Hu Zhou

CoP nanoparticles deposited on reduced graphene oxide sheets as an active electrocatalyst for the hydrogen evolution reaction

A novel composite with CoP nanoparticles uniformly deposited on reduced graphene oxide (RGO) sheets is prepared through a facile two-step approach. The as-prepared CoP/RGO composite is investigated as an electrocatalyst for the hydrogen evolution reaction (HER). It is found that the CoP/RGO composite shows an enhanced catalytic activity with a smaller Tafel slope (104.8 mV per decade), a much larger exchange current density (4.0 × 10−5 A cm−2) and lower estimated HER activation energy (41.4 kJ mol−1) than pure CoP. Besides, the CoP/RGO composite exhibits good stability in acidic solution, the HER catalytic activity of which shows no obvious degradation after 500 cycles. Such enhanced catalytic activity stems from the abundance of active catalytic sites, the increased electrochemically accessible surface area and significantly improved electrochemical conductivity of the CoP/RGO composite. The good catalytic activity demonstrates that the CoP/RGO composite could be a promising electrocatalyst in hydrogen production.

Facile synthesis of Co3O4 porous nanosheets/reduced graphene oxide composites and their excellent supercapacitor performance

Co3O4/RGO composites with Co3O4 porous nanosheets attached on reduced graphene oxide (RGO) sheet were fabricated through a facile refluxing method followed by a thermal annealing process. Pores with sizes of several nanometers are uniformly distributed in Co3O4 nanosheets. The composites as electrode materials for supercapacitors were investigated. They deliver a specific capacitance as high as 518.8 F g−1 at the current density of 0.5 A g−1, and great cycling stability with a decay of about 7.6% after 1500 continuous charge–discharge cycles at the current density of 10 A g−1. The excellent capacitive performance can be attributed to the excellent electrical properties, large surface area and well-connected conductive network derived from the structural advantages of the Co3O4 porous nanosheets and RGO support. The facile synthesis and the excellent capacitive performance make the Co3O4/RGO composites a promising candidate for electrode materials in electrochemical energy storage systems.

Facile synthesis of magnetically separable reduced graphene oxide/magnetite/silver nanocomposites with enhanced catalytic activity

In this study, the combination of magnetite (Fe3O4) with reduced graphene oxide (RGO) generates a new hybrid substrate for the dispersion of noble metal nanoparticles. Well-dispersed silver (Ag) nanoparticles loaded on the surface of Fe3O4 modified RGO are achieved by an efficient two-step approach. Through reducing Ag(+) ions, highly dispersed Ag nanoparticles are in-situ formed on the RGO/Fe3O4 substrate. It is found that the existence of Fe3O4 nanocrystals can significantly improve the dispersity and decrease the particle size of the in-situ formed Ag nanoparticles. Magnetic study reveals that the as-prepared RGO/Fe3O4/Ag ternary nanocomposites display room-temperature superparamagnetic behavior. The catalytic properties of the RGO/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol into 4-aminophenol as a model reaction. The as-synthesized RGO/Fe3O4/Ag ternary catalysts exhibit excellent catalytic stability and much higher catalytic activity than the corresponding RGO/Ag catalyst. Moreover, the RGO/Fe3O4/Ag catalysts can be easily magnetically separated for reuse. This study further demonstrates that nanoparticles modified graphene can act as an effective hybrid substrate for the synthesis of multi-component and multifunctional graphene-based composites.

