Vials containing the rhodamine B test dye used in the study, both before (left) and after (right) photocatalytic degradation by the composite under white light illumination. Photo: Daniel Jones/Swansea University.
Vials containing the rhodamine B test dye used in the study, both before (left) and after (right) photocatalytic degradation by the composite under white light illumination. Photo: Daniel Jones/Swansea University.

A novel composite material developed by scientists in the Energy Safety Research Institute (ESRI) at Swansea University in the UK shows promise as a catalyst for the degradation of environmentally-harmful synthetic dye pollutants. These are released at a rate of nearly 300,000 tonnes a year into the world's water.

This novel, non-hazardous photocatalytic material effectively removes dye pollutants from water, adsorbing more than 90% of the dye and enhancing the rate of dye breakdown by almost 10 times using visible light. The scientists, led by Charles Dunnill and Daniel Jones, reported their discovery in a paper in Scientific Reports.

The composite is synthesized by growing ultra-thin ‘nanowires’ of tungsten oxide on the surface of tiny particles of tantalum nitride within a sealed container at high temperatures and pressures. Due to the incredibly small size of the two material components – both the tantalum nitride nanoparticles and tungsten oxide nanowires are typically less than 40nm in diameter – the composite provides a huge surface area for dye capture.

The material then proceeds to break the dye down into smaller, harmless molecules using the energy provided by sunlight, in a process known as ‘photocatalytic degradation’. Having removed the harmful dyes, the catalyst can simply be filtered from the cleaned water and reused.

The photocatalytic degradation of dyes has been investigated for several decades, but researchers have only recently developed materials capable of absorbing the visible part of the solar spectrum. Other materials, such as titanium dioxide, are also able to break down dyes using solar energy, but their efficiency is limited as they can only absorb higher-energy ultra-violet light. By making use of a much greater range of the solar spectrum, materials such as those developed by the ESRI team are able to remove pollutants at a far superior rate.

Both of the materials used in this study have attracted significant interest in recent years. Tungsten oxide, in particular, is considered one of the most promising materials for a range of photocatalytic applications, owing to its high electrical conductivity, chemical stability and surface activity, as well as 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, allowing it to extract a high amount of energy from sunlight to power the degradation processes.

Nevertheless, the true potential of the two materials was only realised when they were combined into a single composite. Due to the exchange of electrons between the two materials, the test dye used within the study was broken down by the composite at around double the rate achieved by tantalum nitride on its own. Tungsten oxide, on the other hand, was shown to be incapable of dye degradation on its own. In contrast to other leading photocatalytic materials, many of which are toxic to both humans and aquatic life, both parts of the composite are classed as non-hazardous materials.

The scientists believe that their research provides just a taster of the material's potential. "Now that we've demonstrated the capabilities of our composite, we aim to not just improve on the material further, but to also begin work on scaling up the synthesis for real-world application." said Jones. "We're also exploring its viability in other areas, such as the photocatalyzed splitting of water to generate hydrogen."

This story is adapted from material from Swansea University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.