Photocatalytic Properties of WO₃/TiO₂ Core/Shell Nanofibers prepared by Electrospinning and Atomic Layer Deposition

Abstract

ore WO 3 nanofibers (140-300 nm in diameter, several hundred mm long) are made by a novel, water-based electrospinning process using ammonium metatungstate (AMT) and polyvinylpyrrolidone (PVP) as precursors. TiO 2 shells (1.5-20 nm) are grown by atomic layer deposition (ALD) using TiCl 4 and water at 2508C. The WO 3 /TiO 2 composite fibers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectroscopy (RS), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The optimal photocatalytic conversion under visible light is reached by the WO 3 /1.5 nm TiO 2 nanofibers, which have higher activity compared to bare WO 3 and Degussa TiO 2 . Thicker TiO 2 layers fill the pores of the nanowires and reduce the specific surface area, weakening the photocatalytic activity.

Structure and thermal decomposition of ammonium metatungstate

“…In contrast, to the best of our knowledge, the thermal decomposition of AMT and AT has not been investigated in detail. This is unexpected, especially in the case of AMT, as it is the most water soluble ammonium tungstate, and AMT is widely used to prepare various tungsten oxide nanostructures by annealing [35,36].…”

Preparation and characterization of WO3 nanoparticles, WO3/TiO2 core/shell nanocomposites and PEDOT:PSS/WO3 composite thin films for photocatalytic and electrochromic applications

“…The sample was highly crystalline, which was important, as from our previous studies it was determined that WO 3 with higher degree of crystallinity had better both photocatalytic [6] and electrochromic properties [21]. Since the TiO 2 layer was too thin, it could not be detected by XRD [13]. On the composite PEDOT:PSS/WO 3 thin films cyclic voltammetry measurements were performed and the electrochromic effect was observed.…”

“…But since WO 3 absorbs visible light in the most intensive part of the solar spectrum, this makes it a very good material for preparing composite photocatalysts, for example combined with TiO 2 , which though has excellent photocatalytic properties, absorbs only UV light [5,13]. In addition, preparing composites of WO 3 and other transition metal oxides, could be beneficial also for many electrochromic applications [2,3,14].…”

“…To prepare pure monoclinic WO 3 nanoparticles we optimized the annealing conditions of hexagonal ammonium tungsten bronze, (NH 4 ) x WO 3 . Recently, we also demonstrated the atomic layer deposition (ALD) can be effectively used to deposit TiO 2 shell layer on WO 3 nanostructures [13]. ALD is a vapor phase deposition technique based on sequential, self-limiting reactions, capable to produce highly conformal and uniform thin films with thickness control of sub-nanometer precision [16][17][18].…”

“…The precursor pulse times were 1 s for both TTIP and H 2 O, while the purge times were 30 s, and 130 ALD cycles were used. Such ultra-thin ALD TiO 2 films were previously prepared and characterized by our team [13,20].…”