## 2 Results and Discussion
### CECs Degradation  
Four contaminants of emerging concern, namely benzotriazole (BTA), bisphenol A (BPA), diclofenac (DIC) and sulfamethoxazole (SMZ), were treated in the presence of the developed materials. Preliminarily, dark adsorption toward the considered molecules and direct photolysis experiments were carried out with all the materials. Both contributions were found to be negligible over the examined time window.  
The degradation results obtained for the studied CECs in the presence of the different synthesized photocatalysts and the TiO\({}_{2}\) P25 benchmark are displayed in Figure 2. The degradation profile obtained for ZCC is shown as example in Figure 2a. In all cases, the degradation process can be fitted to a pseudo first-order kinetics, with the calculated constants displayed in Figure 2b.  
Figure 1: Mercury removal using the synthetized photocatalysts and the benchmark Evonik P25 under irradiation in a solar light simulator, after N\({}_{2}\) stripping and 15 min of equilibration in the dark.  
Except for bisphenol A for which P25 showed a greater photodegradation efficiency, ZnO-based materials exhibited higher photoactivity than P25, significantly enhanced by the incorporation of CeO\({}_{2}\) and Cu\({}_{2}\)O. In fact, with ZCC a 50% abatement of all the contaminants was attained after 15 min.  
The results obtained with ZC and ZCC were comparable, with BTA as the only exception, for which double heterojunction with the addition of CeO\({}_{2}\) and Cu\({}_{2}\)O led to a significantly faster degradation. Further tests were also performed on other CECs and their degradation profiles (Figure S5) confirmed the greater photodegradation performance of ZCC compared with other ZnO-based materials and in three out of four cases also with respect to the benchmark P25. Recyclability tests of the photocatalysts were performed using phenol as the model pollutant (Figure S6) demonstrating that the materials can be reused, albeit with a slight decrease in the degradative efficiency.  
The results of experiments carried out in the presence of scavengers are shown in Figure S7. The degradation mechanism changed depending on the investigated contaminant and the employed photocatalyst. In the case of benzotriazole, the results obtained were consistent for all of the photocatalysts: the addition of tert-butyl alcohol, scavenger of 'OH, did not noticeably affect the degradation of the molecule while 'O\({}_{2}\)' seemed to play a more important role; once p-benzoquinone was added, the degradation rate decreased from 100% in the absence of scavengers to 45% after one hour of irradiation. Sulfamethoxazole was significantly less degraded by ZCC in the presence of tert-butyl alcohol, suggesting that hydroxyl radicals are majorly involved; in the case of ZC and ZnO, on the other hand, the addition of scavengers did not greatly decrease the degradation rate, suggesting that another ROS such as singlet oxygen could drive the degradation.  
The photodegradation of bisphenol A and diclofenac was meaningfully affected by the presence of p-benzoquinone, with a degradation rate close to 0 after one hour, as such, superoxide radicals played a key role in the degradation mechanism while hydroxyl radicals were not involved at all in the degradation of diclofenac by ZC and ZnO and only marginally in the case of ZCC and in the degradation of bisphenol A by the prepared materials.  
At the same time, we performed supplementary experiments with the EPR spin label technique using DMPO as the spin trap for the detection of 'OH radicals. The results are reported in the Supplementary Materials Figure S8 and are in agreement with the experiments carried out in the presence of scavengers. The most active sample in the production of 'OH radical was the ternary sample ZCC.  
Figure 2: Degradation profiles of CECs obtained using ZCC photocatalyst (**a**) and kinetic constants estimated for CECs abatement reaction (**b**).