Tungsten Oxide Nanoplates: Facile Synthesis, Controllable Oxygen Deficiency and Photocatalytic Activity

Abstract

Monoclinic tungsten oxide (WO3) nanoplates were synthesized via a two-step simple process: acid precipitation at room temperature to prepare WO3.H2O nanoplates and annealing at high temperature (400 and 500 oC) in ambient air to obtain WO3 nanoplates. The effect of annealing temperature on physical properties (morphology, oxygen deficiency, crystallinity, optical properties, and photocatalytic activity) of WO3 nanoplates was studied. At both two studied annealing temperatures, all samples have the stable monoclinic structure and visible light-range optical bandgap, but the morphology and photocatalytic activity of the samples vary significantly with annealing temperature. At higher annealing temperature (500 oC), the sample has both nanoplate and nanograin morphologies with round edges, higher crystallinity, larger optical bandgap (2.71 eV), and lower photocatalytic activity. The sample annealed at 400 oC has nanoplate morphology with sharp edges, lower optical bandgap (2.63 eV), and higher photocatalytic which shows a high potential for photocatalytic application under visible light irradiation. The effect of the annealing temperature on the properties of WO3 nanoplates is assigned to the dehydration, the coalescence, and/or the melting processes at high temperatures. Dehydration causes the formation of oxygen vacancy – oxygen deficiency. The coalescence and/or the melting result in the changing of morphology and the decrease of the oxygen vacancies. These results imply a simple, cost-effective method to prepare highly oxygen-deficient WO3 nanoplates.

Functionalization-Mediated Preparation via Acid Precipitation and Photocatalytic Activity of In Situ Ag2WO4@WO3.H2O Nanoplates

“…3 .2H 2 O to orthorhombic WO 3 .H 2 O in the AgNO 3 -functionalized samples.The formation of orthorhombic WO 3 .H 2 O and monoclinic WO 3 .2H 2 O nanoplate structures could be explained by the oxolation in the highly acidic environment,4,[22][23][24][25][26] in which neutral tungstic acid was first produced from the acidification of tungstate (WO 4 ) 2− in accordance with Eq. 3:The tungstic acid H 2 WO 4 has weakly acidic and base properties.…”

Humidity Sensing Mechanism and Respiration Monitoring of WO3 Nanoplates with a Monoclinic Crystal Phase

“…The porous morphology formed due to random orientation of particles which act as trapping agent for gaseous molecules which provide more reactive sites for gas sensing applications. 53 The average diameter of nanoplates is measured as 279 nm while the plate thicknesses are ranging from 26 to 42 nm. The HR-TEM image of WO 3 again confirms the formation of microstructured nanoplates as shown in Fig.…”

Temperature-mediated Phase Transformation and Optical Properties of Tungsten Oxide Nanostructures Prepared by Facile Hydrothermal Method

“…3 presented Raman spectra of all samples, which implied the change of samples' phase with the reaction temperature. In sample RT's Raman spectrum, the characteristic peaks of both monoclinic WO 3 • 2H 2 O and orthorhombic WO 3 •H 2 O were observed at 658, 945, and 956 cm −1 [30][31][32]. In Raman spectra of sample T100, only characteristic peak of orthorhombic WO 3 •H 2 O appeared, but in Raman spectra of samples T120, T150, and T180, the characteristic peaks of both orthorhombic WO 3 •H 2 O (at 638 and 945 cm −1 ) and monoclinic WO 3 (at ∼ 711 and 806 cm −1 ) were observed [16][17][18].…”