Co-reporter:Xiangkang Meng;Shaochun Tang;Hongbin Lu;Junaid Ali Syed
Industrial & Engineering Chemistry Research March 25, 2015 Volume 54(Issue 11) pp:2950-2959
Publication Date(Web):Publication Date (Web): March 3, 2015
DOI:10.1021/ie5046395
Water-soluble polyaniline–poly(acrylic acid) (PANI–PAA) composites with excellent processability and electroactivity were prepared by a one-step in situ polymerization. PAA as a matrix not only improves the solubility of PANI in water but also prevents the formation of macroscopic PANI clusters. The corrosion-inhibition performance of 316 stainless steel (316SS) was evaluated in 0.5 M HCl by electrochemical measurements in the presence of PANI–PAA composites. The results show that PANI–PAA acts as a mixed-type inhibitor, and its inhibition efficiency (IE(R)) increases with inhibitor concentration. The adsorption of the inhibitor on 316SS surface obeys a Langmuir adsorption isotherm. The PANI–PAA composite with an optimized concentration of 200 ppm shows marked increase in IE(R), i.e., 91.68%. The enhanced efficiency is attributed to an insulating interfacial layer formed by the adsorption of PANI–PAA, which obstructs the corrosion reaction at the interface.
Co-reporter:Li Jiang, Junaid Ali Syed, Yangzhi Gao, Qiuxiang Zhang, Junfeng Zhao, Hongbin Lu, Xiangkang Meng
Applied Surface Science 2017 Volume 426(Volume 426) pp:
Publication Date(Web):31 December 2017
DOI:10.1016/j.apsusc.2017.07.077
•The anti-corrosive performance of large spatial structure molecular group CSA doped PPY coating was compared with the small acid doped PPY and PPY/PPY coatings.•CSA doped PPY coating sustain the barrier effect and anodic protection during long-term immersion in the simulated PEMFC working environment.•CSA dopants enhanced the conductivity of PPY coating and the coated 304SS has low interfacial contact resistance.•Mechanism involved in durable anti-corrosive performance of PPY-CSA coating was envisaged.Conductive polymer coating doped with large molecular organic acid is an alternative method used to protect stainless steel (SS) bipolar plates in proton exchange membrane fuel cells (PEMFCs). However, it is difficult to select the proper doping acid, which improves the corrosion resistance of the coating without affecting its conductivity. In this study, large spatial molecular group camphorsulfonic acid (CSA) doped polypyrrole (PPY) conductive coating was prepared by galvanostatic electropolymerization on 304SS. The electrochemical properties of the coating were evaluated in 0.1 M H2SO4 solution in order to simulate the PEMFC service environment. The results indicate that the coating increased the corrosion potential and shifted Ecorr towards more positive value, particularly the jcorr value of PPY-CSA coated 304SS was dropped from 97.3 to 0.00187 μA cm−2. The long-term immersion tests (660 h) show that the PPY-CSA coating exhibits better corrosion resistance in comparison with the small acid (SO42−) doped PPY-SO42− or PPY/PPY-SO42− coatings. Moreover, the PPY-CSA coating presents low contact resistance and maintains strong corrosion resistance during the prolonged exposure time due to barrier effect and anodic protection.Download high-res image (53KB)Download full-size image
Co-reporter:Y.J. Ma, M.Z. Wei, C. Sun, Z.H. Cao, X.K. Meng
Materials Science and Engineering: A 2017 Volume 686(Volume 686) pp:
Publication Date(Web):16 February 2017
DOI:10.1016/j.msea.2017.01.048
The annealing induced grain growth (GG) and heterogeneous interface evolution of Cu/Ag multilayers with individual layer thickness (h) varying from 5 to 50 nm were investigated by transmission electron microscopy (TEM). The results demonstrate that the thermal stability of Cu/Ag multilayers exhibits strong length scale dependence. For samples with h<20 nm, the heterogeneous interfaces completely disappear when the annealing temperature exceeds 200 °C. However, the temperature for stable layered structure can reach 300 °C as the h≥20 nm, where the interfaces remain remarkably intact. The existence of a large number of grain boundaries (GBs) decrease the stability of multilayers, while more heterogeneous interfaces contribute to resisting atomic diffusion, inhibiting GG. The equilibrium is achieved by a competitive process between GBs diffusion and heterogeneous interfaces resistance. Moreover, the formation of annealing twins in multilayer also significantly improve the microstructural stability.
Co-reporter:Z.H. Cao, M.Z. Wei, Y.J. Ma, C. Sun, H.M. Lu, Z. Fan, X.K. Meng
International Journal of Plasticity 2017 Volume 99(Volume 99) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.ijplas.2017.08.005
•Cyclic deformation induced strengthening/softening in multilayers is studied by nanoindentation.•Unusual rate sensitivity is found at nanoscale multilayers during cyclic loading.•Size dependent Bauschinger effect is observed in multilayers during cyclic loading.•Heterogeneous interface structure evolution with layer thickness is analyzed by HRTEM.•Transition from dislocation accumulation to interface amorphization mechanism is revealed.In this work, we have systematically investigated the effect of cyclic deformation on the strength and rate sensitivity of Cu/Ru multilayers with different individual layer thickness (h) by nanoindentation tests. It was found that cyclic deformation remarkably enhances the hardness of Cu/Ru multilayers comparing with the specimens by monotonic loading. The rate sensitivity (m) of multilayer exhibits an anomalous size dependence after nanoscale cyclic deformation. When h > 10 nm, the m linearly increases with increasing cycle number of loading-unloading (s). However, the m sharply decreases with increasing s when h < 10 nm, presenting an inverse cyclic deformation effect on m. An obvious Bauschinger effect is observed during cyclic loading, where the evolution of effective stress is consistent with the m. Cyclic deformation induced dislocation accumulation and arrays at the heterogeneous interface are the intrinsic plastic mechanism for the enhanced rate sensitivity. The formation of amorphous layers at the critical h is mainly responsible for the inverse size m.
Co-reporter:Baogang Zhu, Shaochun Tang, Sascha Vongehr, Hao Xie, Jian Zhu and Xiangkang Meng
Chemical Communications 2016 vol. 52(Issue 12) pp:2624-2627
Publication Date(Web):04 Jan 2016
DOI:10.1039/C5CC08857G
Template-free chemical growth on Ni foam and thermal treatment results in homogeneous FeCo2O4 submicron-tube arrays which serve as binder-free electrodes with high capacitance, rate-capability and cycling-stability owing to FeCo2O4 conductivity, high porosity, and strong bonding between tubes and Ni foam, all allowing even symmetric devices to have superior energy density.
Co-reporter:Baogang Zhu, Shaochun Tang, Sascha Vongehr, Hao Xie, and Xiangkang Meng
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 7) pp:4762
Publication Date(Web):January 29, 2016
DOI:10.1021/acsami.5b11367
The current problem of the still relatively low energy densities of supercapacitors can be effectively addressed by designing electrodes hierarchically on micro- and nanoscale. Herein, we report the synthesis of hierarchically porous, nanosheet covered submicrometer tube forests on Ni foam. Chemical deposition and thermal treatment result in homogeneous forests of 750 nm diameter FeCo2O4 tubes, which after hydrothermal reaction in KMnO4 are wrapped in MnO2-nanosheet-built porous covers. The covers’ thickness can be adjusted from 200 to 800 nm by KMnO4 concentration. An optimal thickness (380 nm) with a MnO2 content of 42 wt % doubles the specific capacitance (3.30 F cm–2 at 1.0 mA cm–2) of the bare FeCo2O4-tube forests. A symmetric solid-state supercapacitor made from these binder-free electrodes achieves 2.52 F cm–2 at 2 mA cm–2, much higher than reported for capacitors based on similar core–shell nanowire arrays. The large capacitance and high cell voltage of 1.7 V allow high energy and power densities (93.6 Wh kg–1, 10.1 kW kg–1). The device also exhibits superior rate capability (71% capacitance at 20 mA cm–2) and remarkable cycling stability with 94% capacitance retention being stable after 1500 cycles.Keywords: core−shell structure; hierarchical; nanosubmicrometer composites; property optimization; supercapacitors
Co-reporter:Yangzhi Gao, Junaid Ali Syed, Hongbin Lu, Xiangkang Meng
Applied Surface Science 2016 Volume 360(Part A) pp:389-397
Publication Date(Web):1 January 2016
DOI:10.1016/j.apsusc.2015.11.029
Highlights
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H3PMo12O40 doped PAIN coatings were prepared via de-doping and re-doping process.
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H3PMo12O40 provides direct and quick deposition of doped PANI coatings on 304SS.
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The presence of phosphomolybdic acid significantly enhances the anti-corrosive performance of coating.
Co-reporter:Junaid Ali Syed, Shaochun Tang, Xiangkang Meng
Applied Surface Science 2016 Volume 383() pp:177-190
Publication Date(Web):15 October 2016
DOI:10.1016/j.apsusc.2016.04.178
Highlights
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Multilayer coatings were prepared with good self-healing and anti-corrosion ability.
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The lifespan of SS is much improved and it is stable even after 120 h in 3.5% NaCl.
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Multilayer structure with redox catalytic and self-healing ability leads to high Pe.
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Saline-triggered self-healing and anti-corrosion mechanisms were envisaged.
Co-reporter:Jun Ma, Hongjun Ni, Dongyun Su, Xiangkang Meng
International Journal of Hydrogen Energy 2016 Volume 41(Issue 36) pp:16191-16195
Publication Date(Web):28 September 2016
DOI:10.1016/j.ijhydene.2016.05.255
•The MFC constructed with a spherical configuration as a cathode compartment has a better anti-leakage performance.•Carbon brush anodes achieve a good dispersion of the graphite filaments and contain an efficient current collector.•A benthic strain of proteobacteria was isolated and identified.As microbial fuel cell (MFC) technology is getting nearer to practical applications, the microorganisms can convert chemical energy from a wide range of organic substances into electric current directly. In this paper, the MFC with a spherical configuration as cathode compartment was constructed. The MFC with a brush-shaped anode, platinum/carbon cathode, pre-treated Nafion 117 were constructed using pig farm wastewater as substrate. The biofilm analysis was used by bacterial community structure and diversity by denaturing gradient gel electrophoresis (DGGE). A benthic strain of proteobacteria was isolated and identified, wastewater was treated with proteobacteria to decrease the chemical oxygen demand, phosphorus, nitrogen and to produce electricity, which had an excellent electrogenic qualities.
Co-reporter:Yongguang Wang, Xiangyu Wang, Bo Sun, Shaochun Tang, Xiangkang Meng
Journal of Materials Science & Technology 2016 Volume 32(Issue 1) pp:41-47
Publication Date(Web):January 2016
DOI:10.1016/j.jmst.2015.10.015
Silver nanowires (NWs) coated with platinum (Pt) nanoparticles were synthesized via a galvanic partial replacement of Ag NWs in an aqueous K2PtCl6 solution at room temperature. The products were characterized using a combination of electron microscopies, selected area electron diffraction, energy-dispersive X-ray mapping and X-ray diffraction. The surface morphology and Pt/Ag composition ratios are controlled by adjusting the K2PtCl6 concentration. Different concentrations result in various surface morphologies including rough nanoparticle coating, porous and relatively smooth surfaces. The formation mechanism was discussed based on the lattice constants' difference, concentration driven nucleation, consumption of Ag NWs, and stoichiometry of the replacement reaction. The effects of the bimetallic interface on the catalytic activity toward the reduction of 4-nitrophenol by sodium borohydride were studied. The activity of Ag–Pt NWs is highly enhanced over monometallic nanostructures, and optimized by a low Pt loading of 1.34 at.%, which indicates a catalytic role of the inter-metallic interface for the electron transfer.
