Chengyin Wang

Solvothermal synthesis of CoS2–graphene nanocomposite material for high-performance supercapacitors

A CoS2–graphene nanocomposite was prepared by a facile solvothermal method. FESEM and TEM analyses have confirmed that CoS2 nanoparticles with sizes of 5–15 nm are densely anchored on graphene nanosheets. The as-prepared nanocomposite was electrochemically tested as an electrode material for supercapacitors. The CoS2–graphene nanocomposite exhibited specific capacitances of 314 F g−1 in the aqueous electrolyte and 141 F g−1 in the organic electrolyte at a current rate of 0.5 A g−1 with excellent cycling stability. The electrochemical performance of the nanocomposite has been significantly improved, compared to bare graphene nanosheets and CoS2 nanoparticles. This could be credited to the 3D nanoarchitecture, in which CoS2 nanoparticles were sandwiched between graphene nanosheets, and the additional electrochemical contribution of the decorated CoS2 nanoparticles.

Single Crystalline Na0.7MnO2 Nanoplates as Cathode Materials for Sodium‐Ion Batteries with Enhanced Performance

Single crystalline rhombus-shaped Na(0.7)MnO2 nanoplates have been synthesized by a hydrothermal method. TEM and HRTEM analyses revealed that the Na(0.7)MnO2 single crystals predominantly exposed their (100) crystal plane, which is active for Na(+)-ion insertion and extraction. When applied as cathode materials for sodium-ion batteries, Na(0.7)MnO2 nanoplates exhibited a high reversible capacity of 163 mA h g(-1), a satisfactory cyclability, and a high rate performance. The enhanced electrochemical performance could be ascribed to the predominantly exposed active (100) facet, which could facilitate fast Na(+)-ion insertion/extraction during the discharge and charge process.

Fabrication of highly ordered microporous thin films by PS-b-PAA self-assembly and investigation of their tunable surface properties

A facile approach is presented to fabricate three-dimensional ordered microporous thin films by self-assemblyvia an amphiphilic block polymer, polystryene-b-polyacrylic acid (PS-b-PAA). The highly ordered microporous thin films were formed by casting a PS-b-PAA tetrahydrofuran (THF) solution onto a glass slide under high humidity conditions. The condensed water droplets act as sacrificial templates on the air–polymer solution interface based on thermocapillary convection. Some critical influencing factors, such as the concentration of the block polymer solution, the relative humidity of the atmosphere, the properties of the solvent, the spreading volume and the substrates, were investigated to control micropore size and tune film surface properties. The surface composition and wettability of the film were found to be dramatically changed in aqueous solution, and the contact angle of the film surface was interestingly reduced from nearly hydrophobic to super-hydrophilic, which was shown by optical contact angle measurements. The influence of porosity and the ionization degree of PAA on the above properties was investigated. Micropore diameters of the films determine the initial contact angle, while the PAA ionization degree determines the transformation time of the wettability behavior and the final contact angle. The microporous thin films, as potential functional materials, are expected to play an important role in future applications.

3D Networked Tin Oxide/Graphene Aerogel with a Hierarchically Porous Architecture for High‐Rate Performance Sodium‐Ion Batteries

Low-cost and sustainable sodium-ion batteries are regarded as a promising technology for large-scale energy storage and conversion. The development of high-rate anode materials is highly desirable for sodium-ion batteries. The optimization of mass transport and electron transfer is crucial in the discovery of electrode materials with good high-rate performances. Herein, we report the synthesis of 3 D interconnected SnO2 /graphene aerogels with a hierarchically porous structure as anode materials for sodium-ion batteries. The unique 3 D architecture was prepared by a facile in situ process, during which cross-linked 3 D conductive graphene networks with macro-/meso-sized hierarchical pores were formed and SnO2 nanoparticles were dispersed uniformly on the graphene surface simultaneously. Such a 3 D functional architecture not only facilitates the electrode-electrolyte interaction but also provides an efficient electron pathway within the graphene networks. When applied as anode materials in sodium-ion batteries, the as-prepared SnO2 /graphene aerogel exhibited high reversible capacity, improved cycling performance compared to SnO2 , and promising high-rate capability.

Layer-by-layer assembly of polyelectrolyte and graphene oxide for open-tubular capillary electrochromatography.

In this paper, open-tubular capillary column coated with graphene oxide (GO) was prepared through ionic adsorption of negatively charged GO nanosheets onto the capillary wall pre-modified with positively charged poly(diallydimethylammonium chloride) (PDDA). Thus prepared coating was very stable and could endure over 200 separations. The electroosmotic flow (EOF) characteristics of bare fused silica capillary column, PDDA coated column, and GO-PDDA coated column (GO-PDDA@column) were investigated by varying the percentage of methanol in buffer and the buffer pH value. The run-to-run, day-to-day, and column-to-column reproducibilities of EOF on GO-PDDA@column were satisfying with relative standard deviation values of less than 2% in all cases. The stationary phase displays a characteristic reversed-phase behavior. The GO-PDDA@column was also used to separate proteins in egg white. Both basic and acidic proteins were separated in a single run.

