Development of La2-xCexO2CO3 solid solution for low-concentration phosphate removal and recovery: manipulating Ce ratio and valence to boost phosphate capture

The removal and recovery of low-concentration phosphates from water have become crucial due to the dual challenges of eutrophication and the phosphorus crisis. Herein, we engineered a highly efficient and recyclable phosphate trapping agent of La_2-xCe_xO₂CO₃ solid solution. The incorporation of Ce enhances the surface area and surface potential of La_2-xCe_xO₂CO₃, providing abundant adsorption sites for phosphate. Surprisingly, we found that adjusting the Ce proportion affects the carbonate content, thereby influencing the anion-exchange capacity between carbonate and phosphate. Specifically, at 3 % Ce content (3 %-CeL), the carbonate ratio is maximized, resulting in an optimal sorption capacity (196.4 mg P/g) and a rapid removal rate (under 40 min) for phosphate, unaffected by interfering ions. Remarkably, 3 %-CeL achieved nearly 100 % phosphate removal efficiency in diverse water samples from sewage treatment plants, rivers, reservoirs, and groundwater. After five adsorption-desorption cycles, the phosphate removal and recovery efficiency of 3 %-CeL remained above 90 %. Mechanistic studies revealed that 3 % Ce content yielded the highest proportion of Ce⁴⁺/Ce³⁺, enabling greater carbonate binding for anion-exchange. This study proposes a high-performance phosphate trapping agent with broad applicability for treating actual waters and provides a new perspective on enhancing low-concentration phosphate removal in La-based materials through manipulating Ce ratio and valence.