Lignosulfonate and chitosan-based nanoparticles for heavy metal ions removal via forward osmosis process

Treating industrial and municipal wastewater has become crucial for addressing the global challenge of freshwater scarcity. Forward osmosis (FO) has emerged as a promising membrane-based technology for this purpose. However, developing high-performance FO membranes remains essential to enhance water flux and selectivity. In this study, chitosan (CS) and sodium lignosulfonate (LS) were covalently cross-linked to produce CS-LS nanoparticles. These nanoparticles were subsequently embedded into the polyamide (PA) selective layer during interfacial polymerization to fabricate thin-film nanocomposite (TFN) membranes. The impact of CS-LS nanoparticle concentrations on membrane morphology, surface characteristics, and FO performance was systematically evaluated. SEM analysis confirmed that incorporating CS-LS nanoparticles resulted in a smooth, thin PA layer. Among the fabricated membranes, the TFN-CLS-2 membrane (modified with 400 ppm of CS-LS nanoparticles) exhibited optimal performance, significantly enhancing water flux (18.5 LMH) and improving selectivity. Additionally, the TFN-CLS-2 membrane exhibited higher rejection of heavy metals (99.7 % for Cr³⁺ and 98.2 % for Pb²⁺ ions) than the TFC membrane (95.4 % for Cr³⁺ and 94.2 % for Pb²⁺ ions). The zwitterionic properties of CS-LS nanoparticles endow the PA layer with hydrophilicity and enhance the Donnan mechanism's ion rejection. These results demonstrate a promising, potentially sustainable strategy for efficient wastewater treatment and heavy-metal removal by fabricating high-performance TFN-FO membranes.