Adsorption mechanism of fluorion removal from water by structure and valence-regulated Ce-MOFs and their derivatives
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Abstract:
Controlling the concentration of fluorion in drinking water is crucial for reducing the risk of bone and dental fluorosis. In recent years, cerium-based adsorption materials, particularly cerium organic framework materials (Ce-MOFs) and their derivatives, have emerged as effective solutions for fluorion pollution. In this study, Ce-MOFs, namely CeT1 and CeT2 were synthesized using ammonium cerium nitrate (Ce(NH4)2(NO3)6) and homophenic acid (H3BTC) at different reaction times, while CeD1 and CeD2 were generated by replacing H3BTC with terephthalic acid (H2BDC). Structural, surface area, elemental content and constituent group analyses were conducted using XRD, BET, SEM, XPS and FTIR techniques. Adsorption properties of the four materials were studied by controlling adsorption parameters, such as time, initial solute concentration, pH, and competing ions. Kinetic and isothermal models were employed to explore the adsorption mechanism. Characterization showed CeT1 as Ce(Ⅳ)-MOFs with high coordination unsaturation, CeD1 as Ce(Ⅳ)-MOFs with the largest specific surface area (1 003.10 m2/g), and CeT2 and CeD2 as Ce(Ⅲ) adsorption materials. Maximum adsorption capacities for CeT1, CeT2, CeD1 and CeD2 were determined as 99.38 mg/g, 142.45 mg/g, 60.45 mg/g and 124.55 mg/g, respectively. CeT1, CeT2 and CeD2 conformed to the pseudo-second-order kinetic model, while CeD1 conformed to the pseudo-first-order kinetic model. Adsorption mechanisms of fluorion in the four materials involved electrostatic attraction, ion exchange and precipitation, with CeT1 providing adsorption sites for ion exchange and electrostatic attraction due to unsaturated coordination. CeD1’s large specific surface area increases collision probability between pollutants and materials, while Ce(Ⅲ) in CeT2 and CeD2 facilitated precipitation by forming CeF3 (Ksp=8×10-16) with minimal solubility product constant. The study provides insights into the characteristics and defluorination abilities of Ce-MOFs and their derivatives, offering valuable reference for their preparation and optimization.
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Supported by the High and New Technology Research and Cultivation Program of the Central Universities (300102281201), China Postdoctoral Science Foundation (2021M692510), Shaanxi Provincial Foundation (2020JM-264), Natural Science Basic Research Project of Shaanxi Province (2021JQ-222), and Young Talent fund of University Association for Science and Technology in Shaanxi (20200413).
