Removal performance of banana stem activated carbon and derivatives towards carcinogenic dye and polyethylene terephthalate microplastics

The rapid growth of plastic production and dye-intensive industries has increased the discharge of dyes and microplastics into aquatic environments, creating an urgent need for sustainable and cost-effective removal materials. This study prepared banana stem derivatives and compared the adsorption performance of raw banana stem powder (RBP), banana stem biochar (BB), and banana stem activated carbon (BSAC) for removing methylene blue (MB) and polyethylene terephthalate (PET). Comprehensive characterization using proximate and ultimate analyses, Fourier transform infrared spectroscopy, field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis, and point of zero charge determination confirmed that pyrolysis and activation produced thermally stable, highly porous materials enriched with oxygen-containing functional groups and favourable surface charge. These properties significantly enhanced adsorption performance. Batch adsorption experiments evaluated the effects of initial MB concentration (10–110 mg/L), contact time (10–1440 min), pH (2–11), and temperature (303.15–333.15 K). BSAC exhibited the highest MB adsorption capacity (316 mg g−1), followed by RBP (193.9 mg g−1) and BB (75.2 mg g−1). For PET removal, BB achieved 64.10% removal, while RBP and BSAC removed 90.67% and 92.24%, respectively. The adsorption process followed the Langmuir isotherm and pseudo-second-order kinetic model, indicating monolayer chemisorption. Thermodynamic analysis revealed that adsorption was spontaneous and exothermic. Overall, BSAC demonstrated superior performance for both dye and microplastic removal. This study highlights the potential of agricultural waste-derived materials as sustainable adsorbents for water treatment, contributing to the mitigation of dye and microplastic pollution.