Preparation and characterization of titania based trimetallic metal oxide photocatalysts for photodegradation of 1,2-dichlorobenzene and polychlorinated biphenyl compounds in aqueous phase

Abstract

The deterioration of water quality has raised serious safety concerns due to the discharge of chlorinated industrial wastes such as 1,2-dichlorobenzene (DCB) and polychlorinated biphenyls (PCBs) which are highly toxic and cause dangerous effects on human health. The polluted water is usually treated using adsorption method, Fenton, ozonation and photocatalysis. Among these methods, photocatalysis is the most promising technique for the easy decomposition of pollutants in the presence of suitable photocatalyst. Hence, in this research, a series of titania based photocatalysts have been prepared and were utilized to investigate its efficiency in the photocatalytic degradation of DCB in aqueous solution. The influence of catalyst preparation methods (sol-gel, sol-immobilization and mechanical mixing) were explored under different calcination temperatures, ratios and a light source. Further, the potential photocatalyst was then investigated by hydrothermal and hydrogenation techniques. Relatively, trimetallic oxide SnO2/WO3/TiO2 (10:10:80) prepared by mechanical mixing of hydrothermal SnO2, WO3, TiO2 calcined at 850°C, 850°C and 950°C respectively, exhibited the highest degradation of 98.43% under visible light irradiation at the DCB concentration of 100 ppm. The high activity of mechanically mixed hydrothermal trimetallic oxide Sn850/W850/T950 (10:10:80)HY was associated with the exposed surface with edges as observed in the field emission scanning electron microscope (FESEM) morphologies, and also the presence of Ti3+ analyzed by X-ray photoelectron spectroscopy (XPS). The existence of surface defects was further confirmed by photoluminescence (PL) spectroscopy. The reduction in the band gap energy of the trimetallic oxide and the absorption shift towards the visible light region was observed in the absorption band edge using diffuse reflectance-ultraviolet visible (DRUV) spectroscopy. Meanwhile, transmission electron microscope (TEM) images confirmed the absence of an interface gap between the metal oxides which is beneficial for the occurrence of charge transfer and enhancement of the activity. The effectiveness of this photocatalyst when immobilized on polyvinyl chloride (PVC) film, nevertheless decreased the photocatalytic activity to 93.67%. Eventually, the degradation activity of DCB was improved to 95.70% upon increasing the photocatalyst loading on PVC film of up to 0.25 g and under neutral pH. The optimization utilizing response surface methodology with Box-Behnken design was in good agreement with the obtained experimental result. The degradation of DCB in water was justified by the identification of two intermediates using gas chromatography-mass spectrometry (GCMS) analysis. Consequently, the investigation on removal of PCBs from green mussels using polyethylene glycol (PEG), and subsequent degradation of PCBs in aqueous phase utilizing immobilized photocatalysts, capable to degrade 83% of the total PCBs content under the optimized conditions.