Abstract
Tungsten oxide-based bulk and nanocrystalline materials are widely used as photocatalytic and photo- and electrochromic materials, as well as materials for biomedical applications. In our work, we focused our attention on the effect of sodium cations on the structure and photochromic properties of the WO3@PVP aqueous sols. To establish the effect, the sols were synthesized by either simple pH adjusting of sodium or ammonium tungstates’ solutions, or using an ion exchange technique to remove the cations from the materials to the greatest possible extent. We showed that the presence of sodium cations in WO3@PVP favors the formation of reduced tungsten species (W+5) upon UV irradiation of the materials, strongly affecting their photochromic and photocatalytic properties. The pronounced photoreductive properties of WO3@PVP sols in photocatalytic reactions were demonstrated. Due to photoreductive properties, photochromic sols of tungsten oxide can act as effective photoprotectors in photooxidation processes. We believe that our work provides a considerable contribution to the elucidation of photochromic and redox phenomena in WO3-based materials.
Highlights
Tungsten oxide is a semiconductor material widely used in heterogeneous catalysis [1] and in photo- and electrochromic devices [2]
Sodium tungstate dihydrate (Na22WO44 ≥ 99%, Sigma-Aldrich, Darmstadt, Germany), ammonium metatungstate hydrate ((NH4 )6 H2 W12 O40 ·xH2 O ≥ 99%, Sigma-Aldrich), polyvinylpyrrolidone metatungstate hydrate ((NH4)6H2W12O40·xH2O ≥ 99%, Sigma-Aldrich), polyvinylpyrrolidone (PVP K(PVP K-30, average mol. wt. 40,000), HCl, NaOH, NaCl (99%, Sigma-Aldrich), methyl orange
The samples were symbol N designated the samples synthesized from sodium tungstate, and x indicated an approximate marked M(N)x, where symbol M designated the samples synthesized from ammonium pH value of the solution
Summary
Tungsten oxide is a semiconductor material widely used in heterogeneous catalysis [1] and in photo- and electrochromic devices [2]. Tungsten oxide nanoparticles have been considered a promising nanomaterial for biomedical applications: In recent years, WO3 -based materials have been used in advanced medical and biological research as antibacterial coatings, biosensors, theranostic materials, and materials for proliferation control [3,4,5,6,7]. The majority of applications of these materials are due to the photochromic effect and the ability to participate in reversible redox reactions due to the. Despite the fact that tungsten oxide-based bulk materials and thin films. The oxygen effect on the optical and photochromic properties of materials based on WO3 is a common phenomenon [11]
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