Simple preparation and efficient fluoride removal of La anchored Zr-based metal–organic framework adsorbent
Excess fluoride in drinking water from groundwater can cause dental and skeletal fluorosis affecting millions of people worldwide. Adsorption is an appealing strategy for defluoridation due to its simple operation and environmental friendliness. However, conventional adsorbents exhibit low adsorption capacity because few exposed active sites. In this work, La anchored Zr-based metal-organic framework (La-UiO-66-(COOH) 2 ) adsorbent with dual-metal sites was designed and synthesized to remove fluoride effectively. The doping of La(III) using uncoordinated carboxyl group of UiO-66-(COOH) 2 increased the adsorption capacity. The morphology, composition, structure, surface area, and thermal stability of adsorbent were carefully characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometer (EDX), fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) techniques. The adsorbent is a polyhedral shape with aggregated and smaller crystalline particles and La is uniformly distributed over the adsorbent, favoring the effective adsorption of fluoride. La-UiO-66-(COOH) 2 showed excellent adsorption performance in a wide pH range of 3–9, and the maximum adsorption capacity was 57.23 mg g −1 . The fluoride removal rate of as-prepared adsorbent reached as high as 87 % within 5 min. The adsorption process conformed to the pseudo-second-order equation model and the Freundlich isotherm model. Thermodynamic research indicated that the adsorption process was spontaneous and endothermic. After four adsorption-desorption cycles, the fluoride removal rate of the adsorbent was still retained at 79.7%. The design of dual-metal site adsorbents provides a potential strategy for highly efficient removal of fluoride.
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