Self-Competitive Adsorption Behavior of Arsenic on the TiO₂ Surface

TiO₂ is a commonly used material to remove arsenic from drinking water by adsorption as well as photocatalytic oxidation (PCO). In the present paper, arsenic adsorption and PCO at different pH environments are studied on the (1 1 0) facet of rutile TiO₂ (r-TiO₂). A self-competitive adsorption (SCA) behavior of arsenic is observed; i.e., arsenic species compete to adsorb on the surface. Related DFT calculations are carried out to simulate adsorption. SCA behavior is the key to connecting calculation results with experimental results. Furthermore, PCO of arsenite is performed at different pH values. Of note, PCO is related to adsorption; namely, the adsorption process determines the whole PCO reaction speed. Therefore, SCA is also helpful for the PCO reaction. The SCA behavior is useful not only for arsenic on r-TiO₂ but also for arsenic on anatase TiO₂ (a-TiO₂). It may be helpful to further study arsenic adsorption and PCO on other materials such as Fe₂O₃ and MnO₂. The SCA behavior extends our understanding of arsenic and provides new insights into arsenic removal and its cycle in nature.