## 3 Results and Discussion
### Effect of UV Light on the Removal of VOCs  
In the previous section, we discussed the breakthrough of the semi pilot reactor without the use of UV irradiation. In this section, the effect of the UV treatment on the cyclic use of the reactor was evaluated. In this experiment, the reactor catalysts were activated by UV irradiation for 45 min (this was 30 min for a batch in order to be on the safe side due to the small lamp sizes), which was followed by BTEX flow for 5 min at the optimum linear velocity of 3.5 cm/s. This process was repeated six times, and the results are displayed in Figure 7. This shows the results of the samples taken at the outlet of the reactor after 1, 3, and 5 min of continuous flow of VOCs. The results of the samples taken at the center of the reactor are shown in Figure S4. From Figure 7, we observed that the efficiency of the removal of VOCs during cycles 1-6 remained constant at more than 75% for xylene and ethylbenzene. This proportion of VOCs that are removed are reduced to be less than 50% in the case of Figure 6,  
Figure 6: Blank test of the semi pilot reactor without the application of UV.  
where there was no UV applied. Similarly, the removal efficiency of the components of the VOCs, such as toluene and benzene, varied from 40-58% and 30-38% for cycles 1-6, respectively, as shown in Table 1. Although these efficiencies are lower than the other two components, they are still higher than in Figure 6, which has lower values of 20% and 8%, respectively. Another interesting point that was observed in this experiment, was that the VOC components followed an order of X \(>\) E \(>\) T \(>\) B, which is different from previous findings (E \(>\) T \(>\) B \(>\) X) [21]. This behavior is possibly due to the coating, which altered the morphology and pore sizes of the catalytic material, Fe-ZSM-5. Apart from the different removal order, we found strong evidence that the UV-pretreatment coupled system is capable of the sustainable removal of VOCs from air. In our system, the VOCs removal is not a single process, it is adsorptive catalysis. First, VOCs are trapped in the pores of ZSM-5, and then the interaction of UV with Fe present in the structure of ZSM-5 initiates' oxidation, which ultimately ends at the degradation of VOCs, which is catalysis. We have not studied the actual ratio between adsorption and catalysis, as it is truly very hard to distinguish between adsorption and catalysis. However, in our previous studies [21; 28], we reported evidence that VOCs were first adsorbed, as the base material is porous, followed by catalytic degradation. Furthermore, our study purpose was more related to total removal, rather than finding the scientific ratio between adsorption and catalysis, as the developed system is at semi pilot scale. Moreover, the authors have the opinion that in the developed system, it is also \"adsorptive catalytic oxidation\" instead of adsorption or only catalysis. Furthermore, in our study, we used 50 \(\upmu\)mol/mol of BTEX, which is a very high concentration. The obtained results were compared with other materials in Table S1. However, in the real-life scenario, these concentrations can only be in the range of 0.1-2.0 \(\upmu\)mol/mol. Therefore, the presented system can be used for an extended period of time in real life.