Solar desalination of seawater using double-dye-modified PTFE membrane.

The production of purified water by seawater desalination is now a significant countermeasure against recent severe water shortage. As the global warming is thought to be a dominant cause of the water scarcity problem, the energy employed for the desalination should be free from fossil fuels. We recently reported a simple membrane desalination combining the harvesting of solar energy and the membrane permeation of vaporized water. Water on a PTFE (polytetrafluoroethylene) membrane modified with disperse red 1 (DR1) as an azobenzene dye that photo-isomerizes with visible light permeates through it under visible light irradiation. The penetrated water was efficiently desalinated to produce purified water by membrane distillation mechanism, where water was evaporated by DR1 using solar energy. In this paper, we report that the aqueous solution of rhodamine B on non modified PTFE membrane permeated the membrane to be purified under visible light irradiation. This paper also reports that a PTFE membrane modified with disperse blue 14 (DB14) was active for the desalination. Thus, even these non-azobenzene dyes were revealed to be available for the light induce water permeation. When DR1 and DB14 were modified to PTFE membrane concurrently, a higher performance of seawater desalination using simulated sunlight was achieved by efficient absorption of the irradiated light with DR1 and DB14.