Incorporation of Zr-based metal-organic polyhedron into the PDA/PVDF adsorptive membrane for rapid removal of Cr(VI)

Zirconium-based metal-organic polyhedra (ZrMOPs) have gained significant attention owing to their well-defined cavities, stability and potential applications. Herein, a novel composite membrane (PDA/ZrT-1-NH2/PVDF) was developed by incorporating amino-functionalized ZrMOP (ZrT-1-NH2) into polydopamine (PDA) and trimesoyl chloride (TMC) cross-linking system. Notably, the cationic ZrT-1-NH2 cages were immobilized onto the membrane surface by a simple vacuum filtration method, which thus endowed the surface positive charge for the membrane. A pre-prepared composite membrane was used to remove Cr(VI) from the wastewater. The effects of pH, contact time, initial Cr(VI) concentration, temperature, coexisting ions competition and reusability were investigated in batch experiments. The results revealed the as-prepared composite membrane exhibited high removal efficiency of 96.6 % for Cr(VI) ions within 5 min. In addition, the adsorption rate was very fast, reaching adsorption equilibrium in less than 30 min. Finally, a possible adsorption mechanism was proposed. The adsorption process was dominated by physical adsorption accompanied by a partial reduction of Cr(VI) to Cr(III).