EFFECTS OF CHARGED POLYMERS ON INTERFACIAL ELECTRON-TRANSFER PROCESSES IN CDS COLLOIDAL SYSTEMS

The present work concerns the study of several electron and hole scavengers in CdS colloid systems. The colloid particles were stabilized by different polymers: the negatively charged poly(styrenesulfonate) and polyacrylate, the positively charged polybrene (repeating unit -(CH2)4N(CH3)2-(CH2)6-N(CH3)2), and the neutral poly(vinyl alcohol). The scavengers used were the positively charged methyl viologen and the double zwitterion sulfonatopropyl viologen [and several polymers including viologen groups in their repeating units]. Hole scavengers studied were tetramethylphenylenediamine and dimethoxybenzene. The latter is not oxidized by CdS holes. The polymers adsorb to the colloid surface and affect the concentrations of the solute scanvengers in the vicinity of the colloid particles. Both electrostatic and hydrophobic forces are involved. Comparison between the results of the various polymers shows that the yields of the scavenging products cannot be accounted for in terms of the polymer effect on the local scavenger concentration alone. Interaction between the electric field of the charged polymer and the semiconductor colloid particle is suggested to affect the potential of the colloid and the rate of charge migration to the surface. This influences the scavenging yield, which depends on the competition between recombination and charge transfer through the colloid surface.