## 3 Results and Discussion
### Transformation of Diclofenac via UVA Light in the Presence of PVDF
#### 3.2.2 Regeneration of PVDF  
As discussed in previous sections PVDF acts as an adsorbent for phototransformation products of the phototransformation of diclofenac. Every adsorbing material has a limited capacity and will stop adsorbing after collecting a certain number of molecules. Therefore, PVDF was reused up to five times for phototransformation of diclofenac (0.5 h) and the alteration of diclofenac transformation was analyzed after each usage (see Figure 7). The alteration of diclofenac transformation after each cycle was set in relation to the transformation after the first UVA irradiation. Reusing PVDF without washing leads to a reduction in diclofenac transformation since less phototransformation products can adsorb to PVDF. After the second usage, the transformation of diclofenac decreased by 10.6% (\(SD\) = 1.8%) with further reduction to 15.6% (\(SD\) = 3.5%) after the fourth usage. The removal of TOC after repetitive usage  
Figure 5: (**a**) Absorbance spectrum of non-irradiated and 30 min UVA irradiated diclofenac with and without PVDF. (**b**) The change of absorbance is shown over time for diclofenac UVA irradiation with and without PVDF. The area under the absorbance vs. wavelength was calculated for the non-irradiated region from 230–309 nm and the irradiated region from 309–400 nm. The change of absorbance was calculated by setting the area of absorbance of the non-irradiated diclofenac solution at 100%.  
for up to five times decreases from 3.9% (\(SD\) = 0.7%) to 8.5 (\(SD\) = 1.1%), respectively. However, PVDF can be regenerated. The adsorbing phototransformation products can be desorbed by water (partially) or ethanol (see Figure 7). The alteration of transformation of diclofenac after 0.5 h of UVA irradiation with repeatedly used and regenerated PVDF does not change significantly regarding the different irradiation cycles. Washing PVDF in between UVA irradiation with ethanol regenerates the adsorbent totally. The same amount of diclofenac is transformed, and equal amount of TOC is removed from the solution when PVDF is regenerated with ethanol in between. Water as a washing agent partially regenerates PVDF. A decrease in transformation of diclofenac by 4.9% (\(SD\) = 0.4) after the fifth cycle is observed, while the reduction of TOC stays constant.  
Thus, the PVDF adsorbing capacity can be maintained by simply washing the membrane in between with water or ethanol.  
Figure 6: (**a**) Amount of product X in relation to other phototransformation products found via GC-MS after 2 h and 18 h of irradiation with and without PVDF. (**b**) The transformation of diclofenac with UVA for 0.5 h followed by analyzing the relative concentration of diclofenac via HPLC is shown. The irradiation was performed without PVDF, with PVDF irradiated during transformation and with PVDF shielded (not irradiated) during photoreaction.  
Figure 7: PVDF was reused up to five times (each 0.5 h UVA light irradiation) and either washed with water or ethanol in between or used untreated. Transformation with fresh and unused PVDF was set to 100% and is indicated as new PVDF. The relative alteration of transformation of diclofenac (DF) in (**a**) and TOC in (**b**) in relation to unused PVDF is shown.