7 shows that CV photodegradation
increases with increases the heterogeneous photocatalyst concentration upto 150 mg but decreases at 200 mg.
It can be seen that the photocatalytic activity of the ZnO with dumbbell-like structures (7c) was higher that of the ZnO rods for the photodegradation
of phenol under UV light irradiation.
Its removal from water will be examined here by photodegradation
. This strategy is important for further practices aiming at purifying water from pharmaceutical wastes that are commonly found in the environment [39-42].
Figure 5 shows the FTIR spectra of the hydrotalcites activated at 500[degrees]C before the photodegradation
in which it is observed that there are no signals in the range of 4000 to 3000 [cm.sup.-1] corresponding to the hydroxyl groups because the phases have evolved to amorphous and periclase spinel as confirmed by XRD.
The ZnO sample (SA1) showed in Figure 7 features high photocatalytic activity in paraquat photodegradation
. It is well known that as the concentration of the pollutant increases, the photocatalytic activity decreases due to the decrease of the tendency of the irradiating light beam to meet the catalyst particles.
Thus, it is indicated that the as-prepared [In.sub.2][S.sub.3]/CNF-2 heterojunction structures have the appropriate Eg for photodegradation
of organic pollutants under visible light irradiation.
This observation suggests that the strongest electrostatic attraction force between the dye molecules and the surfaces of catalysts is at this value of pH, leading to maximum activity of oxidation, and thereby, high photodegradation
efficiency of the CR dye is obtained.
The outcome of pH on the photodegradation
of Cr(VI) is revealed in Figure 6.
An important characteristic of the photodegradation
is that this process occurs on the surface of the polymer  and the depth of penetration of light, of the order of only some [micro]m of thickness, depends on the wavelength .
The application of this treatment process was more favorable in the photodegradation
of DDT compared to lindane which resulted 73-87% and 36-68% of removal respectively.
Nowadays, several authors have already studied the influence of (POA) on the photooxidation of polymers; for instance, Pablos and coworkers  studied the effect of iron and calcium stearates on the photodegradation
of polyethylene (LDPE and LLDPE) under natural and artificial exposure using chemiluminescence.
There are different types of nanoparticles that can be used for the photodegradation
of organic pollutants.