Modifying the electronic structure of hematite to be an efficient adsorbent for the removal of 2,4-dichlorophenoxyacetic acid from water and food samples

Abstract

The widespread use of 2,4-dichlorophenoxyacetic acid (2,4-D) in agriculture has raised significant health and environmental concerns, highlighting the need for effective removal techniques. In this study, we propose a strategy to modify the electronic structure by doping zinc into the hematite structure (ZDH) via a hydrothermal method for the removal of 2,4-D from real samples. The synthesized adsorbent was thoroughly characterized using XRD, FTIR, SEM, elemental mapping, and XPS to confirm structural and surface modifications. The highest adsorption capacity for 2,4-D was found to be 123.5 mg g⁻¹ when using the 4% Zn-doped hematite (ZDH4) adsorbent. The adsorption of 2,4-D was best explained by the Langmuir isotherm model, while the kinetics were best described by the pseudo-second-order model. The ΔH° of +65.6 kJ mol⁻¹ indicated an endothermic process and a chemisorption mechanism, while the negative ΔG° values confirmed that the adsorption process is spontaneous. The as-prepared adsorbent exhibited remarkable reusability, maintaining up to 95% efficiency after four cycles of adsorption–desorption processes. ZDH4 achieved impressive adsorptive removal efficiencies of 98.9%, 99.2%, and 99.6% when applied to real samples, including river water, onion, and potato, respectively, using 60 mg of adsorbent at pH 3. The adsorption mechanism was primarily attributed to hydrogen bonding, electrostatic interactions, and van der Waals forces, as evidenced by post-characterization using FTIR, XPS, and XRD. This study highlights the design of a highly efficient adsorbent for removing pollutants from aqueous environments and real samples.