Photocatalytic pretreatment

Yasuda, M., Miura, A., Yuki, R., Nakamura, Y., Shiragami, T., Ishii, Y., et al. (2011). The effect of Ti02-photocatalytic pretreatment on the biological production of ethanol from ligno-celluloses. Journal of Photochemistry and Photobiology A Chemistry, 220, 195—199. 

G.-J. Chee, Y. Nomura, K. Dcebukuro, and I. Karube. Biosensor for the evaluation of biochemical oxygen demand using photocatalytic pretreatment. Sensor. Actual. B, 80 15-20, 2001. 

To enhance the formation of Ti species by reduction and nitration together, treatment with H2+N2 plasma and H2+Ar/N2+Ar (H2+Ar treatment followed by N2+Ar) were tried. However, there was no further improvement. H2+Ar/N2+Ar plasma treatment reduced the optimum treatment time to 20 minutes but improvement of photocatalytic activity imder fluorescent light was just 2.0 times. H2+Ar pretreatment seems to make substitutional doping of N easier through reduction reaction. 

At the same time Markham and Laidler (70) and also Veselovsky and Shub (71, 72) have shown that the photocatalytic activity of zinc oxide diminishes as a result of the calcination of specimens at high temperatures (around 1000°C) in the reduced atmosphere (such pretreatment results in an increase of the concentration of superstoichiometric zinc in the specimen). In other words, a donor impurity (zinc in excess of stoichiometry) retarded the reaction. 

Regardless of the exact mechanism at work, HCl catalyst pretreatment have been demonstrated to enhance the photocatalytic oxidation of toluene at low concentrations [68,69]. The apparent deactivation of the photocatalyst is noticeably delayed over HCl-pretreated catalyst samples in a manner similar to that seen with cofed toluene and TCE (Fig. 13). However, the pseudo-steady-state level of conversion appears to be nearly identical on both untreated and HCl-pretreated catalysts. Because the batch HCl pretreatment process incorporates a limited quantity of HCl into the catalyst surface structure, this similarity in longterm activity may be the result of surface chlorine depletion. 

Figure 13 Photocatalytic oxidation of (a) toluene (from Ref. 68) and (b) benzene (from Ref. 56) on HCl-pretreated TiO, catalysts.

The photocatalytic oxidation of w-xylene on an HCl-pretreated catalyst showed little or no enhancement [51]. This result is unusual, because enhanced photocatalytic oxidation of m-xylene has been demonstrated with cofed TCE [17]. Lewandowski and Ollis suggested that xylene, which adsorbs onto TiO2 in larger quantities than other aromatic contaminants, may be present at levels sufficient... 

Photocatalytic oxidation over illuminated titanium dioxide has been demonstrated to be effective at removing low concentrations of a variety of hazardous aromatic contaminants from air at ambient temperatures. At low contaminant concentration levels and modest humidity levels, complete or nearly complete oxidation of aromatic contaminants can be obtained in photocatalytic systems. Although aromatic contaminants are less reactive than many other potential air pollutants, and apparent catalyst deactivation may occur in simations where recalcitrant reaction intermediates build up on the catalyst surface, several approaches have already been developed to counter these potential problems. The introduction of a chlorine source, either in the form of a reactive chloro-olefin cofeed or an HCl-pretreated catalyst, has been demonstrated to promote the photocatalytic oxidation of... 

Alternatively, for an ABS polymer, a photocatalytic reaction can be applied as a pretreatment method prior to electroless plating. Unlike the conventional wet chemical method, this method can improve the adhesion strength without severe morphological changes (96). The pretreatment method uses a photocatalytic reaction in a TiC>2 dispersed solution. 

Either photocatalysis or ozonation alone achieved rapid disappearance of aromatic pesticide. In contrast, mineralization (TOC removal) was slow for both. However, photocatalytic mineralization was enhanced considerably by ozone pretreatment (Fig. 9.16).31) This effect may be explained by ozonolytic cleavage of the aromatic ring and subsequent formation of aliphatic compounds which are more degradable by photocatalysis. Simultaneous use of photocatalyst and ozonation (illuminated by 254 nm light) showed synergetic effect on TOC removal (Fig. 9.17).32) In this process scavenging of electrons by ozone is considered to play the most important role. 

Fig. 9.16 Effect of ozone pretreatment on photocatalytic degradation of the pesticide DEP. O 03, A Ti02, 03 + Ti02.

Akmehmet, I. and Arslan, I., Application of photocatalytic oxidation treatment to pretreated and raw effluents from the Kraft bleaching process and textile industrial, Environ. Pollut., 103(2-3), 261-268, 1998. 

Kim JS, Itoh K, Murabayashi M. Effect of humidity on the gas phase photocatalytic degradation of trichloroethylene over pretreated Ti02. Denki Kagaku 1997 65 966-968. 

Pulgarin C, Kiwi J (1996) Overview on Photocatalytic and Electrocatalytic Pretreatment of Industrial Non-Biodegradable Pollutants and Pesticides, Chimia 50, No. 3 50-55. 

Thus, surface effects and adsorption equilibria can dramatically influence the relative reactivity of photoelectrochemical transformations. Not only does the surface effectively control the movement of reagents from the electrolyte to the photo-activated surface and the desorption of products (avoiding overreaction or complete mineralization), but it also influences the stability and accessibility of photogenerated intermediates toward secondary intermolecular reactions [87]. Because the efficiency of diffusion and mass transfer to and from the photocatalyst surface depends on the solvent and catalyst pretreatment, quantitative predictions of photocatalytic reactions have proved to be difficult, although the qualitative principles governing each step of these events can be easily recognized. 

The surface crystal structure and particle size can also influence photoelectro-chemical activity. The mode of pretreatment, for example, dictates whether titanium dioxide exists in the anatase phase (as is likely in samples which have been calcined at temperatures below 500 °C) or in the rutile phase (from calcination temperatures above 600 °C) or as a mixture of the two phases for pretreatments at intermediate temperature ranges. The effect of crystalline phase could be easily demonstrated in the photocatalytic oxidation of 2-propanol and reduction of silver sulfate, where anatase is active for both systems. But when the catalyst was partially covered with platinum black, alcohol oxidation was easy, but silver ion reduction was suppressed. On rutile, redox activity was observed for Ag+, alcohol oxidation was negligible [85]. 

In fact, primary alcohols can be selectively oxidized to the corresponding aldehydes, without appreciable overoxidation, whereas poorer yields were obtained with secondary aliphatic aromatic alcohols [106c. Similarly, phenols can be converted to quinones [118]. The efficiency of the photocatalytic oxidation depends on the pretreatment and size of the photocatalyst [119], and analogous conversions are also obtained on heteropolyacids, which can be considered soluble analogs of Ti02 suspensions [120]. 

Effects of pretreatment on photocatalytic Photocatalytic activity of Cu-loaded and... 

UV irradiation. Regarding the development of photocatalytic water-purification technology, some of the specific challenges are more complete mineralization, higher quantum yields, better regeneration of the photocatalyst, and lower costs. Photocatalysis may play a dominant role in the purification of pretreated wastewater, and this may be more economical than treating raw wastewater directly. In addition, domestic photocatalytic water purifiers may be an attractive new prospect for commercial development. 

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