Photon efficiency

Side-chain photochlorination of toluene isocyanates yields important industrial intermediates for polyurethane synthesis, one of the most important classes of polymers [6]. The motivation for micro-channel processing stems mainly from enhancing the performance of the photo process. Illuminated thin liquid layers should have much higher photon efficiency (quantum yield) than given for conventional processing. In turn, this may lead to the use of low-intensity light sources and considerably decrease the energy consumption for a photolytic process [6] (see also [21]). 

Colyer, R. A., Lee, C. and Gratton, E. (2008). A novel fluorescence lifetime imaging system that optimizes photon efficiency. Microsc. Res. Tech. 71, 201-13. 

The overall process performance, as measured by photon efficiency (number of incident photon per molecule reacted, like the incident photon to current conversion efficiency, or IPCE, for PV cells), depends on the chain from the light absorption to acceptor/donor reduction/oxidation, and results from the relative kinetic of the recombination processes and interfacial electron transfer [23, 28]. Essentially, control over the rate of carrier crossing the interface, relative to the rates at which carriers recombine, is fundamental in obtaining the control over the efficiency of a photocatalyst. To suppress bulk- and surface-mediated recombination processes an efficient separation mechanism of the photogenerated carrier should be active. 

Despite recent achievements in active materials, PEC configuration and thermal catalysis, hydrogen production through direct water photosplitting with good solar photon efficiency and low cost apparatus is still far from practical exploitation. 

The key requirement for a SET step in the photocatalytic process seems to be the surface complexation of the substrate, according to an exponential dependence of the probability of electronic tunneling from the distance between the two redox centers [66]. However, as was pointed out in the preceding section on the key role of back reactions, the presence of a SET mechanism could be a disadvantage from an applicative point of view. If the formed SET intermediate (e.g., a radical cation) strongly adsorbs and/or does not transform irreversibly [e.g., by loss of CO from a carboxylic acid or fast reaction with other species (e.g., superoxide or oxygen)], it can act as a recombination center, lowering the overall photon efficiency of the photocatalytic process. 

Lanthanides activated luminescent materials are widely used for solid-state lasers, luminescent lamps, flat displays, optical fiber communication systems, and other photonic devices. It is because of the unique solid-state electronic properties that enable lanthanide ions in solids to emit photons efficiently in visible and near IR region. Due to the pioneer work by Dieke, Judd, Wyboume, and others in theoretical and experimental studies of the... 

Matsushita et al. (2007) subsequently demonstrated the ability to N-alkylate amines (Scheme 57) under continuous flow, again employing a quartz microreaction channel coated with a Ti02 or Pt-loaded Ti02 layer. As Table 28 illustrates, the illuminated specific surface area per unit of liquid attained within a microchannel is large even without taking into account the surface roughness of the catalyst however, it can be seen that a shallow reaction channel provides optimal photon efficiency. 

Side-chain photochlorination of toluene isocyanates leads to important industrial intermediates for polyurethane synthesis, one of the most important classes of polymers [264]. Irradiated thin liquid layers in microchannels should have much higher photon efficiency (quantum yield) than given for conventional processing. 

Serpone N, Salinaro A. Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part I Suggested protocol. Pure Appl Chem 1999 71 303-20. 

Serpone N, Sauve G, Koch R, et al. Standardization protocol of process efficiencies and activation parameters in heterogeneous photocatalysis relative photonic efficiencies. J Photo chem Photobiol A Chem 1996 94 191-203. 

Photonic Efficiency and Quantum Yield in Photocatalytic Systems... 

Sakthivel, S., M.V. Shankar, M. Palanichamy, B. Arabindoo, D.W. Bahnemann and V. Murugesan (2004). Enhancement of photocatalytic activity by metal deposition Characterisation and photonic efficiency of Pt, Au and Pd deposited on Ti02 catalyst. Water Research, 38(13), 3001-3008. 

---