Aqueous photocatalytic decomposition

In situ metallization has been claimed to provide a convenient method for the preparation of metal-deposited and metal sulfide deposited CdS during photocatalytic decomposition of aqueous sulfide. As-prepared MS/CdS and M/CdS bifunctional photocatalysts (MS = Pt or Ir sulfide M = Pt or Ir) were reported to be more active photocatalysts than CdS and ex-situ metallized CdS [285]. 

Oosawa, Y. 1984. Photocatalytic decomposition of aqueous hydroxylamine solution over anatase and precious metal anatase. J Phys Chem 88 3069-3074. 

Table 3.2 Rate of photocatalytic decomposition of malachite green by Ti02 thin films immersed in its aqueous solution (2.5 x 10-4 mol dm-3)...

Muneer et al. [129] examined the photocatalytic oxidation of three pesticide derivatives, propham, propachlor and tebuthiuron in aqueous TiC>2 suspensions. The rates of degradation of each compound were found to be strongly affected by the type of TiC>2 used, pH, catalyst and substrate concentration. For each compound several intermediate products were identified using GCMS. This study indicated that the photocatalytic oxidation process proceeded by reactions involving electron transfer, hydroxyl radical and superoxide radical anions. Scheme 2 displays the proposed mechanism for the photocatalytic decomposition of propham. 

Lee et al. reported that a colloidal solution containing nano-sized Ti02 (anatase) particles was obtained by solvothermal treatment of titanium isopro-poxide in 1-butanol at 200°C in the presence of a small amount of aqueous HCl. They found that the particles coated on y-alumina showed excellent performances for photocatalytic decomposition of CHCI3. 

Fig. 19.16. Experimental setup of a flowthrough quartz photoreactor used for photocatalytic decomposition in aqueous Ti02 dispersions using cylindrical electrodeless mercury discharge lamps. A, cylindrical EDL...

Alumina beads Heat attachment Photocatalytic decomposition of leather dye, acid brown 14 in aqueous solution [564]... 

Figure 19.11 The photocatalytic decomposition of H2O and the separate evolution of Fl2 and O2 under light irradiation with a 500 W Xe arc lamp on the Vis-Ti02/Ti/Pt thin film photocatalyst having an H-type ceU with two aqueous phases of different pH values, at 298 K...

The effect of heat treatment and crystal structure of dense Ti02 coating on the photocatalytic decomposition of aqueous acetic acid was also reported [43]. The efficiency increases with the content of anatase phase and thickness up to 300 nm. Yu et al. [44] prepared dip coatings on fused quartz and/or soda-lime glass with a barrier layer of Si02 and studied the degradation of MO as a function of the number of layers, finding that activity increases when the thickness and temperature are increased. Films treated at 500 °C show maximum photocatalytic activity. 

HPLC-UV-MS was further applied for the monitoring of the degradation of Methyl Red and Methyl Orange by separating and identifying the decomposition products. The photocatalytic degradation was carried out in aqueous media containing oleic acid and... 

Photocatalytic reduction of C02 can be accomplished by suspending photosensitive semiconductor powders in aqueous solutions under irradiation, usually using UV light.129156 Photoreduction of C02, however, is in competition with H2 formation due to water decomposition, and leads to mixtures of reduced carbon products. Selectivity, therefore, is one of major problems of these processes. 

After the finding of photocatalytic water decomposition by Pt Ti02, many new semiconductor photocatalysts which are able to photolyze watei ir. ar. aqueous suspension have been reported.383 These photocatalysts are characterized... 

Supported mixed metal catalysts are also prepared by other means such as the deposition of bimetallic colloids onto a support O and the decomposition of supported bimetallic cluster compounds.208 The photocatalytic codeposition of metals onto titania was also attempted with mixed results.209 with a mixture of chloroplatinic acid and rhodium chloride, very little rhodium was deposited on the titania. With aqueous solutions of silver nitrate and rhodium chloride, more rhodium was deposited but deposition was not complete. In aqueous ammonia, though, deposition of both silver and rhodium was complete but the titania surface was covered with small rhodium crystallites and larger silver particles containing some rhodium. With a mixture of chloroplatinic acid and palladium nitrate both metals were deposited but, while most of the resulting crystallites were bimetallic, the composition varied from particle to particle.209... 

The initial steps OF photocatalytic oxidation of aromatic compounds in aqueous suspensions of TiOa or other semiconductors have been described in terms of several mechanisms (1-13). The most important and widely accepted of these mechanisms is the generation from water decomposition of hydroxyl radicals that attack the aromatic ring. 

Reaction Mechanisms. Our analysis of intermediates and reactions reported by other researchers leads to proposed reaction pathways describing the photocatalytic oxidation of 4-chlorophenol in TiOz aqueous suspensions. The photocatalytic oxidation reaction is brought about by OH radicals, which are formed mainly from water decomposition on the Ti02 surface upon UV light irradiation (9-13). The OH radicals can either directly react with the adsorbed organic species on the TiOa surface or diffuse to the solution and then react with the dissolved organic species in the solution phase. Both reactions lead to formation of hydroxylated products such as 4-chlorocatechol, hydroquinone, 4-chlororesorcinol, and hydroxyhydroquinone as the initial products (Figure 6). Eventually, the reaction will mineralize these interme-... 

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