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−, and . The adsorbent La2O3(14.7)@PCMK-3 remained stable after five regeneration cycles.
Highlights
Phosphorus (P) is an essential nutrient for organism growth and a nonrenewable resource [1,2,3]
Compared with La2O3(14.7)@pristine mesoporous carbon material CMK-3 (PCMK-3) before phosphate adsorption, new diffraction peaks were observed at 2θ = 19.9°, 31.0° and 41.8° from the pattern of La2O3(14.7)@PCMK-3 after phosphate adsorption, which were corresponding to the peaks of LaPO4/ LaPO4·0.5H2O crystal (JCPDS No 75-1881/46-1439) [38], indicating that phosphate was adsorbed on La2O3(14.7)@PCMK-3
In order to confirm the distribution of La in the adsorbent, transmission electron microscope (TEM)-EDX analysis of La2O3(14.7)@PCMK-3 after adsorption was conducted, and the result is illustrated in figure 2
Summary
Phosphorus (P) is an essential nutrient for organism growth and a nonrenewable resource [1,2,3]. It is essential to develop effective methods to remove and recover P before its discharge into natural waters. Previous studies showed that adsorbents modified by La(III) oxide were effective for phosphate removal [19,20,21]. To enhance the dispersion of active species, metal oxide/hydroxides are usually loaded on various carriers with large surface areas. Shin et al [29] reported that compared with activated alumina, Al-impregnated mesoporous material exhibited more rapid adsorption kinetics and higher phosphate adsorption capacity. We believed that porous materials as carrier matrixes could effectively improve the adsorption property of active species and played a very crucial role in phosphate adsorption. The regeneration property of La-confined adsorbent was evaluated by consecutive adsorption–regeneration experiments for phosphate adsorption
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