**2. Materials and methods**

**1. Introduction**

242 Titanium Dioxide - Material for a Sustainable Environment

Several human activities may result in the presence of numerous and various types of emerging chemical contaminants and toxicants in water or wastewater. Pesticide is one of the most common groups of chemical pollutants found in wastewater effluents due to their widespread use in agriculture in order to maintain crop quality and quantity [1, 2]. Their widespread use for the prevention, control, or elimination of pests has led to public health concerns in recent years. According to an extended published literature, pesticides are usually detected in trace concentrations (ng L−1 or μg L−1) and consequently are considered as micropollutants, which among other characteristics are specific water and wastewater constituents that cannot be removed by primary or secondary conventional treatment. As a result, the adaptation and application of advanced oxidation processes (AOPs) are necessary to decompose these persis-

AOP is a class of oxidation techniques and procedures that are based on the in situ generation of highly reactive and oxidizing radical species (mainly powerful hydroxyl radicals (•OH)), which interact with the molecules of the organic pollutants and lead to their progressive degradation. AOPs can be classified as photochemical or non-photochemical processes that furthermore can be categorized either as homogeneous or heterogeneous. More specifically, heterogeneous AOPs require the addition of a solid semiconductor (such as metal oxides and sulfurs of Ti, Al, Zn, V, Cr, Mn, etc., or organometallic catalysts) to produce a colloidal suspension that is stable under radiation and is required to stimulate a photochemical reduction reaction in the solid/liquid interface (occurrence of accelerated photoreaction). In particular,

recombine or dissociate (both reactions take place in competition); when dissociation occurs, conduction band electrons and valence band holes are produced, which are able to migrate to the particle surface and interact with adsorbed electron acceptors (oxygen) and oxidize elec-

AOPs, the heterogeneous AOPs have the advantage of the easier separation from the product

The use of heterogeneous photocatalysis has been shown as an ideal methodology for the decontamination and restoration of water contaminated with persistent organic pollutants (POPs) in developing countries [6–8]. Nowadays, among the most promising and successful applications of heterogeneous photocatalysis applied for the removal of various toxicants

onstrated as one of the most frequently used methodologies employed for the treatment of chlorinated phosphate esters and carbamic, thiocarbamic, and triazine pesticides [4–6, 9–11]. The focus of the present chapter is to provide the results of the photocatalytic degradation study conducted with five selected organophosphorus pesticides (OPPs) (azinphos methyl, azinphos ethyl, disulfoton, dimethoate, and fenthion) by heterogeneous photochemical pro-

. The process of UV-TiO<sup>2</sup>


dimethoate and fenthion as they proved to be more resistant in the previous set of photolysis

, bandgap energy)

, respectively, acting as energy carriers) that can

) is included, since it has been dem-

system was applied to the photooxida-

system was applied only to degradation of

O) yielding in hydroxyl radicals. Compared with the homogeneous

tent compounds from contaminated environmental matrices [3].

illumination of the catalyst with radiation of the proper wavelength (≥E<sup>g</sup>

and h+

generates electron and hole pairs (e−

OH and H<sup>2</sup>

(meaning the treated effluents) [4, 5].

cess using UV light and TiO<sup>2</sup>

tion of all selected OPPs, while the UV-TiO<sup>2</sup>

from water, photocatalysis over titanium dioxide (TiO<sup>2</sup>

tron donors (−
