Surface basicity, indicator dyes

Mason et al. [13] used indicator dyes to determine the effect of pretreatment on the surface acidity of Ti-6,4. They found that surfaces treated with a basic etchant left a basic surface with an isoelectric point between 7.3 and 9.2. A phosphate-fluoride etch left the surface acidic with an isoelectric point between 5.4 and 7.3. 

Surface basicity can also be examined by indicator dyes, but there has beef much less study of surface basicity than of surface acidity. Phenolphthalein, bromothymol blue and various nitro-analines have been used to assess the effect of dehydration on the basicity of alkaline earth oxides or hydroxides, using benzoic... 

At present the dye techniques are very useful and economical but are somewhat approximate. Advances in use of indicator dyes for measuring surface acidity and basicity may be expected to include a two-parameter measure of acid or base strength similar to the E and C equation of Drago, and the use of fluorescent indicators for colored solids. 

Titration methods [29-32], that is, the study of the interaction of indicator dyes with the solids from solutions, have been proposed as a technique for both qualitative and quantitative characterization of solid surfaces. If a basic indicator B is used, the proton acidity of the surface is expressed by the Hammett acidity function. 

From an experimental standpoint, information on the dye binding modes at the semiconductor/dye interface, are conventionally accessed by vibrational spectroscopy [Fourier Transform InfraRed (FT-IR) spectroscopy and Surface-Enhanced Raman Spectroscopy (SERS)] [228-237]. These techniques can provide structural details about the adsorption modes as well as information on the relative orientation of the molecules anchored onto the oxide surface. Photoelectron Spectroscopy (PES) has also been successfully employed to characterize the dye/oxide interface for a series of organic dyes [238-242]. The analysis of the PES spectra yields information on the molecular and electronic structures at the interface, along with basic indications of the dye coverage and of the distance of selected atoms from the... 

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