Preparation of MIL-53(Cr) and MIL-101(Cr)/reduced graphene oxide/polyaniline composites for Cr(VI) adsorption

The rapid development of industrialization has brought a series of difficulties and challenges to mankind, especially the heavy metal Cr(VI) pollution in water, which has become an important research topic. In the study, the reduced graphene oxide/polyaniline (rGO/PANI) material was synthetically synthesized by in-situ polymerization of polyaniline (PANI) with reduced graphene oxide (rGO) for adsorption of Cr(VI) in simulated wastewater. The Cr(VI) adsorbed on the layer of rGO/PANI utilized as metal ion center, MIL-53(Cr)/rGO/PANI (M-53/G-P) and MIL-101(Cr)/rGO/PANI (M-101/G-P) composites were prepared by hydrothermal method. The prepared composite adsorbs Cr(VI) again, and the composites were characterized by XRD, XPS, BET, and FTIR before and after adsorption, and the adsorption mechanism was elucidated by XPS. Results indicate: compared with rGO/PANI (38.98 m²·g⁻¹), the M-53/G-P (137.87 m²·g⁻¹) and M-101/G-P (70.91 m²·g⁻¹) show higher BET surface area. When pH is 2, initial concentration is 100 mg L⁻¹ and dosage is 0,10 g (per 100 mL), the maximum adsorption capacities of M-53/G-P and M-101/G-P composite materials for Cr(VI) are 81.58 and 77.76 mg·g⁻¹, respectively. The adsorption kinetics of Cr(VI) on the two composites conform to the pseudo-second-order kinetic model and the adsorption isotherm follows the Freundlich model. The adsorption mechanisms of Cr(VI) by the two materials involve electrostatic attraction, ion exchange, and complexation. This study found that M-53/G-P has promising applications in removing contaminants and purifying wastewater compared to M-101/G-P.