mechanical performance of our fibers was independent of the molecular weight (MW) of PVA in the wide range of 2–100 kDa, indicating that low MW polymers can also be used to make strong nanocomposites. The tensile stress of fibers immersed in PVA 5 wt% solution reached ca. 200 MPa, surpassing the values of nacre and most of other nacre-mimicking materials. The nacre-mimicking fibers are highly electrically conductive (∼350 S m−1) after immersing in hydroiodic acid, enabling them to connect a circuit to illuminate an LED lamp.
Co-reporter:Sipei Li and Chao Gao
Polymer Chemistry 2013 vol. 4(Issue 16) pp:4450-4460
Publication Date(Web):30 May 2013
DOI:10.1039/C3PY00546A
Multifunctional dendritic molecular brushes (DMBs) with pendent poly(glycidyl methacrylate) (PGMA) chains were synthesized via a sequential reversible addition–fragmentation chain transfer (RAFT) polymerization approach. By controlling the kinetics of the polymerization, DMBs with a high number-averaged molecular weight (Mn) of ∼1.4 × 106 g mol−1 and narrow polydispersity index (PDI) of 1.50 were obtained. DMBs were reacted with sodium azide, giving rise to giant macromolecules with a high density of hydroxyl and azide bifunctional groups. Pyrene moieties (with a conventional chromophore) were efficiently attached to the DMBs by esterification, affording solution-emissive blue-light DMBs. Ultrahigh excimer emission at 475 nm was achieved for these fluorescent DMBs at a very low concentration of pyrene (∼10−7 mol L−1). Alternatively, tetraphenylethylene (TPE, with an aggregation-induced emission (AIE) chromophore) units were attached to DBMs with a conversion of 100% by copper-catalyzed alkyne–azide click chemistry. The solid-state-emissive blue-light TPE-functionalized DMBs exhibited typical AIE (rather than aggregation enhanced emission, AEE) effect which was rarely observed for dendritic scaffolds and its quantum yield at aggregated state is two times higher than that of fluorophore monomer. Such topology-induced unusual emission phenomena were attributed to the cage effect of DMBs.
Co-reporter:Jin Han, Dandan Zhu and Chao Gao
Polymer Chemistry 2013 vol. 4(Issue 3) pp:542-549
Publication Date(Web):13 Sep 2012
DOI:10.1039/C2PY20432K
A novel bulk click polymerization (BCP) approach was determined to prepare alternative multiblock copolymers (AMCs). Poly(ε-caprolactone) (PCL) and polyethylene glycol (PEG) were first modified into azide and alkyne terminated macromonomers by esterification, respectively. Subsequent azide–alkyne click polymerization of the two macromonomers in bulk without any solvents using CuBr/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as a catalyst system afforded AMCs with higher degrees of polymerization (DPs) than those obtained via solution polymerization (SP) in the control experiments. Through this approach, within 1 h (normally 5 min), AMCs were obtained with high DPs of up to 16, as revealed by gel permeation chromatography (GPC). Studies on the thermal properties of the AMCs showed that the alternating structure confined the crystallizations of the PCL and PEG blocks. The solution self-assembly behavior of the amphiphilic AMCs was investigated for the first time, and interesting structures such as globules, fibers, and worms were observed by means of atomic force microscopy (AFM). Additionally, hyperbranched AMCs were also prepared via an A2 + B3 strategy.
Co-reporter:Sipei Li, Jin Han and Chao Gao
Polymer Chemistry 2013 vol. 4(Issue 6) pp:1774-1787
Publication Date(Web):28 Nov 2012
DOI:10.1039/C2PY20951A
A new kind of segmented hyperbranched polymers (SHPs), hyperbranched poly(glycidyl methacrylate)s (HPGMAs), were synthesized via reversible addition–fragmentation chain transfer self-condensing vinyl polymerization (RAFT-SCVP). HPGMAs were efficiently functionalized on the whole scaffold via a collection of click chemistries, including the azidation of oxirane, thiol–epoxy click chemistry, thiol–ene click chemistry, copper-catalyzed azide–alkyne cycloaddition (CuAAC), and Menschutkin chemistry, affording SHPs with hetero-functional groups including hydroxyl + azide, dual hydroxyl, triple hydroxyl, hydroxyl + tertiary amine, hydroxyl + alkene, hydroxyl + carboxyl, alkene + azide, alkyne + azide, hydroxyl + alkyne, dual hydroxyl + alkene etc., all at ∼100% conversion. “Thiol–epoxy + thiol–ene” sequential dual click and “thiol–epoxy + Menschutkin chemistry + CuAAC” triple click strategies were presented, making functional group transformation readily accessible. Hydrophilic dendritic brushes, hydrophobic dendritic brushes and amphiphilic dendritic hetero-brushes were synthesized. Esterification of SHP containing hydroxy and azido groups with 1-pyrenebutyric acid yielded clickable fluorescent macromolecules, which showed a very strong excimer emission.
Co-reporter:Zheng Liu, Zhen Xu, Xiaozhen Hu, and Chao Gao
Macromolecules 2013 Volume 46(Issue 17) pp:
Publication Date(Web):August 21, 2013
DOI:10.1021/ma400681v
Liquid crystals (LCs) of pristine graphene oxide (GO), a kind of novel two-dimensional (2D) macromolecule, have been discovered recently, opening an avenue to high performance neat graphene fibers. Here, we report for the first time LC of polymer-grafted GO and its macroscopic assembled nacre-mimetic composite. Polyacrylonitrile (PAN) chains were covalently and uniformly grafted onto GO surfaces via a simple free radical polymerization process. The PAN-grafted GO (GO-g-PAN) sheets were well dispersed in polar organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), forming nematic and lamellar LCs upon increasing concentration. A strong signal was found in the circular dichroism spectra of the LCs, indicating the formation of helical lamellar structures for the GO-g-PAN LCs. Macroscopic assembled fibers were continuously spun from the GO-g-PAN LCs via the industrially viable wet-spinning technology. The fibers held strict layered structures of GO and PAN, resembling the classic “brick-and-mortar” microstructure observed in nacre. The nacre-mimetic composite showed excellent mechanical property with tensile strength of 452 MPa, Young’s modulus of 8.31 GPa, and breakage elongation of 5.44%. This offers a new approach for the fabrication of continuous, ultrastrong, and tough biomimic composites.
Co-reporter:Jin Han, Bo Zhao, Aijin Tang, Yanqin Gao and Chao Gao
Polymer Chemistry 2012 vol. 3(Issue 7) pp:1918-1925
Publication Date(Web):25 Oct 2011
DOI:10.1039/C1PY00367D
Fast and scalable production of hyperbranched polythioether-ynes was achieved by applying sequential click chemistry (SCC) via couple-monomer methodology (CMM). As a typical example, thiol-halogen click-like reaction employing strong base, KOH and thiol-yne click reaction via UV irradiation were used for precursor preparation and polymerization, respectively. Two series of hyperbranched polythioether-ynes employing two kinds of di-thiols with different reactivity have been prepared within 10 h and characterized with 1H NMR spectroscopy and gel permeation chromatography. The hyperbranched polymers (HPs) derived from 1,6-hexanedithiol reached high weight-average molecular weight (Mw) of 230500, high weight-average degree of polymerization (DPw) of 1224 and high degree of branching (DB) of 0.82–0.68. Postmodification of abundant alkyne terminal groups afford HPs with a greatly enhanced DB of 0.96. Heat-initiated polymerization was also attempted. The present study clearly demonstrates the robustness of application of SCC technique in the CMM strategy for fast, scalable preparation of multifunctional HPs.
