Elucidating the role of interlayer structure in the permeance-selectivity trade-off of ceramic nanofiltration membrane

Reasonable design of a rational interlayer in an asymmetric ceramic nanofiltration (NF) membrane facilitates water transport as well as solute retention. Nevertheless, the inherent relationship between the microstructure of the interlayer and the permselectivity in ceramic NF membrane remains to be unclear. In this study, a quantitative model is developed to predict the influence of the factors (i.e., particle diameter and layer thickness) controlling the structure of interlayer on the permselectivity by integrating the cake filtrated theory and Donnan-Steric Pore model with the Dielectric Exclusion model. The simulations demonstrate that interlayer thickness dominates the solute rejection rather than particle diameter that constitutes the interlayer when an appropriate top-layer structure is applied. However, the enhancement of water permeance requires simultaneous regulation of the microstructures of both interlayer and top layer. For negatively charged ceramic NF membranes, the comprehensive effect of diffusion, convection, and electro-migration is the transport mechanism of positively charged counter-ion (i.e., Na+), whereas the transport of negatively charged co-ion (i.e., SO42-) is merely dominated by diffusion. This study thereby elucidates the role of the interlayer in terms of improving the permeance-selectivity trade-off relationship, which is of great significance to the future development of a high-performance ceramic NF membrane.