Sustainable modification of sugarcane bagasse with a novel banana peel ash extract for enhanced ammonium adsorption

Excessive ammonium (NH₄⁺-N) in aquatic environments poses a major ecological challenge, especially in regions that are reliant on intensive agriculture activity. This study developed a simplified waste-based strategy for modifying sugarcane bagasse biochar using a banana peel and banana ash extract to improve ammonium adsorption. Both pre- and post-treatment with acidic and basic extracts were evaluated, and pre-treatment using the basic extract (SC-Pre-B) showed the best performance. Physicochemical characterization indicated that modification enriched the biochar with oxygen-containing functional groups and alkali metal species, and increased the surface negativity (ζ-potential= − 52 mV), despite a reduction in the BET surface area from 123.62 m2 g− 1 to 1.0 m2 g− 1. Batch adsorption experiments showed that SC-Pre-B achieved an experimental maximum adsorption capacity of 17.11 mg g− 1. The Langmuir-Freundlich model provided the lowest RSS, AIC, and BIC values, although the small difference from the Langmuir model indicated that both models described the adsorption data reasonably well. The pseudo-second-order model best described the overall adsorption kinetics, while the segmented intraparticle diffusion analysis indicated that diffusion contributed to, but did not solely control, adsorption. The improved performance was mainly associated with increased surface negativity, oxygen-containing groups, and exchangeable mineral sites, which suggested that electrostatic attraction and non-specific cation exchange were the primary contributors of NH4+-N uptake, with hydrogen bonding acting as a secondary interaction. SC-Pre-B retained approximately 57% of its initial adsorption capacity after five water regeneration cycles, corresponding to a 43% capacity loss. These results indicated that banana peel-ash modification is a promising waste-based technique that can improve ammonium’s adsorption by biochar; however, further validation using real wastewater, better selectivity testing, and the optimization of the regeneration protocol must be considered before we can confirm practical application. Direct FTIR/EDS analysis verified the oxygen-rich and alkali-metal nature of the extract. Banana peel-ash modification improved NH4+-N uptake despite reduced BET surface area. SC-Pre-B achieved 17.11 mg g− 1 NH4+-N adsorption under a 24 h operational endpoint. Langmuir-Freundlich gave the lowest RSS, AIC, and BIC, but Langmuir remained comparable. K+ competition and water regeneration revealed selectivity and reusability limitations.