Co-reporter:Jin Han, Sipei Li, Aijin Tang, and Chao Gao
Macromolecules 2012 Volume 45(Issue 12) pp:4966-4977
Publication Date(Web):June 15, 2012
DOI:10.1021/ma300718d
A series of novel and narrowly polydispersed regular chain-segmented hyperbranched poly(tertiary amino methacrylate)s (HPTAM)s with hydrophilic core and hydrophobic shell were synthesized via the combination of self-condensing vinyl copolymerization (SCVCP) and reversible addition–fragmentation chain transfer (RAFT) methodology. 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and 2-((2-(((dodecylthio)carbonothioyl)thio)-2-methylpropanoyl)oxy)ethyl acrylate (ACDT) at various molar feed ratios (γ, [DMAEMA]:[ACDT]) were chosen as monomers for linear segment formation of the structure. The copolymerization kinetics revealed that during the polymerization the real-time γ value kept almost constant and was consistent with the initial feed ratio. So HPTAMs possesses regular linear chains between every two neighboring branching units, which closely resemble HyperMacs in structure. Fast click-like Menschutkin reaction (i.e., quaternarization) of the segmented hyperbranched polymers with propargyl bromide and 2-azidoethyl 2-bromoacetate readily afforded water-soluble and clickable poly(propargyl quaternary ammonium methacrylate) (HPPrAM) and poly(azide quaternary ammonium methacrylate) (HPAzAM), respectively. Through Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC), the HPPrAMs were functionalized with 1-azidododecane and 2-azidoethyl 2-bromoisobutyrate, giving birth to amphiphilic hyperbranched polyelectrolytes (or hyperbranched surfactants) and hyperbranched ATRP macroinitiators, respectively. The HPAzAMs were efficiently decorated with monoalkynyl poly(ethylene glycol) (PEG-Alk) via CuAAC, generating dendritic polymer brushes, a novel architecture reported for the first time. In addition, core-functionazlied star-shaped HPPrAM-star-poly(tert-butyl acrylate) was synthesized by RAFT copolymerization and Menschutkin reaction.
Co-reporter:Yi Han;XiaoHua He
Science China Chemistry 2012 Volume 55( Issue 4) pp:604-611
Publication Date(Web):2012 April
DOI:10.1007/s11426-011-4421-9
Reversible assembly and disassembly of rod-like large complex micelles have been achieved by applying photoswitching of supramolecular inclusion and exclusion of azobenzene-functionalized hyperbranched polyglycerol and α-cyclodextrin as driving force, promising a versatile system for self-assembly switched by light. Hydrogen-nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy were applied to characterize the azobenzene-functionalized hyperbranched polyglycerol. Atomic force microscopy (AFM), transmission electron microscopy (TEM) and dynamic laser light scattering (DLS) were employed to investigate and track the morphology of the rod-like large complex micelles before and after irradiation of UV light.
Co-reporter:Haiyan Sun, Jin Han, Chao Gao
Polymer 2012 Volume 53(Issue 14) pp:2884-2889
Publication Date(Web):21 June 2012
DOI:10.1016/j.polymer.2012.04.038
An easy, one-pot, high-yield preparation of high molecular weight polyrotaxanes (PRs) from poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) by click chemistry is presented with novel water soluble and clickable end-capping agents containing quaternary ammonium and propargyl groups. The threading numbers of α-CD on the PEG chain were investigated by means of 1H NMR spectroscopy and gel permeation chromatography (GPC). When Mn of the PEG axis is 35 kDa, the yield is up to 614 mg per 100 mg PEG axis and the average number of α-CDs on each PEG axis is 193. Wide-angle X-ray diffraction (WAXD) revealed that PRs form a column-type crystalline structure. The prepared PR possesses terminal alkyne groups which can connect with functional molecules to make the PR more useful. As a typical example, fluorescent rhodamine B has been successfully installed on the PR terminals.
Co-reporter:LanYan Kan;BingNa Zheng
Science Bulletin 2012 Volume 57( Issue 23) pp:3026-3029
Publication Date(Web):2012 August
DOI:10.1007/s11434-012-5252-6
Graphene, a perfect two-dimensional (2D) nanostructure, is an ideal template for 2D material design. We developed a graphene- templated method to synthesize 2D silica nanosheets through the crosslinking of poly(3-methacryloxypropyl trimethoxysilane)-grafted graphene oxide (GO-g-PMPS), followed by pyrolysis at 700°C for 10 h.
Co-reporter:Zhen Xu, Yuan Zhang, Peigang Li, and Chao Gao
ACS Nano 2012 Volume 6(Issue 8) pp:7103
Publication Date(Web):July 16, 2012
DOI:10.1021/nn3021772
Liquid crystals of anisotropic colloids are of great significance in the preparation of their ordered macroscopic materials, for example, in the cases of carbon nanotubes and graphene. Here, we report a facile and scalable spinning process to prepare neat “core–shell” structured graphene aerogel fibers and three-dimensional cylinders with aligned pores from the flowing liquid crystalline graphene oxide (GO) gels. The uniform alignment of graphene sheets, inheriting the lamellar orders from GO liquid crystals, offers the porous fibers high specific tensile strength (188 kN m kg–1) and the porous cylinders high compression modulus (3.3 MPa). The porous graphene fibers have high specific surface area up to 884 m2 g–1 due to their interconnected pores and exhibit fine electrical conductivity (2.6 × 103 to 4.9 × 103 S m–1) in the wide temperature range of 5–300 K. The decreasing conductivity with decreasing temperature illustrates a typical semiconducting behavior, and the 3D interconnected network of 2D graphene sheets determines a dual 2D and 3D hopping conduction mechanism. The strong mechanical strength, high porosity, and fine electrical conductivity enable this novel material of ordered graphene aerogels to be greatly useful in versatile catalysts, supercapacitors, flexible batteries and cells, lightweight conductive fibers, and functional textiles.Keywords: aerogel; aligned pores; graphene fiber; graphene oxide; liquid crystal
Co-reporter:Li Zhou, Chao Gao, Xiaozhen Hu, and Weijian Xu
Chemistry of Materials 2011 Volume 23(Issue 6) pp:1461
Publication Date(Web):February 22, 2011
DOI:10.1021/cm1030359
A general strategy to synthesize multifunctional aqueous nanocrystals is presented and demonstrated in this paper. Using multihydroxy hyperbranched polyglycerol (HPG) with high molecular weight (>20 KDa) as a stabilizer, a variety of nanocrystals (e.g., monometallic, alloy of noble metal, semiconductor, magnetic, rare-earth, and silver halide nanocrystals) are readily and rapidly synthesized at room temperature in water or N,N-dimethylformamide (DMF) with high yield (>90%). The resulting HPG-stabilized nanocrystals show uniform and small sizes, good solubility in water and polar organic solvents (e.g., DMF, methanol, ethylene glycol (EG), and ethanol), favorable biocompatibility, excellent stability, and multihydroxyl groups. The surface hydroxyl groups of nanocrystals can be further tailored with various functional molecules (e.g., amino acids). Our methodology paves the way for fast, facile, and large-scale fabrication of multifunctional aqueous nanocrystals, opening up enormous opportunities to use the nanocrystals for many technological applications.Keywords: hybrid inorganic/organic materials; nanomaterials (nanoparticles, nanotubes, etc.); semiconductors;
Co-reporter:Liang Kou and Chao Gao
Nanoscale 2011 vol. 3(Issue 2) pp:519-528
Publication Date(Web):25 Nov 2010
DOI:10.1039/C0NR00609B
We report a facile strategy to synthesize silica nanoparticles-coated graphene oxide (GO–SiO2) nanohybrids in a water–alcohol mixture at room temperature. AFM observations revealed that silica nanoparticles with ca. 50 nm in size were densely and evenly covered on graphene oxide sheets. Due to the space layer of silica nanoparticles, micro-scale GO–SiO2 hybrid plates could be individually dispersed in water and polar organic solvents, promising good solution-based processibility. The growth process of GO-supported silica is traced by TGA and XRD measurements, showing that 24 hours is enough to achieve a fine cover effect for the disappearance of (002) diffraction peak of GO. Based on the high dense overlaying of silica nanoparticles, up to micro-scale silica sheets with thickness of ca. 8 nm were readily fabricated by burning GO–SiO2 at 650 °C in air. Likewise, a centimeter-scale semitransparent film of silica nanosheets was prepared by calcining a GO–SiO2 film. Interestingly, the GO–SiO2 nanohybrids exhibit excellent hydrophilic nature and can be directly applied as a general kind of building blocks to construct large-area superhydrophilic surfaces on arbitrary substrates (e.g., lotus leaf, ceramic tile and polypropylene) through the simple drop-coating method. Such a coating methodology paves the way for making large-area superhydrophilic surface without extra process treatments and damaging the intrinsic structure of substrates.
Co-reporter:Jin Han, Bo Zhao, Yanqin Gao, Aijin Tang and Chao Gao
Polymer Chemistry 2011 vol. 2(Issue 10) pp:2175-2178
Publication Date(Web):29 Jul 2011
DOI:10.1039/C1PY00235J
Sequential thiol–ene and thiol–yne click chemistry via the A2 + CB2 protocol is presented for simple, rapid, and scalable production of hyperbranched polymers, affording hyperbranched polythioether–ynes with high molecular weight and high degree of branching.
