Efficient arsenate capture using mixed-metal La/Zr-MOF internal complexation

Abstract

The low adsorption capacity of metal–organic frameworks (MOFs) limits their practical application in high-arsenic wastewater for adsorption owing to their insufficient active sites and suboptimal pore structure. Accordingly, we employed a one-pot hydrothermal method to synthesise mixed-metal La/Zr-MOFs with complex pore structures. Notably, the material possesses both La-BDC and Zr-BDC morphology features and integrates the advantages of monometallic MOFs through a framework symbiotic structure. This complex pore structure promotes the migration and diffusion of arsenic ions in the pore channels, improving the adsorption kinetics. Moreover, mixed-metal functional centres can expose more active sites, which is conducive to enhancing adsorption capacity. Experiments showed that mixed-metal La/Zr-BDC-4 rapidly reached adsorption equilibrium in 60 min, corresponding to a maximum adsorption amount of 694 mg g⁻¹. Batch adsorption experiments and X-ray photoelectron and Fourier-transform infrared spectroscopy analyses revealed that mixed-metal La/Zr-BDC-4 arsenates tend to form internal complexes with each other, suggesting that As(V) adsorption is an exothermic and spontaneous chemisorption process. After four adsorption–desorption cycles, the material maintained an arsenic removal rate of 85%, exhibiting its potential application in wastewater treatment. Therefore, the mixed-metal La/Zr-BDC-4 MOF is a promising material for wastewater treatment.