Green kaolin-tailored hydrophobic composite membrane for efficient desalination of high-salinity water

This study reports a novel approach to tune the surface and activate ceramic-polymeric based membranes from widely available and naturally occurring kaolin materials for the desalination of highly saline water via membrane distillation. Electrospraying was used to endow the membrane surface with a fine distribution of silica particles to build on roughness and enhance the grafting of long-chain (F21) fluoroalkyl silane (FAS). Interestingly, the adopted approach significantly transformed the surface properties from hydrophilic with water contact angle WCA ∼ 40° to superhydrophobic nature with WCA ∼ 160° along with significant increase in the liquid entry pressure. In air-gap membrane distillation with 70,000 ppm NaCl feed solution, the developed membranes exhibited a stable salt rejection (∼ 99.99 %) and a high water permeate flux of 9.3 kg/m²h. Notably, the membranes developed via the adopted approach outperformed direct FAS-modified kaolin membranes and other reported ceramic-based membranes. Hence, electrosprayed silica and subsequent FAS treatment approach on the membrane surface can effectively activate and make way for actual applications of the ceramic-based membranes for the desalination of highly saline water.