Ultraviolet–visible absorption spectra of Thymol Blue during the sol–gel–xerogel transition of tetraethyl orthosilicate: in situ probe of microchemical environment

Abstract

The absorption spectra of Thymol Blue (TB) in TEOS dispersions during a sol-gel-xerogel transition catalysed by acig or base at constant temperature have been observed as a function of time. We have observed for the first time the spectra of TB throughout the transitions for one of the systems studied. On mixing the solutions, TB exists mainly in the anionic (yellow) form for both mild acid and base conditions. The system is assumed to have an effective pH of ca. 7 at this stage. No change in colour was observed just before and after gelation. At the next stage of the sol-gel reaction, the zwitterion (red) of TB became the major species in the doped systems under mild conditions. These colour changes indicate that the doped systems increase in acidity throughout the transitions, regardless of the catalysts used. In the xerogel, the weak proton donating tendency of the surface functional group is insufficient to convert TB to the cation but is strong enough to convert it to the zwitterion.

Characterization of the sol-gel process using raman spectroscopy organically modified silica gels prepared via the formic acid-alkoxide route

“…In addition to the characterization of the acidolysis reaction between formic acid and silicon alkoxides with Raman spectroscopy, we demonstrate the possibility of monitoring the sol-gel process and the following post-gelation thermal treatment, using spectral features of the organic residues linked covalently to the siloxane network. This approach is an interesting alternative to studies on the sol-gel process performed with dye-doped silica gels, where the emission [13][14][15][16][17] or absorption [18][19][20] characteristics of the dopant is used for sol-gel process characterization. Typically, 20 mmol of a mixture of TEOS and PhTREOS were placed in the container.…”

Molecular forms and fluorescence processes of 9-aminoacridine in thin sol–gel films

“…The pH value was found to be equivalent to ca. 4−6 in water by using the absorption spectrum of thymol blue [22,23]. Consequently, the pH change only slightly influences the molecular forms of the 9AA species during the reaction.…”

Substituent effects on absorption spectra of pH indicators: An experimental and computational study of sulfonphthaleine dyes

“…[1,34] The dye set in this work contains 10 molecules and covers most commercially available sulfonphthaleine compounds. These products have numerous applications, [35][36][37][38][39][40][41] often in biological and medical fields. [42][43][44][45][46][47][48][49][50][51][52][53] Sulfonphtaleine dyes are not only sensitive to pH, but are also used in sensor applictions for detecting pesticides, CO 2 and ammonia.…”