Defective MOFs doped with cerium (III) for enhanced phosphate removal and dye adsorption

Abstract

Phosphates and dyes are two common pollutants in wastewater, yet research on their simultaneous removal remains limited. In this study, defective Ce_XZr₁-1,3,5-Benzenetricarboxylic acid (BTC) were synthesized via a metal doping strategy, where x denotes the molar ratio of Ce to Zr. Defective MOFs were synthesized using water and acetic acid (HAc) as the solvent and modulator, respectively, replacing N, N-dimethylformamide (DMF) and formic acid (FA) in the traditional synthesis method. The number of missing linkers was quantified using thermogravimetry analysis and potentiometric acid-base titration. The successful synthesis of Ce_XZr₁-BTC was confirmed by powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS). Ce_0.75Zr₁-BTC showed a great phosphate adsorption performance (234.7 mg/g) under optimized conditions, with a dosage of 0.2 g/L, an initial phosphate concentration of 200 ppm, pH 2, and a temperature of 303 K. Additionally, benefiting from more adsorption sites and reduced internal diffusion limitations, it retained more than 95 % phosphate removal efficiency after four consecutive applications and was able to treat 392 bed volumes of phosphate solution. Furthermore, Ce_0.75Zr₁-BTC could selectively adsorb anionic dyes in mixed dyes solution, and the adsorption mechanisms mainly involve electrostatic attraction, π-π stacking, and hydrogen bonding. It reduced phosphate concentrations to 1.17 μg/L and significantly lowered the COD of simulated phosphate-containing dye wastewater, demonstrating its potential for practical wastewater treatment applications.