Relative photonic efficiency

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. 

Serpone N, Salinaro A (1999) Terminology Relative Photonic Efficiencies and Quantum Yields in Heterogeneous Photocatalysis. Part 1 Suggested Protocol, Pure Appl. 

The difficulty of quantum yield determination in heterogeneous photocatalysis is related to reflection and scattering of UV/VlS radiation by suspended catalyst grains. Consequently, Serpone and Salinaro (1999) proposed a detailed protocol for the determination of photonic efficiencies (quantum yields) or relative photonic efficiencies, suggesting the photocatalyzed degradation of phenol as a standard reaction (using Ti02 as photocatalyst). 

Salinaro a, Emeline AV, Zhao J, Hidaka H, Ryabchuk VK, Serpone N (1999) Relative Photonic Efficiencies and Quantum Yields in Heterogeneous Photocatalysis. Part II Experimental Determination of Quantum Yields (Technical Report), Pure Appl. Chem. 71 321-335. 

The efficacy of semiconductor devices in photocatalysis is typically described by the quantum yield (j). While determining this parameter in homogeneous photochemistry presents no great difficulties, in heterogeneous media the challenges have been insurmountable to many workers for several years owing to the lack of an appropriate protocol. This was remedied by Serpone and Salinaro (1999), and appropriate experimental details were enumerated by Salinaro et al. (1999). Another useful parameter, the relative photonic efficiency 4ei (defined in Section 5.4.1) also provided a method by which work from many laboratories in environmental photochemistry could be calibrated when the more fundamental parameter 4> could not be accessed because of experimental limitations (Salinaro et al, 1999). 

We have seen that the relative photonic efficiency ( rei) introdnced earlier (Serpone et at, 1996) can compare photochemical activities of different heterogeneons systems. It can also be represented as the ratio between the photonic efficiency of a given reaction ( ) to the photonic efficiency st of a standard reaction (the photodegradation of phenol and TiOi Degnssa (now Evonik) P-25 were chosen for simplicity to describe the standard process and photocatalyst, respectively) see eq. 5.93. 

The relative photonic efficiency can also be expressed as the ratio of the appropriate quantnm yields of the corresponding processes (eq. 5.95). 

Thus, relative photonic efficiencies permitted for the first time the establishment of a correlation of the efficiency of a given process with similar work from other laboratories in the complex and active area of heterogeneous catalysis. The procedure for measuring rei is relatively simple and requires no sophisticated instrumentation. 

Once the photonic efficiency for a given snbstrate has been estimated, and an analogous photonic efficiency for phenol has been determined under identical experimental conditions of reactor geometry, light irradiance from the same light source, and the same batch of photocatalyst material, then the relative photonic efficiency can be calculated. Relative photonic efficiencies have been reported for several aromatic substrates by Serpone and co-workers (1996). The recommended protocol to determine rei follows the steps below ... 

The relative photonic efficiency is calculated from eq. 5.93, in which is the photonic efficiency of the substrate, which is given by R uhstiaJPo.x and st is the photonic efficiency for phenol, given by / phenoi/yO o.JL-... 

The above procedure has been further tested by determining the quantum yield of the disappearance of 4-chlorophenol (4-CP) by the method of photonic efficiencies the result was 4nm = 4-cp = 0.19 + 0.02, in good agreement with the method of relative photonic efficiencies (eq. 5.95), which gave 4 cp = 0.17 + 0.02 based on phenol as a sort of secondary actinometer. 

The relative photonic efficiency, rei> for the degradation of 4-chlorophenol over titania with respect to the degradation of phenol also scales with /(Emetine and Serpone, 2002c). The spectral dependencies of rei and of the ratio 5BQ/5ocat are illustrated in Fig. 5.52, which shows that the two dependencies correlate with each other, as expected theoretically. Again, there exists a spectral variation of /which is reflected in the spectral variation of the selectivity of the photocatalyst. 

Figure 5.52 Experimental spectral dependencies of the relative photonic efficiency of the photodegradation of (1) 4-chlorophenol and (2) S(BQ)/S(ClCat) of the ratio between the initial selectivity of the formation of benzoquinone and chlorocathecol, which scales with y. Reprinted with permission from Emeline and Serpone (2002). Copyright (2002) American Chemical Society.

Salinaro A., Emeline A. V., Zhao J., Hidaka H., Ryabchuck V. K. and Serpone N. (1999), Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part 11. Experimental determination of quantum yields . Pure Appl. Chem. 71, 321-335. 

SerponcN. (1997), Relative photonic efficiencies and qnantiun yields in heterogeneous photocatalysis , J. Photochem. Photobiol. A Chem. 104, 1-11. 

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