Sorption properties of porous spray-dried microspheres functionalized by phosphonic acid groups

We have shown that mesoporous silica microspheres with phosphonic groups ≡Si(СН2)2P(O)(ОН)2 in their pore surface layer have interesting properties for the sorption of neodymium(III) and dysprosium(III) from aqueous solutions, as well as for the adsorption of n-hexane, water, and triethylamine molecules from the gas phase. Such systems form the complexes LnL3 and LnL2+ in the surface layer in case of Lanthanide sorption. We found that at low equilibrium concentrations of metal ions in the solution the composition of the formed complexes is mainly LnL3, quickly reaching their saturation limit in the surface layer. Therefore, the further increase of sorption with the growing equilibrium concentration is observed due to the formation of complexes LnL2+. However, the ratio between these two types of complexes for neodymium(III) and dysprosium(III) are different probably because of the differences in Lanthanide radius. The mesoporous microspheric sorbents used are easily regenerated by hydrochloric acid, without substantial changes in their structure and in the composition of their surface layer. During sorption from the gas phase (in the absence of water molecules on the surface) phosphonic group could form hydrogen bonds among themselves or with silanol groups, which prevents their interaction with the electron-donor molecules (e.g. triethylamine).

Graphical abstractSorption isotherms of Nd3+ and Dy3+ on microspheres, functionalized with phosphonic acids (points – experimental data, lines – calculated by proposed model). Adsorption isotherm of nitogen, n-hexane, water and triethylamine vapors on microspheres with ≡Si(CH2)2P(O)(OH)2 groups.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The sorption of Nd3+, Dy3+ was studied on the silica microspheres with ≡Si(СН2)2P(O)(ОН)2 groups. ► The ratio between LnL3 and LnL2+ complexes on the sorbent surface for Nd3+ and Dy3+ are different. ► The mesoporous microspheres can be regenerable of 2 cycles of metal ions adsorption–desorption. ► The adsorption of n-C6H14, H2O, (С2Н5)3N vapors was studied on the spray-dry silica microspheres.