Biomimetic Nanocomposite Membranes for Efficient Acid Recovery from Cadmium Effluents

Abstract

The compromise of permeability and selectivity is a central paradigm in gills by which the gill filaments perform rapid intake of oxygen (O 2 ) and rejection of carbon dioxide (CO 2 ) in a benign physiological environment. Such an efficient separation in nature is a key dogma in designing biomimetic separation systems, yet the fundamental challenge of the permeability−selectivity trade-off still remains a nascence. In this study, we report a gill-inspired diffusion dialysis membrane for acid recovery from heavy metal wastewater with a high permeation efficiency of acid ions (H + ) and robust rejection of cadmium ions (Cd 2+ ) plus stable performances against repeated separations. This membrane was fabricated by vacuum filtration of a nanocomposite regime featuring natural protein nanoparticles attached to the rod-shaped attapulgites. The stacking of such anisotropic building blocks endowed the membranes with capacious channels for H + transport, while the electropositivity of proteins enabled robust rejection of Cd 2+ . The enhanced separation performance of this membrane mimicked the art of gills with gill arches, enlarging the specific area of gill filaments arresting O 2 but expelling CO 2 . As a result, the membrane exhibited a high H + dialysis coefficient (0.049 m•h −1 ) and H + /Cd 2+ selectivity (S H/Cd = 23.3) with excellent long-term operational stability and general applicability (S H/Cu = 26.3, S H/Pb = 18.1, S H/Ca = 23.3, and S H/Mg = 18.6) suitable for practical applications.