Enhancing Zeolite X−Polyamide Compatibility in Thin-Film Nanocomposite Forward Osmosis Membranes via Decoration with N-Doped Graphene Quantum Dots

Abstract

The integration of hydrophilic, porous, and polymer-compatible nanofillers into thin-film nanocomposite–forward osmosis (TFN-FO) membranes is a promising strategy for enhancing water treatment efficiency. This research focuses on synthesizing an N-doped graphene quantum dots@zeolite X (N-GQDs@Z) nanocomposite by decorating Z with N-GQDs to improve the compatibility of pristine zeolite with the polyamide (PA) selective layer while exploiting the complementary properties of both components. The as-synthesized N-GQDs@Z nanocomposites were embedded into the PA layer of TFN-FO membranes during the interfacial polymerization. The findings reveal that N-GQDs@Z effectively modulates the surface properties and structure of the PA skin layer, causing enhanced hydrophilicity, reduced thickness, controlled roughness, and the formation of a continuous, defect-minimized rejection layer. With the optimal addition of N-GQDs@Z (0.010 wt %), the water flux increased to 31.62 LMH in FO mode, approximately 1.64 times that of the unmodified TFC membrane, accompanied by a high selectivity of 0.36 g/L (31% improvement). The augmentation in water/ion separation efficiency stems from improved N-GQDs@Z/PA interfacial compatibility, enhanced surface hydrophilicity, shorter transport pathways associated with the thinner PA layer, and the potential contribution of transport channels within N-GQDs@Z, whose effective pore accessibility may be regulated by the surrounding PA matrix. Moreover, the top-performing membrane exhibited enhanced antifouling performance against both bovine serum albumin and sodium alginate, with flux recovery ratios of 89.4% and 87.7%, respectively, and substantially reduced flux decline compared with the pristine TFC membrane. The optimized TFN-QZ2 membrane also exhibited excellent long-term operational stability with minimal Al leaching under simulated seawater desalination conditions, confirming the enhanced stability of the incorporated N-GQDs@Z nanofiller within the PA layer. This study demonstrates that N-GQDs@Z nanocomposites provide an effective strategy for simultaneously improving permeability, selectivity, antifouling behavior, and the long-term stability of TFN-FO desalination membranes while addressing the compatibility limitations of conventional zeolite fillers.