Abstract
The titanium dioxide-silicon dioxide (TiO2-SiO2) nanocomposite used for the study was synthesized using a sol-gel method followed by UV-treatment. The physicochemical properties of the synthesized catalyst, TiO2-SiO2 were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL). The photocatalytic degradation of methylene blue (MB) dye was evaluated in the presence of TiO2-SiO2 and reactive chlorine species (RCS) under experimental conditions. By comparing the important reaction processes in the study, including photocatalysis, chlorination and photocatalytic chlorination, it was found out that the process of photocatalytic chlorination had the highest photodegradation efficiency (95% at 60 min) of the MB under optimum reaction conditions (MB = 6 mg L−1, catalyst = 0.1 g and pH = 4). The enhanced removal of MB from the aqueous medium was identified because of the synergy between chlorination and photocatalysis activated in the presence of TiO2-SiO2. The mechanism of the photocatalytic chlorination process was scrutinized in the presence of various RCS and reactive oxygen species (ROS) scavengers. Based on the experimental data attained, Na2S2O3 exhibited the highest inhibitory effect on the degradation efficiency of MB, indicating that the RCS is the main contributor to visible light-induced photodegradation of MB.
Highlights
In a recent United Nations (UN) report, around 80% of total wastewater is released directly into nearby land before any proper and prior degradation procedure
The phase composition of the samples was identified by X-ray diffraction (XRD) characterization; the diffraction data evolved are shown in Figure S2 which exhibits the presence of both anatase and rutile phases in all three samples (TiO2, TiO2 -SiO2 and UV-treated TiO2 -SiO2 ) [21]
This can lead to enhanced photocatalytic activity of the composite since the electrons and holes can be efficiently converted to O2− and HO, which can efficiently break down methylene blue (MB) molecules
Summary
In a recent United Nations (UN) report, around 80% of total wastewater is released directly into nearby land before any proper and prior degradation procedure This causes severe water pollution and affects the natural ecosystem and public health [1]. As there are more active adsorption sites on the surface of the TiO2 -SiO2 catalyst composite, there is a reduction in recombination of photogenerated holes and electrons, thereby increasing the chance of photogenerated holes to reach the active surface sites This enhances photocatalytic activity in the presence of. UV/chlorine is one of the AOP processes, and chlorine is a widely used disinfectant [12] This technique can oxidize a large number of recalcitrant organic compounds such as dye molecules, pharmaceutical products and microorganisms etc. In this study, we combined chlorination and photocatalysis to achieve complete mineralization of MB molecules in an aqueous system under solar light
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