Title: Phosphoric acid-modified banana peel and rice straw as low-cost sorbents for the removal of Pb(II) and Cu(II) from aqueous solution
Authors: Pham Hoang Giang, Do Quang Huy, Phan Quang Hung, Nguyen Ha Dan Khanh
Volume: 10
Issue: 9
Pages: 316-323
Publication Date: 2026/09/28
Abstract:
Agricultural by-products are attractive precursors for low-cost heavy-metal sorbents, yet their native binding capacity is usually modest and comparative data for materials treated under one and the same modification protocol remain scarce. In the present study, eight by-products collected around Hanoi, Vietnam - sugarcane bagasse, banana peel, coir, sawdust, corn husk, rice husk, rice straw and peanut shell - were esterified with H3PO4 in the presence of urea and screened for cation-exchange capacity using methylene blue as a cationic probe. Phosphoric acid modification raised methylene blue removal by a factor of 1.6-5.0 relative to the corresponding unmodified material, and the two best performers, modified banana peel (79.44%) and modified rice straw (81.75%), were selected for batch adsorption of Pb2+ and Cu2+. Scanning electron micrographs showed that the outer layer of both materials was disrupted by the treatment, exposing the underlying fibre bundles. Metal uptake increased with pH up to the working value of pH 5, and equilibrium was reached within 60-180 min. The equilibrium data were described better by the Langmuir (R2 > 0.91) than by the Freundlich model (R2 ? 0.88), giving maximum capacities (Qmax) of 121.95 mg Pb2+/g and 53.2 mg Cu2+/g for modified banana peel, and 55.56 mg Pb2+/g and 46.3 mg Cu2+/g for modified rice straw; except for Pb2+ on modified rice straw, these values lie beyond the highest measured uptake and are therefore upper estimates. These findings identify phosphorylated banana peel as the more promising of the two sorbents and warrant further work on sorbent characterisation, regeneration and real wastewater.