Sonochemical synthesis of mesoporous ZrFe2O5 and its application for degradation of recalcitrant pollutants

Abstract

In this paper, we have reported the sonochemical synthesis and characterization of zirconium ferrite (ZrFe₂O₅), and its use as a catalyst in advanced oxidation processes (AOPs) using decolorization/degradation of azo and non-azo dyes as model processes. The efficacy of ZrFe₂O₅ for dye decolorization has been compared with the conventional catalyst TiO₂ synthesized using sonochemical sol–gel method. Sonochemically synthesized ZrFe₂O₅ and TiO₂ have been characterized using PSD, XRD, FESEM, TEM, DRS, BET and TGA. ZrFe₂O₅ is revealed to have a lower band gap energy than TiO₂. However, the α-Fe₂O₃ (hematite) phase in ZrFe₂O₅ acts as a recombination center of photogenerated electrons and holes, which adversely affects the photo-activity of ZrFe₂O₅. In the context of degradation of recalcitrant pollutants, this adverse effect is compensated by Fenton activity of the α-Fe₂O₃ (hematite) phase which is stimulated by addition of H₂O₂. Sonochemically synthesized ZrFe₂O₅ also has high adsorption capacity for the textile dyes that assists their effective degradation through Fenton and photocatalytic mechanisms. The decolorization experiments have employed individual AOPs of sonolysis, photocatalysis, (heterogeneous) Fenton and various combinations of these as hybrid AOPs. Due to combined facets of photo- and Fenton-activity, ZrFe₂O₅ is a better catalyst for hybrid AOPs than TiO₂. Nonetheless, the Fenton-activity of ZrFe₂O₅ overwhelms the photo-activity in dye decolorization. The most efficient hybrid AOP is revealed to be sono-photo-Fenton, in which both photo- and Fenton- activities of ZrFe₂O₅ are utilized. Analysis of decolorization experiments has also provided interesting mechanistic insight into interactions and synergies between different competing mechanisms of hybrid AOPs.