Bio-inspired CaCO3 coating for superhydrophilic hybrid membranes with high water permeability

Surface hydrophilicity is a prerequisite of polymer membranes used for clean water regeneration, although commercial membranes are generally manufactured from hydrophobic polymers. Here, we report a promising approach to hydrophilize hydrophobic membranes using a CaCO3-based mineral coating inspired by biomineralization. Poly(acrylic acid) (PAA) brushes, which are negatively charged and can induce nucleation of CaCO3, were tethered on the pore surface of microporous polypropylene membranes (MPPMs) via photoinitiated graft polymerization. The CaCO3-based coating was then fabricated on the pore surface by an alternate soaking process. The resulting mineral coating is composed of CaCO3 nanoparticles which are much smaller than the pore diameter and distributed evenly on the pore surface throughout the membrane, ensuring the separation performance of membranes. Due to the intrinsic superhydrophilicity of CaCO3, the hybrid membranes are superhydrophilic, and show excellent water permeability with high water flux and ultralow operational pressure. As such, this work provides a generally applicable and cost-effective chemical route to improve the surface hydrophilicity of membranes or other porous materials which have potential in chemical separation, microfluidics, catalysis and other applications.