Adsorption of Uranium over NH₂-Functionalized Ordered Silica in Aqueous Solutions

Abstract

The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N physisorption, Fourier transform infrared spectroscopy, and elemental C-H-N-S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mg·g for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption-desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption-desorption cycles without any noticeable capacity decrease.

Efficient Removal of U(VI) Using Functionalized Hollow Mesoporous Silica Nanospheres

“…Other parameters of the Langmuir formalism interpreting experimental data are reported in Table S2. The results confirm also the higher capacity of HMSNs‐NH 2 with respect to HMSNs‐SA, which could be ascribed to the higher organic moieties density and reduced steric hindrance in comparison of the two functional groups …”

“…Desorption and reusability . The pH dependency of the adsorption of uranyl ions onto HMSNs‐NH 2 and HMSNs‐SA as well as the stability of these functionalized mesoporous silica under acidic condition give the possibility of the removal of adsorbed ions by controlling the acidity of the elution solution . The U(VI) loaded material can be eluted by 0.01 M nitric acid easily and the removed U(VI) was found to be 98 ± 1% by both functional adsorbents.…”

“…The main species are UO 2 2+ cations at the U(VI) concentration of 100 ppm with pH below 4. With pH in the range of 5∼7, formation of multinuclear hydroxyl species including [(UO 2 ) 3 (OH) 5 ] + and [(UO 2 ) 4 (OH) 7 ] + occur . On the other hand, at pH of 2, the surface charges of all the sorbents are negative, and almost no uranium uptake on these sorbents (Figure S3).…”

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

“…Huynh et al reported 250 mg U(VI) uptake per g of a sorbent composed of amine functionalized mesoporous silica (SBA-15). Both IR (v 3 = 909 cm −1 ) and Raman (v 1 = 827 cm −1 ) spectroscopies suggested inner sphere coordination with the surface amines of the sorbent [239]. Amidoxime-containing materials have been shown to selectively uptake U(VI).…”

Amidoxime Functionalized Mesoporous SBA-15 with Various Mesostructures for Highly Efficient Concentration of U(VI)

“…For instance, considering the characteristic of metal ion sorption, recent e®orts have been devoted to synthesize functional SBA-15 with organic ligands containing N, O, S and P elements to selectively interact with actinide ions. Speci¯cally, dihydroimidazole, 19 amine groups, 20 phosphonate, 21 Schi® base 22 and others 23 are proposed to improve the surface a±nity and selectivity of SBA-15 to U(VI). Moreover, the synthesis of SBA-15 with various mesostructures and their structure-dependent sorption behaviors has also been reported.…”