Chengzhen Wei

Microwave-assisted synthesis of NiS2 nanostructures for supercapacitors and cocatalytic enhancing photocatalytic H2 production

Uniform NiS2 nanocubes are successfully synthesized with a microwave-assisted method. Interestingly, NiS2 nanocubes, nanospheres and nanoparticles are obtained by controlling microwave reaction time. NiS2 nanomaterials are primarily applied to supercapacitors and cocatalytic enhancing photocatalytic H2 production. Different morphologies of NiS2 nanostructures show different electrochemical and cocatalytic enhancing H2 production activities. Benefited novel nanostructures, NiS2 nanocube electrodes show a large specific capacitance (695 F g−1 at 1.25 A g−1) and excellent cycling performance (the retention 93.4% of initial specific capacitance after 3000 cycles). More importantly, NiS2 nanospheres show highly cocatalytic enhancing photocatalytic for H2 evolution, in which the photocatalytic H2 production is up to 3400 μmol during 12 hours under irradiation of visible light (λ>420 nm) with an average H2 production rate of 283 μmol h−1.

Two-Dimensional β-MnO2 Nanowire Network with Enhanced Electrochemical Capacitance

Conventional crystalline β-MnO2 usually exhibits poor electrochemical activities due to the narrow tunnels in its rutile-type structure. In this study, we synthesized a novel 2D β-MnO2 network with long-range order assembled by β-MnO2 nanowires and demonstrated that the novel 2D β-MnO2 network exhibits enhanced electrochemical performances. The 2D network is interwoven by crossed uniform β-MnO2 nanowires and the angle between the adjacent nanowires is about 60°. Such a novel structure makes efficient contact of β-MnO2 with electrolyte during the electrochemical process, decreases the polarization of the electrode and thus increases the discharge capacity and high-rate capability. The specific capacitance of the obtained 2D β-MnO2 network is 453.0 F/g at a current density of 0.5 A/g.

NiS Hollow Spheres for High-Performance Supercapacitors and Non-Enzymatic Glucose Sensors

α-NiS and β-NiS hollow spheres were successfully synthesized via the Kirkendall effect under different hydrothermal conditions. The obtained α-NiS and β-NiS hollow spheres were evaluated as electrode materials for supercapacitors. Importantly, the α-NiS hollow sphere electrode has a large specific capacitance (562.3 F g(-1) at 0.60 A g(-1)) and good cycling property (maintaining about 97.5% at 2.4 A g(-1) after 1000 cycles). Furthermore, the as-prepared α-NiS and β-NiS hollow spheres were successfully applied to construct electrochemical glucose sensors. Especially, the α-NiS hollow spheres exhibit a good sensitivity (155 μA mM(-1)  cm(-2)), low detection limit (0.125 μM), and a wide linear range.

Mesoporous 3D ZnO–NiO architectures for high-performance supercapacitor electrode materials

3D ZnO–NiO mesoporous architectures were synthesized through annealing the zinc hydroxide carbonate–nickel hydroxide carbonate composite precursor, which was prepared via a one-pot hydrothermal route. More importantly, we successfully explore the application of the 3D ZnO–NiO composite mesoporous architectures as electrochemical capacitors. Electrochemical study presented that the as-prepared 3D ZnO–NiO composites under different annealing conditions have different electrochemical supercapacitor properties. The as-synthesized sample obtained at 400 °C shows a high specific capacitance of 2498 F g−1 at a current density of 2.6 A g−1, a good rate capability at high current densities and an excellent long-term cycling stability (about 3.0% loss of the maximum specific capacitance after 2000 cycles), which are mainly attributed to its morphological characteristics of mesoporous and nanosheet self-assembling architectures, as well as a rational composition of the two constituents. These results suggest that such 3D ZnO–NiO mesoporous architectures are promising materials for supercapacitors.

Controlled Growth and Applications of Complex Metal Oxide ZnSn(OH)6 Polyhedra

We successfully controlled the crystallographic surface of ZnSn(OH)(6) crystals and systematically obtained ZnSn(OH)(6) crystals in different shapes including cubes, truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons using a simple solvothermal method in a methylcellulose (MC) ethanol/water solution. By simply adjusting the amount of the NaOH solution added to the reaction system, we observed the shape evolution of ZnSn(OH)(6) particles from cube to octahedron, with the sizes gradually increasing from about 200 nm to 1-2 μm. These results not only provide ZnSn(OH)(6) polyhedra bound by different lattice planes, but also make it possible to investigate the morphology-property relationship of ZnSn(OH)(6) particles with different morphologies obtained under similar conditions. The antibacterial activities of the as-prepared ZnSn(OH)(6) polyhedral particles were studied. It was found that the antibacterial activities of ZnSn(OH)(6) particles against Escherichia coli depend on the shape of the ZnSn(OH)(6) particles, demonstrating that the surface structure of nanocrystals affects the antibacterial activity. Additionally, the obtained ZnSn(OH)(6) polyhedra can be applied as precursors for Zn(2)SnO(4)/SnO(2) composites with different morphologies by calcining at 600 °C.

