Rod-shaped lanthanum oxychloride-decorated porous carbon material for efficient and ultra-fast removal of phosphorus from eutrophic water

Removal of excess phosphorus (P) from water systems can effectively prevent eutrophication and maintain the ecological balance. In this study, we used a novel freeze-drying thermal oxidation process to prepare a rod-shaped lanthanum oxychloride decorated porous carbon material, polyvinylpyrrolidone /LaOCl (PL). PL showed excellent performance in removing P from water; the preparation method had not been reported previously. Specifically, the adsorption capacity of PL for P was as high as 90.9 mg P/g, and the removal rate was greater than 92.0 % over a wide pH range (2.5–11). Fast adsorption kinetics is an important feature for P removal. The high removal rate of PL for P could be achieved in a short time; that is, more than 97.8 % of the P species could be removed in only 25 min (initial concentration: 20 mg P/L). For water samples from the natural Laoyu River (24 μg P/L), 0.01 g of PL could reduce approximately 53 L of water to below the eutrophication threshold value (20 μg P/L). Furthermore, after five repetitions of the adsorption–desorption process, no significant decrease in the P removal efficiency was observed. The high adsorption capacity, fast adsorption kinetics, and persistent cyclic stability of PL for P in water were attributed to the advanced preparation process, in which freeze-drying ensured the porosity of the adsorbent and the uniformity of LaCl₃ distribution; and the subsequent heat treatment created conditions for the generation of LaOCl species with stable adsorption activity. The adsorption mechanism mainly involved ion exchange, electrostatic attraction, and hydrogen bonding. This study provides a theoretical basis for preparing new adsorbing materials of P and technical support for preventing water eutrophication.