## 3 Results and Discussion
### Application of the Pd-Based Photocatalyst in the Degradation Process of Phenol
#### 3.2.1 Influence of the Photocatalyst Nature  
UV-vis molecular spectrometry allows both qualitative and quantitative analysis. The correlation between the UV absorption bands and the structure of the compounds (both for phenols and for the products resulting from the oxidation of phenols), so the qualitative analysis is a fast and economical identification technique. The shifting of the absorption maxima at a certain wavelength gives information about the functional groups that appear or disappear at a certain time of reaction.  
The UV-vis spectra of phenol at a different time of the photodegradation process for all the studied materials are presented in Figure 6. Initially, the phenol solutions were stirred for 30 min with the photocatalyst in the dark to achieve the adsorption-desorption equilibrium between the phenol and the surface of the photocatalysts.  
Figure 6: UV-vis spectra of the photodegradation process of phenol: (**a**) photolysis; and photocatalysis in the presence of (**b**) F; (**c**) F-IL; (**d**) F-IL-Pd1; (**e**) F-IL-Pd2.  
It is noted that in all the cases, the adsorption profile of phenol does not undergo any changes during this time. After the irradiation starts, a hyperchromic effect and a hypsyochromic (blue shift) effect of the absorption maximum occur. This means that the photodegradation process of phenol started, and the intermediate compounds are forming [32; 33]. At higher irradiation time occur the hypochromic effect when impregnated Florisil and impregnated Florisil and loaded with different amounts of Pd are used as photocatalysts.  
The degradation degree of phenol versus the photocatalyst nature at two different treatment time is presented in Figure 7. It is noted that both the presence of IL in the catalyst structure and the Pd leads to an increase in the degree of phenol degradation from aqueous solutions. In addition, increasing the amount of Pd from the catalyst has a positive influence on the process of phenol degradation. Further studies were performed using F-IL-Pd2 as a photocatalyst. Maybe a 10% increase of efficiency does not represent a significant increase, but it is a great increase taking into account the fact that F-IL is a prime material that could be used for Pd adsorption, and F-IL-Pd is a waste resulted from another process. Furthermore, if the photocatalyst contains Pd ions, it represents much higher stability in the degradation process of phenols because Pd ions are bounded on the IL and, in this case, is avoided the degradation of IL from the surface of Florisil during the photolysis process. If it is used as photocatalyst only the F-IL the TOC concentration increase during the treatment process, which suggest that a part of IL from the Florisil surface is degraded by the UV-vis irradiation, so the efficiency of this material decrease continuously, especially when is used in more cycles of treatment until it present, no photocatalytic activity. Furthermore, the increased efficiency of the F-IL-Pd is underlined by the fact that this efficiency for the phenol degradation is obtained much quickly (at 120 min) than in the case of using only F-IL as photocatalyst when this efficiency if obtained only after 180 min of treatment. This means that a shorter time is needed for treatment, which leads to decreasing treatment costs.