The assessment of the photocatalytic activity of magnetically retrievable ZnO coated γ-Fe2O3 in sunlight exposure

Abstract

The photocatalytic activity of magnetically retrievable ZnO@γ-Fe2O3, synthesized by coating γ-Fe2O3, with ZnO in 5:1 and 10:1 ratio, was assessed for the mineralization of chlorophenol derivatives (2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-tri chlorophenol) and compared with that of pure ZnO in natural sunlight exposure. The diffuse reflectance spectroscopy revealed the composite nature of the synthesized catalysts with the existence of dual band edges representing ZnO and γ-Fe2O3. The decreased emission intensity in the photoluminescence (PL) spectra rendered the contributory role of γ-Fe2O3 in suppressing the charge carrier annihilation. The growth of Raman active bands of ZnO was observed with increasing density of coated layers. The morphology and structural changes were examined by XRD and FESEM. The cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS) measurements, in the dark and under illumination, verified the elimination of photocorrosion and better trapping of the excited states in the synthesized coated catalysts as compared to pure ZnO. A noticeable increase in the degradation/mineralization ability, in comparison to pure ZnO, was observable for the ZnO coated on γ-Fe2O3 support. The progress of the photocatalytic degradation process was monitored by HPLC while the mineralization ability of the synthesized catalysts was estimated by TOC and measuring the release ions by ion chromatography (IC). Based on repeated precise weight measurements, a 99% and 85% magnetic retrieval of 5:1 (ZnO@γ-Fe2O3) and 10:1 (ZnO@γ-Fe2O3) catalysts was established. The synthesized catalysts exhibited excellent stability and reproducibility in the photocatalytic performance.