REMOVAL OF POLYSTYRENE MICROPLASTICS USING FUNCTIONALIZED COCONUT FIBER ADSORBENTS

Microplastics have attracted increasing global attention as emerging pollutants that represent potential risks to the health of living organisms and threaten aquatic ecosystems. In response to the urgent need for efficient and low-cost removal methods, this work aimed the use of coconut fiber, an abundant agro-industrial waste, as an adsorbent for removing polystyrene microplastics. The fiber was evaluated in natura and after functionalization with polyethyleneimine in order to enhance its adsorption capacity. The materials were characterized using Fourier Transform Infrared Spectroscopy and point of zero charge analysis. Additionally, adsorption kinetics and isotherm studies were conducted during 24 h using an aqueous solution of 8 mg.L^-1 polystyrene and 2 g.L^-1 of adsorbents. The cationic modification of the fiber promoted the complete adsorption of polystyrene microplastics (removal efficiency; 100 ± 6.28%) after 20 h at pH 5.08 ± 0.25, 25 °C and 150 rpm, reaching its equilibrium at 20 h (adsorption capacity; 3.79 ± 0.02 mg.g^-1). To describe the adsorption process, pseudo-first-order and pseudo-second-order kinetic models were applied, with the latter showing the best correlation with the adsorption kinetics. This enhanced performance is likely attributed to electrostatic interactions established between the polyethyleneimine-functionalized fiber and polystyrene particles, which are negatively charged at pH 5.0. Also, it was applied the Langmuir and Freundlich adsorption isotherm models and observed that the Freundlich model better fit the experimental data. Therefore, this work demonstrates potential not only to contribute to the mitigation of microplastic pollution in aquatic environments but also to promote the development of alternative sustainable technologies and the valorization of agro-industrial residues, with the promise for significant global socio-environmental impact.