Photodegradation of malachite green in the aqueous medium

Abstract

Ti02 assisted photodegradation of malachite green (MG) has been examined in Ti02 dispersions under both UV and visible light and found that degradation is faster in UV-light (A 320 nm). Adsorption is prerequisite for the Ti02 assisted photodegradation and the extent of degradation have been discussed in terms of the Langmuir-Hinshelwood model. Like most semiconductors the photocatalytic nature of Ti02 is pH dependent because of its amphoteric nature. It has been found that pH ranging from 3-5 is suitable for the photodegradation of this system. Much attention has been directed at investigating degradation of organic pollutants mediated by Ti02 particles in aqueous dispersion under UV -light irradiation. Mechanistically, it is now commonly accepted that the photo catalyst Ti02 is first excited by UV light and subsequently initiates the photo degradation process. However, artificial UV light and Ti02 particles tend to be somewhat expensive and the UV component in sunlight reaching the earth surface and available to excite Ti02 is relatively small (ca. 35%). Therefore, our efforts have been focused on exploring means to utilize the sunlight and artificial inexpensive UV or visible light sources and degrading agents for treating polluted water. Organic pollutants like dyestuffs have the ability to absorb visible light. The electron transfer process from dye to semiconductor, especially Ti02 have been found to be very effective. Kamat and co-workers reported the photo-degradation of Acid-Orange 7 and Napthol Blue Black dyes pre-adsorbed on the surface of Ti02 particles I. The visible light mechanism suggests that the light excite the dyestuff.