Enhancing removal of acid orange II by heterogeneous catalytic ozonation using ZnO nanoparticles-modified fly ash composite

Abstract In this study, heterogeneous catalytic ozonation using fly ash (FA) modified ZnO nanoparticles to the decolorization of acid orange II (AOII) was studied. The combination of ZnO and fly ash via an incipient wetness impregnation method to form ZOFA composites created a synergistic effect that led to efficient catalytic ozonation activity towards AOII degradation and decolorization compared with individual ozonation processes. From the experimental results, ZOFA composite with the optimal weight ratio between ZnO NPs and FA was 20 wt% (denoted as ZOFA-20) that exhibited outstanding catalytic ozonation activity. Moreover, through other investigations including initial pH conditions and catalyst dosage, AOII could be effectively and optimally eliminated by 0.5 g of ZOFA-20 with an initial pH value of 11. The corresponding k value was measured as 0.248 min− 1 with a maximum TOC removal content of 77.27%. Besides, ZOFA-20 could show high catalytic ozonation activity even at highly concentrated AOII concentrations while it could also retain its excellent stability and reusability over 5 continuous AOII removal cycles. From the experimental and electron paramagnetic resonance (EPR) results, hydroxyl radical (•OH) was the main active species during the catalytic ozonation of AOII. The present study provides a promising approach to prepare novel composite-based fly ash that would be applicable for removing azo dye and other dye pollutants in water via a catalytic ozonation strategy.