ABSTRACT
An ion-exchange membranes having a viologen moiety as anionexchange groups were prepared by the reaction of copolymer membranes composed of chloromethylstyrene and divinylbenzene and chloromethylated polysulfone with 4,4'-bipyridine. The viologen moiety of the membranes was reduced from a dication to a monocation radical and biradical by photoirradiation in organic solvents and aqueous salt solutions to release electrons. The active wavelength to reduce a viologen moiety of the membranes was below around 450 nm due to polymer effect. The anion-exchange membranes with a viologen moiety generated a photovoltage and photocurrent by photoirradiation after the membranes had been swelled with solvents, clamped between two ITO electrodes, and sealed with adhesive. This is based on the photoreduction of the viologen moiety of the membranes at photoside to release electrons and the electrochemical reduction of a viologen moiety at the dark side. Though the generation of photovoltage and photocurrent was very slow at the first irradiation, the generation speed was rapid once photoirradiation had been carried out due to the existence of the monocation radical. The 50-150 mV of photovoltage was observed at 200 k£J load resistance which was dependent on membrane species, species of solvent, additives in the photocell, etc. Another property of the anion-exchange membranes was the change in the transport numbers of sulfate, bromide, fluoride and nitrate ions relative to chloride ions in electrodialysis in the presence or absence of photoirradiation. In general, the permeation of anions larger than chloride ions through the membranes decreased in the presence of photoirradiation compared with those without the irradiation. It was concluded that the change in the transport numbers of various anions relative to chloride ions was due to the decrease in the pore size of the membrane because the charge density of the membrane decreased with photoirradiation.
