Samples of iron-doped titania prepared by the wet impregnation method from TiO2 (Degussa P-25) and two different precursors, Fe(NO3)3.9H2O and Fe(III) acetylacetonate, were tested as photocatalysts in two reactions: nitrite oxidation and Cr(VI) reduction at pH 6.5. Whereas samples prepared from Fe(NO3)3.9H2O containing low amounts of iron (less than 2wt.%) were more efficient for nitrite oxidation than pure TiO2, specimens obtained from Fe(III) acetylacetonate were less active. In the case of Cr(VI) reduction, all doped samples were less active than TiO2 with no sensibly differential activity. Different mechanistic pathways and structural and surface properties of the samples are invoked to explain the observed behavior.

The photodegradation of phenol, 2,4-dichlorophenol, phenoxyacetic acid and 2,4-dichlorophenoxyacetic acid using TiO2 as photocatalyst is investigated. The photodegradations of these compounds have been conducted in a continuous mode by means of a flow system, in which TiO2 remains fixed onto glass pearls. The use of this system gives high yields of degradation for the chemicals tested, except for 2,4-dichlorophenol for which a slow dechlorination process is observed. The rate of photodegradation depends on the pH of the solution, the point of zero charge of TiO2 and the pKa of the chemicals being the key parameters. The main aromatic intermediates detected have been hydroquinone,paraquinone and hydrohydroquinone during phenol degradation; phenol and hydroquinone during phenoxyacetic acid degradation; chlorohydroquinone and chlorophenol during 2,4-dichlorophenol degradation; and dichlorophenol during 2,4-dichlorophenoxyacetic acid degradation. Finally, some long term irradiations with phenol as model compound have been performed, showing high degrees of photodegradation. It has been observed that only a periodic evacuation of the effluent out of the reactor is needed to sustain high percentages of photodegradation.

The photodegradation of 2,4-dichlorophenoxyacetic acid using titanium dioxide as photocatalyst was investigated. The yield of 2,4-D photodegradation depends on the mass of the semiconductor, temperature and light intensity. The highest conversion rates were obtained at pH = 3.5, which is close to the pKa of the acid and lower than the point of zero charge of TiO2. The experimental data fit a Langmuir-Hinshelwood kinetic model. The rate and equilibrium adsorption constants were obtained from those data at different temperatures. Some aromatic intermediate products of 2,4-D photodegradation were detected (2,4-dichlorophenol, hydrohydroquinone, chlorohidroquinone). An analysis of total organic carbon (TOC) showed that a complete mineralization of 2,4-D can be easily achieved. On the other hand, the results obtained in experiments using platinized TiO2 lead us to assume that both oxidation and reduction steps should be taken into account if an explanation of the experimental data is to be made.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Titanium dioxide has been used as photocatalyst for the degradation of 2,4-dichlorophenol. This process takes place under UV-illumination obtaining high yields for diluted aqueous solutions. The yield of 2,4-dichlorophenol oxidation depends on the irradiation time, the incident light intensity, the mass of semiconductor in suspension, the initial concentration and very slightly on the pH and temperature. The initial rate values of 24-dichlorophenol oxidation follows Langmuir-Hinshelwood kinetics, with a rate constant and an equilibrium adsorption constant of 4.5 x 10(-5) M/min and 3.2 x (103)/M, respectively, at 25 degrees C. From this data it is assumed that the oxidation of 2,4-dichlorophenol occurs through reaction with OH radicals originated from valence band processes in the surface-hydroxylated TiO2 particles under illumination.

The stability of carboplatin in aqueous solutions at different experimental conditions was studied. It was observed that the degradation rate of carboplatin under illumination increases notably with respect to the rate obtained in the dark. The time course of carboplatin in solution follows a first-order kinetics with rate constants that depend on the incident light intensity and little with temperature. The quantum yield of the carboplatin degradation lies between 0.05 and 0.2 depending on the experimental conditions. From the results obtained in the present work it is concluded that carboplatin is degraded under illumination by means of a photoaquation process.

The study of the heterogeneous photocatalytic oxidation of phenoxyacetic acid in presence of near-UV illuminated TiO2 is carried out. The Langmuir-Hinshelwood kinetics model fits the experimental data of phenoxyacetic disappearance, and reaction rate and equilibrium adsorption constants are reported. The effect of temperature, pH, intensity of incident light and mass of catalyst on the reaction rate is ascertained. Some intermediate products are detected and carbon dioxide was found to be the final product of the reaction.

The heterogeneous photocatalytic oxidation of phenol in aqueous diluted solutions over TiO2 particles under UV-illumination has been investigated. It has been observed that the yield of the phenol photooxidation depends strongly on the pH of the solution. Maximum yields are obtained at pH 8 and also in very alkaline media. These results are explained considering the processes that take place at the surface of the semiconductor, in which OH radicals have an important role. With respect to the initial charge transfer steps a kinetic analysis has been performed. From this analysis it was deduced that the constant rate of formation of OH radicals is about 4.0 x 10(4) times greater than the constant rate of the direct reaction between phenol and photogenerated holes in the TiO2 particles. Finally, from HPLC analysis, hydroquinone, paraquinone and 1,2,4-benzenetriol have been detected as intermediate products prior to the total phenol mineralization.

The amount of chloride released when aqueous solutions of cisplatin are illuminated under various experimental conditions has been determined; from the results the kinetics of cisplatin degradation are deduced, and the mechanism is analysed on the basis that a photoaquation process takes place.

The photocatalytic elimination of Cr(VI) from aqueous solutions using CdS supported on glass pearls as catalyst is investigated. The study has been carried out by measuring the amount of Cr(VI) eliminated at different pH, initial Cr(VI) concentrations and temperatures. It has been observed that after flushing dilute Cr(VI) solutions at a wide range of pH (from 5 to 10) through the CdS-coated glass pearls, 100% of Cr(VI) elimination is achieved. By means of this experimental system the kinetics of Cr(VI) photoreduction to Cr(III) over CdS in flow conditions has been determined. Finally, the stability of CdS in long-term experiments and the application of this catalytic method in a real case has been studied.