The degradation of 2-phenylphenol (OPP), commonly used as fungicide, can be photocatalysed by TiO 2 and ZnO. The latter is a little more efficient but cannot be used in acidic solution. In both cases, the main identified photoproducts are hydroquinone (HQ), p -benzoquinone (BQ), phenylhydroquinone (PHQ), phenylbenzoquinone (PBQ), 2,2′- and 2,3-dihydroxybiphenyls (2,2′- and 2,3-BPh(OH) 2 ). The observed minor formation of 2-hydroxydibenzofuran is due to the photocyclisation of PBQ. The influence of various parameters is considered. The phototransformation of OPP is slightly favoured by increasing pH. It is enhanced by the addition of small amounts of H 2 O 2 , but it is inhibited by high concentrations of chloride, sulphate or nitrate. From the inhibiting effect of alcohols, it is deduced that the main degradation pathway involves hydroxyl radicals, but a direct oxidation by positive holes h + is probably not negligible. The observed slow photodegradation of ZnO in unbuffered solution is attributed to an electrochemical process. A mechanism is proposed for the photocatalytic transformation of OPP.

Photocatalytic degradation of 2-phenylphenol on TiO2 and ZnO in aqueous suspensions

Various titania samples of industrial origin (Degussa and Tioxide) have been characterized by electrical photoconductance measurements and tested as photocatalysts in various liquid media (either pure organic liquids or aqueous solutions) as a function of their structure (anatase versus rutile). Anatase was constantly found more active than rutile, whatever the reaction chosen (mild oxidation of pure cyclohexane and 2-propanol; total degradation of phenol and nitrophenol isomers in water). In identical conditions, Degussa was found more active, but the intrinsic activity, expressed in moles converted per hour and per square meter of active surface, was found slightly higher for anatase Tioxide. The higher activity of anatase with respect to that of rutile could be explained by the interpretation of the photoconductance measurements, which evidence the higher aptitude of anatase (i) to photoadsorb oxygen, in O2- and O- forms; (ii) to photodesorb it; and (iii) to have a lower relative electron−hole recombin...

Comparison of the Photoelectronic and Photocatalytic Activities of Various Anatase and Rutile Forms of Titania in Pure Liquid Organic Phases and in Aqueous Solutions

Photodegradation kinetics of 4-nitrophenol in TiO2 suspension

A set of polycrystalline TiO2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump−probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the parti...

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Preparation of Polycrystalline TiO2 Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

The photocatalytic degradation of 4-chlorophenol (4-CP) in aqueous titanium dioxide suspensions has been studied and compared for two different catalysts:  Sachtleben Hombikat UV 100 and Degussa P25. The influence of pH and initial 4-CP concentration on reaction rate and product distribution has been investigated in detail. Regarding the initial 4-CP concentration, the degradation kinetics formally can be discribed by a Langmuir−Hinshelwood expression. While the degradation of 4-CP itself is hardly influenced by the pH, the overall mineralization rate (measured in terms of total organic carbon reduction) changes considerably, decreasing strongly at pH > 7. With P25 used as the photocatalyst the mineralization of 4-CP is slightly faster than that with Hombikat UV 100, but smaller concentrations and numbers of intermediates are detected in the latter case. Most of the intermediates observed during this photocatalytic degradation process are identical with those identified during direct photolysis. In acidic...

Fausto Miano

Papers

Photocatalytic degradation of nitrophenols in aqueous titanium dioxide dispersion