Ion-imprinted covalent organic framework/PVDF mixed matrix membrane: Preparation, selective removal of Cr(VI) and its...

A Cr(VI) ion-imprinted covalent organic framework (IICOF) with a three-dimensional porous structure was developed at room temperature for the first time. The IICOF was then blended with polyvinylidene fluoride (PVDF) to synthesize a novel mixed matrix membrane for the selective removal of Cr(VI). The morphologies and properties of membranes with varying IICOF contents were characterized, demonstrating that the uniform distribution of positively charged IICOF within the membrane enhanced Cr(VI) adsorption. Increasing the IICOF content significantly improved Cr(VI) adsorption on the membrane, with the removal efficiency from 1.99 % to 91.8 %. The ion imprinting effect enabled the mixed matrix membrane to exhibit excellent selectivity for Cr(VI), even in the presence of 100-fold competing ion concentrations. Functional groups in the IICOF within the mixed matrix membrane provided the active sites with electrostatic attraction and hydrogen bonding, forming the primary driving forces for Cr(VI) adsorption. Under acidic conditions, the protonation of =N- and its conversion to =NH⁺- generated additional active sites and further enhanced adsorption. The study also identified a critical saturation point and corresponding critical initial concentration for Cr(VI) adsorption. Furthermore, the 10 %-IICOF/PVDF membrane demonstrated excellent recyclability, indicating that it is a promising candidate for the selective and efficient removal of Cr(VI).