Electron Donation and Positive Hole Injection

In the early days of colloid chemistry, it has occasionally been observed that metal solutions degrade when exposed to light. The ongoing photochemistry, however, has rarely been investigated. The question is, whether hot electrons that are produced in a metal by the absorption of photons are able to initiate chemical reactions before they recombine with the holes Photo-electron emission from compact electrodes has been studied in photo-electrochemistry. The quantum yield of this process is of the order of lO electrons per absorbed photon. It increases with the negative potential of the electrode. However, electron emission into the solvent from nano-sized particles might be facilitated since 1) the rate of thermalization of hot electrons is decreased due to the lower density of states, and 2) only a short distance has to be traversed by a hot electron in order to reach the surface. 

When the solution contains propanol-2 in addition to N2O, nitrogen still is formed, but the silver particles do not dissolve. Under these conditions, the OH radicals from reaction 12 react with the alcohol, forming reducing radicals, see reaction 1, which in turn reduce the Agn intermediate. The net result is a silver catalyzed photoreaction between nitrous oxide and propanol-2  

Silver particles also dissolve in deaerated solution when illuminated in the presence of cyanide, the efficiency being even greater than in the presence of N2O. In the presence of CN , hydrogen is produced, the overall reaction being 

---