Co-reporter:Sascha Vongehr, Shaochun Tang, Xiangkang Meng
Journal of Materials Science & Technology 2016 Volume 32(Issue 5) pp:387-401
Publication Date(Web):May 2016
DOI:10.1016/j.jmst.2016.01.003
Today's emergence of nano-micro hybrid structures with almost biological complexity is of fundamental interest. Our ability to adapt intelligently to the challenges has ramifications all the way from fundamentally changing research itself, over applications critical to future survival, to posing globally existential dangers. Touching on specific issues such as how complexity relates to the catalytic prowess of multi-metal compounds, we discuss the increasingly urgent issues in nanotechnology also very generally and guided by the motto ‘Bio Is Nature's Nanotech’. Technology belongs to macro-evolution; for example integration with artificial intelligence (AI) is inevitable. Darwinian adaptation manifests as integration of complexity, and awareness of this helps in developing adaptable research methods that can find use across a wide range of research. The second half of this work reviews a diverse range of projects which all benefited from ‘playful’ programming aimed at dealing with complexity. The main purpose of reviewing them is to show how such projects benefit from and fit in with the general, philosophical approach, proving the relevance of the ‘big picture’ where it is usually disregarded.
Co-reporter:M.Z. Wei, J. Shi, Y.J. Ma, Z.H. Cao, X.K. Meng
Materials Science and Engineering: A 2016 Volume 651() pp:155-159
Publication Date(Web):10 January 2016
DOI:10.1016/j.msea.2015.10.107
In this work, the hardness and elastic modulus were investigated in Ag/Nb multilayers with the individual layer thickness (h) ranging from 1 to 50 nm. The hardness increases with decreasing h, and the magnitudes of hardness of multilayers with h≤5 nm are higher than that of either constituent. This ultra-high strengthening results from the coherency stresses and high density stacking faults in Ag layers. Meanwhile, the enhancement of elastic modulus is achieved due to the lattice contraction when h≤20 nm, where the modulus values are higher than that of either constituent, showing a supermodulus effect.
Co-reporter:Mingjin Cui, Haiming Lu, Haiping Jiang, and Xiangkang Meng
ACS Nano 2016 Volume 10(Issue 12) pp:
Publication Date(Web):December 27, 2016
DOI:10.1021/acsnano.6b03701
Co-reporter:Hao Xie, Shaochun Tang, Jian Zhu, Sascha Vongehr and Xiangkang Meng
Journal of Materials Chemistry A 2015 vol. 3(Issue 36) pp:18505-18513
Publication Date(Web):31 Jul 2015
DOI:10.1039/C5TA05129K
In order to achieve high energy densities, an asymmetric all-solid-state supercapacitor is developed by synthesizing a novel composite of cobalt carbonate hydroxide (CCH) nanowire covered N-doped graphene (NG) as positive and porous NG as negative electrodes. The CCH–NG composite is obtained from a one-step hydrothermal method, where optimization of the CCH content triples the specific capacitance of porous NG, reaching 1690 F g−1 at 1.0 A g−1. The optimal composite exhibits a remarkable cycling stability retaining 94.2% of the initial capacitance after 10000 cycles, and good rate capability (still 1358 F g−1 at 10 A g−1). The assembled asymmetric supercapacitor based on the optimal composite has a high discharge areal capacitance of 153.5 mF cm−2 (at 1.0 mA cm−2), can cycle reversibly in the high-voltage region of 0–1.9 V, and thus provide superior energy and power densities (0.77 W h m−2 and 25.3 W m−2).
Co-reporter:Z.H. Cao, L.J. Xu, W. Sun, J. Shi, M.Z. Wei, G.J. Pan, X.B. Yang, J.W. Zhao, X.K. Meng
Acta Materialia 2015 Volume 95() pp:312-323
Publication Date(Web):15 August 2015
DOI:10.1016/j.actamat.2015.05.036
Abstract
The formation mechanisms and grain size dependence of annealing coherent multiple-fold twins, such as twofold and fivefold twins, were investigated in nanocrystalline Cu with zero applied stress by a combination of transmission electron microscopy and molecular dynamics (MD) simulation. It was found that the formation frequency of twofold and fivefold twins with coherent twin boundaries (CTB) increases with decreasing grain size (d), reaching a maximum frequency at the critical size of 35 nm, followed by a reduction at d < 35 nm. Numerous stacking faults (SFs) ribbons are also observed and associated with the formation of multiple-fold twins. Dislocation mediated grain rotation and SFs overlapping become the dominant formation mechanisms of multiple-fold twins, which are demonstrated by experiment and MD simulation. The competition between grain growth by GB migration and the transformation of GBs to intersectant CTBs via grain rotation causes the inverse grain size dependence.
Co-reporter:Junaid Ali Syed, Hongbin Lu, Shaochun Tang, Xiangkang Meng
Applied Surface Science 2015 Volume 325() pp:160-169
Publication Date(Web):15 January 2015
DOI:10.1016/j.apsusc.2014.11.021
Highlights
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PANI-PAA/PEI multilayers with controllable thickness were fabricated by spin assembly.
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PAA matrix results in the homogeneous dispersion of PANI in the composite coatings.
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Spin coating combined with heating assures the linear increase in thickness with n.
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The corrosion protection property of PANI-PAA/PEI coatings were optimized at n = 20.
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Enhanced protection owing to multilayer structure that lengthens the diffusion pathway of ions.
Co-reporter:Xiangyu Wang, Pinghui Zhang, Sascha Vongehr, Shaochun Tang, Yongguang Wang and Xiangkang Meng
RSC Advances 2015 vol. 5(Issue 56) pp:45194-45200
Publication Date(Web):15 May 2015
DOI:10.1039/C5RA06679D
We report a novel method for the large-scale fabrication of porous bulk silver thin sheets (PSTS) built from three-dimensionally interconnected nanoparticles (NPs). The synthesis starts with synthesizing silver sponges via an in situ growth of NPs which assemble into networks. The sponges are pressed into thin sheets before etching in acid. The resulting porosity is nearly homogeneous throughout the whole volume. The dependence on acid concentration was investigated and the average pore diameter can be controlled in a range of 83–145 nm by etching time. Growing metal oxides results in PSTS/Co3O4 composites which can be used directly as binder-free supercapacitor electrodes. The Co3O4 growth is optimized and the optimized composite electrode provides a much higher specific capacitance (1276 F g−1 at 1 A g−1) than previously reported for pure Co3O4 nanostructures with different shapes or those for Ag–Co3O4 composite nanowire array electrodes. The optimal electrode has a superior rate capability (still 986 F g−1 at 10 A g−1). The improvements are attributed to the continuous open porosity of PSTS and a direct contact between Co3O4 and Ag ligaments. The method can be extended to many other metals or alloys, promising wide application.
Co-reporter:Yongguang Wang, Xiangyu Wang, Shaochun Tang, Sascha Vongehr, Junaid Ali Syed and Xiangkang Meng
RSC Advances 2015 vol. 5(Issue 77) pp:62670-62677
Publication Date(Web):08 Jul 2015
DOI:10.1039/C5RA05486A
In the present work, we report the preparation of graphene (G) doped polyacrylic acid/polyaniline (G-PAA/PANI) composites with excellent processibility for ensuring ultrathin, defect-free and highly flexible films, as well as high electrochemical performance. The weight content of PANI is maximized under the constraint of still allowing defect-free films, and the G content is optimized. Interestingly, we combine two steps that both, if taken in isolation as a strategy, worsen the solubility. The PANI and G contents are optimized to be 20 wt% and 1.3 wt%, respectively. The optimal G-PAA/PANI composite film has a gravimetric capacitance of 399 F g−1 at 10 mV s−1, which is more than twice that of pure PANI nanoparticles. Considering the film thickness of only 50 μm, its specific areal and volumetric capacitances are as high as 1.20 F cm−2 and 240 F cm−3. The film still has a gravimetric capacitance of 342 F g−1 at a high scan rate of 100 mV s−1 (86% of that at 10 mV s−1), which promises great potential for applications needing a rapid charge/discharge. An assembled all-solid-state supercapacitor using two such flexible G-PAA/PANI films provides 93 F g−1; an eighteen-fold improvement over that of a previously reported similar device. The capacitor also exhibits excellent electrochemical stability under different bending angles.
Co-reporter:Nanting Li, Shaochun Tang, Xiangkang Meng
Journal of Materials Science & Technology 2015 Volume 31(Issue 1) pp:30-36
Publication Date(Web):January 2015
DOI:10.1016/j.jmst.2014.09.007
In this work, we report the growth of uniformly dispersed bimetallic cobalt–palladium nanoparticles (NPs) on reduced graphene oxide (RGO) nanosheets to prepare CoPd–RGO composites via a two-step procedure, where firstly formed Co NPs are used as seeds for the subsequent growth of Pd. The generation of Co NPs on RGO is performed by an in-situ reduction reaction with the reducer ethylene glycol under oil bath at 180 °C. According to composition, size and microstructure analyses, NPs in the resulting CoPd–RGO have an average particle size of 5 nm, and Pd is added to one side of Co NPs, thus forming Co–Pd bimetallic interfaces. The involved formation mechanism is suggested. The composite is used as an electro-catalyst for the formic acid oxidation in alkaline electrolyte, and the catalytic performance is investigated by cyclic voltammetry and chronopotentiometry etc. The results show that the composite has the highest electro-catalytic activity, the best electrochemical stability and the highest resistance to CO poisoning than those of the monometallic composite and commercial Pd black at the same loading. This is due not only to the small size of NPs with Co–Pd bimetallic interfaces providing more active atoms accessible for reactants, but also to the electric synergistic effect between metals and graphene.
Co-reporter:Min Sun, Sascha Vongehr, Shaochun Tang, Lan Chen, Yongguang Wang, Xiangkang Meng
Materials Letters 2015 Volume 141() pp:165-167
Publication Date(Web):15 February 2015
DOI:10.1016/j.matlet.2014.11.019
•We analyze morphology, crystallinity, porosity, and capacity over wide a range of shapes.•The influences of shape and porosity on the capacitance are separated.•Two capacitance decline regions are identified and discussed quantitatively.•Precise shapes are determined from many particles by image recognition algorithms.A wide range of Co3O4 nanoshapes has been synthesized by calcinations, all from the same precursor to distinguish the influence of porosity and shape, which has been determined by image recognition algorithms analyzing many particles. We survey morphology transitions, crystallinity (single- to poly- to single-crystalline again), porosity, and electrochemical capacity from 200 to 900 °C. A maximally porous structure is confirmed near 300 °C. A steep capacitance decline is due to loss of pore access. Capacitance is shown to decline further because the shape changes, with only 39% being due to lost porosity. This decline is surprisingly linear with 0.65 F/(g °C) over 500 °C, although the shapes even pass through a ring topology, likely from a kinetic Kirkendall mechanism.
