TiO2-reduced graphene oxide nanocomposites for the trace removal of diclofenac

Synthesis of TiO2 graphene oxide-based material for textile effluent decontamination: characterization, kinetic, and mechanism studies

In this work, a hydrothermal method was proposed to fabricate a nanomaterial composed of titanium dioxide and graphene oxide (10 wt%) (TiO₂-GO). The GO was synthesized according to the modified Hummers and Offeman method, followed by exfoliation. Several characterization analyses were performed in order to investigate the structure, functional groups, and elemental composition of the nanomaterial. XRD analysis showed that the presence of GO does not change the crystalline structure of TiO₂. FTIR evidenced the characteristic peaks present in both precursor materials (TiO₂ and GO) and EDX confirmed the presence of GO on the TiO₂-GO material. The nanomaterial was used as a photocatalyst in the TWW treatment, where the color and COD removal and the decrease of the characteristic peaks presented in the UV-Vis spectrum were investigated. The dosages of TiO₂-GO and pH were studied to find the optimum operating condition. The results revealed that 0.5 g of photocatalyst with an initial pH of 3 achieve the best results under UV-A radiation. The kinetic test shows a COD removal of 87% after 90 min. The reuse test shows a decrease in COD removal after four cycles attributed to the deposition of some oxidized compounds on the catalyst surface. Finally, the efficiency of the photocatalyst was evaluated under solar radiation and it was shown that despite the good results, the performance of the TiO₂-GO was better under UV-A radiation.

Fabrication and characterization of pectin-graphene oxide-magnesium ferrite-zinc oxide nanocomposite for photocatalytic degradation of diclofenac in an aqueous solution under visible light irradiation

Wastewater containing pharmaceutical contaminants has become a critical environmental concern due to rising population and drug consumption caused by increased life expectancy. Diclofenac (DCF) is one of the most applicable drugs for veterinary and human health purposes, polluting surface waters in different ways. This work aims to synthesize a novel pectin-graphene oxide (GO)-magnesium ferrite (MgFe₂O₄)-zinc oxide (ZnO) nanocomposite (PGMZ) for photocatalytic degradation of DCF in an aquatic environment under visible light irradiation. The single and synthesized nanocomposites were characterized by several analyses, confirming the successful synthesis of the nanocomposite. Effects of four operation conditions, including nanocomposite dosage (1-1.25 g/L), nanocomposite type, initial contaminant concentration (35-55 mg/L), and solution pH (3-11), were investigated on the degradation performance. From the kinetic study, the effect of mixing two composites, i.e., synergy percentage, was 38.7% when ZnO-MgFe₂O₄ particles were added to the GO-pectin structure. By examining the effect of different free radical enhancers and scavenging compounds on the DCF photodegradation, the most influential scavenging components were in the following order; NaCl > Na₂CO₃ > Na₂SO₄, while K₂S₂O₈ was a better enhancer than H₂O₂ at their optimal concentration. Finally, the PGMZ photocatalyst was reused six times with a reduction of about 20% in its removal efficiency, indicating excellent reusability and stability.

Integration of coagulation-flocculation and heterogeneous photocatalysis for the treatment of pulp and paper mill effluent

A two-step process involving coagulation-flocculation followed by solar photocatalysis - based Advanced Oxidation Process (AOP) using TiO₂-Reduced Graphene Oxide (TRGO) nanocomposite as catalyst has been employed for the treatment of pulp and paper mill effluent. As the effluent is loaded with a high amount of organics with initial chemical oxygen demand (COD) as high as 3516, a pre-treatment is required before applying photocatalytic treatment. Coagulation-flocculation was identified as an effective pre-treatment strategy. Among the various coagulants tested, CuSO₄.5H₂O showed the best % COD reduction of 84 at pH 6, at a loading of 5 g/L. The primary treatment of coagulation improved the biodegradability index from 0.23 to 0.37. TRGO photocatalyst, employed in the second stage of photocatalytic treatment was synthesised by an ultrasound assisted solvothermal method and well characterised by various spectroscopic/analytical tools. The composite was found to be an efficient solar photocatalyst and achieved 1.76 and 2.1 times more COD reduction than synthesised TiO₂ and commercial P25 respectively. The final effluent after the combined treatment was neutral and the biochemical oxygen demand (BOD) and COD were 11.7 and 120 mg/L respectively which were below the given limit of National Environmental Quality Standards.

Integration of heterogeneous photocatalysis and persulfate based oxidation using TiO2-reduced graphene oxide for water decontamination and disinfection

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 TiO2-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 andSO 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.