Photocatalytic performance of ZnO and ZnO/Zn3(PO4)2 coatings formed by plasma electrolytic oxidation of zinc

In this study, plasma electrolytic oxidation (PEO) of zinc in a water solution containing 10 g/L Na3PO4⋅12H2O + 2 g/L KOH, was used for the preparation oxide of coatings for application in photocatalysis for degradation of organic dyes. Degradation of methyl orange (MO) as a model of organic dyes under simulated sunlight was used. In coating formed after 2 min of PEO, the pure phase hexagonal wurtzite ZnO was identified, while in coatings formed for a long time of PEO (up to 5 min) monoclinic phase of Zn3(PO4)2 was identified together with ZnO (ZnO/Zn3(PO4)2 coatings). ZnO/Zn3(PO4)2coatings show better photocatalytic activity (PA) than ZnO coating. The ZnO/Zn3(PO4)2 coating with the highest PA was formed after 4 min. Coupling ZnO with Zn3(PO4)2 reduce the recombination rate of photo-generated electron/hole pairs in ZnO which leads to an increase in PA of ZnO/Zn3(PO4) coatings compared to pure ZnO coating. This is confirmed by photoluminescent measurements. According to photocatalytic and photoluminescence measurement mechanism of the light-induced degradation of MO over ZnO/Zn3(PO4)2 coatings is suggested.