Co-reporter:L.J. Xu, Z.H. Cao, M.Z. Wei, J. Shi, G.J. Pan, X.K. Meng
Materials Letters 2015 Volume 145() pp:295-298
Publication Date(Web):15 April 2015
DOI:10.1016/j.matlet.2015.01.134
•High density V-shaped multiple twins were observed in annealed Cu thin films.•The propensity of V-shaped multiple twins exhibits an obvious grain size dependence.•A new formation mechanism of V-shaped multiple twins has been proposed.•The mechanism based on cooperative grain rotation and grain boundary migration.•The mechanism well explains the apparent peak in V-shaped multiple twins.V-shaped multiple twins have been observed in annealed nanocrystalline Cu by high-resolution transmission electron microscopy. The density of V-shaped multiple twins depends on the grain size remarkably. With decreasing grain size, the amount of V-shaped multiple twins increases initially and then decreases, reaching the maximum at a critical grain size of 40 nm and exhibiting an obvious grain size dependence. The formation mechanism of V-shaped multiple twins is proposed based on cooperative grain rotation and grain boundary migration. However, the amount of V-shaped multiple twins decreases significantly below the critical grain size, which is attributed to the grain rotation-mediated single crystal growth.
Co-reporter:M.Z. Wei, Z.H. Cao, J. Shi, G.J. Pan, L.J. Xu, X.K. Meng
Materials Science and Engineering: A 2015 Volume 646() pp:163-168
Publication Date(Web):14 October 2015
DOI:10.1016/j.msea.2015.08.068
The evolution of interfacial structures and creep behavior of Cu/Ta multilayers at room temperature were investigated as the individual layer thickness (hL) varies from 2.5 to 100 nm. The interface structures exhibit different configurations at different length scales. The main crystal phase in Ta layers changes from α-Ta to β-Ta with the increase of hL from 5 to 10 nm, and amorphous regions appear at the interface when hL=25 nm. These variations affect the creep behaviors deeply. The creep stress exponent (n) increases with the decreasing hL and reaches maximum at hL=5 nm. According to the variation of n values, the creep behavior is dominated by the dislocation climb from the grain boundaries in Cu layers to the heterogeneous interfaces between two constituent when decreasing the hL. In addition, the change of Ta phases also contributes a lot to the stress exponent at several nanometer scale.
Co-reporter:Junaid Ali Syed, Shaochun Tang, Hongbin Lu, Xiangkang Meng
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2015 Volume 476() pp:48-56
Publication Date(Web):5 July 2015
DOI:10.1016/j.colsurfa.2015.03.021
•Eco-friendly multilayers with enhanced self-healing and anti-corrosion ability.•LBL technique allows fine control over layer numbers and coating thickness.•The properties of the multilayer coatings were optimized at n = 40.•Self-healing is attributed to the stimuli responsive swelling and electrostatic repairing.We report the design and fabrication of smart polydiallyldimethylammonium chloride (PDDA)/polyacrylic acid (PAA) multilayer coatings with enhanced stimuli responsive self-healing and anti-corrosion ability for 430 stainless steel (SS). The multilayer coatings were prepared by layer-by-layer (LBL) technique, which allows a fine control over layer numbers (n) and coating thickness. The dependence of anti-corrosion and self-healing properties on layer number was investigated in 3% NaCl solution. The involved self-healing is attributed to the stimuli responsive swelling and electrostatic repairing of the polyelectrolyte multilayers (PEMu) in the vicinity of the scratches. The enhanced corrosion resistance ability is mainly due to the multilayer structure and the self-healing behavior that lengthens and hinders the diffusion pathway of corrosive species.
Co-reporter:J. Shi, Z.H. Cao, M.Z. Wei, G.J. Pan, L.J. Xu, X.K. Meng
Materials Science and Engineering: A 2015 623() pp: 104-108
Publication Date(Web):
DOI:10.1016/j.msea.2014.11.046
Co-reporter:J. Shi, M.Z. Wei, Y.J. Ma, L.J. Xu, Z.H. Cao, X.K. Meng
Materials Science and Engineering: A 2015 Volume 648() pp:31-36
Publication Date(Web):11 November 2015
DOI:10.1016/j.msea.2015.09.042
In this paper, we prepared alloying Ti/Ni multilayers through changing modulation periods (λ) and subsequent annealing. Strain rate sensitivity of the multilayers was investigated by nanoindentation. It was found that the multilayer became full alloying with the highest value of hardness at λ=5.4 nm. Both the alloying degree and the corresponding hardness are remarkable dependent on λ. Only the multilayers accompanied by obvious stress-induced pop-in events exhibit negative strain rate sensitivity resulted from stress-induced martensitic transformation, while hardness of the other multilayers does not change with strain rate. In addition, the critical load for the first pop-in increases with strain rate, meaning that larger stress is needed to induce martensitic transformation at higher strain rate.
Co-reporter:Shaochun Tang, Sascha Vongehr, Yongguang Wang, Juan Cui, Xiangyu Wang and Xiangkang Meng
Journal of Materials Chemistry A 2014 vol. 2(Issue 10) pp:3648-3660
Publication Date(Web):10 Dec 2013
DOI:10.1039/C3TA14541G
We report a template- and surfactant-free synthesis of multi-metallic nanosponges with controllable composition, porosity, ligament and grain sizes, as well as control over alloying. The inexpensive approach is scalable to industrial production and produces not only sponges of various pure metals such as Ag, Au, Pd, Pt, Co, Ni, Cu, but also bi- and trimetallic alloys or non-alloys. The synthesis involves fast reduction of metal salts followed by a slow network assembly in ethanol–glycerol mixed solvents shaken in a temperature range of 25–90 °C. Freeze drying conserves the pores to ensure a high surface area. The involved growth mechanisms are discussed. Tri-metallic alloyed Ag34Au33Pd33 sponges with a specific surface area of 96 m2 g−1 exhibit the highest reported catalytic rate for the degradation of azo dyes and 4-nitrophenol reduction. They show higher catalytic activity and better long-term stability for formic acid electro-oxidation compared with Pd-based mono- and bimetallic nanostructures. The excellent catalytic performance is mainly attributed to the high porosity and large number of interfaces. Pressed into discs, the Ag sponges' sensitive SERS activity is highly reproducible over area.
Co-reporter:Jian Zhu, Shaochun Tang, Hao Xie, Yuming Dai, and Xiangkang Meng
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 20) pp:17637
Publication Date(Web):September 25, 2014
DOI:10.1021/am505622c
Hierarchically porous yet densely packed MnO2 microspheres doped with Fe3O4 nanoparticles are synthesized via a one-step and low-cost ultrasound assisted method. The scalable synthesis is based on Fe2+ and ultrasound assisted nucleation and growth at a constant temperature in a range of 25–70 °C. Single-crystalline Fe3O4 particles of 3–5 nm in diameter are homogeneously distributed throughout the spheres and none are on the surface. A systematic optimization of reaction parameters results in isolated, porous, and uniform Fe3O4–MnO2 composite spheres. The spheres’ average diameter is dependent on the temperature, and thus is controllable in a range of 0.7–1.28 μm. The involved growth mechanism is discussed. The specific capacitance is optimized at an Fe/Mn atomic ratio of r = 0.075 to be 448 F/g at a scan rate of 5 mV/s, which is nearly 1.5 times that of the extremely high reported value for MnO2 nanostructures (309 F/g). Especially, such a structure allows significantly improved stability at high charging rates. The composite has a capacitance of 367.4 F/g at a high scan rate of 100 mV/s, which is 82% of that at 5 mV/s. Also, it has an excellent cycling performance with a capacitance retention of 76% after 5000 charge/discharge cycles at 5 A/g.Keywords: composite materials; hierarchically porous structures; manganese dioxide; supercapacitors
Co-reporter:Yuming Dai, Shaochun Tang, Sascha Vongehr, and Xiangkang Meng
ACS Sustainable Chemistry & Engineering 2014 Volume 2(Issue 4) pp:692
Publication Date(Web):January 5, 2014
DOI:10.1021/sc400403q
We report a facile, low-cost, ultrasound-assisted synthesis of nanowire-covered porous MnO2 spheres with superior supercapacitance at high charging rates with long-term durability. The use of catalytic silver nanoparticles is crucial to the growth mechanism in the initial stage, and the resulting silver oxides later grow the nanowires in such a way that they always terminate the wires, thus automatically covering the structures and increasing conductivity. The optimal Ag2O–MnO2 structures have a specific capacitance of 536.4 F/g at 5 mV/s. At a high scan rate of 100 mV/s, only 200 F/g remain for the reported carbon nanotube/MnO2 material with an excellent capacitance at low scan rate (1230 F/g, 1 mV/s), while the Ag2O–MnO2 reported here still has 417.2 F/g. The material reaches a stable region of 91.3% capacitance retention over 10000 charge/discharge cycles at 5 A/g.Keywords: Hierarchical structures; Long-term stability; Manganese oxide; Rapid charging; Supercapacitors
Co-reporter:Shaochun Tang, Sascha Vongehr, Xiangyu Wang, Yongguang Wang and Xiangkang Meng
RSC Advances 2014 vol. 4(Issue 26) pp:13729-13732
Publication Date(Web):04 Mar 2014
DOI:10.1039/C4RA00371C
Palladium shells are prepared via a one-step solvothermal synthesis involving nanobubbles as soft templates although no stabilizer is present, while still allowing control over diameter, thickness, and grain size, leading to grain-monolayer thin and porous shells with very high and durable electrocatalytic activity.
Co-reporter:Hao Xie, Shaochun Tang, Zilun Gong, Sascha Vongehr, Fei Fang, Min Li and Xiangkang Meng
RSC Advances 2014 vol. 4(Issue 106) pp:61753-61758
Publication Date(Web):03 Nov 2014
DOI:10.1039/C4RA10333E
We report a simple hydrothermal synthesis of nanocomposites, constructed by 3D nitrogen-doped graphene (NG) networks with hexagonal Co(OH)2 nanoplates, which are optimized for applications as electrochemical pseudocapacitor materials. Single-crystalline Co(OH)2 plates are distributed homogeneously inside the conductive interconnected NG networks. The 71% Co(OH)2 weight content achieves a capacitance of 952 F g−1 at 1.0 A g−1, more than triple that of the pure NG and nearly four times that of Co(OH)2 plates; moreover, this value exceeds the recently reported values for 2D graphene/Co(OH)2 composites. Capacitance retention over 2000 cycles is still high as 95%. The improvements are attributed to the regular morphology of Co(OH)2 and the 3D porosity, which prevents the stacking of the Co(OH)2 plates as well as the composite, and the continuously connected pores and highly conductive NG networks, which facilitate electron and ion transport.
