Enhancing catalytic ozonation activity of aluminum oxide via fluorine-doping engineering for water purification

Abstract

Manipulating the electron density of active sties to develop highly efficient catalysts is expected to be one of the most ideal approaches to facilitate overall efficiency of the heterogenous catalytic ozonation (HCO) process. In this study, we demonstrate a fluorine-doping engineering to optimize the HCO activity of aluminum oxide through an improved sol–gel method using NH4F (NF-Al2O3) and HF (HF-Al2O3) as the fluorine source. We provide evidence that the fluorine atom is successfully incorporated into crystal structure of NF-Al2O3 via the formation of Al-F-Al bonds, accompany with the generation of oxygen vacancy defects, which allow for ozone molecule adsorption and activation. In contrast, the fabricated HF-Al2O3 only features the presence of AlxFy·nH2O instead of Al-F-Al structure probably due to the unexpected etching reaction. The introduction of fluorine atom largely decreases the local electron density of neighboring Al of NF-Al2O3 catalyst evidenced by the two-fold increment in the amount of strong Lewis acid sites. Consequently, the HCO activity of NF-Al2O3 catalyst is found promotion by 42.9% over pure Al2O3 in terms of the degradation kinetic rate constant (kobs). The NF-Al2O3 catalyst exhibits a powerful capacity to selectively catalyze ozone molecule into singlet oxygen (1O2), rendering the HCO system with high-tolerance to coexisting water matrixes (e.g., humic acid, chlorine ions, carbonate). Moreover, NF-Al2O3 initiated HCO system can effectively purify wastewaters from textile industry with high-quality enough to be reused for textile dyeing. Therefore, our study provides a novel strategy to develop effective HCO catalysts for promoting wastewater treatment and reuse.