Dy(III) sorption from water solutions by mesoporous silicas functionalized with phosphonic acid groups

The sorption properties towards dysprosium(III) ions of three samples of mesoporous silicas functionalized with phosphonic groups a parts per thousand Si(CH2)(2)P(O)(OH)(2) were studied. It was found that for the sample synthesized by spray-drying using OTAB as a template both sorption and desorption rate of Dy3+ ions is high, due to the defined porosity of the sorbent. Sorption of Dy3+ ions by bridged silsesquioxane xerogels with disordered structure is significantly hindered by diffusion processes, due to the chaotic packing of globules. Using a model for the chemical reactions, the composition of dysprosium(III) complexes with surface phosphonic groups were determined, and their formation constants were calculated. It was shown that xerogels with higher surface concentration of ligand groups (L), can form complexes DyL3 and DyL4 (-). Meanwhile, the sample synthesized by spray-drying method forms only DyL2 (+) and DyL3 complexes. For this sample, complexes DyL3 are more stable than for xerogels. So, mesoporous silica derived by spray-drying method, with defined spatial porosity and relatively low surface concentration complexation groups, is characterized by the best sorption properties towards dysprosium(III) (adsorption and desorption kinetics, the value of the static sorption capacity).