Development of LaCeOCO 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 LaCeOCO solid solution. The incorporation of Ce enhances the surface area and surface potential of LaCeOCO, 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 Ce/Ce, 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.