Thermochemical upcycling of banana stem fibers into biochar and activated carbon for rapid, high-capacity removal of methylene blue from water

The toxicity and environmental persistence of synthetic dyes present significant challenges for the treatment and disposal of dye-contaminated wastewater. In this context, agricultural residues as bio-based adsorbents are gaining increasing significance due to their lower cost and high adsorption capacity. The feasibility of utilizing banana fibers, which are available in abundance as agriculture waste, and are rich in cellulose and hydroxyl functional groups is investigated as an adsorbent for cationic dye removal in the present study. Low surface area, less reusability potential and low adsorption capacity of raw fibers limits its applicability in adsorption process. Therefore, this study explores the potential of thermochemically upcycled banana fibers in removing methylene blue, a commonly used dye, from aqueous solutions. The technique adopted for upcycling was converting raw banana fiber (RBF) into biochar (BBF) and activated carbon (ABF), thereby enhancing its adsorption capacity. Adsorbent surface characterization was performed using SEM, BET, and FTIR analyses. The thermochemical treatment markedly increased the surface area of the adsorbents, with increases of approximately 183% for BBF and 362% for ABF relative to RBF. Isotherm analyses further revealed that, under optimal conditions, the adsorption capacity increased by 51.01% for BBF and 98.63% for ABF, indicating a significant enhancement in adsorption performance after thermochemical modification. In addition, ABF exhibited superior regeneration stability compared with BBF and RBF. Overall, these findings demonstrate the potential of thermochemical upcycling as a sustainable strategy for valorizing waste banana stem fibers into effective adsorbents for treating dye-contaminated water.