Confined La 2 O 3 particles in mesoporous carbon material for enhanced phosphate adsorption

Novel phosphate adsorbents with confined La 2 O 3 inside mesoporous carbon were fabricated by the solid-state grinding method using pristine mesoporous carbon material CMK-3 (PCMK-3) and oxidized CMK-3 (OCMK-3) as the matrixes (denoted as La 2 O 3 @PCMK-3 and La 2 O 3 @OCMK-3). Compared with pure La 2 O 3 , La 2 O 3 @PCMK-3 and La 2 O 3 @OCMK-3 exhibited higher normalized phosphate adsorption capacity, indicative of efficient loading of La 2 O 3 inside the mesopores of the carbon materials. Furthermore, La 2 O 3 loading led to substantially enhanced phosphate adsorption. The adsorption capacities of La 2 O 3 @OCMK-3 samples were higher than those of La 2 O 3 @PCMK-3 samples, possibly owing to the oxygen-containing groups forming in OCMK-3 during HNO 3 oxidation, which enhanced the dispersion of La 2 O 3 in the mesopores of OCMK-3. The adsorption capacities of La 2 O 3 @PCMK-3 and La 2 O 3 @OCMK-3 increased with the La 2 O 3 loading amount. Phosphate adsorption onto La 2 O 3 (14.7)@PCMK-3 followed the pseudo-second-order kinetics with respect to correlation coefficient values (larger than 0.99). As pH increased from 3.4 to 12.0, the phosphate adsorption amounts of La 2 O 3 (14.7)@PCMK-3 and La 2 O 3 (15.7)@OCMK-3 decreased from 37.64 mg g −1 and 37.08 mg g −1 to 21.92 mg g −1 and 14.18 mg g −1 , respectively. Additionally, La 2 O 3 @PCMK-3 showed higher adsorption selectivity towards phosphate than coexisting Cl − , NO 3 − and SO 4 2 − . The adsorbent La 2 O 3 (14.7)@PCMK-3 remained stable after five regeneration cycles.