Co-reporter:HongKun He
Science China Chemistry 2011 Volume 54( Issue 2) pp:397-404
Publication Date(Web):2011 February
DOI:10.1007/s11426-010-4191-9
We report that noble metal nanopartcles (Pd, Pt, Au, and Ag) decorated-graphene nanosheets can be synthesized with the template of graphene oxide by a one-pot solution-based method. The resulting hybrid materials are characterized by transmission electronic microscopy, energy dispersive X-ray spectroscopy, scanning electronic microscopy, atomic force microscopy, X-ray diffraction, and Raman spectroscopy, which demonstrate that the metal nanoparticles have been uniformly deposited on the surfaces of graphene nanosheets. Our results in turn verify that the carboxylic groups of graphene oxide are statistically distributed on its whole sheet surface rather than just at its edges. The graphene-metal nanohybrids can be used as catalysts in the reduction of potassium hexacyanoferrate(III) with NaBH4 in aqueous solution. Our results suggest that graphene is a superior substrate to support metals for applications in the heterogeneous catalysis.
Co-reporter:Xiaozhen Hu;Li Zhou
Colloid and Polymer Science 2011 Volume 289( Issue 12) pp:1299-1320
Publication Date(Web):2011 August
DOI:10.1007/s00396-011-2457-1
Colloid nanocrystals (NCs) mainly include metal nanocrystals, semiconductor nanocrystals, and insulator nanocrystals, exhibiting interesting size-dependent electrical, optical, magnetic, and chemical properties that cannot be achieved by their bulk counterparts. However, there’s a critical problem that NCs tend to aggregate, which induces degradation of their performance. Hyperbranched polymers (HPs) possess excellent attributes of three-dimensional topology, low viscosity, good solubility, and plenty of modifiable terminal groups. The combination of NCs and HPs to form nanohybrids cannot only endow NCs with multifunctionality, uniform dispersibility, and splendid solubility but also can impart extra properties to HPs. This article reviews the recent progress and state-of-the-art of the synthesis and applications of NCs-HPs nanohybrids (NHBs). NHBs can be obtained by three approaches: HPs first (i.e., NCs are formed with the stabilizer of HPs), NCs first (i.e., HPs are grafted on the surface of as-prepared NCs), and ligand exchange (the original ligand of NCs is replaced with HPs). Various HPs including hyperbranched poly(amidoamine), polyethylenimine, polyglycerol, polyester, polyamide, polyurethane, and poly(3-ethyl-3-hydroxymethyloxetane), as well as sorts of NCs such as metals (e.g., Ag, Au, Pd, Pt, and Rh), quantum dots (e.g., ZnO, CdS, CdTe, CdSe, and SnO2), magnetic oxides (e.g., Fe3O4), rare earth compounds, and so forth, have been used to obtain NHBs. The NHBs can be applied in nanocatalysis, antimicrobia, biosensor, biological labeling, and other fields promising their bright future.
Co-reporter:Zhen Xu and Chao Gao
ACS Nano 2011 Volume 5(Issue 4) pp:2908
Publication Date(Web):March 4, 2011
DOI:10.1021/nn200069w
The formation of liquid crystals (LCs) is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. Herein, we have discovered that well-soluble and single-layered graphene oxide (GO) sheets can exhibit nematic liquid crystallinity in water and first established their isotropic−nematic solid phase diagram versus mass fraction and salt concentration. The zeta potential of GO dispersion is around −64 mV, and its absolute value decreases with increasing salt concentration, implying that the electrostatic repulsive force between negatively charged GO sheets is the dominant interaction in the system of GOLCs and also explaining the salt-dependent phase behavior. For single-layer GO sheets with average diameter of 2.1 μm and polydispersity index of 83%, the isotropic−nematic phase transition occurs at a mass concentration of ∼0.025%, and a stable nematic phase forms at ∼0.5%. Rheological measurements showed that GO aqueous dispersions performed as typical shear flows and confirmed the isotropic−nematic transition. The ordering of GO sheets in aqueous dispersions and the solid state is demonstrated by the characterizations of polarized-light optical microscopy, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The direct, real-time fluorescent inspections by confocal laser microscopy further reveal that the individually dispersed fluorescent GO sheets align with orientational directions along their long axes. These novel findings shed light on the phase behaviors of diversely topological graphenes and lay the foundation for fabrication of long-range, ordered nano-objects and macroscopically assembled graphene-based functional materials.Keywords: graphene oxide; liquid crystal; nematic; orientational ordering; phase transition
Co-reporter:Lanyan Kan, Zhen Xu, and Chao Gao
Macromolecules 2011 Volume 44(Issue 3) pp:444-452
Publication Date(Web):December 31, 2010
DOI:10.1021/ma102371d
We present a general strategy for facile synthesis of 2D macromolecular brushes. The ultraflat one-atomic layer of graphene oxide with micrometer-scale sheet topology was employed as the macromolecular backbone; more than 10 types of polymer chains were covalently tethered to the nanosheets through free radical polymerization, producing various 2D molecular brushes with multifunctional arms covering from polar to apolar, water-soluble to oil-soluble, acidic to basic, and functional to common polymers. The resulting molecular brushes are well soluble in desired solvents in the forms of individually dispersed hairy nanosheets. The growing process of 2D molecular brushes was clearly visualized by AFM. The giant 2D brushes with arm density up to 1.59 × 104 arms per μm2 of single side of graphene show high solubility (∼15 mg/mL), low intrinsic viscosity (∼100 mL/g), and fine electrical conductivity (∼8.4 × 10−3 S/cm), and they can possess numerous epoxy and other functional groups at their arms if necessary, promising a luciferous foreground in both scientific research and industrial applications. The polymer-grafted graphene oxide can be well dispersed in free polymer matrix and can be well soluble in solvents again, suggesting that nanocomposite of polymer-grafted graphene oxide and polymer can be readily produced by the solution-processing technique.
Co-reporter:Hongkun He and Chao Gao
Chemistry of Materials 2010 Volume 22(Issue 17) pp:5054
Publication Date(Web):August 10, 2010
DOI:10.1021/cm101634k
A unified approach to covalently functionalize graphene nanosheets based on nitrene chemistry is reported. This strategy is simple and efficient, allowing various functional moieties (e.g., hydroxyl, carboxyl, amino, bromine, long alkyl chain, etc.) and polymers (e.g., poly(ethylene glycol), polystryene) to covalently and stably anchor on graphene to produce single-layer functionalized graphene from graphene oxide in a one-step reaction. The structure and morphology of nanosheets are characterized using microscopy (AFM, SEM, TEM), spectroscopy (FTIR, XPS, Raman), thermal gravimetric analysis (TGA), and X-ray diffraction (XRD) measurements. The resulting functionalized graphene nanosheets are electrically conductive, readily dispersible in solvents and easily processable, making them promising candidates for further modification and applications such as nanohybrids, and polymer composites, etc. The presented work provides a general methodology to prepare individually dispersed graphene nanosheets with various functionalizations and properties, paving the way for the synthesis and applications of functionalized graphene materials.
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
Journal of Materials Chemistry A 2010 vol. 20(Issue 27) pp:5675-5681
Publication Date(Web):07 Jun 2010
DOI:10.1039/C0JM00211A
Quantum dot (QD)-polymer nanocomposites that simultaneously possess stable photoluminescence and enhanced mechanical properties are presented for the first time based on the facile blending of the ultrasmall silica-hybridized CdTe QDs (SiO2-h-QDs) or 3-(trimethoxysilyl)propyl methacrylate-modified SiO2-h-QDs (SiO2-h-QD-MSMAs) with polymer. Typically, for SiO2-h-QD-MSMA/poly(methyl methacrylate) (PMMA) nanocomposite films, the tensile strength, Young's modulus, and elongation at break improved by about 46%, 74% and 6%, respectively, upon the loading of only 0.2 wt% of SiO2-h-QD-MSMAs. It is found that the mechanical enhancement effect of the silica-hybridized QDs is general for both hydrophilic polymers such as polyvinyl alcohol and hydrophobic polymers such as PMMA or polystyrene due to the strong interfacial adhesion between SiO2-h-QDs and polymer matrix as well as the fine dispersibility of the nanofillers in composites. SEM measurements showed a ductile-rupture behavior for the materials in which the surface-modified nanofillers were well compatible with the polymer matrix, but a brittle-rupture behavior for the composites loaded with pristine nanofillers due to their local aggregation. The loading of silica-hybridized QDs simultaneously endowed the composites with desired and stable optical properties. No obvious decreases of both photoluminescence and transparency were found for the nanocomposite films exposed to daylight even for one year. Such dual functional SiO2-h-QD-polymer nanocomposites promise great potential to upgrade the conventional polymer materials.
