Arsenite is a carcinogen in groundwater in many places worldwide. Adsorption and photooxidation on TiO2 nanomaterials provide a promising technique for arsenite removal. Though the adsorption mechanism is well known to involve the formation of a bidentate binuclear surface complex, even TiO2 of the same anatase phase from different sources exhibit distinct adsorption and photo-catalytic capacities. The lack of conformity of many experimental observations with the general belief that particle size or surface area regulates TiO2 adsorption and photo-catalysis motivates our study. Our results from multiple complementary characterization techniques suggest that anatase {001} facets have stronger Lewis acid sites than those on {101} facets, resulting in a higher As adsorption affinity (Figure 1). Density functional theory (DFT) calculations confirmed that the As surface complex is more energetically favorable on {001} than on {101} facets. In addition, the strong interaction of {001} facets with molecular O2 facilitates the transfer of photo-excited electrons to the adsorbed O2 to generate superoxide radical (O2●-), which is the primary As(III) oxidant as evidenced by our radical-trapping experiments. Meanwhile, the oxygen vacancies on {001} facets could expedite the interfacial electron transfer and electron-hole separation, which promote the generation of O2●- and ultimately catalytic efficiency. The insights gained from this study provide a firm basis for the proposition that As adsorption and photoactivity can be mediated by tailoring the exposed TiO2 facets, which is of essence in the design and application of TiO2-based environmental technologies.

TiO2 facets determine arsenic adsorption and photo-oxidation

252nd National Meeting (2016)

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