Types of Oxygen Vacancy Tungsten Oxide (WO3-x)

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:

  1. 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.

  1. 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.

  1. 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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