(769a) Dye-Sensitized Photocatalyst – a Breakthrough In Green Energy and Environmental Applications

It has long been recognized that the sunlight falling on the earth surface is more than adequate to supply all the energy that human activity requires. The sun creates its energy through a thermonuclear process that converts about 6.5×10⁸ tons of hydrogen to helium every second. This process creates heat and electromagnetic radiation. The electromagnetic radiation streams out into space in all direction.

            In photocatalytic process photons are utilized to excite the semiconductor material producing electron/hole pair which ultimately involves in the degradation of pollutants and/or producing hydrogen from aqueous solution. These processes can be considered as green or semi green process as they uses solar energy (photons) to mineralize pollutants or to generate green fuel (hydrogen) without any CO₂ formation.

            Till date people have mainly used high energy photons (UV-A or UV-B) with different photocatalysts such as TiO₂, TiSrO₃, ZnO, etc. for environmental applications. At the same time photocatalytic water splitting showed remarkable progress in last decade under UV light which was started with the pioneering work of Fujishim and Honda (1972).  Due to the high cost and environmental impacts of utilization of artificial UV light in photocatalytic process, there has been a great deal of interest in the application of solar energy.

            The main drawback with these catalysts lies in their visible light inactivity (l ≥ 400-700 nm).  A lot of efforts have been made to improve the photocatalytic activity in the visible range.  Semiconductor photocatalyst were modified to expand the photo-response to visible region in several ways such as doping with cation/anion, sensitizing with dye, coupling with another small band gap semiconductor and implantation of metal ion. 

            In this work, we are using different dyes as the sensitizer of semiconductor catalyst (TiO₂, ZnO). Dye is adsorbed chemically onto the semiconductor surface by conventional adsorption process and the chemisorbed dye molecules play the role of spectral sensitizer, which upon excitation with visible light inject electron into the conduction band of the semiconductor.

            The main focus of this paper is to discuss the photo-degradation of phenol and photocatalytic hydrogen generation mechanism under UV and visible light; to elaborate the effect of different parameters such as dye concentration, electron donor concentration, amount of co-catalyst, light intensity, solution pH, and catalyst dose in dye-sensitized photocatalysis.

Keywords: solar, photocatalyst, dye-sensitization, phenol, hydrogen, water