Complex investigations of structural and thermal properties of silica-titania adsorbents

Abstract

Mesoporous titanium-containing silicas with different Titania contents were investigated. The structural parameters of the materials were characterized by low-temperature adsorption/desorption of nitrogen and X-ray diffraction analysis. The thermodesorption of water using the quasi-isothermal thermogravimetry as well as the differential scanning calorimetry were used to characterize thermal and surface properties of these materials. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent/water interfaces were calculated. It was stated that the increase of Titania content causes a gradual decrease of specific surface area and formation of biporous structure inside the tested materials. The water thermodesorption from the surface proceeds in two or three stages, which is connected mainly with pore distribution and TiO2 content. One can observe the increase of the total surface free energy (ΔGΣ) with the increasing TiO2 content, but the largest ΔGΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbent of intermediate content (30%) of TiO2. Freezing temperature of water contained in the pores of the studied materials is connected largely with their porous structure. Due to the well developed porous structure, the water freezing process is a multi-stage one.

Characterization of Multimodal Silicas Using TG/DTG/DTA, Q-TG, and DSC Methods

“…When measurements are performed over a temperature range without sample mass changes, then the ∆m = f(T) dependence reflects the changes in concentration of the water adsorbed on the adsorbent surface under equilibrium. The procedure has been previously described in detail [11,12,[26][27][28].…”

“…Many modern research methods are used to assess the characteristics of silica materials. These include, among others, adsorption of different gases and liquids, thermal analysis under dynamic or quasi-isothermal conditions [8][9][10][11][12][13][14][15], FTIR and NMR spectroscopies [8,9,14,[16][17][18], ESR [8], SEM or TEM imaging [8,9], and many other methods.…”

Application of differential scanning calorimetry to study porous structure of hydrothermally modified silicas

“…The differential PSDs with respect to pore volume were re-calculated as incremental PSD (IPSD v ). In the calculations, there was estimated contribution of individual kinds of pores: nanopores (V nano , S nano for R p \ 1 nm), mesopores (V meso , S meso for 1 nm \ R p \ 25 nm) and macropores (V macro , S macro for R p [ 25 nm) [11,[26][27][28][29][30][31]. The pores of nanosize radii (R \ 1 nm) were designated as the ''nanopores'' [11,27].…”

Structural, thermal and energetic characteristics of synthetic active carbons prepared on the basis of ion-exchange resin Amberlite IRC 84

“…The nitrogen desorption data were used to calculate the dV/ dR and dS/dR dependencies using the procedure described elsewhere [23]. The values and contributions (%) of micro-(V micro and S micro at R \ 1 nm), meso-(V meso and S meso at 1 \ R \ 25 nm), and macropores (V macro and S macro at 25 \ R \ 100 nm) were determined [24][25][26][27].…”