Search

Bismuth vanadate, BiVO4, is a visible-light response semiconductor for photocatalysis applications such as organic pollutants degradation, oxygen production and carbon dioxide reduction. However, as a single-phase photocatalyst, BiVO4 efficiency is limited by the unpreferable recombination of the photoexcited electron (e−) and hole (h+). Thus, strategies have been designed to enhance the photocatalytic efficiency by promoting the separation of electrons and holes. This can be done by controling the morphology and crystallographic facets of BiVO4, and by building p–n junction photocatalytic systems with a combination of n-type semiconductors (BiVO4) and p-type semiconductors or a monoclinic–tetragonal heterostructure of BiVO4. In particular, a direct p–n junction photocatalytic system with tetragonal zircon-structured BiVO4 (t-z) and monoclinic scheelite-structured BiVO4 (m-s) combination has recently attracted attention. Here we review the synthesis of the monoclinic–tetragonal heterostructured BiVO4 photocatalyst (m–t BiVO4) by calcination, hydrothermal, microwave-assisted hydrothermal and solvothermal methods. m–t BiVO4 formation and the transmission phase between t-z and m-s are controlled by the calcining temperature, precursor pH, metal doping content, type of solvent, implementation of precursors and reaction conditions. We discuss m–t BiVO4 crystal structure, optical characteristics and photocatalytic principles. Successful formation of BiVO4 crystals with a m-s/t-z heterostructure is based on data from X-ray diffraction (XRD), Raman and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS). In the m–t BiVO4 heterostructure, a direct p–n junction photocatalytic system is established. When this system is exposed to visible light, the electrons in the conduction band of m-s BiVO4, a n-type semiconductor, migrate easily to the conduction band of t-z BiVO4, while the holes on valence band of t-z BiVO4, a p-type semiconductor, move to the valence band of m-s BiVO4 through an internal electric field. As a result, the e−/h+ charge carriers are spatially separated. [ABSTRACT FROM AUTHOR]

In this study, we investigated sulfate-modified BiVO4 with the high photocatalytic activity synthesized by a sol-gel method in the presence of thiourea, followed by the annealing process at different temperatures. Its structure was characterized by thermal gravimetric analysis (TGA), powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The BiVO4 synthesized in the presence of thiourea and calcined at 600 °C (T-BVO-600) exhibited the highest photocatalytic degradation efficiency of methylene blue (MB) in water; 98.53% MB removal was achieved within 240 min. The reaction mechanisms that affect MB photocatalytic degradation on the T-BVO-600 were investigated via an indirect chemical probe method, using chemical agents to capture the active species produced during the early stages of photocatalysis, including 1,4-benzoquinone (scavenger for O2−), ethylenediaminetetraacetic acid disodium salt (scavenger for h+), and tert-butanol (scavenger for HO•). The results show that holes (h+) and hydroxyl radicals (HO•) are the dominant species of MB decomposition. Photoluminescence (PL) measurement results of terephthalic acid solutions in the presence of BiVO4 samples and BiVO4 powders confirm the involvement of hydroxyl radicals and the separation efficiency of electron-hole pairs in MB photocatalytic degradation. Besides, the T-BVO-600 exhibits good recyclability for MB removal, achieving a removal rate of above 83% after five cycles. The T-BVO-600 has the features of high efficiency and good recyclability for MB photocatalytic degradation. These results provide new insight into the purpose of improving the photocatalytic activity of BiVO4 catalyst. [ABSTRACT FROM AUTHOR]

• A facile hydrothermal synthesis route of Ag@ZnO@rGO was developed. • The efficiency of electrochemical CO 2 reduction is highly dependent on the porosity and conductivity properties. • The effective interaction in porous material enhances high-performance CO 2 reduction. Carbon dioxide (CO 2) accounts for the most significant proportion of greenhouse gas emissions, progress towards decrease the existence of atmospheric CO 2 have received considerable attention. Therefore, focus on carbon capture and utilization, which reduces the content of CO2 and provides an excellent solution to generate value-added and renewable fuels. Herein, the electrochemical CO 2 reduction activity of Ag@ZnO@rGO electrocatalysts prepared by facile synthesis route has been systematically investigated. The good incorporation of Ag in the ZnO NPs matrix (Ag@ZnO) was synthesized through the thermal calcination of Ag+-impregnated ZIF8. Then, Ag@ZnO was coated by rGO using a hydrothermal technique. We found that the efficiency of electrochemical CO 2 reduction is highly dependent on the porosity and conductivity properties. The effective interaction of rGO in Ag-based ZnO porous nanoparticles showed high activity, leading to reach Faradaic efficiencies of about 70% at −1.6 V vs. SCE. To the best of our knowledge, the performance in this work is comparable to the literature. Additionally, the electrocatalyst stays for more than 30 min without any significant change of activity, possessing the ability for applications to reducing CO 2. [ABSTRACT FROM AUTHOR]