Co-reporter:Yao Tu, Li Zhou, Yi Zheng Jin, Chao Gao, Zhi Zhen Ye, Ye Feng Yang and Qing Ling Wang
Journal of Materials Chemistry A 2010 vol. 20(Issue 8) pp:1594-1599
Publication Date(Web):06 Jan 2010
DOI:10.1039/B914156A
A solution casting approach was developed to obtain flexible and self-supporting ZnO-polystyrene (PS) nanocomposite thin films (ca. 360 μm) which were highly transparent in the visible region and exhibited excellent UV-absorbing properties. The nanocomposite films were prepared from homogeneous solutions of ligand-modified ZnO nanocrystals and PS. UV-Vis spectra, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and photoluminescence (PL) characterization techniques were employed to study optical and structural properties, as well as thermal stabilities of the nanocomposite films. Results revealed the high UV-shielding efficiency of the composites: for a film containing 1.0 wt. % of ZnO nanocrystals, over 99% of UV light at wavelengths between 200 and 360 nm was absorbed while the optical transparency in the visible region was slightly below that of a neat PS film. Minute amounts of organic ligands minimized aggregation of the ZnO nanocrystals, leading to the homogeneous blend solutions and eventually the well dispersed ZnO-PS nanocomposite films with stable optical properties. The present work is of interest for developing transparent UV-shielding materials and should help in the understanding and design of inorganic-polymer nanocomposites with desired properties.
Co-reporter:Li Zhou, Chao Gao, Xiaozhen Hu and Weijian Xu
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 4) pp:1211
Publication Date(Web):March 23, 2010
DOI:10.1021/am9009296
A facile one-pot strategy for synthesis of silica-hybridized CdTe quantum dots (SiO2-h-CdTe QDs) in aqueous solution is presented, and subkilogram scale fluorescent SiO2-h-QDs can be readily produced in one batch. This approach also makes the tuning of emission wavelength and absorption bandgap of SiO2-h-QDs accessible for the first time. In the case of using MPA as ligand, the emission wavelength and absorption bandgap can be tuned in the range of 546−584 nm (the corresponding diameter of QDs increased from 2.0 to 3.2 nm) and 2.55−2.27 eV, respectively. The content of QDs in the resulting nanohybrids can also be readily adjusted in a wide range of 2−95 wt % by the feed ratio of QDs to silica precursors. The resulting SiO2-h-QDs are ultrafine with diameters 8−16 nm, and show excellent optical properties, high stability, low toxicity, and versatile surface functionality compared with the neat QDs. Various functional groups such as amino, epoxy, and hydroxyl can be readily introduced to the surface of SiO2-h-QDs by silane-coupling chemistry and surface-initiated polymerization. Our strategy opens up enormous opportunities to make full use of these robust fluorescent nanohybrids in various applications because of their facile availability, cost-effective productivity, and high stability.Keywords: fluorescent; large-scale; nanohybrids; quantum dots; silica
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 5) pp:1483
Publication Date(Web):May 11, 2010
DOI:10.1021/am100114f
A versatile and robust adsorbent with both magnetic property and very high adsorption capacity is presented on the basis of functionalization of iron oxide-silica magnetic particles with carboxylic hyperbranched polyglycerol (Fe3O4/SiO2/HPG-COOH). The structure of the resulting product was confirmed by Fourier transform infrared (FTIR) spectra, thermo gravimetric analysis (TGA), zeta-potential, and transmission electron microscopy (TEM). According to the TGA results, the density of the carboxylic groups on the surface of Fe3O4/SiO2/HPG-COOH is calculated to be as high as 3.0 mmol/g, posing a powerful base for adsorbing dyes and drugs. Five kinds of dyes and one representative anticancer drug were chosen to investigate the adsorption capacity of the as-prepared magnetic adsorbent. The adsorbent shows highly efficient adsorption performance for all of the adsorbates especially for the cationic dyes and drug. For example, the saturated adsorption capacity of the Fe3O4/SiO2/HPG-COOH for methyl violet (MV) can reach 0.60 mmol/g, which is much higher than the previous magnetic adsorbents (usually lower than 0.30 mmol/g). 95% of MV and 90% of R6G could be adsorbed within 5 min, and both of the adsorptions reached equilibrium in about 15 min. The adsorption kinetics and isotherm of the adsorbents were investigated in detail and found that the kinetic and equilibrium adsorptions are well-modeled using pseudo-second-order kinetics and Langmuir isotherm model, respectively. In addition, the influences of pH and ionic strength on the adsorption capacity were also examined and found that pH has much greater effect on the adsorption capacity compared with the ionic strength. Regeneration experiments showed that the Fe3O4/SiO2/HPG-COOH can be well-regenerated in ethanol and partially regenerated in 1 M HCl aqueous solution. After regeneration, the magnetic adsorbents can still show high adsorption capacity even for 10 cycles of desorption−adsorption. No obvious decreases of magnetic intensity and aggregation of adsorbents can be observed even after 10 cycles of adsorption−desorption.Keywords: adsorption; dye; hyperbranched polymer; iron oxide; Langmuir isotherm; magnetic adsorbent
Co-reporter:Hongkun He and Chao Gao
ACS Applied Materials & Interfaces 2010 Volume 2(Issue 11) pp:3201
Publication Date(Web):October 19, 2010
DOI:10.1021/am100673g
The amazing properties of graphene are triggering extensive interests of both scientists and engineers, whereas how to fully utilize the unique attributes of graphene to construct novel graphene-based composites with tailor-made, integrated functions remains to be a challenge. Here, we report a facile approach to multifunctional iron oxide nanoparticle-attached graphene nanosheets (graphene@Fe3O4) which show the integrated properties of strong supraparamagnetism, electrical conductivity, highly chemical reactivity, good solubility, and excellent processability. The synthesis method is efficient, scalable, green, and controllable and has the feature of reduction of graphene oxide and formation of Fe3O4 nanoparticles in one step. When the feed ratios are adjusted, the average diameter of Fe3O4 nanoparticles (1.2−6.3 nm), the coverage density of Fe3O4 nanoparticles on graphene nanosheets (5.3−57.9%), and the saturated magnetization of graphene@Fe3O4 (0.5−44.1 emu/g) can be controlled readily. Because of the good solubility of the as-prepared graphene@Fe3O4, highly flexible and multifunctional films composed of polyurethane and a high content of graphene@Fe3O4 (up to 60 wt %) were fabricated by the solution-processing technique. The graphene@Fe3O4 hybrid sheets showed electrical conductivity of 0.7 S/m and can be aligned into a layered-stacking pattern in an external magnetic field. The versatile graphene@Fe3O4 nanosheets hold great promise in a wide range of fields, including magnetic resonance imaging, electromagnetic interference shielding, microwave absorbing, and so forth.Keywords: conductivity; graphene; magnetism; magnetite; nanoparticles
Co-reporter:Xue Wang, Yongjie He, Jiayan Wu, Chao Gao and Yuhong Xu
Biomacromolecules 2010 Volume 11(Issue 1) pp:
Publication Date(Web):November 11, 2009
DOI:10.1021/bm901091z
Hyperbranched poly(amido amine) (HPAMAM), which is structurally analogous to PAMAM dendrimers, has been proposed to be an effective agent for gene delivery. The facile synthesis of HPAMAM with scalable productivity by one-pot polymerization of monomers of methyl acrylate (MA) and diethylenetriamine (DETA) has been set up previously. In this study, the HPAMAM was further modified on the terminal amino groups with phenylalanine to various degrees (HPAMAM-PHE30, PHE45, PHE60). We showed that HPAMAM and HPAMAM-PHEs were all able to form complexes with plasmid DNA (pDNA) at various mass ratios. The cytotoxicity and transfection efficiencies of these polymers were evaluated in SMMC-7721 and COS-7 cell lines. The PHE modifications affected the cell transfection efficiency significantly. The HPAMAM-PHE60 was the most efficient, with transfection activities consistently higher than the commercial transfection reagent PEI. Our study demonstrated that HPAMAM-PHEs may be good new materials for gene delivery and other applications because of its large-scale availability, economical cost, and low toxicity.
