Nanocomposites and nanomaterials

The influence of synthesis conditions, oligosaccharide additive and functional silane on the structure and composition of sol-gel silicas
I.M. Trofymchuk, L.A. Belyakova
Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., 03164 Kyiv, Ukraine. 
E-mail: trofymchuk_iryna@ukr.net

The synthesis of hybrid silicas is usually performed using sol-gel method, which is considered effective to modify the surface of materials. Characteristics of silica materials obtained by sol-gel method depend on the experimental conditions applied (composition of the initial feedstock, variations in temperature, time, and type of treatment (like hydrothermal or microwave)). It is possible to obtain silicas with desirable structural characteristic (surface area, pore diameter, ordered or disordered pores) as well as solids with improved surface properties, which makes them widely used materials in separation, catalysis and drug delivery processes.
In this work, the influence of different experimental conditions on the structure and composition of silicas was elucidated. Sol-gel synthesis of silicas was realized in the presence of silica precursors (tetraethylorthosilicate and (3-chloropropyl)triethoxysilane)) as well as β-cyclodextrin additive in various molar ratio of initial reagents. In addition, the effect of temperature on hydrolysis and condensation of silicon alkoxides (in the presence or absence of oligosaccharide) at room temperature, 70 °C and 150 °C (hydrothermal treatment) was compared. Synthesized sol-gel silicas with different surface groups were characterized by IR spectroscopy, chemical analysis, low-temperature adsorption-desorption of nitrogen, and thermogravimetric analysis. Chemical immobilization of functional groups on the surface of silica materials was proved by IR spectroscopy. The content of oligosaccharide moieties introduced into silicas in the process of sol-gel synthesis was estimated by acid hydrolysis of surface groups to glucose and its subsequent spectrophotometric determination. The porous structure of synthesized silicas was elucidated by low-temperature adsorption-desorption of nitrogen. Thermogravimetric analysis was performed for modified sol-gel silicas. Gas phase adsorption and liquid sorption experiments were carried out to study the role of silica structure and composition on the benzene and phenol uptake, respectively. Synthesized silicas with chloropropyl and oligosaccharide moieties demonstrate adsorption level performance of known samples and expect to be the promising for the treatment of aqueous solutions from aromatics.