Arsenate and arsenite removal using nano.TiO2-feldspar impregnated chitosan: pH-dependence and UV irradiation studies

In this study, an environmentally friendly bio-based photoactive composite, nano.TiO2-feldspar impregnated chitosan, has been successfully tested for arsenic removal. The effect of initial solution pH on the adsorption of both arsenate and arsenite is investigated. No significant effect of pH on arsenite uptake was observed over studied pH range (4-10), which can be due to the dominant neutral H3AsO3 species in most of the pH range. In the case of arsenate uptake, a slight pH-dependence was observed. Arsenate predominantly appears as negatively charged species, H2AsO4− and HAsO42−, under this pH range which can favor its adsorption process by the positively charged surface of the composite in acidic medium. However, unlike other TiO2-based adsorbents, the composite was able to remove arsenic in a wide range of pH (> 70% removal efficiency). Due to the photo-catalytic characteristic of TiO2, the effect of UV irradiation on both arsenate and arsnite removal by the composite was explored. It was observed that UV irradiation results in enhanced arsenic removal for both species. In addition to the improved properties compared with chitosan, the developed composite would also eliminate the need for an energy intensive post-filtration, which is needed in the case of nano-sized TiO2 application as adsorbent. Therefore, this composite can be superior to each of its precursor materials from the perspective of implementation for arsenic remediation.