PHOTOCHEMICAL OXIDATION OF WATER ON A 1 MU-M AG+ ZEOLITE LAYER

When silver zeolites are illuminated in the presence of water, Ag+ ions are reduced and molecular oxygen is evolved with a high quantum yield. The lowest energy transition in the previously unilluminated zeolite is a charge transfer which excites an oxygen lone-pair electron to the silver species coordinated by the zeolite and initiates the oxidation of water. Investigation of the spectral sensitivity shows that self-sensitization takes place: as the reaction proceeds, the sensitivity ''tends initially from the near-UV-visible wavelengths to the red range. We have developed a technique for the preparation of monograin zeolite layers and have been able to demonstrate the self-sensitization of photo-oxygen evolution on these samples. The self-sensitization is a quantum size effect in which, during the photoreaction, new chromophores are produced with bathochromically shifted absorption. The total amount of zeolite irradiated was 70 mug, coated as a thin layer on a quartz window. This is 10(3) times less than in earlier investigations. Therefore a new experimental technique was developed based on a very small reaction volume.