OH Surface Density of SiO₂ and TiO₂ by Thermogravimetric Analysis

Abstract

Thermogravimetric analysis (TGA) is investigated for determination of the OH surface density (OH/ nm 2 ) and carbon content of silica and titania powders made by flame aerosol and sol-gel processes. It is shown that it is possible to distinguish between physically adsorbed and chemically bound water and to rapidly determine the OH surface density even of small powder samples (<0.2 g) by TGA calibrated with LiAlH 4 titration data. The high accuracy of the OH surface density determination by TGA is confirmed further with additional LiAlH4 titration data of silica powders and by comparison with the specifications of commercially available silica Aerosil and titania P25 powders. Furthermore, by connecting a CO2 sensor or a mass spectrometer to the TGA balance, it is possible to verify the carbon content and determine other components (organic residues) of the powders. Thereby, it is shown that flame-made powders have high purity while the preparation conditions of sol-gel powders greatly affect their purity. At a water-toprecursor ratio of 1000:1, no organic residues are detected in sol-gel powders, while lower ratios result in residues in the product powder from the precursor, solvent, or catalyst.

Poly(methyl methacrylate) (PMMA)-based hybrid materials with reactive zirconium oxide nanocrystals

“…According to reports in the literature, 40,41 physically adsorbed water can be removed at 120 1C, indicating that weight loss above 120 1C resulted from the removal of hydroxyl groups on the ZrO 2 -NC surface. Weight loss could potentially arise from the desorption of volatile organic compounds left from particle processing; however, FT-IR spectra (Figure 1a) confirmed that there were no volatile organic compounds on the particles.…”

Carbon-coated titania nanostructured particles: Continuous, one-step flame-synthesis

“…10,11 The thermogravimetric analysis (TGA) curves (not shown) of the carbon-titania powders showed a slight decrease of 0.5-1 wt.% when heating up the powders from 120 to 800°C under nitrogen atmosphere followed by a rapid weight loss (0.5-52 wt.%, depending on the C-content) when switching the atmosphere to oxygen at 800°C. The former weight loss can be attributed to removal of chemisorbed water, surface OH-groups and any volatile organic compounds, while the latter is directly related to non-volatile carbon (soot) oxidation and removal as CO 2 or CO. 5,16 The sample weight remains constant when further heating the powder to 1000°C, since the TiO 2 surface is free of OH groups at this temperature. 16 Figure 3 shows TEM pictures of the carbon-titania powders containing (a) 15 wt.% and (b) 52 wt.% carbon, respectively, as well as HRTEM of the corresponding powders (c) 15 wt.% and (d) 52 wt.%.…”

Study of the Adsorption Space of Modified Clinoptilolites

“…In the case of the modified clinoptilolites, be given to this profile should be related to dehydroxilation; since this process, in zeolites [6] and silica [51], produces the condensation of the OH groups. In the particular case of zeolites is generally accepted that during the process of dehydroxylation at temperatures up to 500 °C, bridged hydroxyls condenses to produce water and left behind the zeolite framework negatively charged [52], trigonal aluminum [53] and different types of positively charged extra-framework aluminum [54], at higher temperatures a dehydrogenation process is as well produced [55].…”