Removal of phenoxy acid herbicide from water by magnetic mesoporous silicate

Abstract

Superparamagnetic iron (II,III) oxide (Fe3O4)–MCM-41 was successfully synthesised using a direct hydrothermal route and was utilised as an excellent adsorbent for the removal of the herbicide 2,4-dichlorophenoxyacetic acid from aqueous solution. The superparamagnetic mesoporous adsorbent was fully characterised using X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, nitrogen (N2) sorption and vibrating-sample magnetometry (VSM). The synthesised adsorbent exhibited a high specific surface area of 444 m2/g, making it a suitable candidate for adsorption, where it provided a higher adsorption capacity. Based on the VSM study, the recorded saturated magnetisation was 15.9 emu/g, which confirmed the viability of easily separating the adsorbent from an aqueous medium using a magnet. The ability of iron (II,III) oxide–MCM-41 to adsorb the herbicide 2,4-dichlorophenoxyacetic acid from water was tested considering various parameters, such as pH, adsorbent dosage, contact time and pollutant concentration. The effectiveness of iron (II,III) oxide–MCM-41 in removing the herbicide reached its highest peak at pH = 5, 0.05 g adsorbent, 60 min contact time and 10 mg/l 2,4-dichlorophenoxyacetic acid. The maximum removal efficiency under optimum conditions was 94.8%. Based on the experimental data and kinetic studies, the adsorption process followed a pseudo-second-order kinetic and Langmuir isotherm model.