Photo initiators hydrogen peroxide

It was previously noted that no evidence for direct photolysis for PFOS or PFOA has been observed experimentally. In aqueous solutions alone and in the presence of hydrogen peroxide (H2O2), iron oxide (Fe203) or humic material, PFOS has been observed to undergo some indirect photolysis [28] whereas PFOA did not undergo indirect photolysis [29]. Using an iron oxide photo-initiator matrix model, the indirect photolytic half-life for PFOS was estimated to be > 3.7 years at 25 °C. The half-life of PFOA was estimated to be > 349 d. 

The radical C-H transformation of ethers is generally initiated by a-hydrogen abstraction with highly reactive radicals generated from such initiators as peroxides [3a, g], photo-activated carbonyl compounds [3b—d], metallic reagents [3i, j], and redox systems [3f, h[. Various combinations of ethers, radical initiators, and radical acceptors (e.g. carbon-carbon multiple bonds) may be used as the reaction components [6], Several notable means of direct C-C bond formation via the radical a-C-H transformation of ethers involve the use of triflon derivatives [7], the phthalimide-N-oxyl (PINO) radical [8], 2-chloroethylsulfonyl oxime ethers [9], and N-acyl aldohydrazones [10],... 

We focus initially on the photochemical behaviour of complexes of Fe(III) with simple carboxylic acids and give particular attention to oxalic acid. This compound is prevalent in atmospheric aerosols [28], provides a simple example of environmentally important light-mediated ligand-to-metal charge transfer (LMCT) processes which result in ligand decarboxylation [27] and is used to initiate the degradation of contaminants both in the absence and presence of added hydrogen peroxide (via the so-called modified photo-Fenton process [29,30]). In addition, the photochemistry of Fe(III)-oxalate complexes has been studied in detail, as it is the basis of... 

UV oxidation of organic water pollutants in the presence of hydrogen peroxide, ozone or both with powerful medium-pressure mercury lamps is performed on industrial scales (Gottschalk et al., 2000). The synergistic combination of ozone and UV is especially suited for water sanitation, i.e. treatment of swimming pool and spa water (Rice, 1997). Many full-scale remediation applications of photo-initiated AOPs using hydrogen peroxide or ozone are already in operation (Chem-viron Carbon, 1997, Freeman and Harris, 1995). 

However, the comparison of the data collected in Tab. 6-4 offers a realistic estimate of process efficiencies. The quantum yield of OH radical formation on Ti02 is only 4 to 10% at best. This is the major reason why Ti02 processes have, in general, not been commercially successful. Pure economic analysis (favored by Bolton) results in an estimate that hydrogen peroxide based photo-initiated AOPs are 50 to 100 times more efficient in their use of electricity than Ti02 photocata-... 

The reactive species in sensitized photo-oxidations appears to be molecular oxygen in an excited singlet state (3, 4, 5, 6). To test whether singlet oxygen reacts with benzene, it has been generated by the action of bromine on alkaline hydrogen peroxide (8). It is necessary to isolate the benzene from the aqueous peroxide since these react at 0°-I0°C. to give phenol and other products similar to those from the photo-oxidation. Initial qualitative results indicate that benzene is not readily oxidized by... 

Central composite design results for the photo-Fenton degradation of tehuthiuron (Teh), 2,4-dichlorophenoxyacetic acid (2,4-d) and diuron (Diu). Hydrogen peroxide and ferrioxalate initial concentrations are in mmol L" ... 

The various types of poly(acrylates) are initially prepared as mesogenic-like monomers in a similar manner to low molar mass liquid crystals. The acrylate group is usually located at a terminal position of the mesogenic monomer (195), which is polymerised (Scheme 48) in a radical process by using an initiator (e.g., AIBN or hydrogen peroxide) under thermal conditions or by photo-induction to generate a liquid crystalline poly(acrylate) (196). 

The literature describes the mechanism of photo-oxidative degradation in isotactic and atactic polypropylene well (Figure 5.25). However, the initiation step - the formation of primary radicals - has not been precisely explained. Photo-oxidative degradation in polypropylene, like thermal-oxidative degradation, also leads to the formation of hydrogen peroxides, ketones, esters, and acids. Figure 5.26 [653]. Simultaneously, molecular weight decreases. Table 5.2. 

When light is absorbed by the zinc oxide, the initial reaction may be a transfer of an electron from zinc to O2 absorbed on the surface, and the resulting -02 is a radical ion. Organic additives undergo oxidation, either by transfer of electrons to the photopositive surface of the zinc oxide after loss of a photo-excited electron by the crystal to O2 or by hydrogen abstraction by the peroxide radical ion to form HO2 . 

DBPOX, a low temperature initiator, decomposes easily at room temperature into t-butoxy radicals and carbon dioxide (Eq. (1)) The t-butoxy radical undergoes both addition to the monomer (Eq. (2)) and hydrogen-abstraction from the N-methyl group (Eq. (3)) Radicals 1 and II attack the monomer and propagate yielding poly(NMAAm) radicals (Eq. (4)). The stable poly(NMAAm) radic was similarly formed in the photo-sensitized polymerization with azo-bis-isobutyronitrile(AIBN) or di-tert-butyl peroxide(DBPO). In the latter system, the concentration of living radical III reached 1 x mol/1... 

Free-radical addition of hydrogen bromide to alkenes can also be initiated photo-chemically, either with or without added peroxides. 

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