Mang Xue

Synthesis, characterization and photocatalytic activity of Cu-doped Zn/ZnO photocatalyst with carbon modification

Herein, we report the preparation of Cu-doped Zn/ZnO composites with carbon modification via a simple replacement–hydrothermal method using Zn powder and CuSO4·5H2O as raw materials. The as-synthesized composites were characterized by powder X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The results showed that Cu doping promotes crystal growth of ZnO, inhibits phase transfer of metallic Zn to ZnO, enhances the optical absorption in the visible region and reduces the recombination of photogenerated electrons and holes. Interestingly, CO2 dissolved in solution was converted to carbon adhered onto the composite surface (supported by the XPS data). The abundant carbon species present on the composite surface is favorable for surface chemical reactions because it can trap or adsorb reactants which facilitate the transfer of reactants to active sites. The photocatalytic efficiency of the as-synthesized catalysts was evaluated by the degradation of anthraquinone dye (reactive brilliant blue KN-R) in solution under sunlight irradiation. The degradation results revealed that the Cu-doped Zn/ZnO composites have better photocatalytic activities than those of ZnO and Zn/ZnO. The enhancement of the photocatalytic activity of the composites can be attributed to the existence of Cu doping, the Zn/ZnO hetero-structure and covered carbon on the surface of the photocatalysts, which causes electrons to be easily excited from the valence band to the conduction band and efficient separation of electron–hole pairs, as well as quick surface reactions in doped ZnO. Furthermore, a possible growth mechanism of the Cu-doped Zn/ZnO composites with carbon modification was proposed.

Ultra-thin C3N4 nanosheets for rapid charge transfer in the core–shell heterojunction of α-sulfur@C3N4 for superior metal-free photocatalysis under visible light

The core–shell heterojunctions of ultra-thin C3N4 nanosheet enwrapping spherical α-S composites (α-S@C3N4) were fabricated via a self-assembly process by electrostatic force to realize enhanced photocatalytic ability under visible light. The photocatalytic ability can be adjusted by tuning the amount of the ultra-thin C3N4 nanosheet. The α-S@C3N4 composite with 35% composition of C3N4 nanosheet has the highest photocatalytic ability. The degradation rate of Rhodamine B (RhB) with α-S@C3N4 (35% C3N4) is 6.72 times faster compared to α-S as photocatalyst. This increase could be attributed to the efficient photogenerated holes and electrons separation by the heterojunction, which has excellent charge transfer ability arising from the ultra-thin C3N4 nanosheet. The stability of the α-S is also largely improved by the heterojunction construction.

Preparation of β-Bi2O3/g-C3N4 nanosheet p–n junction for enhanced photocatalytic ability under visible light illumination

Abstractβ-Bi2O3/g-C3N4 nanosheet (NS) p–n junction of g-C3N4 NS-wrapped β-Bi2O3 was fabricated via self-assembly process by electrostatic force. By the analyses of scanning electron microscopy images and Fourier transform infrared spectra, the g-C3N4 NS has been wrapped on the spherical β-Bi2O3 particles. Constructing p–n junction with g-C3N4 NS can enhance the separation efficiency of photogenerated carriers and light absorption ability of β-Bi2O3 particles obtained by the characterization of fluorescence spectra and diffuse reflectance spectra. The photocatalytic removal rate of RhB is largely enhanced by construction of β-Bi2O3/g-C3N4 NS p–n junctions. The photocatalytic ability of β-Bi2O3/g-C3N4 NS p–n junctions can be adjusted by tuning the loading amount of g-C3N4 NS. The enhanced photocatalytic performance is firstly attributed to the p–n junction effect of efficient separation of photogenerated charge carriers. Furthermore, the increased light absorbance of the composites also contributes to the enhanced photocatalytic ability.

Photonic crystal coupled porous BiVO4 hybrid for efficient photocatalysis under visible light irradiation

A bilayer TiO2 photonic crystal (PC)/porous BiVO4 was constructed by using liquid-phase deposition (LPD) and spin coating method for the enhancement of visible-light-driven photocatalytic ability by the improvement of light absorbance. Crystal form, morphology, film thickness, and light absorption performance were investigated. The photocatalytic activity of the bilayer TiO2 PC/porous BiVO4 film was evaluated by the degradation of MB and was compared with that of porous BiVO4 film. The effect of the film thickness of the porous BiVO4 on its photocatalytic ability was determined. It was found that the film thickness significantly affected the light absorption, and therefore its photocatalytic ability. The bilayer film with 1.03 μm of thickness of porous BiVO4 film exhibited the highest photocatalytic performance. The photocatalytic ability of porous BiVO4 was enhanced by combination with a TiO2 PC layer as the back reflector. This increase could be attributed to the intensified light absorbance produced by reflection from the TiO2 PC layer. The effects of porous structure and the application of photoelectrocatalytic process on the photocatalytic performance were also discussed.

Synthesis, Characterization, and Photocatalytic Activity of N-Doped ZnO/ZnS Composites

The aim of the present study is to enhance photocatalytic performance of ZnO semiconductor by comodification with doping of nonmetal ions and coupling with another semiconductor. Therefore, we synthesized the N-doped ZnO/ZnS photocatalysts via a simple heat-treatment approach using L-cysteine as N and S source in this work. Anthraquinone dye (reactive brilliant blue KNR) is employed as the model contaminants to evaluate the photocatalytic activity of as-synthesized samples under sunlight illumination. The N-doped ZnO/ZnS synthesized by this method shows better photocatalytic activity as compared to that of pure ZnO. The enhanced photocatalytic activity of the N-doped ZnO/ZnS composites may be related to the existence of N doping, ZnS/ZnO heterostructure, and covered abundant carbon species on the photocatalyst surface, which causing high absorption efficiency of light, efficient separation of electron-hole pairs, and quick surface reaction in doped ZnO.