Co-reporter:Haiyan Sun and Chao Gao
Biomacromolecules 2010 Volume 11(Issue 12) pp:
Publication Date(Web):November 29, 2010
DOI:10.1021/bm101060m
We presented a general and facile strategy to prepare biocompatible multiamino polymers. Series of new monomers were synthesized by esterification of 2-hydroxyethyl methacrylate (HEMA) and Boc-amino acids, such as Boc-l-phenylalanine, Boc-glycine, Boc-l-alanine, Boc-l-valine, and Boc-l-lysine. Subsequent vinyl polymerization of monomers gave rise to vinyl poly(amino acid)s with a side primary amino group at each unit if deprotected. Both atom transfer radical polymerization (ATRP) and conventional free radical polymerization (FRP) were employed to prepare the multiamino polymers. A well controlled effect upon molecular weight with the standard first-order kinetics was achieved in cases of ATRP, and high molecular weight polymers were obtained via FRP. MTT assay showed that cell survival rates for the multiamino polymers were almost maintained above 90% and that their cytotoxicities were much lower than that of linear PEI (PEI 25000). Zeta potential measurements demonstrated that the vinyl poly(amino acid)s are electropositive, and AFM measurements showed that the vinyl poly(amino acid)s could tightly condense DNA into granular structures at a suitable concentration. The combination of facile availability, controlled productivity, low cytotoxicity and strong binding ability with DNA promises the great potential of the novel multiamino polymers in bioapplications.
Co-reporter:Zhen Xu and Chao Gao
Macromolecules 2010 Volume 43(Issue 16) pp:6716-6723
Publication Date(Web):July 19, 2010
DOI:10.1021/ma1009337
We reported an efficient method to prepare nylon-6− (PA6−) graphene (NG) composites by in situ polymerization of caprolactam in the presence of graphene oxide (GO). During the polycondensation, GO was thermally reduced to graphene simultaneously. By adjusting the feed ratio of caprolactam to GO, various composites with 0.01−10 wt % content of graphene were obtained. The highly grafting nylon-6 arms on graphene sheets was confirmed by XPS, FTIR, TGA and AFM measurements, showing the grafting content up to 78 wt % and homogeneous 2D brush-like morphology from AFM observations. The efficient polymer-chain grafting makes the graphene homogeneously dispersed in PA6 matrix and depresses the crystallization of PA6 chains. Furthermore, we prepared NG fibers by melt spinning process, and found that the tensile strength increased by 2.1 folds and Young’s modulus increased by 2.4 folds with the graphene loading of 0.1 wt % only, revealing an excellent reinforcement to composites by graphene. The in situ condensation polymerization approach paves the way to prepare graphene-based nanocomposites of condensation polymers with high performances and novel functionalities.
Co-reporter:Jiayan Wu and Chao Gao
Macromolecules 2010 Volume 43(Issue 17) pp:7139-7146
Publication Date(Web):August 12, 2010
DOI:10.1021/ma100956y
A one-step parallel grafting strategy is presented to readily prepare multifunctional complex macromolecules and miktoarm polymer brushes. Typically, a series of amphiphilic “sliding supramolecular polymer brushes” (SSPBs) were synthesized with cyclodextrin-based polyrotaxanes (PRs) as backbones. The amphiphilicity of SSPBs could be facilely tuned by the feed ratio of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic palmitoyl (C16) side chains. Click chemistry of Cu(I)-catalyzed azide−alkyne cycloaddition was employed as the parallel coupling reaction, and high grafting density (ca. 18 side chains immobilized on each α-cyclodextrin ring) and click conversion (∼100%) was achieved in a short reaction time (several minutes to 3 h). The SSPB with close proportion of PEG to C16 miktoarms showed balanced amphiphilicity and could aggregate into a Janus film at the interface of hexane and water, which was confirmed with a dye-labeling method and fluorescence measurements. The amphiphilic SSPBs could also assemble into microporous films on mica surfaces via spin-coating. The formation of the superstructured films was proved to be affected by the relative humidity, rotational speed of spin-coating, and composition of SSPBs.
Co-reporter:Yi Han
Science China Chemistry 2010 Volume 53( Issue 12) pp:2461-2471
Publication Date(Web):2010 December
DOI:10.1007/s11426-010-4134-5
Spherical molecular brushes with amphiphilic heteroarms were facilely synthesized by grafting the arms of hydrophobic 2-azidoethyle palmitate and hydrophilic monoazide-terminated poly(ethylene glycol) onto the core of alkyne-modified hyperbranched polyglycerol (HPG) with high molecular weight (Mn = 122 kDa) via one-pot parallel click chemistry. The parallel click grafting strategy was demonstrated to be highly efficient (∼100%), very fast (∼ 2 h) and well controllable to the amphilicity of molecular brushes. Through adjusting the feeding ratio of hydrophobic and hydrophilic arms, a series of brushes with different arm ratios were readily obtained. The resulting miktoarms hyperbranched polymer brushes (HPG-g-C16/PEG350) were characterized by hydrogen-nuclear magnetic resonance (1H NMR), Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) measurements. The spherical molecular brushes showed high molecular weights up to 230 kDa, and thus could be visualized by atomic force microscopy (AFM). AFM and dynamic laser light scattering (DLS) were employed to investigate the self-assembly properties of amphiphilic molecular brushes with closed proportion of hydrophobic and hydrophilic arms. The brushes could self-assemble hierarchically into spherical micelles, and network-like fibre structures, and again spherical micelles by addition of n-hexane into the dichloromethane or chloroform solution of brushes. In addition, this kind of miktoarms polymer brush also showed the ability of dye loading via host-guest encapsulation, which promises the potential application of spherical molecular brushes in supramolecular chemistry.
Co-reporter:Liang Kou;Hongkun He
Nano-Micro Letters 2010 Volume 2( Issue 3) pp:177-183
Publication Date(Web):2010 September
DOI:10.1007/BF03353638
A facile “click chemistry” approach to functionalize 2D macromolecules of graphene oxide nanosheets with poly (ethylene glycol) of different molecular weights, polystyrene, palmitic acid and various amino acids was presented. FTIR, TGA, Raman spectroscopy, XPS, XRD, TEM, AFM and SEM were utilized to characterize the products. High degree of functionalization was achieved on the flat surfaces of graphene oxide, affording polymer-grafted 2D brushes and amino acids-immobilized nanosheets, which show improved solubility in organic solvents. The click chemistry strategy reported herein provides a facile and general method for functionalization of graphene oxide with macromolecules and desired biomolecules.
Co-reporter:Jin Han
Nano-Micro Letters 2010 Volume 2( Issue 3) pp:213-226
Publication Date(Web):2010 September
DOI:10.1007/BF03353643
Following the conventional carbon allotropes of diamond and graphite, fullerene, carbon nanotubes (CNTs) and graphene as 0D, 1D and 2D graphitic macromolecules have been discovered recently in succession, declaring the unlimited potential of carbon-based nanomaterials and nanotechnology. Although CNTs exhibit significant potential applications in advanced materials and other fields due to their extraordinary mechanical strength and electrical/thermal conductivity properties, their low solubility, poor wettability and bad dispersibility in common solvents and solid matrices have limited their processing and applications. Thus, the attempt to achieve wettable/processable CNTs by functionalization has attracted increasing attention in both scientific and industrial communities. In recent years, azide chemistry has been demonstrated as a powerful means to covalently modify CNTs. It consists of two major approaches: click chemistry and nitrene chemistry, which both involve the usage of various azide compounds. The former one is based on highly reactive and stereospecifical Cu(I) catalyzed azide-alkyne cycloaddition reaction; the latter one is based on the electrophilic attack to unsaturated bonds of CNTs with nitrenes as reactive intermediates formed from thermolysis or photolysis of azides. In this mini-review paper, the azide chemistry to functionalize CNTs is highlighted and the corresponding functionalization routes to build CNT-based complex structures are also discussed. Besides, covalent functionalizations of other graphitic nanomaterials such as fullerence and graphene, via azide chemistry, are commented briefly.
