Valorisation of banana stem into N-doped activated carbon as a selective sorbent for cationic dyes and pharmaceutical contaminants

Abstract

The persistent discharge of synthetic cationic dyes and pharmaceutical residues into aquatic environments necessitates the development of sustainable, high-performance sorbents for wastewater treatment. This study presents the design and synthesis of porous nitrogen-doped activated carbon (PNAC) derived from banana plant stems, demonstrating its excellent potential as a bio-based adsorbent for wastewater purification. PNAC exhibits a remarkably high surface area of 1978.8 m² g⁻¹ and abundant nitrogen functionalities that collectively enhance adsorption capacity, selectivity, and kinetics. It achieves over 95% removal of methylene blue, brilliant green, and crystal violet within 20 minutes, outperforming commercial activated carbon (84%, 54%, and 76% removal, respectively). The adsorption process follows the Langmuir isotherm model, confirming monolayer coverage, and proceeds through hybrid pseudo-second-order and intraparticle diffusion mechanisms. Thermodynamic analysis reveals a spontaneous and endothermic adsorption nature, indicating strong interactions between PNAC and the pollutant molecules. Beyond synthetic dye removal, PNAC also exhibits efficient uptake of pharmaceutical contaminants, 79.8% for ciprofloxacin and 81.1% for cefixime, within 30 minutes and achieves 97% dye removal from real textile effluents within 15 minutes. The material demonstrates excellent recyclability, retaining approximately 80% efficiency after five adsorption–desorption cycles and 85% after eight cycles of acid-assisted regenerations. These findings highlight PNAC as a scalable, eco-friendly, and high-performance sorbent derived from agricultural waste, offering a promising platform for next-generation wastewater treatment and sustainable environmental remediation.