Synergy of Cu2+-Cu(OH)2-CuO with TiO2 coatings, fabricated via plasma electrolytic Oxidation: Insights into the multifaceted mechanism governing visible light-driven photodegradation of tetracycline

Abstract

In this study, copper oxide-embedded TiO2 coatings were introduced on pure titanium via plasma electrolytic oxidation (PEO), which exhibited photocatalytic capacity for tetracycline (TC) degradation. Moreover, the impact of the ionization process and its temperature on the photocatalytic efficiency were investigated. All coatings containing CuO nanoparticles (NPs) exhibited finer micropores, higher specific areas, and higher wettability. The phase analysis results prove that coatings containing CuO NPs are composed of anatase and CuO phases, whereas the addition of ionized CuO NPs into the electrolyte leads to the formation of anatase, rutile, CuO, TiP2O7, and Cu(OH)2. All the CuO-incorporated coatings resulted in highly efficient TC photodegradation, the highest of which was 70 % for the coating containing 1 g/L CuO NPs. Most importantly, the introduction of1 g/L CuO-ionized NPs at 25 °C increased the photocatalytic efficiency to 92 %, whereas increasing the ionization process to 60 °C significantly decreased the photocatalytic activity to 60 % after 6 h of visible light illumination. Moreover, the optimum coating satisfied the photocatalytic efficiency requirement even after five cycles. An in-depth investigation of the effect of photocatalytic parameters, including the concentration and pH of pollutants, as well as the light intensity, was also performed. Appropriate scavenger tests were employed to examine the impact of different reactive oxygen species and photocatalytic mechanisms. Finally, based on the intermediate products, a probable TC photodegradation pathway was suggested.