Co-reporter:Nanting Li, Shaochun Tang, Xiangkang Meng
Journal of Materials Science & Technology 2014 Volume 30(Issue 11) pp:1071-1077
Publication Date(Web):November 2014
DOI:10.1016/j.jmst.2014.07.018
In this paper, we report a simple one-step thermal reducing method for synthesis of bimetallic Au@Pd nanoparticles with core-shell structures on the graphene surface. This new type of Au@Pd–G composites is characterized by transmission electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It is found that Au@Pd nanoparticles with an average diameter of 11 nm are well dispersed on the graphene surface, and the Au core quantity as well as the Pd shell thickness can be quantitatively controlled by loading different amounts of metallic precursors, and the involved core-shell structure formation mechanism is also discussed. The ternary Pt/Au@Pd–G composites can also be synthetized by the subsequent Pt doping. The catalytic performance of Au@Pd–G composites toward methanol electro-oxidation in acidic media is investigated. The results show that Au@Pd–G composites exhibit higher catalytic activity, better stability and stronger tolerance to CO poisoning than Pd–G and Au–G counterparts.
Co-reporter:J. Shi, Z.H. Cao, K. Hu, G.J. Pan, M.Z. Wei, L.J. Xu, X.K. Meng
Materials Letters 2014 Volume 115() pp:79-81
Publication Date(Web):15 January 2014
DOI:10.1016/j.matlet.2013.10.024
•The Ni–Ti–Al thin films with pure L21–Ni2TiAl phases were prepared in this work.•We first study pseudoelasticity of the L21 phases and the highest recovery ratio reaches 92.7%.•The pseudoelasticity strongly depends on grain size and indentation depth.•Hardness versus grain size shows an inverse Hall–Petch effect.Pseudoelasticity of nanocrystalline Ni43Ti38Al19 thin films with thickness of 600 nm is investigated by nanoindentation. It is found that the films with grain size of 12–28 nm are composed of L21–Ni2TiAl phases, Ni3Ti precipitates and few B2–NiTi phases. The films with the L21 phases exhibit prominent pseudoelasticity, which strongly depends on grain size and indentation depth at the nanoscale. The pseudoelasticity decreases gradually with increasing grain size and indentation depth; among them the highest pseudoelasticity recovery ratio reaches 92.7%. With decreasing the grain size from 28 to 12 nm, the hardness of the films increases initially and then decreases, showing an inverse Hall–Petch effect.
Co-reporter:Y.M. Dai, S.C. Tang, Z.X. Ba, S.S. Zhu, Q. Wang, C. Wang, X.K. Meng
Materials Letters 2014 Volume 117() pp:104-107
Publication Date(Web):15 February 2014
DOI:10.1016/j.matlet.2013.11.106
•A low-cost MnO2 nanowire/Ag nanoparticles composites were prepared in this work.•The products have superior electrochemical performance.•Ag nanoparticles improve the electric conductivity of the products.•Ag nanoparticles also enhance the structural stability of the products.MnO2 nanowire/Ag nanoparticles composites for supercapacitor were synthesized with a two-step procedure, which involves preparing MnO2 nanowires and acquiring conductive Ag nanoparticles grown on the surface of MnO2 nanowires with reducing Ag+. The results show that Ag nanoparticles are not only to improve the electric conductivity, but also to enhance the structural stability of the composites. The composites have an excellent specific capacitance of 396.4 F/g at a scan rate of 50 mV/s in 1 M Na2SO4 aqueous solution, which is almost five times that of the pure MnO2 nanowires. Besides, capacitance retention of 95.2% for the MnO2/Ag over 2000 charge/discharge cycles at a charge/discharge current of 5 A/g is much better than that of the pure MnO2 NWs.
Co-reporter:M.Z. Wei, Z.H. Cao, J. Shi, G.J. Pan, L.J. Xu, X.K. Meng
Materials Science and Engineering: A 2014 Volume 598() pp:355-359
Publication Date(Web):26 March 2014
DOI:10.1016/j.msea.2014.01.049
This work presents a length-scale induced anomalous plastic deformation of Cu/Ta multilayers with individual layer thickness (h) varying from 1 nm to 100 nm. The hardness increases with decreasing h and reaches a maximum at 10 nm. A sharp softening has been observed when h is below 10 nm. Furthermore, the results show that the phases of Ta layers vary from the coexistence of α-Ta and β-Ta to single α-Ta as h decreases from 10 nm to 5 nm. The phase transition causes the variation of interface structures as well as the hardness of Ta layers and results in the anomalous decrease in hardness. The strengthening mechanisms at different length scales are discussed separately.
Co-reporter:Nanting Li;Shaochun Tang;Yumin Dai
Journal of Materials Science 2014 Volume 49( Issue 7) pp:2802-2809
Publication Date(Web):2014 April
DOI:10.1007/s10853-013-7986-1
In this work, we report a simple strategy for synthesis of graphene oxide nanostructures with various morphologies including single-, few-layer, and three-dimensional networks. Morphology control is achieved by adding different amounts of Ni2+ into a one-step hydrothermal process. The involved growth mechanisms for the morphology control are discussed. A random arrangement of graphene oxide nanosheets is suggested to induce the networks’ formation. Ni2+ facilitates the formation of graphene oxide’s preferential face-to-face overlapping structure, and high Ni2+ concentrations render adjacent graphene oxide sheets to combine each other tightly to form closely packed, layered structures. Compared with single-, few-layer graphene oxide, the electrode prepared by three-dimensional networks has a mass specific capacitance of 352 F g−1 at v = 5 mV s−1, which is much higher than that of recently reported three-dimensional graphene oxide nanostructures (240 F g−1).
Co-reporter:Guanjun Pan, Zhenhua Cao, Jun Shi, Mingzhen Wei, Lijun Xu, Xiangkang Meng
Sensors and Actuators A: Physical 2014 Volume 217() pp:75-80
Publication Date(Web):15 September 2014
DOI:10.1016/j.sna.2014.06.019
•We compared the different mechanical response of TiNi film by Berkovich and spherical indenters.•Incomplete phase transition (A → R) were clearly depicted by spherical indentation.•The different response is due to the varied stress distribution beneath two types of indenters.•Significant difference in indentation size effect for TiNi film was revealed comparing to traditional metals.Nanoindentation was conducted for magnetron sputtered TiNi thin film, which exhibits different mechanical responses induced by varied indenter shapes. Superelasticity and incomplete phase transition (A → R) were clearly depicted by spherical indentation. Under the peak load of 500 μN, the depth recovery ratios are 100% and 68% determined by spherical and Berkovich indentations, respectively. The different response is due to the varied stress distribution beneath two types of indenters. Large plastic deformation hinders the reverse phase transition (R → A) in Berkovich indentation, resulting lower recovery. Moreover, significant difference in indentation size effect for TiNi film was revealed comparing to traditional metals. And phase transition contributed considerably to the abnormal hardness evolution.
Co-reporter:J. Shi, Z.H. Cao, M.Z. Wei, G.J. Pan, L.J. Xu, X.K. Meng
Materials Science and Engineering: A 2014 618() pp: 385-388
Publication Date(Web):
DOI:10.1016/j.msea.2014.09.019
Co-reporter:Nanting Li, Shaochun Tang, Yi Pan, Xiangkang Meng
Materials Research Bulletin 2014 49() pp: 119-125
Publication Date(Web):
DOI:10.1016/j.materresbull.2013.08.029
Co-reporter:Guanjun Pan, Zhenhua Cao, Mingzhen Wei, Jun Shi, Lijun Xu, Xiangkang Meng
Materials Letters 2014 130() pp: 285-288
Publication Date(Web):
DOI:10.1016/j.matlet.2014.05.129
Co-reporter:Y.M. Dai, S.C. Tang, J.Q. Peng, H.Y. Chen, Z.X. Ba, Y.J. Ma, X.K. Meng
Materials Letters 2014 130() pp: 107-110
Publication Date(Web):
DOI:10.1016/j.matlet.2014.05.090
Co-reporter:Guanjun Pan, Zhenhua Cao, Mingzhen Wei, Lijun Xu, Jun Shi, Xiangkang Meng
Materials Science and Engineering: A 2014 600() pp: 8-11
Publication Date(Web):
DOI:10.1016/j.msea.2014.02.019
Co-reporter:K. Hu, L.J. Xu, Y.Q. Cao, G.J. Pan, Z.H. Cao, X.K. Meng
Materials Letters 2013 Volume 107() pp:303-306
Publication Date(Web):15 September 2013
DOI:10.1016/j.matlet.2013.06.053
•The strength and ductility of Cu/Ru multilayers depend on individual thickness (h).•An optimized combination of strength and ductility is obtained when h is 20 nm.•This finding may play an important role in the working stability of MEMS.The effect of individual thickness on the mechanical properties of Cu/Ru multilayer films deposited onto flexible substrate was investigated by uniaxial tension tests. It is found that both strength and ductility of the Cu/Ru multilayer films are remarkably dependent on the individual thickness. An optimized combination of strength and ductility is obtained when the individual thickness is 20 nm. The strengthening mechanism changes from the confined layer slip of single dislocations to the load-bearing effect and the individual thickness dependent ductility is due to the competition between the stress intensity factor in Ru layers and the plasticity deformation in Cu layers.
Co-reporter:Shaochun Tang, Sascha Vongehr, Neng Wan, Xiangkang Meng
Materials Chemistry and Physics 2013 Volume 142(Issue 1) pp:17-26
Publication Date(Web):15 October 2013
DOI:10.1016/j.matchemphys.2013.06.023
•Synthesis of pentagonal Ag nanowires needs only 2.5 min.•Wire diameters are controllable from 60 to 480 nm.•PVP and microwaves ensure pentagonal shape even at large diameters.•The tensile yield strength is diameter dependent and maximal around 220 nm.We synthesize silver nanowires (NWs) with pentagonal cross sections via a facile and rapid microwave-assisted polyol method in the presence of polyvinylpyrrolidone (PVP) and sodium sulfide (Na2S). The synthesis does not use templates and needs only 2.5 min, which is 570 times faster than solvothermal preparation at 100 °C. The pentagonal Ag NWs grow along the <110> direction and reach lengths between 10 and 30 μm. Adjusting Na2S concentration controls the wire diameters in a wide range from 60 to 480 nm. PVP and microwave irradiation both ensure the cross sections' pentagonal shape even at large diameters. We use different microwave irradiation times to investigate the morphology's evolution and to support the discussion of growth mechanisms. The electrical conductivity was measured in situ inside a transmission electron microscope. Their resistivity is diameter dependent and comparable to that of Ag NWs with round cross sections. Ultrasound fracturing analysis determined the NWs' tensile yield strengths, which is also diameter dependent and maximal around 220 nm.
