Phosphination of amino-modified mesoporous silica for the selective separation of strontium

Radioactive strontium (⁹⁰Sr) is considered as one of the most dangerous radionuclides due to its high biochemical toxicity. For the efficient and selective separation of Sr from acidic environments, a novel functional adsorbent CEPA@SBA-15-APTES was prepared in this work through the phosphorylation of amino-modified mesoporous silica with organic content of approximately 20 wt%. CEPA@SBA-15-APTES was characterized by TEM, SEM, EDS, TG-DSC, BET, FTIR, and XPS techniques, revealing its characteristics of an ordered hexagonal lattice-like structure and rich functional groups. The experimental results demonstrated that the adsorbent exhibited good adsorption capacity for Sr over a wide acidity range (i.e., from 10^-10 M to 4 M HNO₃). The adsorption equilibriums of Sr by CEPA@SBA-15-APTES in 10^-6 M and 3 M HNO₃ solutions were reached within 30 and 5 min, respectively, and the adsorption capacities at 318 K were 112.6 and 71.8 mg/g, respectively. Furthermore, by combining the experimental and characterization results, we found that the adsorption mechanism consisted of ion exchange between Sr(II) and H⁺ (in P-OH) in the 10^-6 M HNO₃ solution and coordination between the Sr(II) and oxygen-containing (CO and P = O) functional groups in the 3 M HNO₃ solution.