Photocatalytic Material Effectively Removes Dye Pollutants

A composite material that functions as an effective catalyst for the photodegradation of waterborne dye pollutants was developed by researchers at Swansea University, Wales.

The material is synthesized by growing ultra-thin “nanowires” of tungsten oxide on the surface of tantalum nitride particles under heat at high pressure inside a sealed container. The composite provides a huge surface area for dye capture since the tantalum nitride and tungsten oxide are typically less than 40 billionths of a meter in diameter.

The material breaks the dye down into smaller, harmless molecules using solar energy to promote 

Vials containing the Rhodamine B test dye used in the study, both before (left) and after (right) photocatalytic degradation. (Source: Daniel Jones/University of Swansea)photocatalytic degradation. After dye removal, the catalyst may be filtered from the cleaned water and reused.

While the photocatalytic degradation of dyes has been investigated for several decades, it is only relatively recently that researchers have developed materials capable of absorbing the visible part of the solar spectrum. Other materials, such as titanium dioxide, have also been demonstrated to break down dyes using solar energy, but their efficiency is limited as they only absorb ultra-violet light. By absorbing visible light, the new material removes pollutants at a far superior rate.

Tungsten oxide is considered one of the most promising materials for a range of photocatalytic applications, due to its high electrical conductivity, chemical stability and surface activity — in addition to its strong light absorbance. As a low band-gap semiconductor, tantalum nitride is red in color due to its ability to absorb almost the entire spectrum of visible light, and therefore extracts a high amount of energy from sunlight to power the degradation processes.

However, the true potential of the two materials is realized when combined into a single composite. The test dye used in the study was broken down by the composite at around double the rate achieved by tantalum nitride on its own, while tungsten oxide alone was shown to be incapable of dye degradation. In contrast to other leading photocatalytic materials, many of which are toxic to both humans and aquatic life, both constituents of the composite are classed as non-hazardous materials.