Edgar Moctezuma

Photocatalytic degradation of paracetamol: intermediates and total reaction mechanism.

The advanced oxidation of paracetamol (PAM) promoted by TiO(2)/UV system in aqueous medium was investigated. Monitoring this reaction by HPLC and TOC, it was demonstrated that while oxidation of paracetamol is quite efficient under these conditions, its mineralization is not complete. HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol in the reaction mixtures. Further evidence of p-nitrophenol formation was obtained following the reaction by UV-vis spectroscopy. Continuous monitoring by IR spectroscopy demonstrated the breaking of the aromatic amide present in PAM and subsequent formation of several aromatic intermediate compounds such as p-aminophenol and p-nitrophenol. These aromatic compounds were eventually converted into trans-unsaturated carboxylic acids. Based on these experimental results, an alternative deacylation mechanism for the photocatalytic oxidation of paracetamol is proposed. Our studies also demonstrated IR spectroscopy to be a useful technique to investigate oxidative mechanisms of pharmaceutical compounds.

Photodegradation of phenol and 4-chlorophenol by BaO–Li2O–TiO2 catalysts

Abstract The catalytic photodegradation of phenol and 4-chlorophenol with white and UV light over TiO2, BaTi4O9 and Hollandite catalysts has been studied in our laboratories. BaTi4O9 and Hollandite catalysts were prepared by solid state reaction at 900°C and 1200°C, respectively. All the catalysts were characterized by different techniques such as surface area measurements by the BET method, atomic absorption spectroscopy and XRD. Photodegradation reaction experiments were monitored by HPLC analysis. The reaction intermediates: hydroquinone and 1,4-benzoquinone were identified by GC–MS analysis. The photocatalytic activities of these catalysts in the degradation of phenol and 4-chlorophenol were evaluated in comparison with titanium oxide. Experimental results showed that BaTi4O9 and Hollandite catalysts exhibit small photocatalytic activity as compared with TiO2.

Photocatalytic degradation of the herbicide “Paraquat”

Abstract The photocatalytic degradation of pure paraquat ( 1,1′-dimethyl-4,4′-bipyridinium dichloride ) aqueous solutions with UV light over titanium oxide was investigated. Experimental results have confirmed that paraquat is slowly degraded by direct photolysis in the presence of dissolved oxygen. Addition of TiO2 to the reaction system substantially increases the initial rate of reaction and the overall conversion of paraquat. Complete photocatalytic degradation of paraquat at high pH values was found to occur in less than three hours of reaction.

Spectrometric and 2D NMR Studies on the Complexation of Chlorophenols with Cyclodextrins

The formation and structure of inclusion complexes of α- andβ-cyclodextrins with 2-chlorophenol (2CP), 3-chlorophenol (3CP),4-chlorophenol (4CP), 2,4-dichlorophenol (24DCP), 2,6-dichlorophenol(26DCP) and 3,4-dichlorophenol (34DCP) have been studied by UV-VIS and1H NMR spectroscopy. Both cyclodextrins were found to form 1:1inclusion complexes. Bindingconstants estimated from titration studies revealed that the stability of the complexes was highly dependent on the structure and polarity of the chlorophenol and on the cyclodextrin used. In general, weaker binding constants were observed for a given chlorophenol with α-cyclodextrin than withβ-cyclodextrin. The weakest binding constants (Kb < 200 M-1) were obtained for the ortho-substituted chlorophenols (2CP and 26DCP) and the largest binding constants were obtained between para-chlorophenols (4CP, 24DCP and 34DCP) andβ-cyclodextrin. 2D-TROESY studies of chlorophenol-cyclodextrincomplexes in D2O provided insight into the structure of the complexes.

Photodegradation of indigo carmine and methylene blue dyes in aqueous solution by SiC–TiO2 catalysts prepared by sol–gel

Indigo carmine and methylene blue dyes in aqueous solution were photodegraded using SiC-TiO(2) catalysts prepared by sol-gel method. After thermal treatment at 450°C, SiC-TiO(2) catalysts prepared in this work showed the presence of SiC and TiO(2) anatase phase. Those compounds showed specific surface area values around 22-25 m(2)g(-1), and energy band gap values close to 3.05 eV. In comparison with TiO(2) (P25), SiC-TiO(2) catalysts showed the highest activity for indigo carmine and methylene blue degradation, but this activity cannot be attributed to the properties above mentioned. Therefore, photocatalytic performance is due to the synergy effect between SiC and TiO(2) particles caused by the sol-gel method used to prepare the SiC-TiO(2) catalysts. TiO(2) nanoparticles are well dispersed onto SiC surface allowing the transfer of electronic charges between SiC and TiO(2) semiconductors, which avoid the fast recombination of the electron-hole pair during the photocatalytic process.

Sonochemical synthesis of Fe–TiO2–SiC composite for degradation of rhodamine B under solar simulator

Fe–TiO2–SiC composite with photocatalytic activity has been synthesized by a low cost sonochemical process in the presence of citric acid. The addition of citric acid during the sonochemical process allows the formation of a photocatalytic coating of Fe–TiO2 onto silicon carbide. Experimental characterization results indicate that the composite was formed over all the surface of the silicon carbide (SiC) with an anatase crystalline TiO2 phase with iron incorporation. The incorporation of iron narrows the band gap of TiO2 which allow the absorbtion of light with a large wavelength. The obtained Fe–TiO2–SiC composite exhibits good enhanced photocatalytic activity for the degradation of rhodamine B under solar simulator irradiation in comparison with the commercial TiO2–P25.

Sm2FeTaO7 Photocatalyst for Degradation of Indigo Carmine Dye under Solar Light Irradiation

This paper is focused to study Sm2FeTaO7 pyrochlore-type compound as solar photocatalyst for the degradation of indigo carmine dye in aqueous solution. Sm2FeTaO7 was synthesized by using conventional solid state reaction and sol-gel method. X-ray diffraction results indicated that Sm2FeTaO7 exhibit a monoclinic crystal structure. By scanning electron microscopy analysis, it was observed that sol-gel material presents particle size of around 150 nm. The specific surface area and energy bandgap values were 12 m2 g−1 and 2.0 eV, respectively. The photocatalytic results showed that indigo carmine molecule can be degraded under solar light irradiation using the synthesized materials, sol-gel photocatalyst was 8 times more active than solid state. On the other hand, when Sm2FeTaO7 was impregnated with CuO as cocatalyst the photocatalytic activity was increased because CuO acts as electron trap decreasing electron-hole pair recombination rates.

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

Photocatalytic Degradation of Caffeine in a Solar Reactor System

Abstract In this paper, solar photodegradation of caffeine in aqueous solution was studied, this organic compound is the most consumed stimulant around the world. The degradation experiments were carried outdoors in a solar reactor and Evonik-Degussa P25 TiO2 was used as catalyst. The photochemical and photocatalytic effect were tested in aqueous solutions of caffeine. Experimental results indicate that the organic compound is easily degraded over a very short period of time using 0.5 g L-1 of catalyst. The kinetic analysis indicates that the initial reaction rate of caffeine is described by the LH-HW model. However, the original compound cannot be mineralized very fast, caffeine is converted to other organic compounds with a longer lifetime before the mineralization, converting caffeine CO2 and water.