Abstract
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.
Highlights
Bismuth vanadate (BiVO4 ) has recently been extensively studied by researchers around the world and has been used as a new catalyst in the photocatalytic field because of the economic advantageMaterials 2019, 12, 2681; doi:10.3390/ma12172681 www.mdpi.com/journal/materialsMaterials 2019, 12, 2681 of synthetic materials, low toxicity, excellent chemical stability, and narrow bandgap [1]
Such approaches mainly involve improving the photocatalytic activity of BiVO4, which is enhanced through either material synthesis with crystal form control or doping with nonmetal elements which have been proven to be efficient and promising research directions recently
There was no observable change in the position of the (121) and (040) planes of both T-BVO-600 and BVO-600 samples, implying that S could not be doped into the lattice of BiVO4 crystal
Summary
Bismuth vanadate (BiVO4 ) has recently been extensively studied by researchers around the world and has been used as a new catalyst in the photocatalytic field because of the economic advantage. In order to improve the separation efficiency of the photogenerated electron-hole pairs to the catalytic surface for high-photodynamic catalysis, the researchers proposed several measures, such as (1) control of crystal structure, crystal form, and crystal surface [8,9], (2) formation of p-n bonds and the establishment of an internal electromagnetic interaction region extending from n-type semiconductor (BiVO4 ) to p-type semiconductor materials [10], and (3) formation of the monoclinic-tetragonal structure of BiVO4 [11] Such approaches mainly involve improving the photocatalytic activity of BiVO4 , which is enhanced through either material synthesis with crystal form control or doping with nonmetal elements which have been proven to be efficient and promising research directions recently. The addition of a surfactant to the reaction solution to control the crystal growth process could facilitate the designing of the ideal catalyst For this purpose, recently, researchers have been using urea for the synthesis of BiVO4. We investigated the effect of heating temperature on the structure of BiVO4 as well as on the photocatalytic activity of the material in the decomposition of organic compounds using visible light
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