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The chapter is a self-review devoted to the features of synthesis and structure of spherical particles functionalized with amino-containing groups, which are produced by the sol-gel method. This review consists of three main parts in addition to introduction and conclusions. The first part deals with the features of the synthesis techniques, identification of the functional groups and silica skeleton by vibrational spectroscopy and with the structure of particles and their surfaces on the basis of the physical and chemical methods. In the second part, the sorption properties of functionalized silica particles towards copper(II) ions and some anionic dyes are discussed and analyzed. Finally, in the third part, the cause of antibacterial properties of amino- as well as copper- amino-containing materials was highlighted, including overview of data by other authors.

Spherical silica particles with bifunctional (≡Si(CH2)3NH2/≡SiCH3, ≡Si(CH2)3NH2/≡Si(CH2)2(CF2)5CF3) surface layers were produced by a one-step approach using a modified Stöber method in three-component alkoxysilane systems, resulting in greatly increased contents of functional components. The content of functional groups and thermal stability of the surface layers were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and 13C and 29Si solid-state NMR spectroscopy revealing their composition and organization. The fine chemical structure of the surface in the produced hybrid adsorbent particles and the ligand distribution were further investigated by electron paramagnetic resonance (EPR) and electron spectroscopy of diffuse reflectance (ESDR) spectroscopy using Cu2+ ion coordination as a probe. The composition and structure of the emerging surface complexes were determined and used to provide an insight into the molecular structure of the surfaces. It was demonstrated that the introduction of short hydrophobic (methyl) groups improves the kinetic characteristics of the samples during the sorption of copper(II) ions and promotes fixation of aminopropyl groups on the surface of silica microspheres. The introduction of long hydrophobic (perfluoroctyl) groups changes the nature of the surface, where they are arranged in alternately hydrophobic/hydrophilic patches. This makes the aminopropyl groups huddled and less active in the sorption of metal cations. The size and aggregation/morphology of obtained particles was optimized controlling the synthesis conditions, such as concentrations of reactants, basicity of the medium, and the process temperature.

The sorption properties towards dysprosium(III) ions of three samples of mesoporous silicas functionalized with phosphonic groups ≡ Si(CH2)2P(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).

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 LnL 2 + 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 LnL 2 + . 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).

International audience; Porous silica-based microspheres with pore surfaces functionalized by phosphonic acids are obtained for the first time from a direct co-condensation route using two alkoxide precursors (Si(OEt)4 and Si(OEt)3(CH2)2P(O)(OEt)2), surfactant self-assembly and spray-drying methods. The synthesis employs octadecyltrimethylammonium bromide as template agent. The post-treatment of the microspheres in boiling concentrated hydrochloric acid insures the hydrolysis of the ethoxy groups initially bound to phosphorus in the organophosphonate-siloxane precursor, without destroying the morphological and textural properties. Final porous materials have the chemical structure [SiO1.81(OZ)0.38]0.91[SiO1.35(OZ)0.29 (CH2)2P(O)(OH)2]0.09 (with Z @ H or Et), and posses interesting textural properties: SBET = 747 m2 g-1, and dp = 2.3 nm.

International audience; 1H solid-state NMR is becoming a routine characterisation tool. In the case of materials textured by self-assembled amphiphile molecules, we present a multi-scale characterisation approach, which can be easily implemented in most recent spectrometers. Valuable information on the interfaces between amphiphile molecules and oxide-based networks is obtained through this approach, as shown in some selected examples: block copolymers, hybrid siloxane membranes, and mesoporous microspheres obtained from spray-drying. We also present new results on 14N and 81Br solid-state NMR and discuss the applicability of direct or indirect proton-detected experiments to the study of mesoporous materials textured by cationic surfactants.

Polysiloxane xerogels containing both –SH and –NH 2 functions have been prepared using the sol–gel method with alkoxysilane precursors [such as Si(OEt) 4 , (MeO) 3 Si(CH 2 ) 3 SH and (EtO) 3 Si(CH 2 ) 3 NH 2 ]. Molar ratios of 3.2:1, 1.1:1 and 0.4:1 for the two functions –SH and –NH 2 were employed. Xerogels which contain only one of the two functions were also synthesized for comparative purposes. It was shown that the use of stannic compounds as catalysts for xerogels with 3-mercaptopropyl groups resulted in a product which possessed a non-porous structure, while the use of fluoride ions allowed the synthesis of a sample with a porous structure (S sp = 216 m 2 /g, V s = 0.152 cm 3 /g, d = 3.5 nm). Xerogels with a bifunctional surface layer possess a bimodal structure. Infrared, Raman and multinuclear solid-state NMR ( 1 H, 13 C, 29 Si) spectroscopy data showed: (i) the absence of deprotonation for the 3-mercaptopropyl groups in the bifunctional surface layer of the xerogels; and (ii) that 3-aminopropyl groups form hydrogen bonds in these surface layers. The type of hydrogen bond formed depends on the ratio of the amount of water to the amount of 3-aminopropyl groups in the surface layer. When this ratio is about 1:1, the amino group forms a hydrogen bond with the silanol group associated with the water molecule. Re-organization of the surface layer is observed when the amount of water decreases, the amino groups forming hydrogen bonds between themselves. Hence, the system of hydrogen bonds in the surface layer of such xerogels depends primarily on the drying regime employed for the samples.

The chapter is a self-review devoted to features of synthesis and structure of spherical particles functionalized with amino-containing groups, which are produced by the sol-gel method. This review consists of three main parts in addition to introduction and conclusions. The first part deals with the features of the synthesis techniques, identification of the functional groups and silica skeleton by vibrational spectroscopy and with the structure of particles and their surfaces on the basis of the physical and chemical methods. In the second part, the sorption properties of functionalized silica particles towards copper(II) ions and some anionic dyes are discussed and analyzed. Finally, in the third part, the cause of antibacterial properties of amino-as well as copper-amino-containing materials was highlighted, including overview of data by other authors.