Mechanism of As(III) removal properties of biochar-supported molybdenum-disulfide/iron-oxide system

Sulfate (SO4•−) and hydroxyl-based (HO•) radical are considered potential agents for As(III) removal from aquatic environments. We have reported the synergistic role of SO4•− and HO• radicals for As(III) removal via facile synthesis of biochar-supported SO4•− species. MoS2−modified biochar (MoS2/BC), iron oxide-biochar (FeOx@BC), and MoS2−modified iron oxide-biochar (MoS2/FeOx@BC) were prepared and systematically characterized to understand the underlying mechanism for arsenic removal. The MoS2/[email protected] displayed much higher As(III) adsorption (27 mg/g) compared to MoS2/BC (7 mg/g) and [email protected] (12 mg/g). Effects of kinetics, As(III) concentration, temperature, and pH were also investigated. The adsorption of As(III) by MoS2/[email protected] followed the Freundlich adsorption isotherm and pseudo-second-order, indicating multilayer adsorption and chemisorption, respectively. The FTIR and XPS analysis confirmed the presence of Fe–O bonds and SO4 groups in the MoS2/FeOx@BC. Electron paramagnetic resonance (EPR) and radical quenching experiments have shown the generation of SO4•− radicals as predominant species in the presence of MoS2 and FeOx in MoS2/[email protected] via radical transfer from HO• to SO42−. The HO• and SO4•− radicals synergistically contributed to enhanced As(III) removal. It is envisaged that As(III) initially adsorbed through electrostatic interactions and partially undergoes oxidation, which is finally adsorbed to MoS2/[email protected] after being oxidized to As(V). The MoS2/FeOx@BC system could be considered a novel material for effective removal of As(III) from aqueous environments owing to its cost-effective synthesis and easy scalability for actual applications.