Jiangwei Ma

Pt-decorated zinc oxide nanorod arrays with graphitic carbon nitride nanosheets for highly efficient dual-functional gas sensing.

In this work, well-aligned ZnO nanorods were grown on the substrate of exfoliated g-C3N4 nanosheets via a microwave-assisted hydrothermal synthesis, and then Pt/ZnO/g-C3N4 nanostructures were obtained after the deposition of Pt nanoparticles. The growth of vertically ordered ZnO nanorods was occurred on g-C3N4 nanosheets through the bonding interaction between Zn and N atoms, which was confirmed by XPS, FT-IR data and molecular orbital theory. The Pt/ZnO/g-C3N4 nanostructures sensor exhibited the remarkable sensitivity, selectivity, and fast response/recovery time for air pollutants of ethanol and NO2. The application of Pt/ZnO/g-C3N4 nanostructures could be used as a dual-functional gas sensor through the controlled working temperature. Besides, the Pt/ZnO/g-C3N4 nanostructures sensor could be applied to the repeating detection of ethanol and NO2 in the natural environment. The synergistic effect and improved the separation of electron-hole pairs in Pt/ZnO/g-C3N4 nanostructures had been verified for the gas sensing mechanism. Additionally, Pt/ZnO/g-C3N4 nanostructures revealed the excellent charge carriers transport properties in electrochemical impedance spectroscopy (EIS), such as the longer electron lifetime (τn), higher electron diffusion coefficient (Dn) and bigger effective diffusion length (Ln), which also played an important role for Pt/ZnO/g-C3N4 nanostructures with striking gas sensing activities.

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.

Hydrothermally Induced Oxygen Doping of Graphitic Carbon Nitride with a Highly Ordered Architecture and Enhanced Photocatalytic Activity

As an amorphous or semicrystalline material, graphitic carbon nitride (g-C3 N4 ) displays poor photocatalytic activity owing to rapid recombination of the photogenerated charge carriers, which is mainly caused by a high density of defects in the graphitic structure. In this work, a porous O-doped g-C3 N4 (P-CNO) nanosheet with a highly ordered architecture is fabricated by introducing a novel hydrothermal treatment to the precursor before the final thermal condensation. The photocatalytic hydrogen evolution rate (HER) and HER per surface area of P-CNO are 13.9 and 1.7 times higher than that of bulk g-C3 N4 . The improved photocatalytic activity is ascribed to a synergistic effect of O doping, a porous sheet-like morphology, and increased crystallinity. This work also provides a new approach for the synthesis of other polymer-based photocatalysts with high crystallinity and excellent performance.

Ag modified bismuth ferrite nanospheres as a chlorine gas sensor

Pure phase bismuth ferrite (BiFeO3, BFO) nanospheres were synthesized via a sol–gel method, and Ag was loaded on the surface of BFO by photodeposition. The effects of the Ag-modification on the morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) analyses. Only BFO peaks but no Ag peaks were observed for all samples in the XRD patterns, which is related to the small size and low loading of Ag. The gas-sensing tests show that the response of 4 mg AgNO3 modified BiFeO3 (ABFO4) was 72.62 to 10 ppm Cl2 at 240 °C, which was 2.5 times higher than that of the pristine BFO. Such outstanding gas sensing performances are attributed to the fact that the presence of Ag not only increases the density of holes and the amount of gas adsorption sites but also has a catalytic effect.