Mechanistic study of simultaneous arsenic and fluoride removal using granular TiO2-La adsorbent

Abstract

Naturally co-occurring arsenic (As) and fluoride (F) in groundwater have caused increasing public concerns, and their simultaneous removal is still a challenge due to the lack of efficient adsorptive materials and their competition for adsorption sites. This study fabricated a novel TiO2-La granular composite adsorbent with LaCO3OH showing orientated growth on TiO2 {100} facet. The material exhibited high As(III) (114mg/g) and F (78.4mg/g) adsorption capacities and a wide application pH, ranging 3–9, achieving a high percentage (>90%) of As(III) and F adsorption. Coadsorption experiment results demonstrated that high F concentrations inhibit As(III) adsorption, whereas the coexisting As(III) has no significant effect on F removal. The molecular-level mechanisms with EXAFS and DFT studies demonstrated that As(III) adsorption is favorable only on Ti sites as evidenced by an As-Ti distance of 3.36Å when pH<7, while La adsorption sites can also be occupied with an As-La distance at 3.42Å when pH>10. The F adsorption is pH-dependent and mainly occurred on La sites. The granular TiO2-La with high As(III) and F adsorption capacities can be used to simultaneously remove As(III) and F. The insights gained from this study shed a new light on the interaction mechanism of As(III) and F with the TiO2-La composite.