Photocatalyst polyoxometallates

Polyoxometalates (POMs) have been the object of growing interest as photocatalysts for the oxidation or reduction of organic or inorganic compounds [225-230], Many of these POM systems share the same general photochemical characteristics as semiconductor photocatalysts. For example,... 

The first popular photocatalysts in homogeneous media were transition metal carbonyls (eg M(CO)6, where M=Cr, Mo, W Fe(CO)5, Fe3(CO)i2, Ru3(CO)i2, Mn2(CO)10) and their derivatives [28], Recently, other systems have been intensively studied, eg iron(III) complexes, especially in the photo-Fenton reactions [63-78, 139-142],polyoxometallates,porphyrins, metalloporphyrins,and other porphyrinoid sensitizers. 

Polyoxometallates (POMs), molecular anionic metal oxides, show the ability to act as homogeneous photocatalysts in electron transfer from organic electron donors to metal ions. In the process, illumination at the LMCT band (visible and near-UV regions) renders POMs strong oxidants that are able to abstract electrons from a... 

This activity is particularly useful for degradation of strongly hazardous substances or recalcitrant pollutants that are difficult to remove in chemical or biochemical processes. In this respect any pathway leading to abatement of chromate(VI) pollution arouses interest. One such pathway seems to be created by cooperation between iron and chromium photocatalytic cycles, which were reported as effective in conversion of chromate(VI) into Crm species [20-23,97]. A synergistic photoreduction of CrVI and Cu11 mediated by Ti02 [98], or photocatalytic reduction of Crvl and oxidation of organic matter by environmental polyoxometallates as photocatalysts [99], may constitute alternative possibilities. 

A series of 1-aryl alkanols were investigated using polyoxometalates such as Wio032" as a photocatalyst (Scheme 6.4). A clean oxidation reaction of the side chain of the aryl alkanol led to the formation of the aryl ketone. This process supports a hydrogen transfer mechanism as the rate determining step. The efii-ciency of the reaction was mainly determined in the presence of oxygen [27]. 

Bonchio, M., Carraro, M., Scorrano, G., et al. (2004). Photooxidation in Water by New Hybrid Molecular Photocatalysts Integrating an Organic Sensitizer with a Polyoxometalate Core, Adv. Synth. Catal., 346, pp. 648-654. 

Early transition metals (V, Nb, Ta, Mo, W) in their highest oxidation states, can form metal-oxygen cluster anions, commonly named polyoxoanions or polyoxometalates (POMs). POMs have been largely used as efficient photocatalyst for the complete degradation of organic pollutants in water (Antonaraki et al., 2002 Kormali et al., 2004 Mylonas and Constantinou, 1996). These compounds have interesting redox properties for catalytic applications. In particular, POMs in the solid state are particularly suitable... 

Li H, Gao S, Cao M, Cao R (2013) Self-assembly of polyoxometalate-thionine multilayer films on magnetic microspheies as photocatalyst for methyl orange degradation under visible light irradiatiotL J Colloid Interface Sci 394 434-440... 

Wang Y, Lu K, Feng C (2013) Influence of inorganic anions and organic additives on photocatalytic degradation of methyl orange with supported polyoxometalates as photocatalyst. J Rare Earths 31 360-365... 

Farhadi S, Zaidi M (2009) Polyoxometalate-ztrconia (POM/Zr02) nanocomposite prepared by sol-gel process a green and recyclable photocatalyst for efficient and selective aerobic oxidation of alcohols into aldehydes and ketones. Appl Catal A 354 119-126... 

Cao M, Lin J, Lu J, You Y, Liu T, Cao R (2011) Development of a polyoxometalate-based photocatalyst assembled with cucurbit[6]uril via hydrogen bonds for azo dyes degradation. J Hazard Mater 186 948-951... 

Bonchio M, Carraro M, Scorrano G, Bagno A (2004) Photooxidation in water by new hybrid molecular photocatalysts integrating an organic sensitizer with a polyoxometalate core. Adv Synth Catal 346 648-654... 

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