*3.2.2. Effect of the pesticides' initial concentration on photocatalytic degradation rate*

In order to investigate the dependence of the photolysis rate *(ro* ) on the pesticide reactants' initial concentration (*Co* ), a set of photodegradation experiments was carried out by varying the initial concentration of the solute from 5 to 60 mg L−1 (a concentration range that facilitated the procedure of LLE method), whereas the catalyst loading was maintained constant (100 mg L−1). Throughout the performed tests, it was assumed that, in the first stages of irradiation (≤20% reduction), no variations took place resulting from other parameters such as competitive effects of intermediates, pH changes, etc. [6, 17]. The effect of the insecticides' initial concentration (*Co* ) of each individual pesticide reactant on the initial reaction rate *(ro* ) was independently obtained and illustrated in **Figure 4** (the inset of **Figure 4** is the linear transform of 1/*ro* versus 1/*Co* values).

From the depicted experimental data acquired in current investigation and are shown in **Figure 4**, it is obvious that the degradation rate increased with the increase of the concentration of all of the studied compounds until it reached a saturation value (10 mg L−1). At higher concentrations above that value (>10 mg L−1), the initial rate started to become constant and independent of target solutes' concentration.
