Adsorption of caffeic acid on titanium dioxide: A spectroscopic study

Caffeic acid is an ortho-phenol found in vegetable tissues presenting important properties such as carcinogenesis inhibitor, anti-oxidant, anti-viral, anti-inflammatory and anti-rheumatic actions. It was observed that caffeic acid was not degraded in daylight during the adsorption on TiO2 at pH 4.8. The adsorption fit very well to a Brunauer–Emmett–Teller isotherm equation with a monolayer coverage of 68.15 mgCA gTiO2−1 and saturation coverage of 195.4 mgCA gTiO2−1. A strong adsorption of caffeic acid was verified on TiO2 for the dry solid obtained from the mixture. The Raman and IR spectroscopies revealed that the adsorption should occur through the interaction of the diphenol oxygens with contribution of CC double bond of the acrylic group, however, the carboxylic acid group did not have participation in the adsorption.

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► Caffeic acid was not degraded in daylight adsorbed on TiO2 at pH 4.8.
► Adsorption fit very well to a Brunauer–Emmett–Teller isotherm equation.
► A strong adsorption of caffeic acid was verified on TiO2 for the dry solid.
► The Raman and IR revealed interaction of the diphenol oxygens and CC of acrylic group.
► Carboxylic acid group did not have participation in the adsorption.