Removal of p-arsanilic acid by an amino-functionalized indium-based metal-organic framework: Adsorption behavior and synergetic mechanism

Organoarsenic compounds are emerging contaminants because of their considerable solubilities in water and the highly toxic inorganic arsenic species formed during their biotic and abiotic degradation in the natural environment. Herein, the adsorption of p-arsanilic acid (p-ASA), a typical organoarsenic compound, was studied by employing an amino-functionalized indium-based metal-organic framework (NH2-MIL-68(In)) and pristine MIL-68(In). Adsorption batch experiments reveal that NH2-MIL-68(In) has a higher adsorption capacity (401.6 mg g(-1)), affinity (0.0552 L mg(-1)), and adsorption rate (5.79x10(-4)g mg(-1) min(-1)) toward p-ASA than those of pristine MIL-68(In). Moreover, the adsorption of p-ASA was spontaneous and exothermic, and obeyed a pseudo-second-order model with intraparticle diffusion. The adsorption mechanism is proposed to involve synergism between pi-pi stacking and hydrogen-bonding interactions. The NH2 moiety introduced into the MIL68(In) greatly improves its adsorption performance by enhancing hydrogen bonding. This study provides an important theoretical and experimental basis for the application of MOFs to the removal of organoarsenic compounds such as p-ASA.