Reactive Magnetron Sputter Deposition of Bismuth Tungstate Coatings for Water Treatment Applications under Natural Sunlight

Abstract

Bismuth complex oxides, in particular, bismuth tungstate, have recently attracted attention as promising photocatalytic materials for water treatment processes. In the present work, photocatalytic bismuth tungstate films were prepared by pulsed direct current (DC) reactive magnetron sputtering of Bi and W targets in an Ar/O 2 atmosphere onto spherically-shaped glass beads. The uniform coverage of the substrate was enabled by the use of oscillating bowl placed underneath the magnetrons. The atomic ratio of Bi/W was varied through the variation of the power applied to the magnetrons. The deposited coatings were analyzed by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy and atomic force microscopy. The photocatalytic properties of the films were studied via the methylene blue (MB) degradation process under artificial (fluorescent light) and natural (sunlight) irradiation, and compared to the photocatalytic performance of titanium dioxide coatings deposited onto identical substrates. The results showed that the photocatalytic performance of bismuth tungstate and bismuth oxide-coated beads was superior to that exhibited by TiO 2 -coated beads. Overall, reactive magnetron co-sputtering has been shown to be a promising technique for deposition of narrow band gap bismuth-based semiconducting oxides onto irregularly-shaped substrates for potential use in water treatment applications.

Characterisation and properties of visible light-active bismuth oxide-titania composite photocatalysts

“…The method provides such obvious advantages, in comparison to chemical methods, as; no requirement for toxic or hazardous precursors, an absence of hazardous process by-products, excellent control over uniformity and composition and great up-scaling potential. Despite the fact that magnetron sputtering is typically used for deposition of coatings onto flat substrates, the authors of the present paper have recently shown that it can be readily used for deposition of functional coatings onto particulates of various shapes and sizes, from several millimeters in diameter [4], to nanoparticulates [4,32].…”

“…Bismuth-oxide coatings were deposited in a one-step process in an arrangement similar to the one described in detail earlier [4,35]. In brief, the vacuum coating system includes two planar 300 × 100 mm 2 unbalanced type II magnetrons installed on the top of the vacuum chamber in a closed field, sputter-down configuration.…”

“…Of the low band gap semiconducting materials, bismuth-based oxides have attracted considerable attention over the past few years. Bismuth (complex) oxides, including bismuth tungstate [4][5][6], bismuth molybdate [7][8][9], bismuth titanate [10] and bismuth vanadate [11,12], are subject to extensive research efforts. A number of them have been reported as photocatalytic materials in their own right, while the others are still mainly used for photosensitizing titania.…”

“…However, compared to bismuth complex oxides, bismuth oxide, Bi2O3, has not been so widely studied. Even though several works report bismuth oxide as a narrow band gap semiconducting material with photocatalytic properties under visible light irradiation [4,13,14], the number of studies using Bi2O3 for coupling with TiO2 is still rather limited. However, the available works clearly reflect the potential of such a composite material.…”

Atmospheric Pressure Plasma Coating of Bismuth Oxide Circular Droplets

“…The production of crystalline layers or particles can be carried out by different processes, such as physical vapor deposition (PVD) [15], chemical vapor deposition (CVD) [16], magnetron sputtering [17,18] and a hydrothermal process [19]. The production of nonstoichiometric bismuth oxide presents a challenge.…”