PHOTOINDUCED HYDROGEN EVOLUTION BY A ZWITTERIONIC DIQUAT ELECTRON ACCEPTOR. THE FUNCTIONS OF SiO2 COLLOID IN CONTROLLING THE ELECTRON-TRANSFER PROCESS.

Article abstract of DOI:10.1021/ja00358a006

Photosensitized hydrogen evolution from a basic aqueous SiO//2 colloid (pH 9-10) is accomplished with N,N prime -bis-(3-sulfonatopropyl)-2,2 prime -bipyridinium (DQS**0, 1) and colloidal platinum as mediating catalysts. In this system Ru(bpy)//3**2** plus acts as a photosensitizer and triethanolamine (TEOA) as ultimate electron donor. No hydrogen formation is observed in a homogeneous aqueous solution under similar conditions. The SiO//2 colloid affects the formation and stabilization of the intermediate photoproducts, Ru(bpy)//3**3** plus and DQS** minus multiplied by (times) , by means of electrostatic interactions. The electric potential of the particles assists the separation of the products from the initial 'encounter cage complex' and results in the repulsion of the reduced product, DQS** minus +19,from the colloidal interface. Consequently, the recombination rate of DQS** minus multiplied by (times) with the oxidized product Ru(bpy)//3**3** plus is retarded. The electrostatic functions of the colloid are confirmed by alteration of the ionic strength and pH of the colloid solution.