Acetic acid functionalized TiO2/kaolinite composite photocatalysts with enhanced photocatalytic performance through regulating interfacial charge transfer

In this study, sol-gel method modified with acetic acid (CH3COOH) was employed to facilely synthesize hydrogen functionalized TiO2/kaolinite composite. Weak acid (CH3COOH) was used to modify the surface of TiO2/kaolinite composite in order to activate TiO2 surface and generate more hydroxyl groups. The modified surface can act as Lewis acid sites to allow the physisorption of uncharged carboxyl acid groups, which is believed to be beneficial for electron injection and transfer. Using ciprofloxacin (CIP) as the target pollutant, in comparison with the use of strong acid such as hydrochloric acid (HCI) or sulfuric acid (H2SO4), it was found that CH3COOH functionalized TiO2/kaolinite composite possessed the strongest adsorption ability and exhibited highest degradation efficiency under broad spectrum (200-800 nm). Moreover, the concentration of CH3COOH required is low (0.1 mol/L) in this work. The results show that the CH3COOH treated sample exhibited much higher degradation rates than bare TiO2 or TiO2/kaolinite composite under both UV light and visible light. The kinetic constants under UV light were almost 2.61 and 1.57 times higher than those of TiO2 and TiO2/kaolinite, respectively. According to the X-ray diffraction (XRD), N-2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR) as well as Raman characterization results, it is revealed that the improved photocatalytic activity can be mainly attributed to the CH3COOH functionalization towards the TiO2/kaolinite composite. Furthermore, density functional theory (DFT) calculations were employed to explore the interface effect between TiO2 and kaolinite as well as the function of newly introduced hydrogen on the surface of the composite, which significantly contributes to better understanding the function of CH3COOH in the constructed system. On the other hand, electron spin resonance (ESR) analysis suggests that the main oxidation species in the degradation process under broad light spectrum illumination was the holes. This study also provides information about the enhancement mechanism. New insights in photocatalysts synthesis and properties adjustment based on natural minerals for the elimination of organic contaminants of emerging concern in water was successfully introduced in the present study. (C) 2018 Elsevier Inc. All rights reserved.