Dissecting the role of nanomaterials on permeation enhancement of the thin-film nanocomposite membrane: ZIF-8 as an example

In recent years, the incorporation of nanoparticles in nanofiltration membranes has received extensive attention as a practical approach to improve membrane performance. However, previous studies attributed the enhancement of TFN membrane performance primarily to the advanced properties of nanoparticles and the structural impact on the polyamide layer, while ignoring the influence and contribution of the substrate. This study provides compelling evidence that the effect on the substrate of blending nanoparticles contributes to the enhancement of membrane permeability. We quantified the changes in permeation resistance composition of the TFC and TFN membranes before and after heat treatment by a resistance-in-series model, combined with the addition of polyvinylpyrrolidone. After incorporation of ZIF-8, the permeation resistance of substrate decreased from 0.177 h bar m(-1) to 0.0313 h bar m(-1) after heat curing, while that of PA layer decreased from 0.1375 h bar m(-1) to 0.0972 h bar m(-1). In addition, we removed the PA layer of TFC and TFN membranes by acid hydrolysis. The results indicated that the PWP of TFN membrane were continuously greater than that of the TFC membrane, which supports our conclusion that nanoparticles impacted the shrinkage of substrate during heat curing. The current study provides a novel mechanistic understanding of the improvement of TFN membrane performance by nanoparticles.