Action spectra in semiconductor photocatalysis

/MeOH system is highlighted as an example of a photosystem that yields an ideal action spectrum. Most photocatalytic systems exhibit non-ideal action spectra, mostly due to one or more of the following: light intensity effects, crystal phase effects, dye-sensitisation, dye photolysis, charge transfer complex, CTC, formation and localized surface plasmon radiation, LSPR, absorption by a deposited noble metal catalyst. Each of these effects is illustrated using examples taken from the literatures and discussed. A suggested typical protocol for recording the action spectrum and absorption/diffuse reflectance spectrum of a photocatalytic system is described. The dangers of using a dye to probe the activity of a photocatalysts are also discussed, and a possible way to avoid this, via reductive photocatalysis, is suggested.