The aim of this paper is to find out the optimal degradation condition for two potential environmental pollutants, chloridazon and metribuzin (herbicide derivatives), employing advanced oxidation process using TiO2 photocatalyst in aqueous suspensions. The degradation/mineralization of the herbicide was monitored by measuring the change in pollutant concentration and depletion in TOC content as a function of time. A detailed degradation kinetics was studied under different conditions such as types of TiO2 (anatase/anatase-rutile mixture), catalyst concentration, herbicide concentration, initial reaction pH, and in the presence of electron acceptors (hydrogen peroxide, ammonium persulphate, potassium persulphate) in addition to atmospheric oxygen. The photocatalyst, Degussa P25, was found to be more efficient catalyst for the degradation of both herbicides as compared with two other commercially available TiO2 powders like Hombikat UV100 and PC500. Chloridazon (CHL) was found to degrade more efficiently under acidic condition, whereas metribuzin (MET) degraded faster under alkaline medium. All three electron acceptors tested in this study were found to enhance the degradation rate of both herbicides. 1. Introduction Clean and safe drinking water is vital for human health, wildlife, and also for a stable environment. Yet, water is being polluted at alarming rates, with chemicals, nutrients, metals, pesticides, and other contaminants from industrial effluents, chemical spills, and agricultural runoffs [1, 2]. A wide variety of herbicides and other chemicals are applied to agricultural field and lawns mainly to control undesirable vegetation. A fraction of herbicides applied to these sites end up as runoff. This runoff goes into the streams, rivers, and lakes. Some of the herbicides also end up in groundwater systems by percolating down through the soil. As a result, herbicides are widely found in rivers, streams, lakes, and even in drinking water [3]. These chemicals due to their toxicity, stability to natural decomposition, and persistence in the environment have been the cause of much concern to the societies and regulatory authorities around the world [4]. The development of appropriate methods to treat these contaminated water is necessary before it is used for any useful purpose. The photocatalysed degradation of various organic systems employing irradiated TiO2 is well documented in the literature [5–14]. Briefly, when a semiconductor such as TiO2 absorbs a photon of energy equal to or greater than its band gap energy, an electron may be promoted
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