Sustainable Bio-Adsorbents From Banana Post-Harvest Agricultural Residues: Kinetics, Equilibrium, and Mechanism Prospection of Methylene Blue Dye Adsorption

Water pollution from industrial-colored effluents, generated by large volumes of liquid effluents containing synthetic dyes, generally harmful and non-biodegradable, affects environmental biota and human health. Considering the potential use as bio-adsorbents of agro-industrial residues, in the present work insights into the kinetics, equilibrium, and mechanism of the methylene blue (MB) dye adsorption by six bio-adsorbents produced from the post-harvest residues from the banana tree, a widely cultivated crop in Brazil, were investigated. The six prepared bio-adsorbents were tested to verify the adsorption capacity as gross residues, after carbonization, and after alkaline-chemical activation. Bench-scale experiments conducted at different conditions showed that experimental data were better described by the Langmuir isotherm, by the intraparticle diffusion model (with external diffusion being the dominant step), followed by the pseudo-second-order model, indicating the predominance of monolayer chemisorption. In addition, maximum adsorption capacities ranged between 10.55 and 25.51 mg/g, with a higher dye removal rate at alkaline pH. The adsorption of the MB dye onto the six produced bio-adsorbents occurred through both polar and nonpolar interactions. The overall study indicated that both the pseudo-stem and the leaves from post-harvest banana crops could be a cost-effective natural bioresource for producing efficient and sustainable bio-adsorbents for treating colored liquid effluents.