Removal of arsenic from drinking water by photo‐catalytic oxidation on MoO_x/TiO₂ and adsorption on γ‐Al₂O₃

Abstract

BACKGROUND A typical approach for removing As from drinking water includes a pre‐oxidation step to transform the more toxic As(III) to As(V) and a subsequent separation process for As(V) removal. Unfortunately, typical oxidants result in the formation of toxic oxidation by‐products, so alternative options, such as TiO2 photocatalysis, have been investigated. But As(V) produced by oxidation of As (III) remains adsorbed on the catalyst surface, thus limiting process efficiency. In this work a new catalyst based on molybdenum oxide supported on titania (MoOx/TiO2) was investigated to overcome this drawback. RESULTS The complete photocatalytic oxidation of As(III) (5 mg L−1) to As(V) took place after 120 min exposure to UV‐A light. Moreover, the removal of As(V) by adsorption treatment downstream of the photocatalytic process was more effective (90% by γ‐Al2O3 after 10 min) compared with the combined photocatalysis–adsorption process. Finally, the experimental set‐up with UV LED irradiation was found to be more effective (96% As(III) converted) than the UV‐A light system (75% As(III) converted). CONCLUSION Photocatalytst did not adsorb As(V) which was completely released into the solution, thus preserving its surface activity and, consequently, drastically reducing operating costs related to catalyst reactivation. © 2014 Society of Chemical Industry

Glass beads immobilized doped TiO2 NPs with enhanced adsorption efficiency for arsenic(III) from aqueous solution

“…Meanwhile, As(III) show a low adsorption performance to various adsorbents compared to As(V) [26]. Generally, As(III) exists in anaerobic waters while As(V) present in aerobic waters [8,25]. Commonly used technologies for the removal of arsenic from drinking water including separation processes (i.e.…”

“…Commonly used technologies for the removal of arsenic from drinking water including separation processes (i.e. coagulation/filtration), ion exchange and adsorption, however, the disposal of arsenic-bearing wastes obtained from these methods are serious problems [4,8]. Therefore, pretreatment such as oxidation of As(III) to the less toxic As(V) are usually required for the adsorption removal processes.…”

“…Therefore, pretreatment such as oxidation of As(III) to the less toxic As(V) are usually required for the adsorption removal processes. Different oxidants such as O 3 , H 2 O 2 , MnO 2 , chlorine, chlorine dioxide, dichloroamine (NHCl 2 ), and ferrate (FeO 4 2− ) were previously used for the oxidation of As(III) to As(V) [8,26]. Unfortunately, conventional oxidants, especially chlorine, chlorine dioxide and ozone resulting in various drawbacks including limited removal efficiency, expensive reagents and dangerous oxidation by-products [20].…”

“…Adsorption process is considered to be the best available technique for the removal of arsenic. Heterogeneous photocatalysis, using TiO 2 NPs has been used as an alternative for the adsorption of arsenic from drinking water [8]. Previously reported study indicated that modified TiO 2 NPs not only adsorb both the species but also photo-oxidizes As(III) species to As(V) followed by adsorption [2,8,26].…”

“…The works Miller and Zimmerman [18] showed that TiO 2 impregnated on chitosan beads successfully posed their arsenic sorption ability as a photocatalytic sorbent. Doped TiO 2 being a good light induced photocatalyst over a wide range of pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) showed good affinity towards arsenic adsorption [5].…”