Comparative study of low-index {1 0 1}-TiO2, {0 0 1}-TiO2, {1 0 0}-TiO2 and high-index {2 0 1}-TiO2 on glyphosate adsorption and photo-degradation

Abstract

TiO2 has attracted widespread concern about its photo-catalysis in regard to water contaminant removal. However, TiO2 with different exposed facets shows considerable variation in adsorption and photo-catalysis performance. This study aims at comparatively investigating the adsorption and photo-catalysis performance of low-index {1 0 1}-TiO2, {0 0 1}-TiO2, {1 0 0}-TiO2 and high-index {2 0 1}-TiO2. The results showed that, compared to low-index TiO2, {2 0 1}-TiO2 exhibited a higher effectiveness on glyphosate (PMG) removal. In detail, the highest Langmuir adsorption capacity was observed on {2 0 1}-TiO2 (0.88, molecules/nm2). Based on 2D-COS and ATR-FTIR analysis, it is proved that the transformation sequence of each PMG functional group adsorbed on TiO2 followed different order. In addition, PMG photo-degradation on {2 0 1}-TiO2 had a higher apparent pseudo-first-order reaction constant (kapp = 3.0h−1) than other three TiO2. This is mainly attributed to a higher generation of reactive oxygen species (ROS), a larger electron transfer and oxygen reduction reaction (ORR) rate of {2 0 1}-TiO2, compared to other three TiO2, as investigated by ESR, photo-current and linear sweep voltammetry measurement, respectively. Furthermore, PMG photo-degradation on the four TiO2 was primarily due to OH. Thus, it can be reasonably inferred that the comparative investigation of high-index and low-index TiO2 can provide an integrated insight into similar adsorption and photo-catalysis behavior in the environment.