An effective and selective stable metal-organic framework adsorbent (Al-MOF-5) for the removal of fluoride from water

A novel aluminum (Al)-containing Al-MOF-5 metal-organic framework (MOF) material for the removal of fluoride from the water was prepared using a hydrothermal method. The structure of the resulting product was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetry, Brunauer, Emmett, and Teller nitrogen adsorption, Fourier transform-infrared spectroscopy, and X-ray photoelectron spectroscopy methods. In batch tests, the effects of adsorbent dosage, pH, and temperature were studied. Result showed that the maximum adsorption capacity of adsorbent for fluoride was 46.08 mg/g. The Langmuir isotherm model and pseudo-second-order kinetics fitted the adsorption process well and the thermodynamics indicated that the adsorption of fluoride on the material was spontaneously endothermic. The Al-MOF-5 displayed a high removal rate of more than 70% at different pHs, and the only PO43- could affect its adsorption efficiency for fluoride. Finally, Al-MOF-5 that had been regenerated six times in NaOH solution at a concentration of 0.3 mol/L still achieved a removal rate of nearly 50% for 10 mg/L fluoride solution.