Visible Light-Responsive Bismuth Tungstate Photocatalysts: Effects of Hierarchical Architecture on Photocatalytic Activity

Abstract

Bismuth tungstate (Bi 2 WO 6 ) particles as a visible light-responsive photocatalyst were prepared by a facile hydrothermal reaction method in a wide range of pH's (1.5-8.0) in a feed solution, and the effects of calcination on photocatalytic activity were investigated. Change in pH affected their crystallite size, shape, assembling morphology, and specific surface area. The tungsten-to-bismuth ratio (W/Bi ratio) of Bi 2 WO 6 gradually decreased with an increase in pH of the feed solution because of dissolution of tungstate in alkaline solution. The photocatalytic activities were evaluated with oxidative decomposition of acetic acid into carbon dioxide under ultraviolet and visible light irradiation. For Bi 2 WO 6 samples of similar W/Bi ratio, the photocatalytic activity increased with an increase in their specific surface area. Spherical assemblies of Bi 2 WO 6 polycrystalline flakes with a hierarchical architecture (flake-ball particles), which were prepared under the conditions of pH 1.2 and W/Bi ratio of 0.55, exhibited the highest level of photocatalytic activity among the hydrothermally prepared samples. Although a light-harvesting effect, which is an effect of photoabsorption enhancement, on the flake-ball particles was confirmed, the high level of photocatalytic activity did not depend on the assembling morphology of flakes. Photocatalytic activity of the flake-ball particles was improved by calcination at 873 K in air. The calcined particles exhibited a markedly high level of visible-light-induced photocatalytic activity. Analyses of the photocatalytic activities and physical properties indicated that the density of electron-hole recombination centers is a primary factor governing the photocatalytic activity of Bi 2 WO 6 and that the photocatalytic activity monotonically increased with an increase in specific surface area for samples having similar densities of electron-hole recombination centers.

Enhanced photocatalytic activity of bismuth-tungsten mixed oxides for oxidative decomposition of acetaldehyde under visible light irradiation

“…The onset wavelength of action spectrum for the reaction was located at 440 nm, and this wavelength corresponds to the band gap energy of ca. 2.8 eV [17,18]. The apparent quantum efficiency at 400 nm was measured to be 3-8%, depending on the kind of reaction [17,18].…”

“…2.8 eV [17,18]. The apparent quantum efficiency at 400 nm was measured to be 3-8%, depending on the kind of reaction [17,18]. Unfortunately, visible-light absorption is not sufficient and quantum efficiency should still be improved.…”

Visible-light sensitive cobalt-doped BiVO4 (Co-BiVO4) photocatalytic composites for the degradation of methylene blue dye in dilute aqueous solutions

“…In a single-phase composite oxide, the Bi(6s) orbital is normally hybrid with the O(2p) orbital to form an up-shift valence band which results in band gap reduction [9]. There are numeral studies on the photocatalytic property of Bi 3+ -containing composites including bismuth titanate [10,11], bismuth germanate [12], bismuth tungstate [13,14], and bismuth molybdate [15,16]. Bismuth vanadate (BiVO 4 ) is a photoactive material used widely as an inorganic yellow pigment during the past two decades [17].…”

Hydrothermal synthesis of visible light-sensitive conduction band-controlled tungsten-doped titanium dioxide photocatalysts with copper ion-grafts

“…6 and Table 2 based on the assumption that "overall photocatalytic activity" = "QE" © "visible-light absorption capability". 20) The QE values for the Cu-grafted photocatalysts decreased with increasing x values from 0 to 0.05. This phenomenon is frequently encountered for photocatalysts because dopants can act as impurities that negatively impact hole and electron transports.…”