Eco-friendly zinc-chitosan/poly(l-lactic acid)/polyurethane nanocomposites for dye removal and antimicrobial wastewater treatment

Abstract

This research explores the development of sustainable zinc-chitosan/poly(L-lactic acid)/polyurethane (ZnCS/PLA/PU) nanocomposites for the dual-purpose treatment of wastewater by removing Acid Blue 25 dye and inhibiting pathogens. The nanocomposites were synthesized at ZnCS-to-PU ratios of 4:1 (ZCPP41), 1:1 (ZCPP11), and 1:4 (ZCPP14) and feature particle sizes of 191-365 nm and zeta potentials ranging from + 39.1 to -9.7 mV. ZCPP41 demonstrates an impressive adsorption capacity of 142 ± 1.9 mg/g and 98.8% removal efficiency at pH 2, facilitated by electrostatic interactions below a pHzpc of 5.6, complemented by charge-assisted hydrogen bonding and surface complexation through chitosan's -OH and -NH₂ groups. Kinetic studies align with the pseudo-second-order model (k₂ = 0.0071 g/mg min, R² = 0.998), while intraparticle diffusion (k_ipd = 3.22 to 5.93 mg/g min^0.5, R² = 0.965) and swelling-enhanced pore filling support deeper dye penetration, corroborated by Langmuir (q_max = 142 ± 1.9 mg/g, R² = 0.956) and Freundlich (R² = 0.979) isotherm fits. ZCPP11 exhibits robust antibacterial activity, with inhibition zones of 27.0 mm against Gram-positive bacteria, surpassing gentamicin (24.3 mm), driven by the synergistic effects of Zn²⁺ and chitosan. Desorption with 0.01 M Na₂CO₃ yields 96.5-98.1% efficiency, retaining 71% activity over three cycles, underscoring practical utility. Despite biodegradability, challenges include untested efficacy in complex matrices and scalability. Future work will optimize neutral pH performance and evaluate fixed-bed systems.