Visible light-driven selective oxidation of multiple organic matters by photocatalysis of BiOX (X = I, Br): New insights into the role of oxygen vacancy generation and electron gain/loss properties of matter

Abstract

Realizing better photocatalytic activity of materials by various strategies has always been a hot topic in the field of environmental catalysis. However, the complex heterogeneous composition and preparation process of catalysts undoubtedly limit their potential for practical pollution control. Therefore, clarifying the selective photocatalytic mechanism of pristine semiconductor oxide and the crucial relationship between catalysts structures and physical–chemical characteristics of target pollutants become more necessary. In our study, based on the combination of density functional theory (DFT) calculation and characterizations, the differences in photocatalytic degradation behavior and intrinsic mechanisms of common organic pollutants including ciprofloxacin (CIP), tetracycline (TC), Rhodamine B (RhB) and bisphenol-A (BPA) over the pristine BiOBr and BiOI were investigated, thereby clarifying the crucial relationship and synergistic effects between photocatalysts microstructure and pollutants characteristics. Under the same reaction conditions, 10 %-BiOBr (BiOBr obtained from the hydrothermal treatment in a 10 % ethylene glycol solution environment) exhibited better degradation performance of CIP (73 %), TC (67 %) and RhB (95 %) than that of BPA (28 %). While 10 %-BiOI (BiOI obtained from the hydrothermal treatment in a 10 % ethylene glycol solution environment) exhibited better degradation performance of BPA (88 %) than those of CIP (27 %), TC (60 %) and RhB (41 %). The obvious selective degradation difference of various target pollutants over the 10 %-BiOBr and 10 %-BiOI could be ascribed as follows: (i) Under the same synthesis condition, the differences in BiO bond lengths due to the halogen layers resulted in BiOI being more susceptible to generate oxygen vacancy than BiOBr, thereby boosting the non-radicalpathway degradation of electron-rich pollutants. (ii) The generation of radicals and non-radicals during photocatalysis were directly affected by the electronic characteristic discrepancies of the pollutants, thereby changing the main degradation pathways of organic matters. Results indicated that the electron-deficient pollutants including CIP, TC and RhB tended to be degraded by radical pathway. On the contrary electron-rich pollutant BPA was more susceptible to degradation via direct electrons transfer to oxygen vacancies of 10 %-BiOI. Our study supplied new insight into adopting pristine photocatalysts based on the difference of oxygen vacancy for selectively degrading various pollutants with different donating/losing electron ability, the corresponding mechanisms and degradation pathway could provide theoretical reference for practical application of pristine photocatalysts.