Adsorption of phosphate on surface of magnetic reed: characteristics, kinetic, isotherm, desorption, competitive and mechanistic studies

Abstract

A magnetic biocomposite was prepared by Fe₃O₄ in situ co-precipitation and amine functionalization processes by using virgin reed as starting material. The characteristics of amine cross-linked magnetic reed (ACMR) as well as phosphate-loaded/regenerated ACMR were evaluated by using FTIR, TEM, SEM, VSM and XPS. Adsorption properties of ACMR for phosphate were also determined. Results indicated that the average particle diameter of present Fe₃O₄ in ACMR was approximately 10.4 nm. Analysis of XPS indicated that uptake of phosphate by ACMR was based on N⁺ in quaternary nitrogen N 1s. The atomic ratio of Fe and N in regenerated ACMR was about 0.41% and 10.75%, which was a bit lower as compared with that in clean sample (0.46% and 11.02%); this indicated a small loss of Fe₃O₄ and amine groups on surface of ACMR during adsorption–desorption cycles. The calculated Q_max from Langmuir model were about 31.4–37.0 mg g⁻¹ at 20–45 °C, which has shown comparable phosphate uptake capacity by contrast with most reported work. In addition, competitive adsorption revealed that the inhibition effect was more significant for anions with greater tendency to undergo ion exchange reaction (e.g. sulfate, nitrate and chloride) with quaternary ammonium groups on ACMR.