Fluoride removal in batch and column systems using La-MOF derived from waste PET: Experimental analysis, DFT calculation, and LCA evaluation

Fluoride-containing wastewater has posed severe threats to the ecological environment and human health. Current mainstream treatment technologies still suffer from difficulties in the deep purification of low-concentration fluoride, poor adaptability to complex actual wastewater, and high treatment costs. Therefore, the development of environmentally friendly and cost-effective functional materials is a critical approach to achieve efficient treatment of such wastewater. This study addresses this need by synthesizing a lanthanum-based metal-organic framework (La-MOF) adsorbent through hydrothermal method by using terephthalic acid derived from waste polyethylene terephthalate (PET) plastics as organic ligand. The synthesized La-MOF exhibited stable fluoride ions removal performance across a wide pH range, achieving 90% removal efficiency and maximum adsorption capacity of 52.0 mg/g at optimal pH 4. The adsorption process of fluoride ions by La-MOF was accurately represented by the Langmuir isotherm model, and the kinetics obeyed the pseudo-second-order kinetic model. Thermodynamic analysis revealed that elevated temperatures were conducive to the adsorption of fluoride ions. Competitive ion experiments show that PO 4 3− , HCO 3 − , ciprofloxacin, and tetracycline have a certain impact on the removal of fluoride ions when their concentrations exceed 20 mg/L. Besides, ion exchange, electrostatic attraction, and coordination are the primary mechanisms for fluoride removal. Life cycle assessment shows that using PET as a synthetic material for La-MOF reduces the environmental footprint of waste plastics and also lowers the cost of synthetic materials. Fixed-bed column dynamic tests with real wastewater demonstrated that La-MOF maintained good treatment efficiency over five cycles. The results indicate that the La-MOF not only exhibits excellent removal performance toward low-concentration fluoride, but also achieves the synergistic treatment goal of “treating waste with waste”, demonstrating a very broad application prospect.