Enhanced photocatalytic activity of w-doped and w-la-codoped TiO 2 nanomaterials under simulated sunlight

W-doped TiO2 and W-La-codoped TiO2 nanomaterials were successfully synthesized via the sol-gel method. The products were characterized by X-ray diffraction, UV-vis diffuse reflectance spectrophotometer, transmission electron microscopy, and X-ray photoelectron spectroscopy. The presence of W and La results in significant red shift of absorption edge for TiO2-based nanomaterials. The weight ratios of La and W in the composites play important roles in the absorption edge for TiO2-based nanomaterials. The photocatalytic activities of both W-doped TiO2 and W-La-codoped TiO2 photocatalysts for decolorization of methyl orange solution were evaluated under simulated sunlight irradiation. The results showed that both W-doped and W-La-codoped can effectively improve the photocatalytic behaviors of TiO2 nanomaterials ascribed to the improved photoinduced charge carriers separation, enhanced light absorption, and large surface area. Furthermore, W-La-codoped TiO2 exhibited higher photocatalytic activity than W-doped TiO2. Considering their high photocatalytic activity, the doped TiO2 nanomaterials could be applied in wastewater treatment and environmental purification.

Construction of g-C3N4 and FeWO4 Z-scheme photocatalyst: effect of contact ways on the photocatalytic performance

Photocatalysis has been regarded as an attractive strategy for the elimination of contaminants, but its performance is usually limited by the fast recombination of photogenerated electron–holes. A heterojunction photocatalyst could achieve the effective separation of electron–holes. However, the electrons migrate to the less negative band while holes move to the less positive band, leading to a weakened redox ability. Z-scheme photocatalysis is a feasible way to realize the efficient separation of photogenerated electron–holes without sacrificing the reductive ability of electrons and oxidative ability of holes. In this work, a new Z-scheme photocatalyst, composed of g-C3N4 (photocatalyst I), FeWO4 (photocatalyst II) and RGO (electron mediator), was fabricated through a facile hydrothermal and mixing method. The effect of contact ways (the electron mediator firstly combined with photocatalyst I or with photocatalyst II) on the Z-scheme photocatalytic performance was investigated. The photocatalytic removal rate of rhodamine B (RhB) was largely enhanced by the construction of a Z-scheme photocatalyst, compared with the g-C3N4/FeWO4 composite without RGO. The contact ways could affect the photocatalytic ability of a Z-scheme photocatalyst. The enhanced photocatalytic performance was attributed to the Z-scheme induced efficient separation of photogenerated charge carriers. Furthermore, remaining holes (on the VB of FeWO4) or remaining electrons (on the CB of g-C3N4) with powerful oxidation or reduction ability would promote the photocatalytic degradation of RhB.

Sewage sludge pretreatment by microwave irradiation combined with activated carbon fibre at alkaline pH for anaerobic digestion

This research focuses on the effects of microwave-assisted activated carbon fibre (ACF) (MW-ACF) treatment on sewage sludge at alkaline pH. The disintegration and biodegradability of sewage sludge were studied. It was found that the MW-ACF process at alkaline pH provided a rapid and efficient process to disrupt the microbial cells in the sludge. The results suggested that when irradiated at 800 W MW for 110 s with a dose of 1.0 g ACF/g solid concentration (SS) at pH 10.5, the MW-ACF pretreatment achieved 55% SS disintegration, 23% greater than the value of MW alone (32%). The concentration of total nitrogen, total phosphorus, supernatant soluble chemical oxygen demand, protein, and polysaccharide increased by 60%, 144%, 145%, 74%, and 77%, respectively. An increase in biogas production by 63.7% was achieved after 20 days of anaerobic digestion (AD), compared to the control. The results indicated that the MW-ACF pretreatment process at alkaline pH provides novel sludge management options in disintegration of sewage sludge for further AD.

Effect of Pypocholoride Pretreatment on the Disintegration of Excess Sludge

This article focuses on the effects of pretreatment on sewage sludge with sodium hypochlorite addition. The solubilization of organic matters of sludge was investigated. It was found that the pypocholoride treatment provided a efficient process to release organics from sludge flocs. When the ClO- dose was about 21mg /g SS with a reaction time of 3 hours, the supernatant soluble chemical oxygen demand (SCOD), total nitrogen (TN), total phosphorus (TP), protein and polysaccharide increased by 400%, 67%, 1791%, 635%, 214%, and 556%, respectively. After hypochlorite pretreatment, the sludge extracelluar polymers (EPS) were disintegrated and the cell walls were broken. Then the intracellular organic matters were released into the supernatant, leading to the increase of organic matters in the supernatant.

Synthesis and Characterization of High Electrocatalytic Active Nanosized RuO2 Powder with Narrow Distribution by Ultrasonic Precipitation

In this paper, synthesis of RuO2 with uniform nanosized sphere-like morphologies by ultrasonic precipitation using ammonia is presented. The structures, properties and electrocatalytic performance of materials were characterized by XRD, FE-SEM, CV and polarization curve. FE-SEM photographs showed that the sample prepared by ultrasonic precipitation has a relatively narrow size distribution compared with the sample prepared by conventional precipitation with magnetic stirring. The CV and polarization curve for OER (oxygen evolution reaction) confirmed that electrochemical active surface area and OER activity of sample by ultrasonic precipitation are higher than that of sample by conventional precipitation under magnetic stirring.