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
Langmuir 2010 Volume 26(Issue 13) pp:11217-11225
Publication Date(Web):April 13, 2010
DOI:10.1021/la100556p
Here we report a facile approach to prepare multicarboxylic hyperbranched polyglycerol (HPG)-grafted SiO2-coated iron oxide (Fe3O4/SiO2) magnetic hybrid support. This support combined the both features of Fe3O4 and HPG, facile magnetic separation, and favorable molecular structure with numerous functional groups. With the use of the grafted-HPGs as templates, various noble metal nanocatalysts such as Pt, Au, and Pd were directly grown on the surfaces of magnetic support with ultrasmall and nearly monodisperse sizes (e.g., the average sizes of Pt, Au, and Pd are 4.8 ± 0.5, 6.0 ± 0.6, and 4.0 ± 0.4 nm, respectively) and high coverage densities. Because of the amplification effect of HPG, high loading capacities of the nanocatalysts, around 0.296, 0.243, and 0.268 mmol/g for Pt, Au, and Pd, respectively, were achieved. Representative catalytic reactions including reduction of 4-nitrophenol, alcohol oxidation, and Heck reaction demonstrated the high catalytic activity of the noble metal nanocatalysts. Because of the stabilization of HPG templates, the nanocatalysts can be readily recycled by a magnet and reused for the next reactions with high efficiencies. The robust multifunctional magnetic hybrids will find important applications in catalysis and other fields such as drug delivery and bioseparations.
Co-reporter:Jiayan Wu, Hongkun He and Chao Gao
Macromolecules 2010 Volume 43(Issue 5) pp:2252-2260
Publication Date(Web):February 4, 2010
DOI:10.1021/ma902255v
Polyrotaxanes (PRs), in which α-cyclodextrins (α-CDs) were threaded onto poly(ethylene glycol) (PEG) chains capped with β-cyclodextrins (β-CDs), were prepared by click chemistry via a one-pot strategy in water at room temperature with high yield, up to 320 mg/100 mg PEG axis. The terminal β-CD cavity could be recognized by phenolphthalein and utilized to form a supramolecular block copolymer with alternate rod and coil segments via the formation of a host−guest inclusion complex with diadamantyl-terminated PEG. The prepared PR could further work as a novel template for the in situ deposition of platinum (Pt) nanoparticles (NPs) to fabricate metallic nanowires. TEM and SEM observations showed that the resulting polycrystalline nanowires with length of 50−200 nm and diameter of ca. 12 nm were composed of close-packed uniform Pt NPs with diameter of ca. 2.5 nm. The catalytic activity of the Pt nanowires was demonstrated by the reduction of 4-nitrophenol. The fascinating β-CD-capped PR is promising in a wide variety of fields such as supramolecular chemistry and bionanotechnology due to its facile and salable availability and biocompatibility.
Co-reporter:Chao Gao, Hongkun He, Li Zhou, Xing Zheng and Yu Zhang
Chemistry of Materials 2009 Volume 21(Issue 2) pp:360
Publication Date(Web):December 29, 2008
DOI:10.1021/cm802704c
A facile, green, low cost and efficient one-step technology to synthesize highly dispersible functional single-walled and multiwalled carbon nanotubes (f-SWNTs and f-MWNTs) up to supergrams is reported. Large-scale (up to hundreds of grams) synthesis of functional azides was developed at first, and various reactive groups (i.e., −OH, −NH2, −COOH, and −Br) were then introduced onto the convex surfaces of CNTs in merely one reaction of nitrene addition under a relatively mild condition without causing significant damage to nanotubes. The contents of the functional moieties can be easily controlled by adjusting the feed ratio of the azide compounds to CNTs. In order to demonstrate the reactivity and functions of the immobilized organic moieties, different chemical reactions, including surface-initiated polymerizations, amidation, and reduction of metal ions, were performed on the functional CNTs, affording various CNT-polymer and CNT-Pt nanohybrids. The resulting materials were characterized by various measurements, such as TGA, Raman, XPS, FTIR, NMR, XRD, SEM, TEM, and HRTEM. The presented one-step methodology opens the avenue for industrial production of functional CNTs.
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
Journal of Materials Chemistry A 2009 vol. 19(Issue 31) pp:5655-5664
Publication Date(Web):19 Jun 2009
DOI:10.1039/B905966K
A straightforward strategy is presented to functionalize aqueous-phase synthesized CdTe quantum dots (QDs) with thermo-sensitive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) via direct surface-initiated oxyanionic vinyl polymerization. The polymer grafting quantity can be facilely controlled in a wide range up to 95.2wt% by adjusting the weight feed ratio of monomer to pristine QDs. The polymer-grafted QDs still retain good fluorescence properties in solution, solid polymer matrix, and on surfaces of silica (SiO2) sphere. The resulting QD@PDMAEMAs show excellent solubility both in water and organic solvents (e.g., chloroform, dichloromethane, dioxane, ethyl acetate, acetone, methanol, and N, N-dimethylformamide). We have called them amphibious QDs. The thermo-sensitive PDMAEMAs make QDs accessible to self-assemble reversibly by adjusting temperature when the grafted polymer content is over a certain value. The self-assembly process and resulting structure were demonstrated by TEM, variable temperature dynamic light scattering (DLS) and UV-vis spectrometer. Because PDMAEMA is a kind of positive polyelectrolyte, QD@PDMAEMAs were used as building blocks in the layer-by-layer self-assembly process on the surface of SiO2 spheres, affording fluorescent SiO2 spheres.
Co-reporter:Hongkun He, Yu Zhang, Chao Gao and Jiayan Wu
Chemical Communications 2009 (Issue 13) pp:1655-1657
Publication Date(Web):09 Feb 2009
DOI:10.1039/B821280E
We have developed a facile and efficient methodology to prepare magnetic nanohybrids from ‘clickable’ magnetic nanoparticles and polymer-coated nanomaterials by Cu(I)-catalyzed azide–alkyne cycloaddition ‘click’ chemistry.
Co-reporter:Chao Gao and Xing Zheng
Soft Matter 2009 vol. 5(Issue 23) pp:4788-4796
Publication Date(Web):01 Oct 2009
DOI:10.1039/B909994H
A facile methodology was presented for scalable synthesis of hyperbranched-star polymers with tens of hydrophilic and hydrophobic hetero-arms, in merely two steps starting from monomers. Self-condensing atom transfer radical polymerization (SC-ATRP) of a clickable initiator-monomer (click-inimer), 3-azido-2-(2-bromo-2-methylpropanoyloxy)propyl methacrylate, resulted in a hyperbranched polymer with azido and bromo multihetero-groups. Subsequently orthogonal one-pot “grafting onto” azide-alkyne click coupling and “grafting from” ATRP with the core of hyperbranched polymer afforded targeted miktoarm globular binary brushes. The brushes could readily assemble into superstructures of 150–300 nm spheres and micro-scale sheets. Furthermore, hyperbranched copolymer possessing azido, hydroxyl and bromo trihetero-groups were synthesized by self-condensing atom transfer radical copolymerization of the click-inimer and 2-hydroxyethyl methacrylate (HEMA). Hyperbranched trinity brushes were then facilely prepared via a one-pot multigrafting strategy by a combination of click chemistry, esterification, and ATRP. The trinity brushes could assemble into superstructures of micron-scale dendritic tubes.
