Tungsten Oxide Photocatalyst Improving Indoor Air Quality

A tungsten oxide/titanium dioxide photocatalyst coating on a substrate such as a honeycomb, purifies the air in a building or a vehicle by oxidizing any contaminants in the air that adsorb onto the coating to water, carbon dioxide, and other substances.

A fan draws air into an air purification system. The air first flows through a particle filter that filters out dust or any other large particles. The air then flows through an open passage or channel of a honeycomb. The surface of the honeycomb is coated with a tungsten oxide/titanium dioxide photocatalytic catalyst. An ultraviolet light source positioned between successive honeycombs activate the tungsten oxide/titanium dioxide photocatalyst coating. The walls of the air purification system are preferably lined with a reflective material to reflect the ultraviolet light onto the interior surface of the open passages of the honeycomb.

When photons of the ultraviolet light are absorbed by the tungsten oxide/titanium dioxide photocatalyst coating, an electron is promoted from the valence band to the conduction band, producing a hole in the valence band. The electrons in the conduction band are captured by oxygen. The holes in the valence band react with water that is adsorbed on the tungsten oxide/titanium dioxide photocatalyst coating, forming reactive hydroxyl radicals.

The tungsten oxide forms a monolayer on the titanium dioxide. When a contaminant in the air is adsorbed onto the tungsten oxide/titanium dioxide photocatalyst coating, the hydroxyl radical attacks the contaminant, abstracting a hydrogen atom from the contaminant and oxidizing the contaminants to water, carbon dioxide, and other substances. The tungsten oxide/titanium dioxide photocatalyst coating has a low sensitivity to humidity. Therefore, humidity has a much lower effect on the photocatalytic activity of the tungsten oxide/titanium dioxide photocatalyst as compared to the titanium dioxide photocatalyst of the prior art.

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