Enhanced boron rejection and permeability of thin-film nanocomposite membranes via g-C3N4-tuned diffusion and reaction

Seawater reverse osmosis (SWRO) membranes often exhibit low boron removal rates and permeability, which limits their practical effectiveness. In this study, graphite-phase carbon nitride (g-C₃N₄) nanosheets were incorporated into the polyamide (PA) layer of thin-film nanocomposite (TFN) membranes via interfacial polymerization to enhance boron removal and membrane permeability. The amino-rich g-C₃N₄ exhibited excellent dispersion in aqueous solutions, which improved compatibility with the PA layer. The incorporation of g-C₃N₄ nanosheets led to an increased effective separation area, a higher crosslinking degree, and increased hydrophilicity, while simultaneously reducing surface roughness and forming a thinner PA layer. These modifications collectively enhanced water flux, boron removal, and antifouling performance. Molecular dynamics simulations revealed that g-C₃N₄ reduced the MPD diffusion rate through hydrogen bonding interactions and steric hindrance effect of the g-C₃N₄ interfacial arrangement and also reduced boric acid diffusion. At an optimal g-C₃N₄ concentration of 150 mg L⁻¹, the boron-removal rate of the g-C₃N₄-TFN membrane in simulated seawater increased from 72.5 % (for the thin-film composite membrane) to 90.5 %, with water flux improving from 35.8 to 46.8 L m⁻² h⁻¹. Additionally, the membrane exhibited excellent water-salt selectivity, antifouling properties, and chlorine resistance. Thus, this study provides a simple and scalable approach for preparing high-performance SWRO membranes with promising potential for large-scale production.