Oxygen vacancy tungsten oxide (WO3-x) is a tungsten oxide material characterized by oxygen atoms partially missing from the lattice of tungsten trioxide (WO3). These oxygen vacancies introduce distinct mechanical, optical, thermal, and electrical properties, making WO3-x valuable across a range of applications. Below are the main types of oxygen vacancy tungsten oxide:
- Blue Tungsten Oxide (WO2.90)
Characteristics:
Blue tungsten oxide (WO2.90) is the most common oxygen vacancy tungsten oxide. It typically has a tungsten content between 80.00% and 80.80%, density between 2.4–2.8 g/cm³, and a particle size ranging from 12–19 µm. Its color changes depending on light exposure: it appears light blue under light and dark blue in the absence of light, a result of its unique crystal structure and oxygen deficiencies.
Applications:
Due to its distinctive properties, blue tungsten oxide is ideal for producing high-quality energy storage products and photothermal devices. It also shows potential for use in optical materials, electronic materials, and catalysts.
- Purple Tungsten Oxide (WO2.72 or W18O49)
Characteristics:
Purple tungsten oxide, also known as γ-tungsten oxide, appears as purple or blue-purple crystalline powder. It exhibits high photocatalytic activity, gas sensitivity, electrochromism, and optical effects, characteristics that are closely linked to its particle size. Purple tungsten oxide has a high mesopore volume, low micropore volume, narrow pore distribution, low fractional dimension, and large average pore diameter, giving it a wide range of applications.
Classification by Particle Size:
Depending on particle size, purple tungsten oxide can be divided into categories like coarse particles, fine particles, ultra-fine particles, and nano-particles. Generally, as particle size decreases, the specific surface area of the powder increases, enhancing its catalytic, gas-sensitive, electrochromic, and optical properties. Larger particle sizes result in a smaller specific surface area and comparatively lower performance in these properties.
Applications:
Purple tungsten oxide is widely used in optical and electronic materials, catalysts, and energy storage batteries. It is especially significant in photocatalysis due to its excellent photocatalytic activity.
- Other Types of Oxygen Vacancy Tungsten Oxide
Beyond the commonly seen types, other forms of oxygen vacancy tungsten oxide exist, varying with oxygen content and preparation conditions. For example:
- Yellow Tungsten Oxide (WO3): While considered a stable form of tungsten oxide, yellow tungsten oxide can exhibit oxygen vacancy characteristics under certain conditions.
- White Tungsten Oxide (WO2.72): Different from purple tungsten oxide, this form may have unique application-specific properties.
- Brown Tungsten Oxide (WO2): This form also may feature oxygen vacancies, but its physical and chemical properties vary and are application-dependent.
Summary
The properties and applications of oxygen vacancy tungsten oxide types are influenced by preparation methods, conditions, and post-treatment. Thus, choosing the appropriate preparation method and conditions is essential to achieve the desired properties of oxygen vacancy tungsten oxide for specific applications.
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