A capillary effect-inspired sponge-structured carboxymethyl cellulose aerogel layer-modified membrane for efficient separation of dye/salt under ultra-low-pressure.

In the field of wastewater treatment, the efficient separation of dyes/salts and the high-pressure drive easily results in concentration polarization and membrane contamination. In this study, inspired by the capillary effect of natural sponge structure, an aerogel layer with a bionic three-dimensional mesh porous sponge structure was designed to construct an ultra-low-pressure membrane. With the assistance of tannic acid, the carboxymethyl cellulose (CMC) aerogel layer were constructed on the surface of polyvinylidene fluoride (PVDF) membrane using the layer-by-layer cross-linking and freeze-drying methods. The unique three-dimensional mesh structure of the aerogel provides a capillary effect that accelerates the rapid transport of water molecules. The introduction of polypyrrole (PPy) to the aerogel improves the mechanical properties of the aerogel, helping avoid the collapse during the separation process. Meanwhile, the formed PPy improves the membrane separation performance. The results showed, that under near-zero pressure conditions, the modified membrane had excellent dye/salt separation performance (dye rejection >99 %, salt rejection <10 %) and high flux of pure water (101.3 L·m·h). Moreover, the membrane also maintained good long-term stability. The study demonstrated the potential of using membrane for dye/salt separation applications by constructing bionic sponge-structured aerogels having capillary effect and good mechanical strength on membrane.