Open‐tubular capillary electrochromatography using a capillary coated with octadecylamine‐capped gold nanoparticles

Octadecylamine‐capped gold nanoparticles (ODA‐Au‐NPs) were prepared and characterized by using UV–Vis adsorption spectrum, transmission electron chromatography (TEM), SEM, and FT‐IR. A simple but robust hydrophobic coating was easily developed by flushing a capillary with a solution of ODA‐Au‐NPs, because the positive charges were carried by the nanoparticles which strongly adsorb to the negatively charged inner surface of a fused‐silica capillary via electrostatic and hydrophobic interactions. The chromatographic characteristics of the coated capillary was investigated by varying the experimental parameters such as buffer pH, buffer concentration, and percentage of organic modifier in the mobile phase. The results show that (i) resolution between thiourea and naphthalene is almost the same when comparing the electrochromatograms obtained using pH 7 buffer as mobile phase after and before the capillary column was operated using pH 11 and 3 mobile phase; (ii) no significant changes in retention time and deterioration in peak efficiency were found after 60 runs of test aromatic mixtures; and (iii) column efficiency up to 189 000 theoretical plates/meter for testosterone was obtained. All of the results indicated that the coating could act as a stable stationary phase for open tubular CEC as well as for bioanalysis.

Open-tubular gas chromatography using capillary coated with octadecylamine-capped gold nanoparticles.

The octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and directly used to coat the capillary wall. The hydrophobic coating acted as the stationary phase for open-tubular gas chromatography (OTGC). The ODA-Au-NPs can be adsorbed tightly onto the inner surface of fused silica capillary column via electrostatic interaction and enhanced interaction of van der Waals between gold nanoparticles and the capillary wall. Thus, the modification of the inner surface of capillary column by ODA-Au-NPs can be achieved simply by flushing the capillary with a solution of ODA-Au-NPs and the resulted ODA-Au-NPs coating is very stable. No perceptible degradation in the ODA-Au-NPs-based separation was observed after approximately 1900 sample runs. This type of columns also provided excellent chromatographic performances: high number of theoretical plates, outstanding run-to-run and column-to-column reproducibility, and high selectivity for a wide range of test mixtures. An efficiency of 2474 theoretical plates per meter for chlorobenzene was obtained on an ODA-Au-NPs-modified 1.6 m x 100 microm i.d. fused silica capillary column.

Capillary column coated with graphene oxide as stationary phase for gas chromatography

The graphene oxide (GO) is carbon based material that has high surface area, high adsorption ability, and is stable at high temperature. In this work, the GO phase was prepared and used for gas chromatographic separation. GO nanosheets were covalently bonded onto the inner surface of fused silica capillary column using 3-aminopropyldiethoxymethyl silane as cross-linking agent. The prepared GO nanosheets were characterized with TEM and the GO coating was characterized with SEM. As a high performance stationary phase, GO provides not only a high surface area to increase the phase ratio but also rich functional groups for the formation of hydrophobicity, hydrogen bonding, and π-π electrostatic stacking interactions with volatile aromatic or unsaturated organic compounds. Thus, mixtures of a wide range of organic compounds including alcohols and aromatic compounds were well separated and an efficiency of 1990 theoretical plates per meter for anisole was obtained on GO coated 1.0m×200μm i.d. fused silica capillary column. The experimental results demonstrate that GO coated capillary columns are promising for gas chromatographic separation.

Voltammetric determination of terbinafine in biological fluid at glassy carbon electrode modified by cysteic acid/carbon nanotubes composite film.

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.

One step fabrication of nanoelectrode ensembles formed via amphiphilic block copolymers self-assembly and selective voltammetric detection of uric acid in the presence of high ascorbic acid content.

A novel one-step approach to glassy carbon nanoelectrode ensembles (NEEs) with the pores of 20-120nm in radii has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods were used to characterize the NEEs prepared using this new procedure. The NEEs drastically suppressed the response of ascorbic acid (AA) and resolved the overlapping voltammetric response of uric acid (UA) and AA into two well-defined peaks with a large anodic peak difference (DeltaE(pa)) of about 310mV. The peak current obtained from differential pulse voltammetry (DPV) was linearly dependent on the UA concentration in the range of 0.25-50microM at neutral pH (PBS, pH 6.86) with a correlation coefficient of 0.999, and the detection limit was 0.04microM (S/N=3). The NEEs has also been demonstrated to be applicable in the detection of UA in serum and urine samples with excellent sensitivity and selectivity. The NEEs will hopefully be of good application for further sensor development.