Waste based chitosan membranes for dye removal

Abstract

Water contamination is an important global issue. This study explores dye removal potential of chitosan-based membranes with lemon waste and Cu²⁺, selected based on circular economy and green chemistry. Lemon waste and chitosan were used to recover Cu²⁺. Membranes were produced by solvent casting, with some treated in NaOH 1 M for structural modification and others in CuSO₄ (ac) for crosslinking. ATR-FTIR and XPS revealed chemical structure modifications. Hydrated membranes exhibited a two-order magnitude decrease in elastic modulus versus dried ones. pH of point zero charge diminished by incorporation of Cu²⁺ and increased by NaOH treatment. Lemon extract and NaOH treatment increased Cu²⁺ sorption from 500 mg/g to 1800-2500 mg/g, with minimum 3 cycles of sorption-desorption. Dye removal was studied at different concentration, times, pH and temperatures. Lemon extract boosted crystal violet sorption but reduced methyl orange sorption, while Cu²⁺ diminished crystal violet sorption without affecting methyl orange. Methyl orange (minimum 72 % removal) could be desorbed with NaOH for at least 5 cycles. Hence, sorption of dyes cannot be explained by coulombic interactions alone. Conclusively, chitosan with lemon peel extract or Cu²⁺ are a sustainable alternative, using biopolymers, waste and Cu²⁺ for sorption from wastewater. Scaling-up would be possible for Cu²⁺-chitosan membrane.

Keywords: Chitosan; Circular economy; Sorption.