Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-018-9222-x Photocatalytic performance of copper-based coatings deposited by thermal spraying Ionut Claudiu Roata 1  · Catalin Croitoru 1  · Alexandru Pascu 1  · Elena Manuela Stanciu 1 Received: 9 March 2018 / Accepted: 30 April 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Visible light-activated photocatalysts are gaining general importance in advanced methods for removing persistent organic compounds. In this study, two types of composite oxide-metal coatings are obtained on copper substrates through thermal spraying of an aluminum bronze powder with diferent time-of-fight distances between the spraying nozzle and the substrate (150 and 200 mm). The surfaces of the coatings consist of nanopatterned α-Fe 2 O 3 and Cu x O produced by oxidation of the metal phase during the thermal spraying process. The optical band gap energies of the coating assemblies are 2.573 and 2.131 eV, respectively, and the Brunauer–Emmett–Teller (BET) specifc surface areas are 4.65 and 4.87 m 2  g −1 , respectively. The photocatalytic performance of the two types of thermally sprayed coatings in the visible region is studied using meth- ylene blue as a model compound. The coatings present remarkable stability in aqueous environments, good hydrophilicity, high photodegradation rates (0.20–0.26 h −1 ), high organic dye mineralization efciencies (75.69 and 92.36%) and unaltered methylene blue removal efciencies during three successive 12 h photodegradation cycles (91–99.60%). 1 Introduction The pollution of water by highly soluble and persistent organic compounds is one of the most severe problems of modern-day society, motivating extensive scientifc eforts towards the design of economically practical removal meth- ods based on advanced oxidation [1–3]. Semiconductor- aided photocatalysis is one of the most highly tunable and efcient methods for initiating of in situ redox reactions and is suitable for the degradation of organic compounds [4–6]. The most widely used photocatalysts, TiO 2 and ZnO, need UV light for activation [1, 2]. As the amount of solar UV light that reaches the earth’s surface is small (~3–5%) [7], a subject of interest is to either extend the responses of traditional photocatalysts to the visible region of the spec- trum through doping [8–10] or design composite n–n or n–p junctions [11, 12]. However, both of these approaches can have a negative impact on the overall price of the photocata- lyst material. While initially having a narrow range of applications (reconditioning of metal parts), thermal spraying (with its various techniques, such as fame spraying, plasma spraying, liquid-feed fame spray pyrolysis, and high-velocity oxygen fuel (HVOF) spraying) has been successfully used to obtain high-performance photocatalytic coatings for advanced oxi- dation of organic compounds [13–15]. While the traditional methods for obtaining photocatalyst coatings ofer the pos- sibility to obtain highly uniform [physical vapor deposition (PVD) and chemical vapor deposition (CVD)] or dense and uniform [sol–gel (SG) process] thin flms and coatings [16, 17], most often, these methods require expensive equipment and a large amount of energy input, making them very costly (PVD and CVD) or produce coatings with low adherence to the substrate, low hardness and a particularly low poros- ity and specifc surface area (SG), which in most cases is detrimental to photocatalytic applications [18, 19]. Another drawback is the usage of highly corrosive or toxic precur- sors (CVD, SG) and vacuum conditions (CVD, PVD) [20]. Only thick coatings (30 µm–2 mm) can be obtained through thermal spraying, but this method ofers several advantages, such as low to moderate costs, versatility with respect to the coating material, and the production of coat- ings with tunable porosity (1–10%) and hardness (20–65 HRC). Higher deposition rates can be achieved through thermal spraying (2–55 kg/h) than through CVD and PVD, * Catalin Croitoru c.croitoru@unitbv.ro 1 Department of Materials Engineering and Welding, Transilvania University of Brasov, Eroilor 29 Street, 500036 Brașov, Romania