Advanced oxidation processes (AOPs) which involve the generation of highly reactive free radicals have been considered as a promising technology for the decontamination of water from chemical and bacterial pollutants. In this study, integration of two major AOPs viz., heterogeneous photocatalysis involving TiO 2 -reduced graphene oxide (T-RGO) nanocomposite and activated persulfate (PS) based oxidation was attempted to remove diclofenac (DCF), a frequently detected pharmaceutical contaminant in water. The enhanced visible light responsiveness of T-RGO would facilitate the use of direct sunlight as a benign and cost effective source of energy for the photocatalytic activation. By combining PS based oxidation process with T-RGO mediated photocatalysis, a DCF removal efficiency of more than 98% was achieved within 30 min. The effect of operating parameters like PS concentration and pH on DCF removal was assessed. Radical scavenging experiments indicated that apart from radical oxidation involving OH and SO ⋅À 4 radicals, a non-radical oxidation pathway was also taking place in the degradation. The antibacterial properties of the integrated system were also evaluated using Escherichia coli and Staphylococcus aureus as representative bacteria. The presence of PS in the photocatalytic reaction system improved the antibacterial activity of the composite against the two strains studied. Cytotoxicity of T-RGO nanocomposite was assessed using human macrophage cell lines and the results showed that the composite is biocompatible and nontoxic at the recommended dosage for water treatment in the present study.
Solar photocatalysis using TiO 2-reduced graphene oxide (T-RGO) nanocomposite as catalyst is explored for the removal of the last traces of diclofenac (DCF) pollutant from water. T-RGO nanocomposites of different compositions were synthesised by a modified process involving solvothermal treatment of titanium isopropoxide and graphene oxide (GO) in isopropanol medium. The prepared catalysts have been characterised by powder X-ray diffraction, infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, photoluminescence emission spectroscopy, UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and N 2 adsorption-desorption measurements. The degradation of DCF is highly facile under solar irradiation in the presence of T-RGO with more than 98% of the 25 mg/L DCF aqueous solution getting degraded in 60 min followed by complete mineralisation in 100 min. Relevant reaction parameters such as catalyst loading, RGO content in the composite, concentration of DCF and the influence of pH on the degradation of the pollutant were identified and optimised. Reaction intermediates were identified by using LC-MS technique. The degradation followed Langmuir-Hinshelwood mechanism and pseudo first order kinetics. The stability and reusability of the catalyst are established. The efficiency of the catalyst in various real water matrices has also been proved thereby affirming its potential for commercial applications.
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