Synthesis of mixed matrix membrane utilizing robust defective MOF for size-selective adsorption of dyes

MOFs/polymer hybrid membranes combine the unique structural activity of MOFs with the excellent carrying capacity of porous polymers, exhibiting remarkable adsorption/separation properties. In this study, a robust defective MOFs material Al-UiO-66 was synthesized by doping Al into UiO-66 material through one-step in-situ synthesis method, which increased the pore size distribution of MOF material. Al-UiO-66 nanoparticles were blended within polyvinylidene fluoride (PVDF) casting solution to fabricate a novel Al-UiO-66-MMM using the phase conversion techniques. The Al-UiO-66-MMM demonstrated excellent solid-liquid separation, avoiding the shortcomings of MOFs such as potential secondary pollution and poor separation performance. It was investigated for the adsorptive removal of six typical dyes with different charges and molecular sizes including cationic Malachite Green (MG), Rhodamine B (RhB), Janus Green B (JGB) and anionic Methyl Orange (MO), Methyl Yellow (MY) and Reactive Black 5 (RB5). Al-UiO-66-MMM exhibited much enhanced removal rates exceeded 99 % for MO, MY, and MG while low adsorption for large molecular dyes RhB, JGB, and RB5, indicating a size exclusion effect. In the separation process of binary mixed dyes with different molecular sizes, the removal rates of the target dyes all reached around 99 %, demonstrating excellent selective adsorption. Additionally, the membrane exhibited outstanding recyclability with over 90 % removal rate with high selectivity after 10 cycles. The outstanding stability, efficient selectivity, sustained cyclic adsorption performance, and good portability, makes Al-UiO-66-MMM highly promising for applications in treating dye-containing wastewater.