Photocatalytic degradation of tetracycline aqueous solutions by nanospherical α-Fe2O3 supported on 12-tungstosilicic acid as catalyst: using full factorial experimental design

Abstract

In this paper, spherical α-Fe2O3 nanoparticles (NPs) were supported on the surface of 12-tungstosilicic acid (12-TSA·7H2O) using two different solid-state dispersion (SSD) and forced hydrolysis and reflux condensation (FHRC) methods. Photocatalytic activity of supported α-Fe2O3 NPs (α-Fe2O3/12-TSA·7H2O) for tetracycline (TC) degradation in aqueous solution was investigated using UV/H2O2 process and the results were compared with that of pure α-Fe2O3 NPs. α-Fe2O3 and 12-TSA·7H2O were synthesized according to previous reports and all products were characterized by using FTIR, SEM, EDX and XRD. Design of experiments (DoEs) was utilized and photocatalytic degradation process was optimized using full factorial design. The experiments were designed considering four variables including pH, the initial concentration of TC, catalyst concentration and H2O2 concentration at three levels. TC concentration reduction in the medium was measured using UV/Vis spectroscopy at λmax = 357 nm. The results of experiments indicated that supporting α-Fe2O3 NPs on the surface of 12-TSA·7H2O through SSD and FHRC methods caused to improve the filtration, recovery and photocatalytic activity of NPs. Also, it was indicated that those NPs supported through SSD method, have better photocatalytic performance than those supported through FHRC method. The statistical analyses revealed that the maximum TC degradation (97.39%) is obtained under those conditions in which pH and catalyst concentration variables are at maximum levels and the initial concentration of TC and H2O2 concentration variables are at minimum levels (pH 8, catalyst concentration = 150 ppm, initial concentration of TC = 30 ppm, H2O2 concentration = 0.1 ppm). A first order reaction with k = 0.0098 min−1 was observed for the photocatalytic degradation reaction.