Sacrificial agents

The very small number of growing polymer chains, when compared to the monomer concentration results in a very low overall concentration of free control agent and leads to inefficient capping of chain ends. One solution to this problem is the addition of a free or unbound control agent to the polymerization medium. This can take the form of a low molecular weight alkoxyamine, ATRP initiator, RAFT agent or, alternatively, free deactivator such as nitroxide or Cu(II). This species is often called a sacrificial agent. This solution also leads to the formation of free polymer that must ultimately be removed from the brush. 

B. Gall. Use of sacrificial agents to reduce carboxymethylated ethoxy-lated surfactant loss during chemical flooding Topical report. US DOE Fossil Energy Rep, 1989. 

Cu-CuO% nanoparticles (with a content of about 10 wt.%) on titania are effective for the production of hydrogen under sacrificial conditions [176-178], A fairly low concentration of Cu (2.5 wt.%) was sufficient to allow promising H2 production from ethanol-water and glycerol-water mixtures in the case of CuO% nanoparticles encapsulated into porous titania [179]. A key limitation of this system is photocorrosion under oxidizing conditions (oxygen and carboxylic adds as by-products of partial oxidation of the sacrificial agent). However, in the presence of UV irradiation, Cu photodeposition can occur, preventing loss of Cu [179]. 

Generation of hydrogen from H2S using cadmium sulfide with waste products as sacrificial agents to avoid photocorrosion of the semiconductor is expected to grow as a niche application. 

New photoelectrocatalytic solutions to separate the production of H2 and O2 by water splitting without sacrificial agents... 

Reactions were carried out in presence of sacrificial agents. O2 evolution aqueous silver nitrate solution. Hi evolution aqueous methanol solution,... 

This is a stringent requirement indeed as further elaborated in the next Section. Instead of actually photosplitting water, sacrificial agents may be added to the solution such that the HER and OER steps may be separately optimized and studied (Figures lb and lc). It must be borne in mind that now the overall photoreaction becomes thermodynamically down hill and is more appropriately termed photocata lytic (see below). Examples of sacrificial agents include sulfite for the photo driven HER case (Figure lb) or Ag+ as the electron acceptor for the photocatalytic oxidation of water (Figure lc). 

The ion-pair approach to the design of photosensitizers for electron transfer processes has been followed also in the case of [Co" (sep)] -oxalate system. In a deoxygenated solution, the excitation in the IPCT band of [Co" (sep)] +-HC204 causes the reduction of [Co" (sep)] + to [Co"(sep)] " and the oxidation of oxalate to carbon dioxide. The [Co"(sep)] + complex is a sufficiently strong reductant to reduce H+ to H2 at moderately acidic pH values. Thus, when the photoreaction is carried out in the presence of colloidal platinum catalyst, such a reaction indeed occurs, and H2 evolves from the solution in addition to carbon dioxide. Under such conditions, the overall reaction is the oxidation of oxalate, which plays the role of sacrificial agent, combined with the reduction of water to yield carbon dioxide and dihydrogen, according to Eq. 8. 

Ability of the alkali to work as a sacrificial agent by reacting with the divalents... 

Tennakone, K., and K.G.U. Wijayantha. 1998. Heavy-metal extraction from aqueous medium with an immobilized Ti02 photocatalyst and a solid sacrificial agent. Journal of Photochemistry and Photobiology A Chemistry 113(1) 89-92. 

In conclusion Fe(II), Mn(II) and Co(II)tetrasulphonato- phthalocyanine catalysed oxidation with molecular oxygen using isobutyraldehyde as sacrificial agent offers an simple and nonhazardous synthetic tool for the oxidation of sulphides to sulphones and olefins to epoxides. As these metal phthalocyanine are largely insoluble in dichloroethane type solvents, they can be recovered by filtration and reused. The isobutyric acid formed as byproduct in these reactions can be largely recovered by distillation when the reaction carried out at large scale. 

Effectiveness of sacrificial adsorbates is based on two basic assumptions No significant desorption of the sacrificial agent takes place when the surfactant solution makes contact with the surfaces with the preadsorbed materials, and the sacrificial agent adsorbs on the same adsorption sites as the surfactant. 

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