Co-reporter:Z.H. Cao, L. Wang, K. Hu, Y.L. Huang, X.K. Meng
Acta Materialia 2012 Volume 60(Issue 19) pp:6742-6754
Publication Date(Web):November 2012
DOI:10.1016/j.actamat.2012.08.047
Abstract
Indentation creep and stress relaxation tests were performed on rolled and annealed nanocrystalline (NC) Ni to study the influence of microstructure evolution on plastic deformation behavior. Dislocation density (ρ) increases with increasing rolling strain, reaching a maximum at 20% strain, followed by a decrease at larger strain. The ρ of Ni decreases significantly with increasing annealing temperature. Softening behavior is observed in NC Ni with grain size <40 nm, i.e., an inverse-like Hall–Petch effect. For rolling NC Ni, both creep strain rate and rate sensitivity first increase and then decrease, while those of annealed Ni continuously decrease. With increasing grain size, creep activation volume unusually decreases first, then starts to rise, which is different from that of coarse-grained metal. A model involving dislocation annihilation and emission at grain boundaries under indenters is used to explain the anomalous behavior of rolled and annealed Ni, respectively.
Co-reporter:Shaochun Tang, Sascha Vongehr, Hua Ren and Xiangkang Meng
CrystEngComm 2012 vol. 14(Issue 21) pp:7209-7216
Publication Date(Web):08 Aug 2012
DOI:10.1039/C2CE25855B
Polycrystalline nickel nanowires (NWs) with a length reaching tens of micrometers were prepared in large quantities by a facile and rapid microwave-assisted polyol method. Characterization by X-ray diffraction and electron microscopy reveal that the NWs are uniform with a narrow size distribution. Their diameters (D) are controllable in a wide range via the concentration of precursor solutions. The diameters of the NWs as well as those of the contained grains increase surprisingly linearly with the concentration. The NWs have rough surfaces at low concentrations but become smoother at high ones. The growth mechanisms leading to the grain and wire diameters and the surface morphology are discussed. The coercivity (HC) decreases with increasing diameter whereas the saturation magnetization increases to approach the bulk value, indicating a strong size dependence of the magnetic properties. Owing to the anisotropic shape and collective grain interactions, these Ni NWs exhibit enhanced HC. At 70 nm, HC reaches as high as 382 Oe at 5 K, which is more than two orders of magnitude higher than that of bulk Ni (0.7 Oe) and exceeds even that of NWs synthesized with strong magnetic fields. Temperature dependent magnetization shows a wide separation between the field-cooled and zero-field-cooled M(T) curves due to the strong nanowire shape anisotropy.
Co-reporter:P. Y. Li, Z. H. Cao and X. K. Meng
Dalton Transactions 2012 vol. 41(Issue 39) pp:12101-12105
Publication Date(Web):06 Aug 2012
DOI:10.1039/C2DT31484C
Ni–Fe nanoalloy nanoparticles with an average grain size of 4 nm in diameter have been prepared by a sol–gel method under a hydrogen atmosphere where ethanol and oleic acid have been used as solvent and surfactant, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) examinations of the nanoparticles show the occurrence of (111), (200), (220) and (311) diffraction peaks and rings, meaning that the nanoparticles have a face-centered-cubic phase structure. Moreover, a superlattice diffraction peak and a diffraction ring/spot can also be observed in XRD and SAED results, indicating the formation of an equilibrium ordered L12 phase structure. The as-prepared Ni–Fe nanoalloy particles show typical superparamagnetic behavior at room temperature and the blocking temperature of the nanoparticles is determined to be about 50 K.
Co-reporter:Hua Ren, Shaochun Tang, Junaid Ali Syed, Xiangkang Meng
Materials Chemistry and Physics 2012 Volume 137(Issue 2) pp:673-680
Publication Date(Web):14 December 2012
DOI:10.1016/j.matchemphys.2012.10.024
A novel route to the synthesis of polymer-coated silver nanoparticles (NPs) was developed on the basis of the reduction of Tollens' reagent using mercaptosuccinic acid/poly(ethylene glycol) (MSA/PEG) copolymer as reducing agent and stabilizer simultaneously. The average size of the polymer-coated silver NPs could be controlled in a wide range from 10 to 120 nm by changing the MSA/PEG molar ratio. These surface-coated silver NPs can be uniformly dispersed in polar solvent and a homogeneous silver NPs/acetone dispersion has been prepared. Silver–epoxy nanocomposites have been developed by incorporating these silver NPs into epoxy. The nanocomposites with silver volume content of 25% showed a more than 3000% increase in dielectric constant as compared to neat matrix and a relatively low dielectric loss below 0.05, which meets the main requirement for embedded decoupling capacitors. Moreover, thermal properties of the silver–epoxy nanocomposites were also characterized by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). The initial decomposition temperature and glass transition temperature were elevated with the increase of silver content, which exhibit great thermal stability and facilitate electrical applications requiring higher heat-resistance.Highlights► Novel route to the synthesis of MSA/PEG copolymer-coated silver nanoparticles developed. ► The size of silver nanoparticles is successfully controlled use different copolymer. ► Developed silver–epoxy nanocomposites exhibit huge increase in dielectric constant.
Co-reporter:L. Wang, Z.H. Cao, K. Hu, Q.W. She, X.K. Meng
Materials Chemistry and Physics 2012 Volume 135(2–3) pp:806-809
Publication Date(Web):15 August 2012
DOI:10.1016/j.matchemphys.2012.05.061
Two bilayers of Ru/TaN with low N concentration and high N concentration (TaNL and TaNH) were used to determine the effect of N effusion on the barrier property. The results show that Ru/TaNH bilayer exhibits a better barrier property, in which RuN existed even after annealing at 650 °C. The improved barrier property is attributed to the formation of RuN and N atoms stuffing in grain boundaries of Ru layer by sufficient effusion N atoms from TaNH during annealing.Highlights► Success synthesis of two bilayers of Ru/N-unsaturated and N-supersaturated TaN. ► RuN exists in Ru/N-supersaturated TaN after annealing at 650 °C. ► Ru/N-supersaturated TaN exhibits high thermal stability. ► N effusion from TaN underlayer is responsible for the high thermal stability.
Co-reporter:Z.H. Cao, K. Hu, X.K. Meng
Materials Science and Engineering: A 2012 Volume 536() pp:244-248
Publication Date(Web):28 February 2012
DOI:10.1016/j.msea.2012.01.006
Co-reporter:Y. Y. Han, J. Shuai, H. M. Lu, and X. K. Meng
The Journal of Physical Chemistry B 2012 Volume 116(Issue 5) pp:1651-1654
Publication Date(Web):January 17, 2012
DOI:10.1021/jp211469e
Although the melting of ice is the most ubiquitous phase transition, (pre)melting and the quasi-liquid layer remain a matter of debate, and little is known about the relationship between the thermodynamic properties of ice nanocrystals and their size and dimensionality. Here, we model analytically the size- and dimensionality-dependent melting temperature, premelting temperature, and melting enthalpy of hydrogen-bonded ice nanocrystals. These three thermodynamic parameters are found to increase with increasing size and dimensionality where the size effect is principle while the dimensionality effect is secondary, and the size dependence of premelting temperature almost follows the same trend as that of melting temperature. The model predictions correspond to the available molecular dynamic simulation and experimental results of ice nanoparticles and nanowires. These agreements enable us to determine theoretically the thickness of the quasi-liquid layer for the first time, which is found to be not constant but slightly increase with increasing size and thus accounts for the occurrence of different reported thicknesses of the quasi-liquid layer.
Co-reporter:Sascha Vongehr, Shaochun Tang, and Xiangkang Meng
The Journal of Physical Chemistry C 2012 Volume 116(Issue 34) pp:18533-18537
Publication Date(Web):August 7, 2012
DOI:10.1021/jp305785w
Statistics often reveals unexpected errors. This is accepted and crucial in mature fields like medicine and experimental high energy particle physics, but usually underappreciated in still relatively novel areas. This work presents our strongest case in support for elevating the status of statistics in nanotechnology. Ultrasound fracturing can analyze tensile strengths of elongated nanostructures. It is rapidly growing in popularity. We calculate the location and shapes of the statistical distributions of fragment lengths and find that the usually employed analysis underestimates yield strengths. In unfortunate special cases, the true yield strength can be up to four times as high. Numerical simulations with generic assumptions still predict true values that are roughly twice as large as the result of the usually applied formulas. We suggest a different data analysis which removes the systematic error. It additionally provides an improved estimate of the statistical error, which combines the variation in yield strengths with the method’s measurement accuracy. A detailed reanalysis of previously published data supports our interpretations. The general discussion of the involved systematic and statistical errors calls for caution. Further confirmation by, for example, micro manipulation, is needed before ultrasound fracturing analysis can be trusted.
Co-reporter:HongBin Lu;YouZhen Zhou;Sascha Vongehr
Science China Technological Sciences 2012 Volume 55( Issue 4) pp:894-902
Publication Date(Web):2012 April
DOI:10.1007/s11431-011-4706-4
This paper describes the effects of temperature on the complex intermediate processes from the precursor to the fully-crystallized anatase TiO2 nanoparticles in hydrothermal synthesis. The anatase TiO2 nanoparticles were synthesized in a wide temperature range below 230°C. The composition, morphology, and methylene blue (MB) decoloration characteristics of the obtained products were investigated by X-ray diffraction, Fourier transform infrared spectroscope, X-ray photoelectron spectroscope, and scanning and transmission electron microscope. The dehydrating polycondensation of Ti(IV)-hydrates and the decomposition of (NH4)2Ti3O7 intermediates with the temperature increase lead to the direct formation of anatase TiO2 nanoparticles under the hydrothermal environments. The strong MB decoloration of the hydrothermal products obtained at the low (⩾130°C) and high (⩽180°C) temperatures are attributed to the adsorption of Ti(IV)-hydrates and the photocatalysis of anatase TiO2 nanoparticles, respectively.
Co-reporter:L. Wang, Z.H. Cao, K. Hu, Q.W. She, X.K. Meng
Applied Surface Science 2011 Volume 257(Issue 24) pp:10845-10849
Publication Date(Web):1 October 2011
DOI:10.1016/j.apsusc.2011.07.119
Abstract
In the present paper, the effects of electric field annealing on interface diffusion of Cu/Ta/Si stacks were studied by means of XRD, XPS and TEM. The barrier property of Ta films was evaluated based on the diffusion of Cu atoms. It was found that the external electric field accelerates the diffusion of Cu atoms through Cu/Ta/Si interfaces during annealing. With the increment of annealing temperature, the effect of the electric field upon the atomic diffusion becomes more significant. The mechanism of accelerated interface diffusion is suggested and the failure of Ta barrier layer is discussed based on the mobility of vacancies and Cu atoms inside Cu/Ta/Si stacks caused by the electric field.
