Guangzhi Dong

A simple melamine-assisted exfoliation of polymeric graphitic carbon nitrides for highly efficient hydrogen production from water under visible light

Polymeric graphitic carbon nitride with a two-dimensional (2D) structure has intensive potential applications in hydrogen production from water splitting under visible light irradiation. Searching for an efficient technology is the key to synthesizing 2D materials from bulk powders. Here, a simple, highly-efficient, large-scale and low-cost melamine-assisted exfoliation route is reported to obtain quasi-2D carbon nitride using an oil bath. Quasi 2D carbon nitride possesses a high specific surface area (116.76 m2 g−1), a larger bandgap (by 0.13 eV), an enhanced electronic transport ability in the in-plane direction, a prolonged photo-excited charge carrier lifetime, and a lowered recombination of photo-induced electrons and holes resulting from the quantum confinement effect. These make enormous contributions to the photoactivity for hydrogen production under visible light. Therefore, the melamine-assisted liquid exfoliation route can be applied to large-scale polymeric carbon nitride photocatalyst production and is envisaged to have great promise for the exfoliation of other materials with layered structures.

Gas-sensing and electrical properties of perovskite structure p-type barium-substituted bismuth ferrite

Pure and Ba-substituted bismuth ferrite (BiFeO3, BFO) powders were successfully synthesized via a sol–gel method. The effects of the Ba-substitution on the morphology, gas-sensing and electrical properties of BFO were studied. The gas-sensing tests show that the sensor based on Bi0.9Ba0.1FeO2.95 (BBFO10) has high sensitivity, quick response, effective selectivity and excellent long-time stability. The conduction mechanism and gas-sensing mechanism of a BBFO10 sample were investigated by the impedance spectroscopy and it was found that the conduction is dominated by p-type hole conduction. The conductivity of the sensor is dependent on the oxygen partial pressures and the type of gas atmosphere. The enhanced gas-sensing performances of the BBFO10 sensor are attributed to the higher oxygen vacancy concentration which was induced by the substitution of Bi3+ ion by an aliovalent Ba2+ ion at the A-site of the perovskite structure.

NiO/ZnO p–n heterostructures and their gas sensing properties for reduced operating temperature

NiO/ZnO p–n heterostructures were successfully synthesized by using a hydrothermal method followed by calcination. The morphology of the NiO/ZnO p–n heterostructures could be controlled by the amount of Ni concentration, with 10% Ni the optimum content. The structural features of the NiO/ZnO p–n heterostructures were characterized in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Additionally, direct current (DC) I–V curves of the NiO/ZnO p–n heterostructures showed diode-like behavior, which is indirect evidence demonstrating that p–n heterojunctions were formed between NiO and ZnO. The 10% NiO/ZnO heterostructures gas sensor exhibited a good gas response, fast response/recovery times and long-term stability to ethanol vapor even at 200 °C, the reduced operating temperature was much lower than for pure ZnO. The decline of the operating temperature was attributed to the formation of p–n heterojunctions. Meanwhile, a possible gas sensing mechanism is illustrated by the calculated energy band positions of the NiO/ZnO p–n heterostructures and alternating current (AC) impedance spectra.

Effects of hyperthermia induced crystalline aggregation on properties of TiO2 thin films

Abstract TiO2 thin films were prepared on fused quartz by using the sol–gel dip coating method followed by annealing. The effects of annealing temperature on the phase transition, crystalline agglomeration, surface topography and optical properties of the TiO2 films were studied. Activation energy of the phase transition from the anatase to rutile phase was estimated about 64 kJ mol−1. Crystallite size did not vary significantly with the annealing temperature, but higher temperature led to the aggregation of nanocrystallines into large particles with wide size distribution due to the surface nucleation (SN) mode gradually replaced the interface nucleation (IN) mode. Both the optical transmittance and band gap of the TiO2 thin films decrease as the annealing temperature increase. The highest optical transmittance over the visible wavelength region was obtained by the film annealed at 800 K, which was composed entirely of anatase phase.