Preparation of MIL-100 via a novel water-based heatless synthesis technique for the effective remediation of phenoxyacetic acid-based pesticide

An iron-based metal-organic framework (MOF), MIL-100(Fe) has been synthesized by a novel water-based heatless recipe. The physical-chemical qualities of MIL-100(Fe) were examined by X-ray diffraction, Field Emission Scanning Electron Microscopy, Nitrogen adsorption-desorption isotherm, Thermogravimetric Analysis and Fourier Transform Infrared Spectroscopy. With a high specific surface area of 1,893 m2/g, the crystalline MIL-100(Fe) exhibited an extraordinary performance for the adsorptive removal of 2,4-dichlorophenoxyacetic acid (2,4-D) pesticide from the aqueous solution under laboratory and on-site conditions. The adsorption equilibria have been simulated by the nonlinear Langmuir, Freundlich, Sips, Dubinin–Radushkevich, and Redlich–Peterson isotherm models, with a monolayer adsorption capacity for 2,4-D of 858 mg/g. The adsorption kinetics was rapid, with exceeding 50% of the adsorbate loading has been completed within the first 5 min of contact time, and best described by the pseudo-second order kinetic equation. Further analyses with the Bangham, Vermeulen, and intraparticle diffusion models concluded that intraparticle pore diffusion is the controlling mechanism, but it is not the sole rate-limiting step. MIL-100(Fe) retained the adsorptive performance in the 2,4-D loaded tap water and lakewater samples. The profound effects with solution pH and ionic strength on the adsorptive uptake suggested that the prevailing interaction was the electrostatic attraction between the deprotonated 2,4-D and positive-charged MIL-100(Fe). The adsorption process was spontaneous with favorable enthalpy and entropy changes as the thermodynamic driving force. Water stability test illustrated negligible iron leaching from the Fe-MOF. MIL-100(Fe) adsorbent could be reused for at least 5 times, with minor deterioration in the adsorptive uptake via simple solvent stripping. The high adsorptive potential and well-developed porosity, supported by the sustainable preparation methodology, rendered MIL-100(Fe) a promising adsorbent for the effective decontamination of water pollutants.