Optimizing the boron rejection and chlorine-resistant performance of reverse osmosis thin film nanocomposite membrane through the positioning of sheet-like nanomaterials

Thin film nanocomposite (TFN) membrane enabled by specific nanomaterials to create innovative and novel membrane structures represents a significant scientific advancement. Despite the improvement exhibited by the state-of-the-art TFN membranes, there is still a need for maximizing the potential and advantages of the nanomaterial. Surface coating and the direct incorporation of nanomaterials are the two major approaches used for the preparation of TFN membrane. Depending on the nature of the nanomaterials and the purpose of the modification, the positions of the nanomaterials, either on the surface or within the polyamide (PA) layer, can significantly affect the separation efficiency of the TFN membranes. By using a well-established two-dimensional TiO₂ as a model nanomaterial, this study systematically evaluates the effects of nanomaterials position in TFN on the physico-chemical properties, consequently the boron rejection and chlorine-resistant performance of the TFN membranes. Due to the varying degrees of alteration in the surface hydrophilicity, smoothness and charge characteristics, it was found that surface coating membrane outperformed the direct incorporation membrane in terms of water permeability and salt rejection by 4.3 % and 1.0 %, respectively. Overall, this study provides an insightful understanding of the correlation between the sheet-like nanofiller position and the corresponding physical and separation properties of the resultant TFN reverse osmosis (RO) membrane.