Adsorption of phosphate in water by defective UiO-66/Ce2(CO3)3 composite: Adsorption characteristics and mechanisms

Abstract

In this study, the defect-rich UiO-66 is first synthesized by a two-step strategy, and then a new T-UiO-66/Ce2(CO3)3 (TUC) adsorbent has been successfully synthesized for phosphate removal from water using a simple co-precipitation method. The pseudo-secondary kinetic model and the Langmuir model, respectively, fit the adsorption kinetics and isotherms. The combined thermodynamic analysis shows the spontaneous and heat-absorbing nature of the adsorption process. TUC has a maximum adsorption capacity of 138.9 mg/g at 298 K, and its adsorption capacity is stable throughout a large pH range (4–9). Electrostatic attraction, defect-induced ligand compensation groups and CO32-active groups with phosphate in ligand exchange make up the majority of the adsorption mechanism. Meanwhile, TUC shows excellent adsorption performance for low concentration phosphorus-containing solution. By applying adsorption for 120 min while treating actual water samples, the phosphate concentration can be reduced from 1.68 mg/L to 0.2 mg/L, which is much less than the primary A phosphorus discharge standard of urban wastewater treatment plants. Moreover, the adsorbent shows good stability after five cycles, and the phosphate may still be adsorbed with an efficiency of up to 81% and desorbed with an efficiency of over 85%.