Confined La2O3 particles in mesoporous carbon material for enhanced phosphate adsorption

Abstract

Novel phosphate adsorbents with confined La₂O₃ 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 La₂O₃@PCMK-3 and La₂O₃@OCMK-3). Compared with pure La₂O₃, La₂O₃@PCMK-3 and La₂O₃@OCMK-3 exhibited higher normalized phosphate adsorption capacity, indicative of efficient loading of La₂O₃ inside the mesopores of the carbon materials. Furthermore, La₂O₃ loading led to substantially enhanced phosphate adsorption. The adsorption capacities of La₂O₃@OCMK-3 samples were higher than those of La₂O₃@PCMK-3 samples, possibly owing to the oxygen-containing groups forming in OCMK-3 during HNO₃ oxidation, which enhanced the dispersion of La₂O₃ in the mesopores of OCMK-3. The adsorption capacities of La₂O₃@PCMK-3 and La₂O₃@OCMK-3 increased with the La₂O₃ loading amount. Phosphate adsorption onto La₂O₃(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 La₂O₃(14.7)@PCMK-3 and La₂O₃(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, La₂O₃@PCMK-3 showed higher adsorption selectivity towards phosphate than coexisting Cl^-, ${\mathrm{NO}}_3^{-}$ and ${\mathrm{SO}}_4^{2-}$ . The adsorbent La₂O₃(14.7)@PCMK-3 remained stable after five regeneration cycles.

Keywords: CMK-3; La2O3; confinement effects; phosphate adsorption; solid-state grinding.