TiO 2 -reduced graphene oxide nanocomposites for the trace removal of diclofenac
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TiO2‑reduced graphene oxide nanocomposites for the trace removal of diclofenac Deepthi John1,2 · A. S. Rajalakshmi2 · Raichel Mary Lopez2 · V. Sivanandan Achari2 Received: 30 January 2020 / Accepted: 31 March 2020 © Springer Nature Switzerland AG 2020
Abstract Solar photocatalysis using TiO2-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. Keywords Degradation · Diclofenac · Kinetics · Pharmaceutical degradation · Solar photocatalysis · TiO2-RGO nanocomposites
1 Introduction The presence of emerging contaminants such as endocrine disrupting compounds (EDCs), personal care products (PCPs) and pharmaceuticals in water bodies is a matter of serious concern nowadays. The environmental problems created by the pharmaceuticals constitute an area where considerably a little attention is paid into. Extensive use of pharmaceuticals by humans and other living organisms has become a major environmental issue as they end up in water and soil, leading to degradation of their quality. Most of the pharmaceutical products are stable and resistant to biological degradation. The occurrence of more than 80 pharmaceutical
compounds upto ppm level is reported in the water bodies [1]. The presence of these contaminants leads to chronic low level exposure and accumulation with deleterious effects such as endocrine disruption as well as drug resistance of microorganisms. Among the various pharmaceuticals, nonsteroidal anti-inflammatory drugs (NSAIDs) are of much environmental concern due to their widespread availability. DCF, [2-(2,6-dichlorophenylamino) phenylacetic acid] is one of the popular NSAIDs in medical treatment as an analgesic, antiarthritic and antirheumatic agent apart
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