Influence of pH variation on CuWO 4 , CuWO 4 /WO 3 and CuWO 4 /CuO structures stabilization: study of the photocatalytic
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Influence of pH variation on CuWO4, CuWO4/WO3 and CuWO4/CuO structures stabilization: study of the photocatalytic properties under sunlight N. F. Andrade Neto1,* F. V. Motta1
, Y. G. Oliveira1, J. H. O. Nascimento2, M. R. D. Bomio1, and
1
LSQM – Laboratory of Chemical Synthesis of Materials, Department of Materials Engineering, Federal University of Rio Grande do Norte – UFRN, P.O. Box 1524, Natal, RN, Brazil 2 LPQT, DET, UFRN, Av. Sen. Salgado Filho, 3000, Natal, RN CEP 59072-970, Brazil
Received: 29 May 2020
ABSTRACT
Accepted: 27 August 2020
In this work, the reaction pH range (from 2 to 10) was used to study the stabilization of the CuWO4 phase in the presence of polyvinylpyrrolidone surfactant synthesized by the sonochemical method. The powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), nitrogen adsorption and desorption using the Brunauer–Emmett–Teller methodology and ultraviolet–visible spectroscopy (UV–Vis). The photocatalytic activity was studied against MB dye under sunlight and CuWO4 powders were tested at 5 reuse cycles. Diffractograms indicated that syntheses at pH 2 and 4 generate WO3/CuWO4 heterostructures, while reaction pH at 8 and 10 generate CuO/CuWO4 heterostructures and at pH 6 generates pure CuWO4. FE-SEM images indicated semispherical morphology for CuWO4, nanoplate morphology for CuO, and large particles without definite form for WO3 powders. The scavenger’s methodology indicates that hydroxyl radicals are the main responsible for the photodegradation of methylene blue in all samples. Also, it indicates that the formation of the WO3/CuWO4 and CuO/CuWO4 heterostructures increase the e-/h? pair recombination rate, reducing the photocatalytic activity in sunlight.
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Springer Science+Business
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https://doi.org/10.1007/s10854-020-04371-x
J Mater Sci: Mater Electron
1 Introduction Environmental research has gained attention over the years [1]. Population growth promotes a greater amount of waste which requires specific treatments that are usually difficult to perform. Industries that generate organic waste, such as textiles and food, receive attention due to the complexity of organic chains being degraded [2]. Wastes from the textile industry are efficiently treated by advanced oxidative processes (AOP), which use semiconductor materials as a catalyst, increasing catalytic efficiency [3]. The actuation of semiconductor materials as photocatalyst is based on energy absorption, usually associated with a light source, which provides the electronic excitation of the valence band (VB) to the conduction band (CB), generating an electron/hole pair (e-/h?) [4]. The e-/h? pairs migrate to the catalyst surface, reacting with the liquid medium, and generating reactive oxidative species (ROS) that have a high ability to degrade organic contaminants [5]. The radiation energy requ
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