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

SiO2/TiO2 Composite Coating on Light Substrates for Photocatalytic Decontamination of Water

In this study, we describe synthesis and characterization of a floating photocatalyst for water treatment consisting of a light substrate coated by SiO2/TiO2 composite. Three supports of natural origin were used: natural cork, expanded clay (Liapor), and volcanic porous glass (Sorbix). The photoactivity of the coated supports was tested in a laboratory photoreactor, with Liapor being the most photoactive support with good mechanical stability. The corresponding rate constant for the degradation of a model pollutant, 4-chlorophenol, was 7.8 × 10−5 s−1. Detail characterization of the coated Liapor was obtained by XRF, SEM/EDX, and UV-Vis diffuse reflectance spectroscopy, and surface area measurements. Outdoor experiments were carried out with calcined Liapor and oxalic acid or methylene blue under sunlight on pilot reactors in the Czech Republic and Vietnam. We demonstrated satisfactory photocatalytic activity, long-term stability, and reusability of the new floating photocatalyst. The photoefficiency to mineralize oxalic acid in water under sunlight was estimated as 6.7% under the applied conditions

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