Co-reporter:Zhou Zheng, Shaochun Tang, Sascha Vongehr, Xiangkang Meng
Materials Chemistry and Physics 2011 Volume 129(1–2) pp:594-598
Publication Date(Web):15 September 2011
DOI:10.1016/j.matchemphys.2011.04.070
In the present paper, large-area, homogeneously distributed lying dendritic silver nanostructures were prepared on a Pt film substrate using a square-wave electrodeposition technique without any additive. Individual dendrites were found to lie on the substrate and have a three-dimensional structure. The number density increases with electrolyte concentration (C) and loose films composed of overlapping dendrites were obtained at high C. The square-wave potential and its frequency determine the formation of the dendritic structure. The Ag dendrites exhibit high surface-enhanced Raman scattering (SERS) activity towards rhodamine B. The SERS activity of the dendrites is comparable to that of Ag films consisting of overlapping dendrites. It is much higher than that of Ag nanoparticles (NPs), and even higher than that of NPs’ aggregates.Graphical abstractLarge-area, homogeneously distributed lying dendritic silver nanostructures were prepared on a Pt film substrate using a square-wave electrodeposition technique without any additive. The Ag dendrites exhibit a high SERS activity towards rhodamine B. A schematic sketch is shown for illustration of square-wave electrochemical growth process of the lying three-dimensional silver dendrites.Highlights► Lying three-dimensional silver dendrites were prepared by electrodeposition. ► The square-wave potential and its frequency determines the formation of the dendritic structure. ► The Ag dendrites exhibit high surface-enhanced Raman scattering (SERS) activity towards rhodamine B, and the SERS activity is much higher than that of Ag nanoparticles (NPs), and even higher than that of NPs’ aggregates.
Co-reporter:Hongbin Lu, Youzhen Zhou, Sascha Vongehr, Kun Hu, Xiangkang Meng
Synthetic Metals 2011 Volume 161(13–14) pp:1368-1376
Publication Date(Web):July 2011
DOI:10.1016/j.synthmet.2011.05.003
A smooth and adherent polyaniline (PANI) coating was electropolymerized in HNO3 solution by cyclic voltammetry in order to protect the ferritic and economic 430 stainless steel (SS) from corrosion. The corrosion resistance was evaluated in 3.5 wt.% NaCl solution by anodic polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PANI coating shifts the corrosion potential of SS to the passive region and provides a strong and steady corrosion resistance. A low growth rate leads to a compact PANI coating that acts as a good physical barrier. However, the strong corrosion inhibition is mainly attributed to the dense oxide layers formed by the catalytic effect of PANI at the polymer/metal interface. The composition of the oxide layers was analyzed via depth profiling using X-ray photoelectron spectroscopy alternating with sputtering. Compared with layers formed on uncoated SS, the iron and chromium oxide layers under the PANI are thinner and denser, absorbing less oxygen, and providing a stronger corrosion inhibition.Highlights► A smooth and adherent PANI coating was electropolymerized on SS via HNO3 solution. ► The PANI coating provides a strong and steady corrosion protection for the SS. ► The corrosion inhibition is mainly attributed to the oxide layers under the PANI. ► The oxide layers under PANI are thinner and denser than those formed on bare SS.
Co-reporter:Lan Chen, Shaochun Tang, Sascha Vongehr, Kun Hu, Xiangkang Meng
Journal of Solid State Chemistry 2011 Volume 184(Issue 11) pp:3055-3061
Publication Date(Web):November 2011
DOI:10.1016/j.jssc.2011.09.009
Cobalt sodium tartrate nanowires are synthesized by a simple hydrothermal method using ethanol–water mixed solvents. The smooth wires are on average 30 μm long. Their diameters are narrowly size distributed with a controllable average in the range from 80 to 250 nm. Interestingly, after the initial two hours, the diameter decreases with further reaction time. The tartrate anions act as coordination ligands with all six oxygen atoms participating in the coordination. The Co2+ and Na+ ions chelate with the O atoms from the carboxylate and hydroxyl groups in the tartrate ligands. The ethanol participates in the formation of pi bonds. The cobalt is divalent while the sodium is monovalent in their tartrates. The respective crystal structures of these metal tartrates are incompatible, and the wires are therefore amorphous. The influence of the reaction time, sodium tartrate concentration, pH value, and the ethanol water ratio are studied in detail.Graphical abstractCobalt sodium tartrate nanowires with smooth surfaces are synthesized hydrothermally. Their narrowly distributed diameters decrease with reaction time after initial two hours and are controllable from 80 to 250 nm.Highlights► Cobalt sodium tartrate nanowires are synthesized by a simple hydrothermal route. ► Nanowires are smooth, amorphous, and up to 30 μm long. ► Diameters of the wires are controllable; they decrease with the reaction time.
Co-reporter:K. Hu, Z.H. Cao, X.K. Meng
Materials Science and Engineering: A 2011 528(29–30) pp: 8546-8550
Publication Date(Web):
DOI:10.1016/j.msea.2011.08.033
Co-reporter:Shaochun Tang, Sascha Vongehr and Xiangkang Meng
Journal of Materials Chemistry A 2010 vol. 20(Issue 26) pp:5436-5445
Publication Date(Web):01 Jun 2010
DOI:10.1039/C0JM00456A
Spherical Ag–C composites containing Ag nanoparticles (NPs) have been synthesized in high yield by microwaving suspensions of porous carbon spheres (CSs) in [Ag(NH3)2]+ solutions with poly (N-vinylpyrrolidone) as the reducing agent. The use of Ag–C composites as precursors enables us to dope Au also into the CSs' interior. Various Ag–Au doped and also predominantly Au composite spheres are prepared via the immersion of the Ag–C composites in chloroauric acid (HAuCl4) solutions without additional reducing agent. The yield of Au is found to be much higher than a replacement reaction could provide, which is explained via a detailed discussion of the involved growth mechanisms that decide the locations of the NPs in/on the CSs. Optical properties and catalytic activities of the composite structures are tunable via the Au versus Ag atomic ratio as controlled by the HAuCl4 concentration. The composites exhibit excellent catalytic activity as demonstrated via the reduction of 4-nitrophenol by sodium borohydride. The catalytic activity of bimetallic composites is highly enhanced over the monometallically doped CSs.
Co-reporter:Shaochun Tang, Sascha Vongehr, Zhou Zheng, Xiangkang Meng
Journal of Colloid and Interface Science 2010 Volume 351(Issue 1) pp:217-224
Publication Date(Web):1 November 2010
DOI:10.1016/j.jcis.2010.07.045
Platinum–cobalt bimetallic structures have been synthesized in high yield via a galvanic replacement of Co dendrites in an aqueous K2PtCl6 solution at room temperature. Increasing the K2PtCl6 concentration results in different surface morphologies. Starting from furry coatings, a higher Pt/Co ratio leads to very rough surfaces built with upright standing nanoflakes, and finally a relatively smooth, cauliflower-like cover is obtained. The growth is discussed as the interplay of several mechanisms like the concentration driven nucleation, consumption of Co substrate, stoichiometry of the replacement reaction, and the electron transfer through the growing flakes. While the mono metallic structures are catalytically inactive towards the reduction of 4-nitrophenol by sodium borohydride, the catalytic activity of the bimetallic structures is quite high and optimized by a Pt atomic percentage of 27%. This indicates a catalytic role of the bimetallic interfaces.Graphical abstractThis plot monitors the reduction of 4-NP catalyzed by various Pt–Co bimetals over time; the catalytic activity of the bimetallic structures is optimized by a Pt atomic percentage of 27%.Research highlights► Increasing K2PtCl6 concentration for galvanic replacement reactions results in different surface morphologies. ► The catalytic activity of the bimetallic products is superior to that of the corresponding monometallic structures and sensitive to the Pt/Co atomic ratio. ► The optimum activity is reached at a low Pt atomic percentage. ► The catalytic activity depends largely on the accessibility of bimetallic interfaces.
Co-reporter:X.K. Meng, S.C. Tang, S. Vongehr
Journal of Materials Science & Technology 2010 Volume 26(Issue 6) pp:487-522
Publication Date(Web):June 2010
DOI:10.1016/S1005-0302(10)60078-3
This article reviews recent advances in the utilization of various water based synthesis routes towards the shape-controlled synthesis of silver nanoparticles and microstructures in a diverse range of shapes and sizes from several nanometers to micrometers. A variety of very simple one-pot methods, at times employing commercial microwave ovens, inexpensive low power ultrasound cleaners, or two-electrode electro-chemistry, can be surprisingly effective in the controlled synthesis of a wide range of nanostructured products, if only parameters are carefully chosen. Many approaches which are adopted include synthesis of Ag nanostructures with various shapes in solution, doping of Ag nanoparticles on unmodified silica and on/inside carbon spheres, kinetically controlled growth of Ag micro-particles with novel nanostructures on flat substrates, and galvanic replacement towards bimetallic Ag-Au dendrites and carbon composites. Characterizations of shape, composition and microstructure are carried out via scanning and transmission electron microscopy, various spectroscopy methods, N2 absorption measurements and suchlike. The involved growth mechanisms are investigated in order to discover new means towards better control. Size, location and shape control, including micro- and nanostructure features, allows tuning the products properties towards desired applications. We focus on the optical properties and catalytic activities, but also the stability of compounds can be an issue of interest.
Co-reporter:H. M. Lu ;X. K. Meng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 49) pp:21291-21295
Publication Date(Web):November 17, 2010
DOI:10.1021/jp108703b
Thermodynamic analytic models have been established first to describe the size dependences of Morin temperature TM and Néel temperature TN in hematite nanocrystals based on size-dependent cohesive energy model. The models indicate that both Morin temperature and Néel temperature reduce with decreasing size D or increasing magnetic proximity effect constant m at the interface, where the size effect is the principle factor while the proximity effect is secondary. Agreements between the model predictions and the corresponding experimental results are found to be reasonable, which enables us to determine the values of correlation length ξ0 and shift exponent λ in the finite size scaling theory thermodynamically for the first time. The calculated ξ0 and λ at infinite size respectively correspond to the result of the mean field theory and that obtained through fitting experimental results. Moreover, the shift exponent λ is found to be size-dependent. It decreases with increasing of the size and then reaches to a plateau in contrast with TM(D) and TN(D) functions.
Co-reporter:Shaochun Tang ; Sascha Vongehr ; Zhou Zheng ; Hanjin Liu
The Journal of Physical Chemistry C 2010 Volume 114(Issue 43) pp:18338-18346
Publication Date(Web):October 8, 2010
DOI:10.1021/jp105871w
We report a facile and efficient approach to prepare bimetallically doped Ag−M−carbon composites. Only if Ag nanoparticles (NPs) are embedded first into the submicrometer carbon spheres (CSs) can the second metal M (Pd, Pt, and Au) also be introduced into their interior. Especially at not too high concentrations of M-precursor ions (CM-ion), the locations and number density of the resulting NPs mirror those of the Ag NPs in/on the CSs. Therefore, the controllability of the Ag predoping allows control over the location dependent distribution of the NPs in the resulting bimetallic composites. The size and shape of the resulting NPs in the composites are largely controlled by the concentration CM-ion. The different shapes include solid core−shell and hollow NPs, as well as hedgehog-like hollow structures and dendritic aggregates. The nucleation and growth mechanisms, which differ between the different metals M, are discussed to explain the morphologies and the location dependence of the NPs in/on the CSs.
