Abstract
The possibility of electrosynthesis and control of the surface composition and morphology of the electrolytic cobalt coatings with refractory metals by varying the parameters of electrolysis has been proved. It was found that oxygen and carbon are included in the composition of the coatings as well as the main components, thus such systems can be considered as composite. The coatings deposited by pulsed current can be considered as composite materials the oxide phase for which is formed directly in the electrode process as an intermediate of incomplete reduction of tungstates and hydrolysis of zirconium (IV) salts. The topography of the films is distinguished by the presence of elliptical and spherical grains with crystallite sizes of 80 - 180 nm. On the surface of the coatings, there are hills (large grains) with a diameter of 1 - 3 μm. The fractal dimension of the surface is 2.77, which indicates the 3D mechanism of crystal growth during the formation of coatings. In terms of phase composition, composites are predominantly amorphous materials that contain nanocrystalline cobalt and the intermetallic compound Co3W and Zr3Co. The study of the morphology and topography of the composite coatings surface, as well as its quantitative and phase composition, indicates the possibility of photocatalytic activity of the Co-Mo-WOх, Co-Mo-ZrO2 and Co-W-ZrO2 coatings. Investigation of the photodegradation of the azo dye methyl orange found that the efficiency of MO removal from the solution was 24%, 18%, and 10% for 30 min of ultraviolet irradiation in the presence of Co-Mo-WOх, Co-Mo-ZrO2 and Co-W-ZrO2 on composite coatings, respectively. The higher photoactivity of Co-Mo-WOx composite coatings can be explained by the presence of non-stoichiometric molybdenum and tungsten oxides.
Highlights
Today, the growth rates of industrial production and economic activities result in the aggravation of the water purification problem that makes the humanity seek for innovative approaches to the ecologization of the technology park [1–3]
Cobalt-based composite coatings are indicative of the fact that a definite amount of carbon and oxygen was detected in addition to basic components, i.e. cobalt, molybdenum, tungsten and zirconium (Fig. 1)
Such systems are viewed as composite electrolytic Co-W-ZrO2, Co-Мо-ZrO2 and Co-МоWOx coatings due to a considerable amount of oxygen in the composition that is related to the incomplete reduction of tungstate-ions and zirconium hydrolysis (IV) and the nonuniform distribution of alloy components on the surface
Summary
The growth rates of industrial production and economic activities result in the aggravation of the water purification problem that makes the humanity seek for innovative approaches to the ecologization of the technology park [1–3]. The use of nanostructured thin-film materials that are based on catalytically active metals [6–8] and oxides [9–11] creates favorable conditions for the efficient solution of the problems relating to the purification of water polluted with organic pollutants and infectious agents. Among the most promising technological approaches to the creation of nanostructured photocatalytic coatings we can distinguish the galvanic approach based on the electrochemical deposition of converted and composite coatings from electrolyte solutions [12, 13]. This method enables the variation of the composition in a wide range and the physical and chemical properties of obtained coatings can be changed. The researchers pay a focused attention to the photoactivity of tungsten oxide WO3 [17] and zirconium oxide ZrO2 through electron beam scanning and that allowed [12, 18]
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