Abstract
In this paper, we employed plasma electrolytic oxidation (PEO) of aluminum in a water solution of sodium tungstate (Na2WO4∙2H2O) with the addition of the pure and Ce-loaded zeolites clinoptilolite and 13 X for the preparation of oxide coatings. The obtained coatings were characterized with respect to their morphologies and chemical and phase compositions using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction. The prepared coatings contained γ-alumina, WO3, and metallic tungsten. The surface morphologies of the obtained coatings strongly depended on the PEO processing time; the roughness of all coatings increased with PEO time, while porosity decreased with PEO processing time as a result of microdischarge coalescence and growth. All coatings contained elements originating from the substrate and from the electrolytes. Coatings containing zeolites with Ce showed higher photoactivity than those with immobilized pure zeolites. The highest photocatalytic activity levels were observed for coatings containing immobilized Ce-exchanged clinoptilolite processed for 10 min. It was observed that both clinoptilolite and 13X zeolites improved the features of the PEO coatings in a similar manner, making natural and abundant clinoptilolite an excellent candidate for various applications.
Highlights
The availability of safe and clean water is vital for human health and the ecosystem, meaning management of wastewater is of crucial importance
The obtained coatings were characterized with respect to their morphologies and chemical and phase compositions using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction
The surface morphologies of the obtained coatings strongly depended on the plasma electrolytic oxidation (PEO) processing time; the roughness of all coatings increased with PEO time, while porosity decreased with PEO processing time as a result of microdischarge coalescence and growth
Summary
The availability of safe and clean water is vital for human health and the ecosystem, meaning management of wastewater is of crucial importance. Many zeolites occur naturally as minerals, while others are synthetic and are manufactured for a specific use Their unique porous properties make zeolites viable for a variety of applications, for example in ion exchangers, sorbents, oxidation and hydrogeneration reactions, supports for catalytic metals, and molecular sieves [14,15,16,17,18,19]. Due to their photochemical stability and large surface areas combined with their channel size, zeolites are used as nanocontainers of semiconducting or photoactive guests, such as CeO2 [15,16]; recent research has shown that zeolites can act as photocatalysts themselves [17]. The degradation stability of the obtained coatings was demonstrated by linear polarization testing and Tafel plots
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