Photocatalytic efficiency

Abstract A convenient method to synthesize metal nanoparticles with unique properties is highly desirable for many applications. The sonochemical reduction of metal ions has been found to be useful for synthesizing nanoparticles of desired size range. In addition, bimetallic alloys or particles with core-shell morphology can also be synthesized depending upon the experimental conditions used during the sonochemical preparation process. The photocatalytic efficiency of semiconductor particles can be improved by simultaneous reduction and loading of metal nanoparticles on the surface of semiconductor particles. The current review focuses on the recent developments in the sonochemical synthesis of monometallic and bimetallic metal nanoparticles and metal-loaded semiconductor nanoparticles. 

Sivakumar M, Atsuya T, Kyuichi Y, Toru T, Teruyuki K, Yasuo I (2010) Dependence of sonochemical parameters on the platinization of rutile titania - an observation of a pronounced increase in photocatalytic efficiencies. Ultrason Sonochem 17(3) 621-627... 

The extension of this approach to artificial leaves based on titanates, niobates, tantalates, metal nitrides and phosphides, metal sulfides, and other transition metal oxides appears possible and useful in order to enhance the photocatalytic efficiency. In addition, the construction of multicomponent systems such as Ti02-CdS or MoS2-CdSe for overall water splitting could also lead to further improvements. This... 

Sakthivel, S., Neppolian, B., Shankar, M.V., Arabindoo, B., Palanichamy, M. andMurugesan, V. (2003) Solar photocatalytic degradation of azo dye comparison of photocatalytic efficiency of ZnO and Ti02. Solar Energy Mater. Solar Cells, 77 (1), 65-82. 

The addition of a second species can cause a decrease in charge recombination and an increase in the TiOz photocatalytic efficiency. Such behavior was examined by loading a series of species on the surface or into the crystal lattice of photocatalysts inorganic ions [148-152], noble metals [153,154], and other semiconductor metal oxides [155], It was thus proven that modifications produced by these species can change semiconductor surface properties by altering interfacial electron-transfer events and thus the photocatalytic efficiency. 

Others impurities such as carbon present in the sample may play a major role in the reduction of the photocatalytic efficiency so far as they behave as recombination sites of electron-hole pairs [309],... 

Ashokkumar, M., Maruthamuthu, P. 1989. Eactors influencing the photocatalytic efficiency of WO3 particles. J Photochem Photobiol A 49 249-258. 

The presence of chlorine radical chain reactions in a photocatalytic reaction system may significantly increase reaction rates and photocatalytic efficiencies. These enhancements would appear to have the potential to overcome the shortcomings typically associated with the photocatalytic oxidation of aromatic contaminants if a chlorine radical chain reaction could be initiated in conjunction with an aromatic photocatalytic reaction and if the chlorine radicals were capable of reacting with (and thus accelerating the conversion of) the aromatic contaminant of interest. Two potential configurations for combining chlorine radical promotion with the photocatalytic oxidation of aromatic contaminants have been examined in some detail mixed contaminant feeds and prechlorinated catalysts. 

It is important to emphasize that the photocatalytic reactivity of the metal ion-implanted titanium oxides under UV light (X < 380 nm) retained the same photocatalytic efficiency as the unimplanted original pure titanium oxides under the same UV light irradiation conditions. When metal ions were chemically doped into the titanium oxide photocatalyst, the photocatalytic efficiency decreased dramatically under UV irradiation due to the effective recombination of the photo-formed electrons and holes through the impurity energy levels formed by the doped metal ions within the band gap of the photocatalyst (in the case of Fig. 6)... 

It was also found that increasing the number (or amounts) of metal ion implanted into the deep bulk of the titanium oxides caused the photocatalytic efficiency of these photocatalysts to increase under visible-light irradiation, passing through a maximum at around 6 X 10 ions/cm of the catalyst, then decreas-... 

Adsorption of 4-aminobenzoic acid (ABZA) and 3-chloro-4-hydroxyben-zoic acid (CHBZA) was studied by Cunningham and Al-Sayyed (1990). Adsorption isotherm data were collected and analyzed to determine what role adsorption plays in influencing photocatalytic efficiencies. The Lang-muir-Hinshelwood kinetic model was applied and limitations of this model are discussed. 

Lichtin and Avudaithai (1996) compared the photocatalytic oxidation of methanol in both aqueous and gas phases. Photocatalytic efficiencies for the two phases were analyzed. Differences in the chemistry of photocatalytic oxidation for the two phases were also studied. Batch reactors were used for both aqueous- and gas-phase reactions. The reactor was a 450-mL, magnetically stirred, cylindrical vessel with an axially aligned 6-W fluorescent lamp emitting light at 360 nm. 02 was bubbled into the reactor at 35 mL/min. Samples were irradiated for 140 min, and product concentrations were determined using gas chromatography. 

Ni et al. [5], in a review on the developments in photocatalytic water splitting using Ti02 for hydrogen production, divided the techniques used to enhance the photocatalytic efficiency in two broad groups photocatalyst modification techniques,... 

The low photocatalytic efficiency of the supported systems is due to several factors that influence the catalyst activity. 

Riegel G, Bolton JR. Photocatalytic efficiency variability in Ti02 particles. J Phys Chem 1995 99 4215-4224. 

Kanai, N., T. Nuida, K. Ueta, K. Hashimoto, T. Watanabe and H. Ohsaki (2004). Photocatalytic efficiency of Ti02/Sn02 thin film stacks prepared by DC magnetron sputtering. Vacuum, 74(3 1), 723-727. 

The presence of platinum as an electron sink (Fig. 4) has long been known to enhance the separation of photogenerated electron-hole pairs [76] and, hence, to improve the photocatalytic efficiency in general [77-79]. However, most of these studies were focused on the influence of the extent of platinisa-tion on the photocatalytic efficiency. 

Mills et al. performed extensive investigations into the photocatalytic degradation of 4-chlorophenol. These included studies on the effects of different titania samples [102], effects of annealing temperature on the photocatalytic efficiency of titania [ 103] and a mechanistic study of the decomposition process. The rate of chlorophenol destruction was found to drop when using titania photo catalysts that had been heated above 600 °C. This was believed to be due to a build up of the rutile phase and a reduction of surface area following heat treatment above these temperatures. A number of intermediates were reported including 4-chlorocatechol, hydroquinone, benzoquinone and 4-chlororesorcinol [104],... 

The effect of metallic species on the photocatalytic degradation of acid orange-7, tartrazine and 3-nitrobenzenesulphonic acid was reported by Rao et al. [144], Only silver ions demonstrated any degree of enhancement with little influence being observed with Cu2+. Vanate, however, resulted in a reduction in photocatalytic efficiency. 

Studies in which additional parameters have been included as a means of enhancing the photocatalytic efficiency include the use of an applied electrical potential or the addition of hydrogen peroxide to the reaction mix-... 

Riegel G, Bolton JR (1995) Photocatalytic Efficiency Variability in 1102 Particles, J. Phys. Chem. 99, No. 12 4215-4224. 

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