Insights into the Adsorption and Photocatalytic Oxidation Behaviors of Boron-Doped TiO 2 /g-C 3 N 4 Nanocomposites toward As(III) in Aqueous Solution

The coupled adsorption–photocatalytic oxidation process provides a great potential scenario to enhance the removal efficiency of arsenite contaminants by converting As(III) to As(V) and simultaneous adsorption. In this study, the boron-doped black TiO 2 /g-C 3 N 4 nanocomposite is synthesized by combination of sol–gel and in situ decomposition-thermal polymerization methods as a photocatalyst for the photocatalytic oxidation and adsorption of As(III). Under dark conditions, the boron-doped samples (B-TiO 2 and B-TiO 2 /g-C 3 N 4 ) display an increase in the As(III) adsorption capacity by one order of magnitude up to circa 3.2 mg g –1 with an initial As(III) concentration of 2 mg L –1 at 298.15 K and pH 5. The adsorption kinetics of As(III) on B-TiO 2 /g-C 3 N 4 conform to the pseudo-second-order kinetic model, revealing the chemical adsorption mechanism. Under visible light irradiation, the total arsenic removal capacity is substantially improved by 20% with a removal capacity of 3.9 mg g –1 . The enhancement of arsenic adsorption is attributed to the chemical complexation and hydrogen bond, in which B–OH bonds play a dominant role. The photocatalytic oxidation mechanism of the as-synthesized B-TiO 2 /g-C 3 N 4 is attributed to the synergism of superoxide radicals, hydroxyl radicals, and photogenerated holes.