Synthesis of Cu3P nanocubes and their excellent electrocatalytic efficiency for the hydrogen evolution reaction in acidic solution

Cu3P nanocubes are synthesized through a facile two-step strategy, which consists of a simple solution based method followed by a low-temperature phosphidation process. The Cu3P nanocubes have an average size of about 198 nm, and show a three-dimensional (3D) cubic architecture with hollow interiors and thin cubic shells. The material as an electrocatalyst for the hydrogen evolution reaction (HER) is investigated in acidic solution. It is found that the Cu3P nanocubes exhibit a low overpotential (145 mV), a small Tafel slope (70.2 mV per decade), and a large exchange current density (0.016 mA cm−2). Moreover, the Cu3P nanocubes show great electrochemical stability in acidic solution since no obvious decay in current density is observed after 1000 cycles. The excellent electrocatalytic performance can be associated with the electronic structures of Cu and P, as well as the hollow interior structure of Cu3P nanocubes, which supplies more active sites for HER. The approach used here provides an effective route for synthesizing metal phosphides with various microstructures and functions.

ZnNi alloy nanoparticles grown on reduced graphene oxide nanosheets and their magnetic and catalytic properties

Reduced graphene oxide (RGO)–ZnNi alloys nanocomposites were synthesized by in situ growth of ZnNi alloy nanocrystals on graphene oxide (GO) accompanied with a chemical co-reduction process. The size and morphology of ZnNi alloy nanoparticles on RGO sheets can be tuned by simply changing initial concentrations of metal ions and molar ratio of Zn2+ to Ni2+ in the reaction system. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy and transmission electron microscopy. Magnetic measurements reveal that the nanocomposites have ferromagnetic characteristics and show composition dependent magnetic properties. Moreover, the RGO–ZnNi nanocomposites show remarkably enhanced catalytic activity and recycling stabilities toward the reduction of 4-nitrophenol (4-NP), and can be easily re-collected from the reaction system by a magnet. It is believed that the obtained magnetic RGO–ZnNi nanocomposites with excellent catalytic properties provide a new opportunity for the application of graphene-based materials.

Facile synthesis and gas-sensing performance of Sr- or Fe-doped In2O3 hollow sub-microspheres

Sr- or Fe-doped In2O3 hollow sub-microspheres were successfully fabricated without the assistance of any additives or templates. The obtained hollow In2O3 sub-microspheres show relatively uniform size and band gap of ∼3.1 eV. Benefited from the hollow microstructure and doping effect, the doped In2O3 sub-microspheres show excellent gas sensing performance towards a series of organic solvents. For 100 ppm of formaldehyde, the Sr- and Fe-doped In2O3 sensors demonstrate sensing responses of 9.4 and 5.5, respectively. These values are much higher than previously reported In2O3-based gas sensors. Interestingly, Fe-doped In2O3 shows relatively higher sensing response to propanol than that of Sr-doped In2O3, although towards formaldehyde, ethanol, acetone and heptane, Sr-doped In2O3 shows relatively higher sensing responses. This investigation therefore indicates that doped In2O3 hollow microstructures could be an effective platform for sensing hazardous indoor formaldehyde gas, and that sensing selectivity could be improved through the doping effect.

A facile and general route for the synthesis of semiconductor quantum dots on reduced graphene oxide sheets

Owing to its unique graphitized basal plane nanostructure and intriguing physicochemical properties, graphene is considered as an ideal support for developing nanocomposites for various applications. In this study, a facile and general method was developed for the first time to synthesize a variety of semiconductor quantum dots (SQDs) supported on reduced graphene oxide (RGO) sheets, including RGO/metal oxide and RGO/metal sulfide nanocomposites. The as-prepared nanocomposites were investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy and transmission electron microscopy. It was found that by using octadecylamine (ODA) as both reductive and dispersing agent, the resulting metal oxide and sulfide SQDs were all homogeneously decorated on the surface of RGO sheets. The optical properties of the as-synthesized RGO/SQDs nanocomposites were studied through ultraviolet-visible and photoluminescence spectroscopy. To demonstrate one potential application, the RGO/NiO nanocomposites were used as electrode materials for electrochemical supercapacitors, which exhibit enhanced capacitive performance and long cycle life. It is expected that our prepared RGO/SQDs nanocomposites could serve as promising candidates for power source, catalysis, optical sensitizer and optoelectronic applications.