## 3 Results and Discussion
### Photocatalytic Performance
The inhibition of MB degradation in the presence of EDTA-2 Na is decreased by 11% compared with the photodegradation efficiency of MB without addition of active species. This suggests that holes are an important factor in our catalytic process. On the other hand, addition of AgNO\({}_{3}\) is less effective and even slightly increases the degradation by 0.7%. The photodegradation rates changed regarding the active component which is added in the photocatalytic process. The active species of photocatalytic activity for immobilised rGO/TiO\({}_{2}\) follows the order: h\({}^{+}\) > none > e\({}^{-}\) > \({}^{\bullet}\)OH. It can be concluded that only addition of EDTA-2 Na, a hole scavenger, inhibited the photocatalytic degradation of MB using immobilised rGO/TiO\({}_{2}\) nanocomposite. Based on obtained experimental results, the decreased photodegradation efficiency suggested that the photocatalytic activity of immobilised rGO/TiO\({}_{2}\) nanocomposite under simulated solar irradiation for removal of MB is driven by the presence of a hole, similarly as in [33; 52; 53; 54; 55]. For the reusability investigation of the immobilised photocatalyst, the photoactivity was carried out by five consecutive cycles of MB removal from an aqueous medium (mill-Q water) within 30 min intervals for 120 min of irradiation using simulated solar light. Figure 7 shows the results of the immobilised rGO/TiO\({}_{2}\) photocatalyst. After five cycles, the photodegradation of MB is slightly decreased, 92.7%, 92.9%, 92.5%, 92.6%, and 91.3%, respectively. The obtained results show very high reusability of immobilised rGO/TiO\({}_{2}\) photocatalyst for removal after each cycle. The reason for such robust appearance is probably due to the strong interaction between photocatalyst and adhesive material (ethylene glycol) where the photocatalyst remained attached to the substrate after five consecutive  
Figure 6: Effects of scavengers on the degradation of MB dye in milli-Q water with scavenger dosage of 0.01 mol L\({}^{-1}\) after 120 min of simulated solar irradiation. cycles. The obtained results clearly indicate the high chemical and operating stability of the immobilised rGO/TiO\({}_{2}\) photocatalyst and point towards significant reusability as a photocatalyst. Moreover, these results are in striking contrast to our previous report where the rGO/TiO\({}_{2}\) powder photodegradation efficiency was decreased because the amount of catalyst was lost between the consecutive cycles [56]. The proposed mechanism of photocatalytic degradation by rGO/TiO\({}_{2}\) nanocomposite is shown in Figure 8. rGO material in the rGO/TiO\({}_{2}\) nanocomposite can improve photocatalytic degradation of MB by promoting separation and charge transfer. The electron-hole pairs have been excited within the TiO\({}_{2}\) molecule after UV-Vis irradiation. The electrons (e\({}^{-}\)) can be quickly shifted from the conductive band (CB) of the TiO\({}_{2}\) molecule to the surface of the rGO material. Then, transferred electrons in combination with present oxygen will favour the radical O\({}_{2}\)\({}^{\bullet-}\). Produced O\({}_{2}\)\({}^{\bullet-}\) has the potential to react with H\({}_{2}\)O/H\({}^{+}\) to form \({}^{\bullet}\)OH radical, which is the primary radical in the degradation of MB dye. In the meantime, the holes (h\({}^{+}\)) on the valence band (VB) of the TiO\({}_{2}\) molecule have the potential to oxidise H\({}_{2}\)O/OH\({}^{-}\) to also form \({}^{\bullet}\)OH radicals [33; 57; 58]. Figure 7: The recyclability of immobilised rGO/TiO\({}_{2}\) photocatalyst during removal of MB from an aqueous medium (milli-Q water) using simulated solar irradiation.