Enhanced Catalytic Activity of Bi2WO6 for Organic Pollutants Degradation under the Synergism between Advanced Oxidative Processes and Visible Light Irradiation

Environmental problems have become more and more serious with the continuous development of industrialized society. Especially, the problem of industrial wastewater has been a hot research issue in the field of catalytic degradation. Coupling photocatalysis and advanced oxidation processes (AOPs) is considered to be an efficient organic pollutant degradation technology due to its high efficiency, non-selectivity, and mild treatment conditions. In this article, the authors focused on the synthesis and characterization of Bismuth tungstate (Bi₂WO₆) nanoflowers, which were prepared using a straightforward hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) surfactant. To investigate the micro-morphology, crystal phase, surface chemical element states, and optical characteristics of the Bi₂WO₆ nanoflowers, various methods such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflection spectroscopy (DRS) were used. The catalytic performance of the Bi₂WO₆ nanoflowers was then investigated for degrading organic pollutants under different catalytic systems. The removal efficiency of Rhodamine B (RhB) was up to 96.39% within 40 min under vis/potassium monopersulfate triple salt (PMS)/ Bi₂WO₆ system, which is obviously superior to that in both PMS/ Bi₂WO₆ (38.77% in 40 min) and vis/Bi₂WO₆ (31.82% in 40 min) systems, indicating that synergistic effects between visible-light irradiation and PMS accelerated the catalytic activity of Bi₂WO₆ on the RhB degradation. The researchers also investigated the effect of ambient conditions on the catalytic performance of the systems, such as catalyst dosage, PMS concentration, pH value, and ion concentration. Interestingly, the vis/PMS/Bi₂WO₆ system demonstrated high removal efficiency (up to 90%) despite changes in these parameters. However, the catalytic degradation rate (k) was influenced by these parameters in this system. Conversely, the environmental parameters have obvious influence on the catalytic degradation rate (k) under vis/PMS/ Bi₂WO₆ system. The results showed that when the catalyst dosage and PMS concentration increased, so did the K value. On the other hand, the K value increased firstly and then decreased with the rise of pH value in the catalytic system. And the catalytic degradation rate reached its maximum value (0.1502 min⁻¹) at pH = 7 in the catalytic system. Interestingly, the presence of Cl⁻ in the system would be beneficial for promoting the catalytic degradation efficiency. Conversely, the existence of ${\text{CO}}_{\text{3}}^{\text{2}-}$ in the system would obviously inhibit the catalytic degradation efficiency. The result of the cycling experiments also verified that the catalyst possessed excellent stability for the degradation of organic dyes. Furthermore, the researchers conducted quenching experiments and EPR (electron paramagnetic resonance) tests, which revealed the crucial roles of superoxide radicals ( $\cdot {\text{O}}_{\text{2}}^{-}$) and singlet oxygen (¹O₂) in the degradation of organic pollutants. Overall, the excellent catalytic activity of Bi₂WO₆ in the vis/PMS synergistic catalytic system was attributed to its outstanding visible-light-response photocatalysis activity and the superior ability of bismuth ions in activating PMS.

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