Advances in Thin-Film Nanocomposite (TFN) Reverse Osmosis Membranes for Desalination and Boron Removal

Abstract

Thin-film nanocomposite (TFN) reverse osmosis (RO) membranes have emerged as a versatile platform for advancing desalination performance beyond conventional salt rejection. Among neutral solutes, boron remains the most persistent challenge, as its dominant species in seawater, boric acid, traverses polyamide active layers with minimal steric or electrostatic hindrance. Commercial seawater reverse osmosis (SWRO) membranes typically achieve only 40–70% rejection at pH ∼ 8, necessitating pH elevation and/or a second RO stage to meet the stringent 0.5 mg/L permeate limit. This perspective highlights layered double hydroxides (LDHs) as chemically active fillers in TFN membranes, focusing on their ability to impart boron selectivity at neutral pH. We critically analyze the roles of LDH composition, interlayer chemistry, and surface functionalization in modulating solute partitioning, diffusion, and affinity interactions within the polyamide matrix. Finally, we discuss key design considerations for LDH-based TFN membranes, including filler placement, functionalization strategies, and long-term stability under diverse desalination conditions.