Bingqian Han

Hydrothermal growth of ZnO nanorods on Zn substrates and their application in degradation of azo dyes under ambient conditions

A new type of catalytic material, large-scale ZnO nanorod arrays grown on self-source substrate, was directly synthesized by a facile hydrothermal approach. The catalytic activity of the ZnO nanocrystals with different exposed surfaces, including ZnO hexagonal nanorods with exposed reactive {0001} facets, hexagonal ZnO nanopyramids with nonpolar {010} planes, and pencil-like morphology with exposed {101} polar planes, was tested towards the degradation of the azo dyes (Congo red (CR) and methyl orange (MO)). The aqueous azo dyes can be degraded efficiently under ambient conditions, requiring neither light illumination nor additional energy (agitation, ultrasonic, etc.). Systematic experiments suggested that the dye degradation proceeds through electron transfers from the anionic dye molecules to the catalyst and then to electron acceptors such as dissolved oxygen. It strongly depends on the exposed polar surfaces of the ZnO nanocrystals, giving rise to the relatively higher catalytic activity and stability of the ZnO hexagonal nanopencils. The present ZnO nanorod arrays grown on the Zn substrate require no additional reagents or external energy input, which thus provides a potentially low-cost alternative for the remediation of azo-dye effluents.

SnO2 nanorods based sensing material as an isopropanol vapor sensor

Well-crystalline tin oxide nanorods assembled with SnO2 nanocrystals were prepared by calcination of SnC2O4 nanorods synthesized by a chemical precipitation method using SnCl2·2H2O and PEG 400 as precursors. The phase and morphology of the resulting material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). Indirect-heating sensors using SnO2 nanorods as sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. The as-fabricated sensor based on SnO2 nanorods showed high response, fast response and recovery toward isopropanol gas, making them promising candidates for practical detectors of isopropanol gas.

Preparation and photocatalytic activity of Nd doped ZnO nanoparticles

Abstract As an important II-VI semiconductor, zinc oxide has attracted a great deal of attention as a photocatalytic material. The quick recombination of charge carriers is the main factor influencing the photocatalytic activity of ZnO. In order to improve the photocatalytic activity, different kinds of ions were doped into ZnO by different methods to inhibit the recombination of photoinduced electrons and holes. Nd doped ZnO study is mainly on the optical performances. However, the Nd–ZnO nanoparticles have reported little work on the photodegradation of organic contaminants under visible light irradiation. In this paper, the mainly research is focused on the preparation process and removal properties of organic pollutants Cong red from the wastewater using the Nd doped zinc oxide nanoparticles. The proposed research investigates the Nd doped zinc oxide nanoparticles with varied Nd content that are important in understanding the structure, morphology and the photocatalytic performances. The undoped and Nd doped zinc oxide nanoparticles were prepared by sol–gel technique using zinc acetate dehydrate and dysprosium chloride and neodymium chloride as precursor. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the nanoparticles. The analysed results indicate that the nanoparticles have a pure hexagonal wurtzite ZnO structure with the good crystal quality and the Nd ion was in a 3+ charge state in the crystal lattice of ZnO. The performance of Nd doped ZnO powders as efficient photocatalyst was further demonstrated in the degradation of Cong red (CR) under visible light irradiation. The Nd doped ZnO nanoparticles show good photocatalytic activity during the degradation of CR under visible light. It was found that an appropriate amount of Nd dopant can greatly increase photocatalytic activity and the sample with 4%Nd doping exhibits the highest photocatalytic efficiency.

Preparation and electrochemical performances of carbon sphere@ZnO core-shell nanocomposites for supercapacitor applications

Carbon sphere (CS)@ZnO core-shell nanocomposites were successfully prepared through facile low-temperature water-bath method without annealing treatment. The morphology and the microstructure of samples were characterized by transition electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. ZnO nanoparticles with several nanometers in size decorated on the surface of the carbon sphere and formed a core-shell structure. Electrochemical performances of the CS@ZnO core-shell nanocomposites electrodes were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge (GDC). The CS@ZnO core-shell nanocomposite electrodes exhibit much larger specific capacitance and cycling stability is improved significantly compared with pure ZnO electrode. The CS@ZnO core-shell nanocomposite with mole ratio of 1:1 achieves a specific capacitance of 630 F g−1 at the current density of 2 A g−1. Present work might provide a new route for fabricating carbon sphere and transition metal oxides composite materials as electrodes for the application in supercapacitors.

Enhanced formaldehyde sensing properties of SnO2 nanorods coupled with Zn2SnO4

Ternary oxide Zn2SnO4 was introduced to a rod-like nanostructured SnO2 gas sensor for formaldehyde detection by a facile one-step hydrothermal synthesis. The effects of the Zn2SnO4 additive on the structure, morphology and gas-sensing property of SnO2 were investigated in this study. It was confirmed that control of the Zn amounts in the precursor solution was effective in realizing well-developed one- and two-dimensional coexisting structured SnO2–Zn2SnO4 (SnZn) nanocomposites. The gas sensing properties of the resulting SnZn composites to HCHO vapor were tested. The results showed that the presence of Zn2SnO4 species in SnO2 powders could effectively enhance electrical conductivity, reduce optimal operating temperature and improve the gas response of the sensors. The composite exhibited the highest response towards HCHO in the case of 35 at% Zn2SnO4 nanoplates coupling with hierarchical branched structures of SnO2 nanorods (SnZn35) at a relatively lower operating temperature of 162 °C. The good gas-sensing performance of the SnZn35 composite can be ascribed to the smaller particle size, the larger surface area and the more absorbed Ox− species, which all are favorable for gas diffusion and sensing reactions. This work renders great potential in the fabrication of gas sensors using a binary–ternary oxide composite, which can be further applied in indoor pollution detection.

Enhancing phosphate removal from water by using ordered mesoporous silica loaded with samarium oxide

A series of ordered mesoporous silica loaded with samarium oxide (Sm-MCM-41) were synthesized by a facile one-step sol–gel route using hexadecyltrimethylammonium bromide (CTAB) as the template, tetraethylorthosilicate (TEOS) as the silica source, and hexahydrated samarium chloride as the precursor. The as-synthesized materials with the Sm/Si molar ratio ranging from 0.2 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption–desorption measurements. All obtained compounds possess an ordered hexagonal mesoporous structure with a high surface area, a large pore volume, and uniform pore size. The mesoporous composites were used as the novel adsorbents for phosphate ion (H2PO4−) removal from synthetic aqueous solutions. The phosphate removal capacity of Sm-MCM-41 with a Sm/Si molar ratio of 0.6 was up to 20 mg P/g. The Sm functionalized mesoporous silica materials show a higher phosphate removal capacity compared to MCM-41 and Sm2O3 particles, making them promising candidates for water quality control and protection.