The color of tungsten oxide nanoparticles varies according to its chemical composition and preparation conditions. The following are several kinds of color variations of tungsten oxide nanoparticles:
- Basic color types
In the W-O system, there exist a variety of stable tungsten oxides, which show different colors:
Yellow tungsten oxide (WO3)
Nano tungsten trioxide is a yellow powder, which is its most typical color.
Blue tungsten oxide (WO2.90)
This is a non-integer-ratio oxide that appears blue in color.
Purple tungsten oxide (WO2.72)
It is easier to obtain in specific chemical processes, and the color is purple.
Brownish-brown tungsten oxide (WO2)
Also known as tungsten dioxide, the color is tan, sometimes described as chocolate.
- Color Change Phenomena
Photoluminescent color change
Blue tungsten oxide
Blue tungsten oxide has the property of changing color when exposed to light, and it will turn a light blue. However, if repacked in a black opaque bag, it will return to its original color.
Temperature-induced discoloration
Brown Tungsten Oxide
It is easy to change in a humid environment. When heated, the color changes from light to dark and becomes deep orange, but it will return to its original color after cooling.
Reduction reaction discoloration
Tungsten trioxide (WO3) can be reduced by a small amount of organic matter at room temperature and may change its color (the specific color change depends on the degree of reduction and conditions), but it will return to its original yellow color when heated in air.
Third, the reason of color change
The color change of tungsten oxide nanometer is mainly related to its crystal structure, the number of oxygen atoms and the environmental conditions (such as light, temperature, humidity, etc.). For example, the photochromic phenomenon may be due to the electron transfer or structural change of tungsten oxide nanoparticles under light, which leads to the color change. While temperature-induced color change may be due to the change of crystal structure or electronic state of tungsten oxide nanoparticles during heating.
The color changes of tungsten oxide nanoparticles are rich and varied, including basic yellow, blue, purple and tan, as well as color changes due to environmental factors such as light and temperature. These color variations not only increase the interest of tungsten oxide nanoparticles, but also provide possibilities for their applications in photocatalysis, sensors, smart materials and other fields.
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