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The binary xerogels TiO2–SiO2 are widely used as catalysts and their carriers in organic synthesis. Characterization and adjustment of the electrostatic properties of the surface and the local acidity inside the pores, are necessary for the further development of TiO2–SiO2 xerogels applications. This research investigates acid–base equilibria in the pores, and the surface electrostatic potential (SEP) of binary TiO2–SiO2 xerogels, by the EPR of stable pH-sensitive nitroxide radicals. These radicals are small enough to penetrate directly into the pores, and to be adsorbed onto the surface of the material under study. This makes it possible to obtain valuable information on the acidic and electrosurface properties of the studied system. The highest negative surface electrical charge associated with surface electrical potential (SEP) was equal to –196 ± 6 mV. It was induced by the surface of the sample with a 7% TiO2 content. Тhe local acidity inside the pores of this sample was found to be higher, by approximately 1.49 pH units, as compared to that in the external bulk solution.

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Titanium dioxide-silicon dioxide systems are widely used as thin film coatings, catalyst supports, selective sorbents, and photocatalysts [1][2][3][4][5][6][7]. The properties of these systems (photocatalytic activity, sorption capacity, reactivity, etc.) depend on the way they were obtained and are governed by their particle size and shape, phase composition, structure, and pore size.An advantage of the sol-gel process over many other synthetic methods is that it ensures homoge neous distribution of the components at the atomic level. The traditional synthesis of TiO 2 -SiO 2 xerogels via this method consists of the hydrolysis of a mixture of titanium and silicon alkoxides in a water-alcohol medium in the presence of an alkali or acid as the cat alyst followed by controlled drying of the hydrolysis product. In order to improve the sol-gel synthesis of TiO 2 -SiO 2 , we suggest conducting the hydrolysis of the organometallic precursors in the absence of aque ous alcohol. This is expected to simplify the synthesis technology and to afford a material with unusual sur face and structural properties.Here, we report the synthesis of TiO 2 -SiO 2 xero gels over a wide range of TiO 2 /SiO 2 ratios by the hydrolysis of tetrabutoxytitanium-tetraethoxysilane mixtures in an aqueous ammonia medium vapor (first experimental series) and in concentrated hydrochloric acid vapor (second experimental series). We also dis cuss how the physicochemical properties of the result ing material depend on the synthetic conditions. EXPERIMENTAL Hydrolysis was carried out in a 3000 cm 3 desicca tor containing a beaker filled with 100 mL of 10% aqueous ammonia or with the same volume of con centrated hydrochloric acid.Tetraethoxysilane (TEOS), tetrabutoxytitanium (TBT), and its mixture (10 mL) were poured into por celain bowls 60 mm in diameter and 30 mL in volume and were placed in the desiccator.For the synthesis of TiO 2 -SiO 2 mixed oxides con taining 7, 14, 31, 50, and 73 mol % TiO 2 (samples 1-5), TBT and TEOS were combined in such proportions that 10 mL of their mixture contained 1, 2, 4, 6, and 8 mL of TBT, respectively.The individual oxides SiO 2 and TiO 2 were synthe sized by hydrolyzing 10 mL of TEOS and TBT, respec tively.Hereafter, the samples synthesized by hydrolysis in the hydrochloric acid atmosphere are labeled with a star.The precursors were kept in the desiccator for 93 h, and the hydrolysis products were dried in air at 24°С for 48 h and then in a drying oven at 90°С for 1 day. The dry samples were placed in a quartz reactor and were calcined at 850°С (heating rate of 10 deg/min) in flowing air (0.075 m 3 /h) for 1 h.The total porosity of the xerogels with respect to water was determined by holding a 0.5 g sample in 20 mL of water for 20 h.Infrared spectra were recorded as solid powders on a Spectrum One (PerkinElmer) IR Fourier transform spectrometer between 4000 and 370 cm -1 using a dif Abstract-TiO 2 -SiO 2 xerogels have been synthesized by the hydrolysis of tetrabutoxytitanium-tetraethox ysilane mixtures in a 10% aqu...