STUDIES ON SOLAR ENERGY CONVERSION DEVICES BASED ON DYESENSITIZED NANO-POROUS TI02 ELECTRODES AND PHOTOCATALYTIC HEAVY METAL REMOVAL FROM AQUEOUS MEDIA USING TI02 PHOTOCATALYSTS

Abstract

This study was undertaken to identify a more convenient prototype dye, compared to the earlier reported cyanidin, for the fabrication of the dye-sensitized nano-porous solid-state photovoltaic device and to further investigate the performance of the device. It was found that copper chlorophyllin can be successfully employed for the fabrication of the n-Ti02/copper chlorophyllin/p-Cul cell. The photo-excited pigment is found to inject electrons into n-Ti02 and holes into p-Cul generating photocurrent and photovoltage that are significant for a solid-state dye-sensitized cell. However, in the presence of oxygen, moisture and UV light the cell exhibits a rapid decay in photocurrent and photovoltage. It was found that the decay of the photocurrent and photovoltage in n-Ti02/copper chlorophyllin/p-Cul cell is almost completely suppressed, provided oxygen, moisture and UV-light (X < 348 nm) are excluded. It was also observed that the peak at 360 nm originating from bandgap excitation of Ti02 in the photocurrent action spectrum of the n-Ti02/cyanidin/p-CuI of n-type semiconductor/dye/p-type semiconductor (NDP) cell, attains a maximum for a certain critical surface concentration of cyanidin. Inorganic heavy metal ions form complex anions with sacrificial oxidizing agents such as citrate ions and tartarate ions. In the oxidative photodegradation of these complexes with TiO^, metals are found to become deposited on Ti02. The reactions are sufficiently sensitive to sunlight and, for practical application, Ti02 can be confined in a transparent dialysis bag to facilitate the disposal of extracted metals. Photocatalytic removal of Cu2+ from aqueous media in the presence of tartarate ions was carried out as a model system by this method. As an alternative method, It was found that Ti02 particles affixed to the surface of polypropylene films can be conveniently utilized to extract metals such as Cd, Pb, Hg, Ag, Bi and Cu in the presence of citric acid which acts as a sacrificial and complexing agent. As an example, photoextraction of lead from aqueous solution is described.