Co-reporter:Shaochun Tang, Sascha Vongehr and Xiangkang Meng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 2) pp:977-982
Publication Date(Web):December 15, 2009
DOI:10.1021/jp9102492
We report a facile method to dope submicrometer carbon spheres with Ag nanoparticles (NPs) to fabricate Ag-NP/C composites via microwaving suspensions of nanoporous carbon spheres in aqueous Ag(NH3)2+ solutions with poly(N-vinylpyrrolidone) as reducer. The composite particles are synthesized in high yield within a short reaction time, and the size, number density, and to some extent even the locations of NPs in/on the carbon spheres can be controlled by adjusting reaction parameters. The controllability is discussed based on the experimental results from transmission electron microscopy, X-ray photoelectron spectroscopy depth profiling, and X-ray diffraction. By controlling the Ag doping, the composite spheres exhibit not only a tunable plasmon resonance shift but also an excellent catalytic activity toward the reduction of 4-nitrophenol by sodium borohydride.
Co-reporter:H. M. Lu and X. K. Meng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 3) pp:1534-1538
Publication Date(Web):December 30, 2009
DOI:10.1021/jp9106475
On the basis of a size-dependent cohesive energy model originally proposed for spherical nanoparticles, we develop an analytical model for the first time to determine the size- and shape-dependent catalytic activation energy of platinum nanoparticles through the introduction of a shape factor. The catalytic activation energy Ea(λ,D) was found to decrease with the decreasing size D or increasing shape factor λ, where the size effect is the principle factor and the shape effect is secondary. For platinum nanoparticles with the same size, the order is Ea(cube) > Ea(sphere) > Ea(octahedron) > Ea(tetrahedron) because λtetrahedron > λoctahedron > λsphere > λcube. The accuracy of the developed model was verified by the available experimental results.
Co-reporter:H. M. Lu and X. K. Meng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 7) pp:2932-2935
Publication Date(Web):February 1, 2010
DOI:10.1021/jp912081f
In terms of the size-dependent second-order Curie temperature model originally proposed for spherical nanoparticles, we develop an analytical model to describe size dependence of magnetostructural transition temperature Tt(D,L) in MnBi cylindrical nanorods through considering the effects of both diameter D and length L. It is found that the size-dependent magnetostructural transition temperature decreases with declining diameter and length where the diameter effect is the principle factor while the length effect is the secondary one. Moreover, the size dependence of Tt(D,L) of nanorods is weaker than that of zero-dimensional spherical nanoparticles while is stronger than that of one-dimensional cylindrical nanowires. The accuracy of the developed model is verified by the available experimental results.
Co-reporter:Jianfeng Huang, Sascha Vongehr, Shaochun Tang, Haiming Lu and Xiangkang Meng
The Journal of Physical Chemistry C 2010 Volume 114(Issue 35) pp:15005-15010
Publication Date(Web):August 18, 2010
DOI:10.1021/jp104675d
Pd−Ag bimetallic dendrites have been synthesized via a galvanic replacement reaction of Ag dendrites in a Na2PdCl4 solution. Scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis reveal that the resulting product is composed of partially depleted Ag dendrites covered with a rough surface with many Pd granules protruding by up to about 20 nm. High-solution TEM combined with EDX and selected area electron diffraction (SAED) confirms the formation of bimetallic interfaces between Pd and Ag. These Pd−Ag dendrites show up to four times higher catalytic activity toward the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) than the best recently reported catalysts. This further enhancement over the already strong performance of similarly synthesized Au−Ag dendrites is explained by the presence of Pd, adding a hydrogen relay mechanism on top of the very effective electron relay capability of bimetallic dendrites.
Co-reporter:H.B. Lu, Y. Hu, M.H. Gu, S.C. Tang, H.M. Lu, X.K. Meng
Surface and Coatings Technology 2010 204(9–10) pp: 1658
Publication Date(Web):
DOI:10.1016/j.surfcoat.2009.11.017
Co-reporter:S.C. Tang, X.K. Meng, S. Vongehr
Electrochemistry Communications 2009 Volume 11(Issue 4) pp:867-870
Publication Date(Web):April 2009
DOI:10.1016/j.elecom.2009.02.016
We report the first fabrication of large-area Cu nano-octahedra with well-defined shape, good monodispersity and uniform distribution on a gold film substrate (GFS) by a very simple, rapid and cost-effective low-potential electrodeposition (LPED) technique. Different from general surfactant-assisted electrochemical approaches, LPED is an additive-free strategy that exploits the subtle surface energy differences among various crystallographic planes of metals themselves. The size of the octahedra depends on deposition time and is adjustable over a wide range. The shape evolution is found to be remarkably different from that of octahedral particles formed in solution. A formation mechanism is proposed for the unique evolution of Cu octahedra as resulting from the anisotropic growth under appropriate applied potentials.
Co-reporter:Z.H. Cao, P.Y. Li, H.M. Lu, Y.L. Huang, Y.C. Zhou, X.K. Meng
Scripta Materialia 2009 Volume 60(Issue 6) pp:415-418
Publication Date(Web):March 2009
DOI:10.1016/j.scriptamat.2008.11.016
Nanoindentation creep tests were carried out at maximum indentation loads from 500 to 9000 μN to study the indentation size effects (ISEs) on the creep behavior of nanocrystalline tetragonal Ta films. The experimental results show that the hardness, creep strain rate and stress exponent are all indentation size-dependent. The ISE on the creep behavior is explained by grain boundary diffusion and sliding, and self-diffusion along the indenter/specimen interface and along the free surface of specimen.
Co-reporter:Shaochun Tang, Xiangkang Meng, Hongbin Lu, Shaopeng Zhu
Materials Chemistry and Physics 2009 Volume 116(2–3) pp:464-468
Publication Date(Web):15 August 2009
DOI:10.1016/j.matchemphys.2009.04.004
The shape-controlled synthesis of silver nanostructures (NSs) via sonoelectrochemistry has been investigated in aqueous solution of AgClO4 with the assistance of poly(N-vinylpyrrolidone) (PVP). The morphology of silver NSs depends strongly on the current density (J) and the molar ratio (R) of PVP monomer to Ag+. By controlling reaction conditions, not only zero-dimensional silver nanoparticles (NPs) of spherical and oval shapes, but also 3D silver NSs composed of dendritic rod, dendritic sheet and flower-like dendrites (consisting of staggered nanosheets) were successfully prepared. We discuss the growth process as being mainly dependent on the adjustable driving force of electroreduction while being modulated by PVP that contributes mainly to the finer structure in the shape-controlled synthesis.
Co-reporter:Shaochun Tang, Sascha Vongehr, Xiangkang Meng
Chemical Physics Letters 2009 Volume 477(1–3) pp:179-183
Publication Date(Web):28 July 2009
DOI:10.1016/j.cplett.2009.06.087
Silver dendrites synthesized by sonoelectrochemical deposition are investigated via transmission electron microscopy (TEM) in order to clarify the formation of specific branching angles. Two kinds of dendrites are found to form simultaneously; one has slanted angles while the other shows orthogonal branching. Investigation of the branch–stem interfacial structures reveals that the vertical branches attach at a characteristic transition layer around the main stem, while the slanted growth involves twinning induced dislocations. It is suggested that oriented attachment of nanoparticles followed by epitaxial growth leads to obliqueness, while crystallization of amorphous phase involving grain rotation and realignment results in vertical branching.Investigation of the branch–stem interfacial structures reveals the formation mechanisms of two kinds of silver dendrites (slanted and orthogonal branchings).
Co-reporter:Z.H. Cao, H.M. Lu, X.K. Meng
Materials Chemistry and Physics 2009 Volume 117(Issue 1) pp:321-325
Publication Date(Web):15 September 2009
DOI:10.1016/j.matchemphys.2009.06.018
The effects of barrier layers and annealing temperature on texture variation, grain growth and void forming of nanocrystalline Cu films were investigated by X-ray diffraction, transmission electron microscope and scanning electron microscope (SEM). The variation in texture and grain size of Cu films with annealing temperature is different for Cu/Ti and Cu/Ta. The activation energies of grain growth of Cu films on Ti and Ta, respectively, are 19.7 and 23.4 kJ mol−1, which are much closer to that of grain boundary diffusion of Cu. The average diameter of about 400 nm for surface voids of Cu/Ti is larger than that of Cu/Ta structure. Furthermore, both the electrical resistivity measurement and SEM observation imply that Cu/Ti rather than Cu/Ta structure tend to fail easier as annealing temperature exceed 400 °C.
Co-reporter:Shaochun Tang, Xiangkang Meng, Changchun Wang, Zhenhua Cao
Materials Chemistry and Physics 2009 Volume 114(2–3) pp:842-847
Publication Date(Web):15 April 2009
DOI:10.1016/j.matchemphys.2008.10.048
Three-dimensional (3D) flowerlike silver microparticles (FSMPs) with novel nanostructure have been synthesized on the surface of a Pt film by a very simple, rapid and cost-effective electrochemical approach without introducing any template, surfactant or modification of electrode surfaces. The as-prepared FSMPs exhibit flowerlike morphologies and are built with many 2D nanoflakes as building blocks. The nanoflakes intersect mutually and have smooth surfaces, outwardly wavy edges and uniform thickness. The density of nanoflakes and the diameter of the FSMPs can be easily controlled by changing the electrodeposition time. A possible mechanism for electrochemical growth of the flake-built FSMPs is suggested on the basis of experimental results.
Co-reporter:Shaopeng Zhu, Jianfeng Huang, Shaochun Tang, Xiangkang Meng
Materials Chemistry and Physics 2009 Volume 118(2–3) pp:442-446
Publication Date(Web):15 December 2009
DOI:10.1016/j.matchemphys.2009.08.015
In this work, three-dimensional (3D) hierarchical silver microparticles (HSMP) composed of 2D nanoflakes were synthesized on the anode of a galvanic cell. A copper plate immersed in CuSO4 solution and a platinum-coated silicon plate immersed in AgNO3 solution served as the cathode and anode, respectively. The two half-cells were linked by a salt bridge. The presence of poly(N-vinyl pyrrolidone) (PVP) in the AgNO3 electrolyte, an optimum AgNO3 concentration and an appropriate reaction time are crucial for the formation of a hierarchical nanostructure. The evolution of the products during growth was tracked to study the formation and metamorphosis mechanisms. The catalytic activity of HSMP was studied via promotion of Rhodamine B reduction by NaBH4.
Co-reporter:H. M. Lu, P. Y. Li, Z. H. Cao and X. K. Meng
The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7598-7602
Publication Date(Web):April 8, 2009
DOI:10.1021/jp900314q
On the basis of a model for size-dependent cohesive energy, the size, shape, and dimensionality effects on melting temperatures of nanocrystals are modeled in a unified form. The model predicts that the melting temperature Tm(D,d,λ) decreases with reducing size D and dimensionality d or increasing shape factor λ. For nanoparticles with the same D values, there is Tm(icosahedron) > Tm(sphere or cube) > Tm(octahedron) > Tm(tetrahedron). Moreover, the ratio of depression of Tm(D,d,λ) is about 1:2λwire:3λparticle for thin films, nanowires, and nanoparticles when D is large enough, for example, 6 nm. The model is found to be in accordance with available experimental, MD simulation, and other theoretical results for Au, Ag, Ni, Ar, Si, Pb, and In nanocrystals.
