Distribution Effect of the Second Phase in Disperse Silica/X Oxides (X = Al₂O₃, TiO₂, GeO₂) on Their Surface Properties

Abstract

Highly disperse oxides X/SiO2 (synthesized by using high-temperature hydrolysis of a SiCl4 and MCl n (M = Al, Ti) blend or chemical vapor deposition (CVD) technique for preparation of CVD-X (X = TiO2, GeO2) on a fumed silica substrate) were studied by means of 1H NMR, one-pass temperature-programmed desorption time-of-flight mass spectrometry (OPTPD-TOFMS), optical and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The nature and the concentration of the X phase (C X), its distribution in (or on) the silica matrix, and pretreatment conditions have a strong influence on the features of the X/SiO2 surfaces, e.g., type, concentration, and strength of active surface sites such as Brønsted (B) and Lewis acid (L) sites. Also, these surface features affect the interaction of X/SiO2 with different adsorbates and other properties, which depend nonlinearly on the C X value and exhibit an extreme character.

TSDC spectroscopy of relaxational and interfacial phenomena

“…Highly disperse fumed silicas A-50, A-300, A-500, fumed oxides Al 2 O 3 , TiO 2 , X/SiO 2 (X = Al 2 O 3 (SA), TiO 2 (ST)) and Al 2 O 3 /SiO 2 /TiO 2 (AST) at different contents of alumina and titania (Table 1) (Pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine) were used as the initial materials [76][77][78][79][80]. A variety of fumed oxides was synthesized using SiCl 4 (on silica synthesis) or corresponding mixture of SiCl 4 with MCl n (M = Ti and Al, AlCl 3 was sublimed, in the synthesis of mixed oxides) burned (hydrolyzed/oxidized) in an oxygen/ nitrogen-hydrogen flame (O 2 /N 2 ≈ 0.25) under controlled conditions (temperature T f = 1000-1400°C measured using a Ranger II (Rayter) optical pyrometer; the flow velocity was from 15 to 40 m/s; the flow turbulence at the Reynolds criterion R e from 10 4 to 2 × 10 5 , the burner diameter d n = 36, 42, 52 or 62 mm; at a stoichiometric ratio of the reagent amounts and their distribution in the flame by using a burner of a specific design).…”

“…This feature, as well as changes in the specific surface area ( Table 1, S BET ), i.e. in the size of primary particles, and Brönsted and Lewis acidity of fumed oxides [18,76] affect interfacial phenomena such as the adsorption of water, metal ions [84] and proteins [23,85], and haemolysis of red blood cells by these oxides [86,87]. One can expect that the interfacial relaxation phenomena at the surface of these oxides depend on the surface composition.…”

Titania deposits on nanosilicas

“…The samples CVD-TiO 2 /A-300 described in detail elsewhere [29][30][31] were used to compare with the ST materials synthesized in the present study.…”

“…CVD-titania typically consists of relatively large particles formed at the outer surface of aggregates of primary nanoparticles of fumed silica [24][25][26][27][28][29][30]32] or silica gel granules [33,35]. Smaller nanoparticles can be formed in the inner space of aggregates (i.e.…”

Aqueous Suspensions of Poly(ethylene Glycol)/Pyrocarbon/Fumed Silica

“…In the case of hydrated PEG, two signals with close widths (Fig. 2a) are observed with increasing C H 2 O , which are linked to CH 2 groups of PEG and water molecules, and behavior of PEG molecules is akin to that of low-molecular organics (30). On freezing, water forms pure ice and PEG molecules concentrate in the unfrozen phase, whose volume enhances with C PEG and the freezing temperature of water lowers.…”