Photocatalytic degradation of trans-cinnamic, dihydrocinnamic, trans-caffeic, and dihydrocaffeic acids and characterization of the products

Green Fabrication of Heterostructured CoTiO3/TiO2 Nanocatalysts for Efficient Photocatalytic Degradation of Cinnamic Acid

In this work, CoTiO₃/TiO₂ (CTO/Ti) heterostructures were prepared by a hydrothermal procedure in a neutral medium using perovskite CoTiO₃ and tetraisopropyl titanate. Characteristics of the synthesized catalysts were analyzed by various techniques including X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, Brunauer-Emmett-Teller adsorption-desorption, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and point of zero charges. The activity in the photodegradation of cinnamic acid (CA) under UV-A irradiation of the CTO/Ti heterostructure was investigated and compared with individual materials TiO₂ (Ti-w) and CoTiO₃ (CTO). The investigation showed that the heterostructured CoTiO₃/TiO₂ catalyst with optimal composition (5% CTO) exhibited much higher photocatalytic activity for degradation of cinnamic acid than individual CoTiO₃ and TiO₂. Under the optimal conditions (C _cat = 0.75 g/L, Q _air = 0.3 L/min, and pH = 3.8) the 90 min conversion of cinnamic acid reached 80.9% on 5CTO/Ti, much higher than those of CTO (4.6%) and Ti-w (75.2%). It was found that the enhancement in activity for the CA removal of the CTO/Ti heterostructure was due to the construction of a heterojunction structure between TiO₂(Ti-w) and CoTiO₃ that resulted in an increase in the specific surface area and porosity, reduction of the band gap energy, and higher efficient separation of charge carriers on the surface to prevent recombination. Alternatively, a comparison of the recyclability of 5CTO/Ti and Ti-w was made for CA degradation. The results showed a decrease in the CA conversion by 38% on 5CTO/Ti and 48% on Ti-w after six reaction cycles.

Validated Stability-Indicating GC-MS Method for Characterization of Forced Degradation Products of Trans-Caffeic Acid and Trans-Ferulic Acid

When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L⁻¹ (r²s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L⁻¹ and 0.50 mg L⁻¹, respectively. The LOD and LOQ for trans-CA were 0.23 mg L⁻¹ and 0.77 mg L⁻¹, respectively.

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 TiO(2) at pH 4.8. The adsorption fit very well to a Brunauer-Emmett-Teller isotherm equation with a monolayer coverage of 68.15 mg(CA)g(-1)(TiO2 and saturation coverage of 195.4 mg(CA)g(-1)(TiO2). A strong adsorption of caffeic acid was verified on TiO(2) 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.