Photodecolorization of methyl orange over α-Fe2O3-supported HY catalysts: the effects of catalyst preparation and dealumination

Abstract

An α-Fe2O3-supported HY zeolite (α-Fe2O3/HY) was prepared by introducing nanosized α-Fe2O3 into an HY zeolite support through in situ (α-Fe2O3/HYIS) and ion-exchange (α-Fe2O3/HYIE) methods. The effect of the preparation methods on the physicochemical properties of the catalyst were studied via XRD, FESEM-EDX, TEM, UV–vis DRS, FTIR, XPS, 29Si and 27Al MAS NMR, ESR and BET surface area analysis. In this study, dealumination was accomplished by using a facile electrolysis system without any strong acids, reactive compounds and/or hydrothermal treatment. Dealumination accompanied by ion exchange of Al with Fe3+ ions in the HY zeolite framework resulted in the formation of an active species that had a higher photoactivity towards the decolorization of methyl orange (MO). A 5 wt% α-Fe2O3/HYIS was found to produce an 80% photodecolorization of 30 mg L−1 of MO at pH 2 with 0.375 g L−1 catalyst, while 5 wt% α-Fe2O3/HYIE only produced 23% photodecolorization under similar conditions (2 h reaction time). This study showed that the kinetics follow a pseudo-first order Langmuir–Hinshelwood model with an activation energy (Ea) calculated for both 5 wt% α-Fe2O3/HYIS and 5 wt% α-Fe2O3/HYIE to be 45.8 kJ mol−1 and 70.2 kJ mol−1, respectively. Measurements of the mineralization of MO by COD, BOD5 and TOC analysis were 27.0%, 69.6% and 16.9%, respectively, after 2 h of contact time. The Fe dissolution from the catalyst showed insignificant leaching of Fe (<1%) when subjected to AAS. A reusability study demonstrated that α-Fe2O3/HYIS could be a promising photocatalyst for the degradation of various dyes in wastewater.