Combined use of photocatalyst and adsorbent for the removal of inorganic arsenic(III) and organoarsenic compounds from aqueous media

A novel method for the removal of inorganic arsenic(III) (As(III)), monomethylarsonate (MMA), and dimethylarsinate (DMA) from aqueous media, was proposed and investigated. This method involves the combined use of TiO2-photocatalyst and an adsorbent, which has a high ability of As(V) adsorption, under photo-irradiation. When an aqueous solution of As(III) was stirred and irradiated by sunlight or xenon lamp in the presence of TiO2 suspension, the oxidation of As(III) into As(V) was effectively attained. By use of the same photocatalytic reaction, MMA and DMA were also degraded into As(V), while the total organic carbon (TOC) in the aqueous phase was decreased. When an aqueous solution of As(III) was stirred with a mixed suspension of TiO2 and an adsorbent for As(V) (activated alumina) under sunlight irradiation, the arsenic removal reached 89% after 24 h. By use of the same photocatalyst-adsorbent system, 98% of MMA and 97% of DMA were removed. The mechanism of the removal of arsenic species by the photocatalyst-adsorbent system was discussed.