Photodegradation of phenylurea herbicides under simulated environmental conditions

Kinetics and mechanicm of the photoinduced degradation of 4-chloroaniline (4-CA), a toxic metabolite of phenylurea herbicides, have been studied in detail

Photoelectrochemical properties of sol-gel and particulate TiO2 layers

Polarization curves on irradiated TiO2 layers were measured in various electrolytes, namely sodium hydroxide, sulphuric acid, oxalic acid and potassium oxalate. Photocurrents measured in 0.1M NaOH are very small and decrease with increasing number of Degussa P25 TiO2 layers. Photocurrents for sol-gel TiO2 layers in 0.1M NaOH are about five times higher than for P25 TiO2 layers and increasing with number of layers. The same holds for Na2SO4, but in H2SO4 the difference between P25 and sol-gel diminishes, however the sol-gel layers still show the higher currents. In solutions of oxidizable substrates the trend is inversed: P25 layers show higher currents, with a steep increase with concentration of solute. The shape of the polarization curves was interpreted in terms of response time to irradiation and photocurrent depletion. Degradation experiments demonstrated that the effect (and advantage) of biasing the electrode depends on adsorption properties of substance and surface area of electrode material

Photocatalytic degradation of dibuthyl phthalate: effect of catalyst immobilization

The degradation processes of dibutyl phthalate (DBP), an important pollutant, are rather slow and do not lead to the complete decomposition. In the present work the photocatalytic degradation of dibutyl phthalate in the presence of TiO[sub]2 was studied. Experiments were carried out in suspensions and with immobilized layers, prepared from powder suspensions and by sol-gel technique.Two different polychromatic light sources (band maxima at 350 nm and 365 nm) were used for irradiation. The results confirmed that the photocatalytic degradation of DBP using TiO[sub]2 is an efficient degradation process and proceeds even at very low concentration of photocatalyst (0.001 g dm-3). Reaction rates were significantly higher in the case of the lamp withthe maximum at 365 nm, which is due to the higher light intensity of thislamp. At comparable TiO[sub]2 amount P25 layers exhibit about 50% of photoactivity using TiO[sub]2 suspension

Preparation Of TiO2-SiO2 composite photocatalysts for environmental applications.

International audienceBACKGROUNDThe objective of this work is to prepare various TiO2/SiO2 composites, determine their photocatalytic activity and suggest the most promising materials for further application.RESULTSTiO2/SiO2 composites were successfully prepared as a powder, obtained by the heterocoagulation of mixed TiO2 and SiO2 aqueous colloidal suspensions. The heterocoagulation of prepared amorphous TiO2 in the presence of SiO2 led to the crystallization of TiO2 with anatase structure. Photocatalytic activity was tested in the liquid phase by dye degradation and in the gas phase by hexane degradation. In aqueous phase the presence of SiO2 increased the rate of degradation of Methylene Blue in comparison with pure TiO2 in acidic conditions, whereas Acid Orange 7 photodegradation was faster in basic solution in the presence of TiO2/SiO2 1:1 composite. In gaseous phase, composites prepared by heterocoagulation showed improved photoactivity (conversion around 35%).CONCLUSIONComposites prepared by heterocoagulation with ratio TiO2/SiO2 1:10 can be used as photocatalyst in self-cleaning paints. SiO2 partly covers the TiO2 surface and acts as a barrier which separates the active surface of TiO2 from contact with the binder or polymeric substrate

Insight into the photocatalytic activity of ZnCr LDH and derived mixed oxides.

International audienceZnCr–CO3 layered double hydroxide (LDH) has been prepared by a two-step process combining direct coprecipitation and anionic exchange. To investigate the influence of thermal treatment on ZnCr–CO3 LDH photocatalytic activity, the thermal decomposition of the matrix was studied by in-situ thermal X-ray diffraction and thermal analysis (TGA/DTA). The structure and the textural properties of the materials obtained upon different thermal treatment have been characterized by several techniques such as X-ray diffraction, FTIR, UV–vis diffuse reflectance spectroscopy, N2 adsorption, scanning and transmission electronic microscopy. Prior to study Orange II (OII) photodegradation, adsorption behavior of uncalcined and calcined ZnCr–CO3 LDH toward OII was studied evidencing that LDH thermal decomposition leads to a net decrease of the adsorption behavior. All the samples induce the photodegradation of OII. The compounds obtained after calcination above 600 °C display the highest photocatalytic activity attributed to the formation of well crystallized ZnO and ZnCr2O4 spinel leading to complete mineralization of OII. Optimal photocatalytic conditions were defined as 0.5 g L−1 of photocatalyst and basic pH conditions. To further highlight the oxidation process, experiments with 4-chlorophenol, which is not adsorbed on LDH surface and with isopropanol and terephthalic acid, used as HOradical dot radical trap, were carried out. In terms of photodegradation mechanism, both hydroxyl radical generation in bulk and direct interaction with hole on the surface of the photocatalysts were evidenced

Effect of TiO2 particle size on the photocatalytic reduction of CO2

Pure TiO2 anatase particles with a crystallite diameters ranging from 4.5 to 29 nm were prepared by precipitation and sol–gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis and scanning electron microscopy (SEM) and tested in CO2 photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14 nm. The observed optimum particle size is a result of competing effects of specific surface area, charge–carrier dynamics and light absorption efficiency