Influence of pH variation on CuWO4, CuWO4/WO3 and CuWO4/CuO structures stabilization: study of the photocatalytic properties under sunlight

Abstract

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.