Textile effluent treatment under artificial and natural irradiation using coupled ZnO-iron ores nanocomposite as photocatalyst

In this work, we have reported the green synthesis of ZnO nanoparticle and coupled ZnO-iron oxide nanocomposite by sol-gel method using a local iron-ores (labelled TIO: Tamra iron oxide) as iron oxide origin collected from the Tamra deposit (Tunisia). Investigated photocatalysts were tested in the treatment of real textile dyeing effluent. The effluent presents a dark blue color, with a maximum absorbance peak at 594 nm, alkaline pH (pH = 12.4) and high organic contents chemical oxygen demand (COD = 1,400 mg L-1). Experiments were conducted on a lab-scale prototype using UV lamp as artificial light source and solar irradiation as natural light source. The chemical composition and the morphology of the investigated nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and nitrogen adsorption-desorption isotherms. ZnO-iron oxide nanocomposite shows much higher photocatalytic performance with 95% and 91% of color and COD removal within 2 h of UV light irradiation than iron oxide and ZnO nanocomposite. Under solar irradiation, all photocatalysts present high activity for effluent photodegradation compared to UV irradiation and coupled semiconductor ZnO-iron oxide achieves 98.6% and 92% of color and COD removal, respectively in the presence of H2O2. Kinetic study was carried out showing that the pseudo-first-order kinetic describes the effluent photodegradation under both irradiation. Characteristics of wastewater after treatment, COD below 250 mg L-1, pH 8.5 and uncolored, respect the condition for releasing in public sewage systems. Experimental findings obtained in this study indicate that ZnO-iron oxide photocatalyst has a great potential application for resolving environmental problems.