Co-reporter:Z.H. Cao, P.Y. Li, X.K. Meng
Materials Science and Engineering: A 2009 Volume 516(1–2) pp:253-258
Publication Date(Web):15 August 2009
DOI:10.1016/j.msea.2009.03.019
Nanoindentation creep tests were carried out at the maximum indentation load from 500 to 9000 μN to study the indentation size effect (ISE) on the creep behavior of amorphous, nanocrystalline (NC) bcc and NC tetragonal Ta films. For NC bcc and tetragonal Ta films, the creep strain rate ε˙ decreases and stress exponent n increases with enhanced peak loads or indent depth, and are therefore both indentation size dependent. However, an inverse ISE on ε˙ and n is found for amorphous Ta films. The difference of the ISE is attributed to the distinct creep deformation process. Several creep mechanisms including self-diffusion along the indenter/specimen interface, grain boundary diffusion and sliding, and dislocation climb have been introduced to interpret the ISE for NC Ta films. The inverse ISE on amorphous Ta films is explained by the shear transformation zone theory.
Co-reporter:H.B. Lu, Y. Hu, M.H. Gu, S.C. Tang, H.M. Lu, X.K. Meng
Surface and Coatings Technology 2009 204(1–2) pp: 91-98
Publication Date(Web):
DOI:10.1016/j.surfcoat.2009.06.035
Co-reporter:Jianfeng Huang, Sascha Vongehr, Shaochun Tang, Haiming Lu, Jiancang Shen and Xiangkang Meng
Langmuir 2009 Volume 25(Issue 19) pp:11890-11896
Publication Date(Web):July 13, 2009
DOI:10.1021/la9015383
Dendritic Ag/Au bimetallic nanostructures have been synthesized via a galvanic replacement reaction (GRR) of Ag dendrites in a chlorauric acid (HAuCl4) solution. After short periods of time, one obtains structures with protruding flakes; these will mature into very porous structures with little Ag left over. The morphological, compositional, and crystal structural changes involved with reaction time t were analyzed by using scanning and transmission electron microscopy (SEM and TEM, respectively), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction. High-resolution TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. A proposed formation mechanism of the original Ag dendrites developing pores while growing Au flakes cover this underlying structure at longer reaction times is confirmed by exploiting surface-enhanced Raman scattering (SERS). Catalytic reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) is strongly enhanced, implying promising applications in catalysis.
Co-reporter:HongBin Lu;MinHao Gu;JianFeng Huang
Science China Technological Sciences 2009 Volume 52( Issue 8) pp:2204-2209
Publication Date(Web):2009 August
DOI:10.1007/s11431-009-0227-9
An in-situ polymerization method was employed to synthesize the nanosilica/acrylic/epoxy (SAE) hybrid coating on AISI 430 stainless steel (430SS), as compared with a traditional blending method. Microstructures of the blending SAE hybrid coating (BC) and in-situ SAE hybrid coating (ISC) were characterized by transmission electron microscopy (TEM). Corrosion resistance of BC and ISC on 430SS was evaluated by the neutral salt spray test and potentiodynamic polarization technique. Failure mechanism of the BC on 430SS was suggested by the microstructures and corrosion behaviors. Serious aggregation of nanosilica particles in the BC impairs its structural uniformity and induces the flaws formation. These flaws in the BC initiates the failures of pitting, filiform corrosion and peeling which are accelerated by the O2 concentration cell and H+ self-catalysis in chlorine-containing moist environments. The ISC-coated 430SS shows a more advantageous corrosion resistance than that of the BC-coated. The ISC-coated 430SS can suffer the salt spray over 1000 h. Besides, it exhibits a high corrosion potential beyond 0.925 V and good passivation characteristics during the potentiodynamic polarization.
Co-reporter:H. M. Lu, F. Q. Han and X. K. Meng
The Journal of Physical Chemistry B 2008 Volume 112(Issue 31) pp:9444-9448
Publication Date(Web):July 15, 2008
DOI:10.1021/jp802888t
Analytical models for size-dependent melting temperature Tm(D), melting enthalpy ΔHm(D), and surface energy γsv(D) of metallic nanowires have been proposed in terms of the unified nanothermodynamical model where D denotes the diameter of nanowire. As D decreases, Tm(D), ΔHm(D), and γsv(D) functions are found to decrease almost with the same size-dependent trend. Due to the inclusion of the effect of dimensionality, the developed model can be applied to other low-dimensional systems. It is found that the ratio of depression of these thermodynamic parameters for spherical nanoparticle, nanowire, and thin film is 3:2:1 when D is large enough (>20h with h being the atomic diameter). The validity of the model is verified by the data of experiments, molecular dynamics simulations, and other theoretical models.
Co-reporter:Shaochun Tang, Yuefeng Tang, Shaopeng Zhu, Haiming Lu, Xiangkang Meng
Journal of Solid State Chemistry 2007 Volume 180(Issue 10) pp:2871-2876
Publication Date(Web):October 2007
DOI:10.1016/j.jssc.2007.08.022
Silica–silver core–shell composite particles with uniform thin silver layers were successfully synthesized by a facile and one-step ultrasonic electrodeposition method. By electrolysis of the slurry consisting of preformed silica spheres and silver perchlorate without any additives, the homogenous composite particles can be prepared. The average size of single silver crystals in the composite is about 12 nm and the thickness of silver layer is 14±2 nm. Moreover, the continuity of Ag distribution, the surface roughness and the thickness of silver layer are controllable by adjusting the current density (I), the concentration of electrolyte (C) and the reaction time (t). Optical properties of the composite particles with different silver content were also investigated.Silica–silver core–shell composite particles with uniform thin silver layers are prepared by a facile and one-step ultrasonic electrodeposition method. Moreover, the continuity of Ag distribution, the surface roughness and the thickness of silver layer are controllable. Optical properties of the composite particles with different silver content were also investigated.
Co-reporter:Baogang Zhu, Shaochun Tang, Sascha Vongehr, Hao Xie, Jian Zhu and Xiangkang Meng
Chemical Communications 2016 - vol. 52(Issue 12) pp:NaN2627-2627
Publication Date(Web):2016/01/04
DOI:10.1039/C5CC08857G
Template-free chemical growth on Ni foam and thermal treatment results in homogeneous FeCo2O4 submicron-tube arrays which serve as binder-free electrodes with high capacitance, rate-capability and cycling-stability owing to FeCo2O4 conductivity, high porosity, and strong bonding between tubes and Ni foam, all allowing even symmetric devices to have superior energy density.
Co-reporter:P. Y. Li, Z. H. Cao and X. K. Meng
Dalton Transactions 2012 - vol. 41(Issue 39) pp:NaN12105-12105
Publication Date(Web):2012/08/06
DOI:10.1039/C2DT31484C
Ni–Fe nanoalloy nanoparticles with an average grain size of 4 nm in diameter have been prepared by a sol–gel method under a hydrogen atmosphere where ethanol and oleic acid have been used as solvent and surfactant, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) examinations of the nanoparticles show the occurrence of (111), (200), (220) and (311) diffraction peaks and rings, meaning that the nanoparticles have a face-centered-cubic phase structure. Moreover, a superlattice diffraction peak and a diffraction ring/spot can also be observed in XRD and SAED results, indicating the formation of an equilibrium ordered L12 phase structure. The as-prepared Ni–Fe nanoalloy particles show typical superparamagnetic behavior at room temperature and the blocking temperature of the nanoparticles is determined to be about 50 K.
Co-reporter:Hao Xie, Shaochun Tang, Jian Zhu, Sascha Vongehr and Xiangkang Meng
Journal of Materials Chemistry A 2015 - vol. 3(Issue 36) pp:NaN18513-18513
Publication Date(Web):2015/07/31
DOI:10.1039/C5TA05129K
In order to achieve high energy densities, an asymmetric all-solid-state supercapacitor is developed by synthesizing a novel composite of cobalt carbonate hydroxide (CCH) nanowire covered N-doped graphene (NG) as positive and porous NG as negative electrodes. The CCH–NG composite is obtained from a one-step hydrothermal method, where optimization of the CCH content triples the specific capacitance of porous NG, reaching 1690 F g−1 at 1.0 A g−1. The optimal composite exhibits a remarkable cycling stability retaining 94.2% of the initial capacitance after 10000 cycles, and good rate capability (still 1358 F g−1 at 10 A g−1). The assembled asymmetric supercapacitor based on the optimal composite has a high discharge areal capacitance of 153.5 mF cm−2 (at 1.0 mA cm−2), can cycle reversibly in the high-voltage region of 0–1.9 V, and thus provide superior energy and power densities (0.77 W h m−2 and 25.3 W m−2).
Co-reporter:Shaochun Tang, Sascha Vongehr, Yongguang Wang, Juan Cui, Xiangyu Wang and Xiangkang Meng
Journal of Materials Chemistry A 2014 - vol. 2(Issue 10) pp:NaN3660-3660
Publication Date(Web):2013/12/10
DOI:10.1039/C3TA14541G
We report a template- and surfactant-free synthesis of multi-metallic nanosponges with controllable composition, porosity, ligament and grain sizes, as well as control over alloying. The inexpensive approach is scalable to industrial production and produces not only sponges of various pure metals such as Ag, Au, Pd, Pt, Co, Ni, Cu, but also bi- and trimetallic alloys or non-alloys. The synthesis involves fast reduction of metal salts followed by a slow network assembly in ethanol–glycerol mixed solvents shaken in a temperature range of 25–90 °C. Freeze drying conserves the pores to ensure a high surface area. The involved growth mechanisms are discussed. Tri-metallic alloyed Ag34Au33Pd33 sponges with a specific surface area of 96 m2 g−1 exhibit the highest reported catalytic rate for the degradation of azo dyes and 4-nitrophenol reduction. They show higher catalytic activity and better long-term stability for formic acid electro-oxidation compared with Pd-based mono- and bimetallic nanostructures. The excellent catalytic performance is mainly attributed to the high porosity and large number of interfaces. Pressed into discs, the Ag sponges' sensitive SERS activity is highly reproducible over area.
Co-reporter:Shaochun Tang, Sascha Vongehr and Xiangkang Meng
Journal of Materials Chemistry A 2010 - vol. 20(Issue 26) pp:NaN5445-5445
Publication Date(Web):2010/06/01
DOI:10.1039/C0JM00456A
Spherical Ag–C composites containing Ag nanoparticles (NPs) have been synthesized in high yield by microwaving suspensions of porous carbon spheres (CSs) in [Ag(NH3)2]+ solutions with poly (N-vinylpyrrolidone) as the reducing agent. The use of Ag–C composites as precursors enables us to dope Au also into the CSs' interior. Various Ag–Au doped and also predominantly Au composite spheres are prepared via the immersion of the Ag–C composites in chloroauric acid (HAuCl4) solutions without additional reducing agent. The yield of Au is found to be much higher than a replacement reaction could provide, which is explained via a detailed discussion of the involved growth mechanisms that decide the locations of the NPs in/on the CSs. Optical properties and catalytic activities of the composite structures are tunable via the Au versus Ag atomic ratio as controlled by the HAuCl4 concentration. The composites exhibit excellent catalytic activity as demonstrated via the reduction of 4-nitrophenol by sodium borohydride. The catalytic activity of bimetallic composites is highly enhanced over the monometallically doped CSs.
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