Photocatalyst Degussa

For photocatalytic reactions in aqueous suspensions, it has been proposed that a standard reactant (phenol) and standard photocatalyst (Degussa P25) be used to calibrate the results from a particular laboratory or a particular experimental arrangement in terms of quantum yield [78]. This proposal appears to have some merit, in that it is not difficult to implement, requiring no specialized equipment. Specifically, one would measure the effective quantum yield for any arbitrary reactant and photocatalyst, normalized to that for phenol and P25 Ti02. 

Ohno, T., K. Sarukawa, K. Tokieda, and M. Matsumura, Morpholotogy of a TiOj photocatalyst (Degussa, P25) consisting of anatase and rutile crystalline phases. 

However, the decomposition of organic compounds does not always lead to nontoxic solutions. Mineralization of melamine (2,4,6-triamino-l,3,5-triazine) and other chemicals was accomplished on Ti02 Degussa P-25. The formation of cyanuric acid prevents the complete mineralization of melamine as observed for atrazine and other. v-tria/incs on Ti02 photocatalysts, and the toxicity of the photocatalyzed solutions was higher than initially found for melamine [199],... 

Figure 2. Kinetic curves of the photocatalytics evolution of molecular hydrogen from aqueous-alcoholic mixtures over Ti02/Ni composites, derived from the samples of mesoporous Ti02, synthesized under various conditions (1 - 4), as well as commercial Ti02 Degussa P25 (5). The sample (i) was not exposed to hydrothermal treatment (HTT) and was only calcinated at 500 °C, the sample (2) was exposed to HTT at 100 °C and then calcinated at 500 °C, the sample (5) was exposed to HTT at 175 °C and then calcinated at 350 °C, and the sample (4) was exposed to HTT at 175 °C and then calcinated at 500 °C. The photocatalyst mass 0.05 g, reactor volume 10 ml, ethanohwater ratio 95 5, light intensity /o = 1.3-1 O 6 einstemmin"1, Ni2+mass ratio 0.5 %.

The photocatalyst was T1O2 Degussa P-25 (mainly anatase, specific surface area 50 m2 g-1). Ti02 in suspension was used in all photocatalytic experiments. Sodium hydrogen phosphate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium chloride, potassium sulfate, potassium bicarbonate, potassium hydrogen phosphate, potassium sulfate, potassium nitrate, potassium chloride, and iron chloride were used without further purification and were supplied by Fluka (Buchs, Switzerland). 

The use of a titanium dioxide photocatalyst for the removal of microcystin-LR in water has been demonstrated by Robertson et al. [163]. They reported a rapid photocatalytic degradation of this toxin using a Degussa P25 photocatalyst. In a subsequent study [68] a primary kinetic isotope effect of approximately 3 was observed when the destruction was performed in a heavy water solvent. Hydroxylated compounds were observed as products of the destruction process, while no destruction was observed when the process was investigated under a nitrogen atmosphere. 

Here, is the experimental mean rate of reaction per unit volume of catalyst, L is a characteristic length of the porous photocatalyst (i.e., the film thickness), t is the pore tortuosity (taken as three), D is the diffusion coefficient of the pollutant in air, Cg is the mean concentration at the external surface, and e is the catalyst grain porosity (0.5 for Degussa s P25). Such a treatment was performed by Doucet et al. (2006) while taking D of the pollutants to be approximately 10 m s. The estimated Weisz modulus ranged between 10 and 10, depending on the type of pollutant, that is, some three to five orders of magnitude smaller than the value of unity, which is often taken as a criterion for internal mass transport limitation. 

Upon stirring a suspension of titania powders in an aqueous solution of H2[PtCl6] in the dark, different maximum amounts were adsorbed. For the anatase hydrate and anatase/rutile samples TH (Kronos) and P25 (Degussa), there were taken up 4.0% and 1.1%, respectively, whereas only traces were adsorbed onto the rutile material Aid. The almost four times larger amount adsorbed by TH corresponds with the about four times larger surface area as compared to P25 (vide infra). Subsequent heat treatment at 200 °C afforded the desired photocatalyst (21). Surface modification may be performed also by simple grinding with PtCU, but the resulting powders are of lower photocatalytic activity and less stability (18,20). 

Because of its many applications, a few attempts are known in which ultrasonic waves have been applied for the synthesis of nanosized titania. Yu and coworkers [126] discovered a novel method for preparing highly photoactive nano-sized Ti02 photocatalysts with anatase and brookite phases. The method has been developed by hydrolysis of titanium tetraisopropoxide in pure water or a 1 1 Et0H H20 solution under ultrasonic irradiation the photocatalytic activity of Ti02 particles prepared by this method exceeded that of Degussa P25. 

Materials 4-Chlorophenol, 4-chlororesorcinol, hydroquinone, and hy-droxyhydroquinone were purchased from Aldrich Chemical Co., Milwaukee, WI 4-chlorocatechol was purchased from TCI American, Portland, OR. Acetonitrile, hexane, methylene chloride, methanol, and pyridine were obtained from the Fisher Scientific Co., Fulton, CA. The photocatalyst was Degussa P-25 titanium dioxide [mainly anatase form surface area 50 m2/g pHzpc (pH at zero point of charge) 6.3 contains some impurities such as Al203 (<0.3%), Si02 (<0.2%), Fe203 (<0.01%), and HCl (<0.3%)]. 

Two different photocatalysts, namely, Hombikat UV100 (Sachtleben Chemie) and P25 (Degussa) have been used in batch experiments [443] to compare their ability to degrade the toxic components of a biologically pretreated landfill... 

The photocatalyst (Ti02) used in this work was Degussa P25. Based on the manufacturer s information, the titania particles are a mixture of anatase and rutile crystalline phases (mostly anatase). Ti02 has an average particle size of 30nm and surface area 50 mVg. The other photocatalyst used was ZnO powder (Merck), about 99% pure, possessing BET surface area 4.5 m /g. The reactive red MSB dye (Chika Ltd) was used as such in the present study. 

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