Preparation Of Amidoxime Functionalized Mesoporous Silica And Its Adsorption Property Of Uranium

Materials containing amidoxime group is considered as a suitable adsorbent to extract uranium from seawater because it can complex with uranium selectively, which result in a high adsorption capacity toward uranium. Current work is mainly focused on the synthesis of amidoxime group functionalized mesoporous silica material, adsorptive properties of uranium, and so on.In the first step, cyano-group modified mesoporous silicas were synthesized by one-pot co-condensation of tetraethoxysilane (TEOS) and 2-cyanoethyltriethoxysilane (CTES), using Pluronic P123 triblock copolymer as the structure-directing agent under strongly acidic conditions. It was found that the order for adding the two silicon sources, namely CTES and TEOS has a profound influence on the content and distribution of cyano group. Within three mixture orders, the sample synthesized with pre-mixed TEOS and CTES as silica sources is best, with highest cyano content and uniform distribution. Amidoxime group functionalized mesoporous silica was prepared using hydroxylamine and cyano group modified mesoporous silica synthesized in the first step as materials. It was found that the best performing adsorbent can be synthesized by reacting under 70℃for three hours with hydroxylamine concentration of 77g·L^-1. The adsorbent obtained can adsorb more than 310mg uranium per gram material. Moreover, pure silica, cyano- and amidoxime- group functionalized mesoporous silica were tested for uranium adsorption. It was found that all these materials can adsorb uranium, within which adsorption capacity of amidoxime modified mesoporous silica can reach 400mg·g^-1.After that, adsorptive properties of uranium ion by amidoxime modified mesoporous silica were investigated. It was found that adsorption equilibrium was reached within 30min. Besides, there was a clear correlation between pH and uranium uptake and had a maximum uptake when pH reached 6.0. However, initial concentration of uranium solution had slightly influce on uranium uptake, implying that adsorbent obtained still can be used when uranium solution concentration was low. The adsorption data followed Langmuir's and Freundlich equation. The maximum uranium uptakes were 704.2mg·g^-1 and 740.8mg·g^-1 at 25 and 35℃, respectively, implying that uptake capacity can be enhanced by heating and uranium adsorption on amidoxime functionalized mesoporous silica is a decalescence process. Moreover, uptake of uranium can be described by pseudo-second order equation model. In artificial sea water containing uranium,natrium,potassium,calcium and magnesium ions, uranium uptake was basically unchanged, which was still high, while the uptakes of other metal ions were low. This shows that the adsorbent obtained, namely amidoxime modified mesoporous silica has high selectivity toward uranium ion.