Abstract

Photocatalysis is an important process used in the decomposition of chemical residues, which are mostly xenobiotics present in contaminated water. The hydroxyl radical technology using a semiconductor with low energy UV light source has the advantage of oxidation and decomposition process when compared to other conventional techniques resulting in the decomposition of toxic chemicals to non toxic CO₂ and water. The early patents on the use of photolysis and photo catalysts go back to 1930 where hydrogen peroxide was used in the presence of direct sun light. Subsequently, introduction of metal catalysts played a role in enhancing the decomposition process of chemicals at industrial level. The thrust for the maximum utilization of solar energy and the introduction of several nano catalysts during the past decade has led to the development of several designs that automate the process of decontamination of pesticide residues at industrial level. Apart from the sunlight, UV and IR, the addition of sonication, heating and flow through systems have added additional advantages to the decomposition technique. The new methods patented have facilitated the decontamination of residues of pesticides which are insecticides, herbicides, fungicides acaricides etc in broad category or the so called xenobiotics from the aquifers, surfaces of fruits and vegetables a boost to the food industry. The cleaning or decomposing process takes place in the aqueous phase with the aid of formation of hydroxyl / oxygen free radicals and in the presence of transition metal catalysts which are mostly metal oxides and semiconductors. The TiO₂ catalyst, in different forms, from micro to nano and coated / doped are extensively used in several of these processes due to its easy excitation under direct sunlight / UV light facilitating the transfer of photon energy to the molecule to breakdown into small and non toxic fragments.

Keywords: Degradation, pesticides, photocatalysis, vegetables, water treatment, xenobiotics.