Sunlight energy can help to control water pollution
A new model for the structure of compounds with photocatalytic properties has been developed by Lobachevsky University scientists. The paper describing the results of the study that open up new opportunities for using the energy of sunlight to to remove organic pollutants from water was published in the Journal of Solid State Chemistry.
Organic pollutants such as cyclic aromatic hydrocarbons, pesticides, phenols, polychlorinated biphenyls and other by-products of human activities are often found in wastewater. These chemicals and compounds have a negative impact on the ecosystem and, consequently, on human health.
Today, scientists around the world are working to improve the efficiency of water treatment systems, including through photocatalytic decomposition of organic poisons and chemicals. Photocatalysis is the acceleration of a chemical reaction through the interaction of a special substance, a photocatalyst, with incident light. Some photocatalysts promote the oxidation of organic substances when absorbing light, which is used for wastewater purification.
Today, titanium dioxide TiO2 is used for this purpose on industrial scale. It is cheap to produce, but reacts to the visible light in a relatively narrow range, which significantly reduces its efficiency. Researchers at Lobachevsky University have synthesised a number of promising substances and experimentally established their photocatalytic properties.
"We were able to establish the characteristics of compounds belonging to the structural type of β-pyrochlore and proposed a new model of their structure, based on which we predicted and synthesised new tellurium-containing compounds. The photocatalysts we obtained on this basis, on the one hand, conform to the criteria put forward to the band structure of the material for the appropriate reactions to be implemented, and on the other hand, they are chemically stable in aqueous solutions and organic solvents, which will allow their use for a long time," - comments Diana Fukina, junior research associate at the Laboratory of High-Purity Materials Technology at the UNN Research Institute for Chemistry.
The researchers estimated the band structure of the obtained materials, i.e. the mutual arrangement of their valence band and the edges of the conduction band. Thus, they determined theoretically which reactions would be photocatalysed by such materials. The results were verified during the experiment with the methylene blue substance: two of the four resulting compounds - CsTeMoO6 and RbTe1·5W0·5O6 - successfully decompose the dye with a decomposition degree of about 100 and 50 percent for 8 hours, respectively, said the scientists.
According to Diana Fukina, the resulting compounds can perform their function in the visible range, that is, directly using the energy of sunlight to initiate the start of photocatalytic oxidation reactions. When such materials are used in countries with high solar activity during the day, no additional electricity costs will be needed to activate the process, in contrast to the case when titanium dioxide is used.
"Scientists around the world are battling to improve the efficiency of the photocatalytic process in various ways. For example, there is a method involving titanium oxide modification by adding silver. In this case, the activity increases, but the production process immediately becomes more expensive and complex. In the case of our compounds, although some reagents may be more expensive than titanium oxide, the synthesis process is quite simple and no modifications are required. Therefore, such compounds that seem complex at first glance, are more attractive from the synthesis point of view making it more simple and avoiding the use of precious metals," explains Diana Fukina.
The research team is continuing to study in detail the mechanism of the photocatalytic decomposition of organic materials with the use of the new compounds. The aim is to achieve a better understanding of how to modify the compounds, of the conditions and processes where they will show the highest effectiveness.