Water Amount Dependence on Morphologies and Properties of ZnO nanostructures in Double-solvent System

ZnO materials with a range of different morphologies have been successfully synthesized via a simple double-solvothermal method in the presence of glycine. The morphologies of the products can be controlled from superstructures to microrods by adjusting the amount of water in the EtOH/H2O system. Photoluminescence (PL) studies reveal that the more amount of water was used, the stronger PL relative intensity of the green emission is, but the weaker ultraviolet emission. This might be attributed to the more defects of the products when the more water was used. The catalytic studies show that all the samples have good abilities to decrease decomposition temperature around 300°C and the decomposition temperature lowers with the increase of the relative intensity of ZnO green emission.

Sodium-Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High-Performance Flexible All-Solid-State Hybrid Supercapacitors

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium-doped Ni2P2O7 hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium-doped Ni2P2O7 hexagonal tablets exhibits a specific capacitance of 557.7 F g(-1) at a current density of 1.2 A g(-1) . Furthermore, the porous sodium-doped Ni2P2O7 hexagonal tablets were successfully used to construct flexible solid-state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg(-1) and a good cycling stability after 5000 cycles, which confirms that the porous sodium-doped Ni2P2 O7 hexagonal tablets are promising active materials for flexible supercapacitors.

Fabrication of Zn2SnO4/SnO2 hollow spheres and their application in dye-sensitized solar cells

Uniform Zn2SnO4/SnO2 hollow spheres were successfully synthesized and hybridized by calcining ZnSn(OH)6 solid spheres in air, and showed a very good efficiency of 4.52% as an electrode material for DSSCs. The in situ hybridization of Zn2SnO4 and SnO2 in Zn2SnO4/SnO2 hollow spheres is beneficial for electron transport and light scattering, and leads to the high efficiency of the Zn2SnO4/SnO2 composite in DSSCs.

Biomolecule‐Assisted Construction of Cadmium Sulfide Hollow Spheres with Structure‐Dependent Photocatalytic Activity

In this study, we report the synthesis of monodispersive solid and hollow CdS spheres with structure-dependent photocatalytic abilities for dye photodegradation. The monodispersive CdS nanospheres were constructed with the assistance of the soulcarboxymthyi chitosan biopolymer under hydrothermal conditions. The solid CdS spheres were corroded by ammonia to form hollow CdS nanospheres through a dissolution-reprecipitation mechanism. Their visible-light photocatalytic activities were investigated, and the results show that both the solid and the hollow CdS spheres have visible-light photocatalytic abilities for the photodegradation of dyes. The photocatalytic properties of the CdS spheres were demonstrated to be structure dependent. Although the nanoparticles comprising the hollow spheres have larger sizes than those comprising the solid spheres, the hollow CdS spheres have better photocatalytic performances than the solid CdS spheres, which can be attributed to the special hollow structure.

Bottom-up-then-up-down Route for Multi-level Construction of Hierarchical Bi2S3 Superstructures with Magnetism Alteration.

A bottom-up-then-up-down route was proposed to construct multi-level Bi2S3 hierarchical architectures assembled by two-dimensional (2D) Bi2S3 sheet-like networks. BiOCOOH hollow spheres and flower-like structures, which are both assembled by 2D BiOCOOH nanosheets, were prepared first by a “bottom-up” route through a “quasi-emulsion” mechanism. Then the BiOCOOH hierarchical structures were transferred to hierarchical Bi2S3 architectures through an “up-down” route by an ion exchange method. The obtained Bi2S3 nanostructures remain hollow-spherical and flower-like structures of the precursors but the constructing blocks are changed to 2D sheet-like networks interweaving by Bi2S3 nanowires. The close matching of crystal lattices between Bi2S3 and BiOCOOH was believed to be the key reason for the topotactic transformation from BiOCOOH nanosheets to 2D Bi2S3 sheet-like nanowire networks. Magnetism studies reveal that unlike diamagnetism of comparative Bi2S3 nanostructures, the obtained multi-level Bi2S3 structures display S-type hysteresis and ferromagnetism at low field which might result from ordered structure of 2D networks.