Co-reporter:Li Zhou;Weijian Xu
Macromolecular Chemistry and Physics 2009 Volume 210( Issue 12) pp:1011-1018
Publication Date(Web):
DOI:10.1002/macp.200900134
Co-reporter:Jiayan Wu
Macromolecular Chemistry and Physics 2009 Volume 210( Issue 20) pp:1697-1708
Publication Date(Web):
DOI:10.1002/macp.200900281
Co-reporter:Jiayan Wu
Macromolecular Chemistry and Physics 2009 Volume 210( Issue 20) pp:
Publication Date(Web):
DOI:10.1002/macp.200990046
Co-reporter:Li Zhou ;Dan Zhu;Weijian Xu ;FanqingFrank Chen ;Amit Palkar Dr.;Luis Echegoyen ;EricSiu-Wai Kong
Chemistry - A European Journal 2009 Volume 15( Issue 6) pp:1389-1396
Publication Date(Web):
DOI:10.1002/chem.200801642
Abstract
Facile functionalization of multilayer fullerenes (carbon nano-onions, CNOs) was carried out by [2+1] cycloaddition of nitrenes. The products were further derivatized by using the “grafting from” strategy of in situ ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Using one-step nitrene chemistry with high-energy reagents, such as azidoethanol and azidoethyl 2-bromo-2-methyl propanoate, in N-methyl-2-pyrrolidone at 160°C for 16 h, hydroxyl and bromide functionalities were introduced onto the surfaces of CNOs. These hydroxyl CNOs (CNO-OH) and bromic CNOs (CNO-Br) were extensively characterized by various techniques such as thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photo electron spectroscopy (XPS). TGA measurements indicated that the surface hydroxyl and bromide group density reached 1.49 and 0.49 mmol g−1, respectively. The as-functionalized CNOs showed much better solubility in solvents than pristine CNOs. The CNO-OH were also observed to fluoresce at λ=453 nm in water. The CNO-OH and CNO-Br can be conveniently utilized as macroinitiators to conduct surface-initiated in-situ polymerizations. Poly(ε-caprolactone) (PCL, 45wt %) and polystyrene (PS, 60 wt%) were then grafted from surfaces of CNOs through the ROP of ε-caprolactone with the macroinitiator CNO-OH and the ATRP of styrene with the macroinitiator CNO-Br, respectively. The structures and morphology of the resulting products were characterized by 1H NMR, scanning electron microscopy (SEM), TEM, and atomic force microscopy (AFM). The polymer functionalized CNOs have good solubility/dispersibility in common organic solvents. The facile and scalable functionalization approaches can pave the way for the comprehensive investigation of chemistry of CNOs and fabrication of novel CNO-based nanomaterials and nanodevices.
Co-reporter:Yu Zhang, Hongkun He, Chao Gao and Jiayan Wu
Langmuir 2009 Volume 25(Issue 10) pp:5814-5824
Publication Date(Web):April 17, 2009
DOI:10.1021/la803906s
The covalent functionalization of multiwalled carbon nanotubes (MWNTs) by layer-by-layer (LbL) click chemistry is reported. The clickable polymers of poly(2-azidoethyl methacrylate) and poly(propargyl methacrylate) were synthesized at first by atom transfer radical polymerization (ATRP) of 2-azidoethyl methacrylate and reverse addition−fragmentation chain transfer (RAFT) polymerization of propargyl methacrylate, respectively. The two polymers were then alternately coated on alkyne-modified multiwalled carbon nanotubes using Cu(I)-catalyzed click reaction of Huisgen 1,3-dipolar cycloaddition between azides and alkynes. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements confirm that the quantity and thickness of the clicked polymer shell on MWNTs can be well controlled by adjusting the cycles or numbers of click reaction and the polymer shell is uniform and even. X-ray photoelectron spectroscopy (XPS) and Fourier tranform infrared (FTIR) measurements showed that there were still a great amount of residual azido groups on the surfaces of the functionalized MWNTs after clicking three layers of polymers. Furthermore, alkyne-modified rhodamine B and monoalkyne-terminated polystyrene were subsequently used to functionalize the clickable polymer grafted MWNTs, giving rise to fluorescent carbon nanotubes (CNTs) and CNT-based polystyrene brushes, respectively. It demonstrates that the residual azido groups on the surfaces of MWNTs are available for further click reaction with various functional molecules.
Co-reporter:Li Zhou, Chao Gao, Weijian Xu, Xue Wang and Yuhong Xu
Biomacromolecules 2009 Volume 10(Issue 7) pp:
Publication Date(Web):June 4, 2009
DOI:10.1021/bm9002877
The synthesis of stable, low toxic, multifunctional, and water-soluble quantum dots (QDs) is of crucial importance for nanobiotechnology. An in situ anionic ring-opening polymerization strategy was successfully employed to grow multihydroxyl hyperbranched polyglycerol (HPG) from surfaces of aqueous synthesized QDs directly, affording multifunctional CdTe@HPG nanohybrids. The grafted HPG content can be adjusted from about 25 to 80 wt % by manipulating the feed ratio of glycidol monomer to QDs. The resultant CdTe@HPGs still show strong fluorescence and well water-solubility, and can conjugate functional biomolecules (e.g., amino acids) with their multiple reactive hydroxyls. Cytotoxicity measurements reveal that the CdTe@HPGs are much less toxic than the pristine QDs in human lung cancer cells SPCAI and more grafted HPG leads to less toxicity, due to the envelope of biocompatible HPG on QDs. It was found that the pristine QDs were unstable and their fluorescence decreased greatly or was even completed quenched after 24 h in SPCAI cells, whereas the QD@HPGs still exhibited strong fluorescence. This report opens the door for using in situ controlled/living polymerization to tailor QDs with biocompatible dendritic polymers readily and casts a light for obtaining robust nontoxic functionalized QDs and applying them in vitro and in vivo.
Co-reporter:Yu Zhang, Hongkun He and Chao Gao
Macromolecules 2008 Volume 41(Issue 24) pp:9581-9594
Publication Date(Web):November 21, 2008
DOI:10.1021/ma801696z
A novel and versatile Gemini-grafting strategy to modify surfaces/substrates is presented by a combination of conventional “grafting to” and “grafting from” strategies. As a typical example, carbon nanotubes (CNTs) were functionalized with amphiphilic/Janus polymer brushes by uniting click chemistry with a macroinitiator approach. A clickable macroinitiator, poly(3-azido-2-(2-bromo-2-methylpropanoyloxy)propyl methacrylate) (polyBrAzPMA), with alkyl bromo groups for initiating atom transfer radical polymerization (ATRP) and azido groups for the click reaction was first synthesized by postmodification of poly(glycidyl methacrylate) with sodium azide, followed by 2-bromoisobutyryl bromide. The clickable macroinitiator was clicked onto alkyne-containing multiwalled/single-walled CNTs via the Cu(I)-catalyzed click reaction of Huisgen 1,3-dipolar cycloaddition between azides and alkynes, resulting in a CNT-based clickable macroinitiator. Poly(n-butyl methacrylate), polystyrene, and poly(ethylene glycol) were subsequently grown on CNTs via ATRP grafting from and click grafting to approaches, affording CNT-supported amphiphilic polymer brushes. The functionalized CNTs were characterized by thermal gravimetric analysis (TGA), FTIR, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. All of the results demonstrated that it is feasible and facile to grow various multifunctional polymer brushes on CNTs by the clickable macroinitiator strategy, and the grafted polymer content can be well controlled. This versatile strategy can be readily extended to prepare other Janus/bifunctional polymer brushes, opening an avenue for building complex polymer architectures and tailoring surface properties.
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
Journal of Materials Chemistry A 2009 - vol. 19(Issue 31) pp:NaN5664-5664
Publication Date(Web):2009/06/19
DOI:10.1039/B905966K
A straightforward strategy is presented to functionalize aqueous-phase synthesized CdTe quantum dots (QDs) with thermo-sensitive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) via direct surface-initiated oxyanionic vinyl polymerization. The polymer grafting quantity can be facilely controlled in a wide range up to 95.2wt% by adjusting the weight feed ratio of monomer to pristine QDs. The polymer-grafted QDs still retain good fluorescence properties in solution, solid polymer matrix, and on surfaces of silica (SiO2) sphere. The resulting QD@PDMAEMAs show excellent solubility both in water and organic solvents (e.g., chloroform, dichloromethane, dioxane, ethyl acetate, acetone, methanol, and N, N-dimethylformamide). We have called them amphibious QDs. The thermo-sensitive PDMAEMAs make QDs accessible to self-assemble reversibly by adjusting temperature when the grafted polymer content is over a certain value. The self-assembly process and resulting structure were demonstrated by TEM, variable temperature dynamic light scattering (DLS) and UV-vis spectrometer. Because PDMAEMA is a kind of positive polyelectrolyte, QD@PDMAEMAs were used as building blocks in the layer-by-layer self-assembly process on the surface of SiO2 spheres, affording fluorescent SiO2 spheres.
