Synergistic Role of Functionalized Chitosan Nanoparticles and Aliquat 336 in Poly(Vinylidene Fluoride-co-Hexafluoropropylene) (PVDF-HFP) Polymer Inclusion Membranes for High-Efficiency Gold(III) Transport

The efficient recovery of gold from acidic aqueous solutions is vital for sustainable resource management and high-value metal recycling. In this work, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer inclusion membranes (PIMs) incorporating chitosan (CS) nanoparticles (0–2.0 wt.%) and Aliquat 336 as the ionic carrier were fabricated via solvent casting and comprehensively characterized. FTIR analysis confirmed intermolecular interactions between CS and PVDF-HFP through hydrogen bonding, while SEM revealed that moderate CS loading (1.5 wt.%) enhanced surface roughness and pore uniformity, whereas excessive loading (2.0 wt.%) induced nanoparticle aggregation. Contact angle and water uptake measurements showed progressively improved hydrophilicity with CS incorporation, correlating with increased aqueous phase accessibility. Thermogravimetric analysis and Coats–Redfern modelling indicated a slight reduction in thermal stability and activation energy with increasing CS content, attributed to thermally unstable CS functional groups and disruption of PVDF-HFP crystallinity. Gold adsorption experiments analyzed by ICP-OES demonstrated consistently high removal efficiencies for all membranes, with a maximum of 99.92% at 2.0 wt.% CS. Kinetic analysis revealed excellent fitting of both pseudo-first-order (PFO) and pseudo-second-order (PSO) models (R ²  ≥ 0.981). The highest adsorption rate constants were observed at 1.5 wt.% CS, confirming rapid uptake dominated by a chemisorption mechanism. Overall, moderate CS incorporation (1.5 wt.%) provided the optimal balance between enhanced hydrophilicity, ion-binding capacity, and structural integrity, offering valuable insights for the design of sustainable, bio-based PIMs for efficient precious metal recovery.