The distribution of adsorption energy of U(VI) onto AEPTES-functionalized porous silica with multiple average pore sizes

Abstract

Amino-functionalized porous silica proved a powerful [U(VI)] adsorbent, yet the adsorption mechanism remains unclear. This study first produces porous silica with different surface areas and average pore sizes. A grafting agent, 3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane (AEPTES), is then used to modify the surface of the obtained porous silica. The mesoporous silica adsorbents are thoroughly characterized with SEM, BET, XPS, NMR, and zeta potentials. The adsorbents are used to adsorb [U(VI)], and experimental results are fitted by the Langmuir adsorption isotherm, Potential of Mean Force (PMF) model, and Surface Complex Formation Model (SCFM), as to estimate the adsorption energy ΔG0ads, which consists of specific chemical energy, ΔG0chem, coulombic energy, ΔG0coul, solvation energy, ΔG0solv, and lateral interaction energy, ΔG0lat. From the result of SCFM, the values of ΔG0chem and ΔG0coul are close, and both are the main contributor to ΔG0ads. The result also indicates that AE@MPS has the lowest surface activate site density in terms of U(VI) adsorption at pore size of 4.1 nm. This work provides a fundamental understanding of how amino groups bond to U(VI) cation in solution. It is a potential reference for the molecular design of uranium collectors.