Co-reporter:Li Zhou, Chao Gao and Weijian Xu
Journal of Materials Chemistry A 2010 - vol. 20(Issue 27) pp:NaN5681-5681
Publication Date(Web):2010/06/07
DOI:10.1039/C0JM00211A
Quantum dot (QD)-polymer nanocomposites that simultaneously possess stable photoluminescence and enhanced mechanical properties are presented for the first time based on the facile blending of the ultrasmall silica-hybridized CdTe QDs (SiO2-h-QDs) or 3-(trimethoxysilyl)propyl methacrylate-modified SiO2-h-QDs (SiO2-h-QD-MSMAs) with polymer. Typically, for SiO2-h-QD-MSMA/poly(methyl methacrylate) (PMMA) nanocomposite films, the tensile strength, Young's modulus, and elongation at break improved by about 46%, 74% and 6%, respectively, upon the loading of only 0.2 wt% of SiO2-h-QD-MSMAs. It is found that the mechanical enhancement effect of the silica-hybridized QDs is general for both hydrophilic polymers such as polyvinyl alcohol and hydrophobic polymers such as PMMA or polystyrene due to the strong interfacial adhesion between SiO2-h-QDs and polymer matrix as well as the fine dispersibility of the nanofillers in composites. SEM measurements showed a ductile-rupture behavior for the materials in which the surface-modified nanofillers were well compatible with the polymer matrix, but a brittle-rupture behavior for the composites loaded with pristine nanofillers due to their local aggregation. The loading of silica-hybridized QDs simultaneously endowed the composites with desired and stable optical properties. No obvious decreases of both photoluminescence and transparency were found for the nanocomposite films exposed to daylight even for one year. Such dual functional SiO2-h-QD-polymer nanocomposites promise great potential to upgrade the conventional polymer materials.
Co-reporter:Yao Tu, Li Zhou, Yi Zheng Jin, Chao Gao, Zhi Zhen Ye, Ye Feng Yang and Qing Ling Wang
Journal of Materials Chemistry A 2010 - vol. 20(Issue 8) pp:NaN1599-1599
Publication Date(Web):2010/01/06
DOI:10.1039/B914156A
A solution casting approach was developed to obtain flexible and self-supporting ZnO-polystyrene (PS) nanocomposite thin films (ca. 360 μm) which were highly transparent in the visible region and exhibited excellent UV-absorbing properties. The nanocomposite films were prepared from homogeneous solutions of ligand-modified ZnO nanocrystals and PS. UV-Vis spectra, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and photoluminescence (PL) characterization techniques were employed to study optical and structural properties, as well as thermal stabilities of the nanocomposite films. Results revealed the high UV-shielding efficiency of the composites: for a film containing 1.0 wt. % of ZnO nanocrystals, over 99% of UV light at wavelengths between 200 and 360 nm was absorbed while the optical transparency in the visible region was slightly below that of a neat PS film. Minute amounts of organic ligands minimized aggregation of the ZnO nanocrystals, leading to the homogeneous blend solutions and eventually the well dispersed ZnO-PS nanocomposite films with stable optical properties. The present work is of interest for developing transparent UV-shielding materials and should help in the understanding and design of inorganic-polymer nanocomposites with desired properties.
Co-reporter:Hongkun He, Yu Zhang, Chao Gao and Jiayan Wu
Chemical Communications 2009(Issue 13) pp:NaN1657-1657
Publication Date(Web):2009/02/09
DOI:10.1039/B821280E
We have developed a facile and efficient methodology to prepare magnetic nanohybrids from ‘clickable’ magnetic nanoparticles and polymer-coated nanomaterials by Cu(I)-catalyzed azide–alkyne cycloaddition ‘click’ chemistry.
Co-reporter:Yu Jin, Jiachen Li, Li Peng and Chao Gao
Chemical Communications 2015 - vol. 51(Issue 84) pp:NaN15393-15393
Publication Date(Web):2015/08/26
DOI:10.1039/C5CC05396J
Silica gel, widely used in chromatography separation and as a catalyst carrier, was employed here for the first time as a fixed-bed catalyst for the S → O acetyl migration to synthesize thiol compounds under mild conditions, showing the merits of high efficiency, high selectivity, long-life recyclability, low cost and scalable availability.
Co-reporter:Jin Han, Yaochen Zheng, Shuai Zheng, Sipei Li, Tiannan Hu, Aijin Tang and Chao Gao
Chemical Communications 2014 - vol. 50(Issue 63) pp:NaN8714-8714
Publication Date(Web):2014/05/19
DOI:10.1039/C4CC01956C
A series of water soluble octa-functionalized POSSs were facilely synthesized via thiol–ene and Menschutkin click chemistry. Among them, octa-alkynyl POSS further reacted with azide-terminal alkyl long chains, resulting in a well-defined, amphiphilic octopus-like POSS. For the first time it was used for host–guest encapsulation and it exhibited an ultrahigh loading capability.
Co-reporter:Yaochen Zheng, Sipei Li, Zhulin Weng and Chao Gao
Chemical Society Reviews 2015 - vol. 44(Issue 12) pp:NaN4130-4130
Publication Date(Web):2015/04/23
DOI:10.1039/C4CS00528G
Hyperbranched polymers (HPs) are highly branched three-dimensional (3D) macromolecules. Their globular and dendritic architectures endow them with unique structures and properties such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. HPs can be facilely synthesized via a one-pot polymerization of traditional small molecular monomers or emerging macromonomers. The great development in synthetic strategies, from click polymerization (i.e., copper-catalyzed azide–alkyne cycloaddition, metal-free azide–alkyne cycloaddition, strain-promoted azide–alkyne cycloaddition, thiol–ene/yne addition, Diels–Alder cycloaddition, Menschutkin reaction, and aza-Michael addition) to recently reported multicomponent reactions, gives rise to diverse HPs with desirable functional/hetero-functional groups and topologies such as segmented or sequential ones. Benefiting from tailorable structures and correspondingly special properties, the achieved HPs have been widely applied in various fields such as light-emitting materials, nanoscience and technology, supramolecular chemistry, biomaterials, hybrid materials and composites, coatings, adhesives, and modifiers. In this review, we mainly focus on the progress in the structural control, synthesis, functionalization, and potential applications of both conventional and segmented HPs reported over the last decade.
Co-reporter:Tieqi Huang, Bingna Zheng, Zheng Liu, Liang Kou and Chao Gao
Journal of Materials Chemistry A 2015 - vol. 3(Issue 5) pp:NaN1895-1895
Publication Date(Web):2014/12/08
DOI:10.1039/C4TA06533F
We fabricated continuous wrinkle-structured graphene film electrodes by a wet-spinning method. The assembled supercapacitors showed an excellent rate performance (79% retention from 1 to 100 A g−1) with a high specific capacitance (177 F g−1 at 1 A g−1). When further functionalized with polyaniline, the electrodes maintained their wrinkled structure and showed an improved rate capability (90% retention from 1 to 100 A g−1) with a superior capacitance as high as 505 F g−1 (1 A g−1).
Co-reporter:Bingna Zheng, Tieqi Huang, Liang Kou, Xiaoli Zhao, Karthikeyan Gopalsamy and Chao Gao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 25) pp:NaN9743-9743
Publication Date(Web):2014/04/28
DOI:10.1039/C4TA01868K
Fiber-based micro-supercapacitors (F-mSCs) are new members of the energy storage family, which facilitate SCs with flexibility and expand their application to fields such as tiny, flexible and wearable devices. One of the biggest challenges for F-SCs is to enhance the energy density (E) and keep the flexibility at the same time. Here, for the first time we assembled a type of fiber-based asymmetric micro-supercapacitors (F-asym-mSCs) with two different graphene fiber-based electrodes. The excellent electrochemical performances (59.2 mF cm−2 and 32.6 mF cm−2) of both electrodes offered a chance to achieve high performance two-ply F-asym-mSCs. The potential window of F-asym-mSCs was expanded to 1.6 V, and both the area energy density (EA: 11.9 μW h cm−2) and the volume energy density (EV: 11.9 mW h cm−3) are the highest E ever reported in F-SCs. The F-asym-mSCs exhibit good cycling stability with a 92.7% initial capacitance retention after 8000 cycles and can be integrated into a fiber-like device to realize the flexibility of fibers.
Co-reporter:Tieqi Huang, Shengying Cai, Hao Chen, Yanqiu Jiang, Siyao Wang and Chao Gao
Journal of Materials Chemistry A 2017 - vol. 5(Issue 18) pp:NaN8260-8260
Publication Date(Web):2017/04/12
DOI:10.1039/C7TA01921A
A meter-length, graphene-confined polypyrrole (GP) film was fabricated by a scalable wet-spinning technology. The GP film-assembled supercapacitors had an extremely high cycling stability (115% retention after 50000 cycles) due to the delicate graphene-confined polypyrrole-layered structures. Highly flexible supercapacitors with different sizes were further assembled with a gel electrolyte.
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