| Summary: | In the present study, we propose a new photocatalytic interface prepared by high-power impulse magnetron sputtering (HiPIMS), and investigated for the degradation of Reactive Green 12 (RG12) as target contaminant under visible light light-emitting diodes (LEDs) illumination. The Cu<sub>x</sub>O/TiO<sub>2</sub> nanoparticulate photocatalyst was sequentially sputtered on polyester (PES). The photocatalyst formulation was optimized by investigating the effect of different parameters such as the sputtering time of Cu<sub>x</sub>O, the applied current, and the deposition mode (direct current magnetron sputtering, DCMS or HiPIMS). The results showed that the fastest RG12 degradation was obtained on Cu<sub>x</sub>O/TiO<sub>2</sub> sample prepared at 40 A in HiPIMS mode. The better discoloration efficiency of 53.4% within 360 min was found in 4 mg/L of RG12 initial concentration and 0.05% Cu<sub>wt</sub>/PES<sub>wt</sub> as determined by X-ray fluorescence. All the prepared samples contained a TiO<sub>2</sub> under-layer with 0.02% Ti<sub>wt</sub>/PES<sub>wt</sub>. By transmission electron microscopy (TEM), both layers were seen uniformly distributed on the PES fibers. The effect of the surface area to volume (dye volume) ratio (SA/V) on the photocatalytic efficiency was also investigated for the discoloration of 4 mg/L RG12. The effect of the presence of different chemicals (scavengers, oxidant or mineral pollution or salts) in the photocatalytic medium was studied. The optimization of the amount of added hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and potassium persulfate (K<sub>2</sub>S<sub>2</sub>O<sub>8</sub>) was also investigated in detail. Both, H<sub>2</sub>O<sub>2</sub> and K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> drastically affected the discoloration efficiency up to 7 and 6 times in reaction rate constants, respectively. Nevertheless, the presence of Cu (metallic nanoparticles) and NaCl salt inhibited the reaction rate of RG12 discoloration by about 4 and 2 times, respectively. Moreover, the systematic study of reactive oxygen species’ (ROS) contribution was also explored with the help of iso-propanol, methanol, and potassium dichromate as <sup>•</sup>OH radicals, holes (h<sup>+</sup>), and superoxide ion-scavengers, respectively. Scavenging results showed that O<sub>2</sub><sup>−</sup> played a primary role in RG12 removal; however, <sup>•</sup>OH radicals’ and photo-generated holes’ (h<sup>+</sup>) contributions were minimal. The Cu<sub>x</sub>O/TiO<sub>2</sub> photocatalyst was found to have a good reusability and stability up to 21 cycles. Ions’ release was quantified by means of inductively coupled plasma mass spectrometry (ICP-MS) showing low Cu-ions’ release.
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