Photocatalyst Weight

Both lamp irradiation and catalyst concentration play vei7 important roles in photocatalytic processes. The effect of the iiTadiation parameter on the overall (apparent) rate of photoconversion can be represented by a power vai ying between 0.5 and 1. The influence of the photocatalyst weight can also be considered using a generic function of the irradiated catalyst. 

Another very important visible light-initiated reaction of alkyl aluminum porphyrins is their 1,4-addition to alkyl methacrylates to produce ester enolate species [Eq. (4)]. This enolate then acts as the active species in the subsequent polymerization of the acrylate monomer. For example, Al(TPP)Me acts as a photocatalyst to produce polymethylmethacrylate with a narrow molecular weight distribution in a living polymerization process [Eq. (4)]. Visible light is essential for both the initiation step (addition of methylmethacrylate to Al(TPP)Me) and the propagation... 

These two complexes were also found to be active photocatalysts for the polymerization of ethylene (77, 47, 47a). Irradiation of solutions of either complex under 1 atm ethylene resulted in the rapid formation of high-molecular-weight polyethylene. The rate of ethylene polymerization was increased by the addition of various metal halides prior to photolysis. The mechanism of this reaction was not investigated but the authors postulated that the active species were photogenerated Ziegler-Natta-type catalysts (77). 

Higher molecular weight olefins (CsHs, C4H8, etc.) are, most likely, produced by the secondary catalyzed reactions of chemisorbed ethylene, (C2H4)d,en,- er the photoreaction, the photocatalyst remains in its photoreduced form (W -OH) at ambient temperature. It could be thermally regenerated to its initial oxidized form (W =0) by releasing hydrogen ... 

Both catalysts are deep UV-absorbers like other iodonium photoinitiators (. The UV absorption spectrum of a. OOOIM solution of each species in methylene chloride is depicted in Figure 1. A bathochromic shift to higher wavelength absorption coupled with lower molecular weight results in Catalyst B being a more efficient photocatalyst than Catalyst A in those systems where both iodonium salts are freely miscible, as will be described in greater detail below. 

The PMR permeate quality depends also on the membrane properties and membrane process applied. MF and UF membranes are efficient in the separation of photocatalyst particles, but are not able to reject low molecular weight compounds. Therefore, products and by-products of photodegradation towards which the membrane does not exhibit separation properties can freely permeate through the membrane. However, it should be mentioned that the quality of permeate obtained in PMRs is higher than in the case of the MF/UF processes conducted without photocatalysis, because of photodegradation of contaminants in the feed solution. 

The film containing ST-01 photocatalyst loses weight rapidly (e.g., reaches 39% loss after 870 h) mainly due to photocatalytic decomposition of the resin by Ti02. 

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