Porous substrate affects fouling propensity of thin-film composite nanofiltration membranes

Fouling is a critical consideration for the design of thin-film composite (TFC) nanofiltration membranes. Traditional wisdom believes that fouling propensity is primarily dictated by membrane surface properties while porous substrates play little role (on the basis on the latter have no effect on the foulant-membrane interaction). Nevertheless, porous substrates can regulate the water transport pathways, resulting in uneven water flux distribution over the membrane surface. For the first time, we experimentally investigated the micro-scale water flux distribution for nanofiltration membranes with different substrate porosities and the impact of such flux distribution pattern on fouling. With gold nanoparticles as tracers, we demonstrated more evenly distributed water flux at increasing substrate porosity. This was found to effectively alleviate membrane fouling by eliminating localized hot spots of high flux. Furthermore, higher substrate porosity also effectively enhanced the membrane water permeance due to the optimized water transport pathways. Our study reveals the fundamental relationship between the micro-scale transport behavior and the membrane fouling propensity, which provides a firm basis for the rational design of TFC membranes toward better separation performance.