Water pollution is one of the problems that industrial regions face. It can be solved by purifying waste water from plants and factories before it reaches water bodies used by the public. Modern means of treatment are effective, but expensive or inconvenient to use. However, SUSU scientists have developed a new method of obtaining material for waste water treatment that supersedes the existing analogues. A patent has already been obtained for the development.
Main problem with waste water
All industrial enterprises, regardless of their activities, pollute water ecosystems with sewage. Waste water contains persistent organic compounds—poisonous substances that have a negative impact on human health and the environment. Such compounds should be removed from water to prevent their spread.
Currently, there are two methods of treating waste water for organic compounds which are actively used: adsorption and reagent oxidation. However, these are considered expensive; it is much cheaper and more profitable to use reagent-free photocatalytic water treatment.
South Ural State University has been working on the development of photocatalysts for several years now. The research is conducted under the supervision of Vyacheslav Avdin, Dean of the Faculty of Chemistry of the Institute of Natural Sciences and Mathematics (INSM). Our scientists work with photocatalysts based on transition metals. The samples are nanopowders. They are highly efficient, but the disadvantage of these catalysts is that nanoparticles are difficult to extract from water after the purification process.
Innovative treatment material
A new study conducted by SUSU scientists has allowed them to obtain a photocatalyst with a thermostable microporous coating based on a mixed titanium-silicon oxide. The macroform is easy to use, and the substance is as active as nanoparticles. The patent certificate No. 2733936 has been obtained for the innovative method of producing the photocatalyst.
"Our method is innovative because it allows us to obtain mechanically durable thermostable microporous coatings based on anatase with the help of relatively inexpensive and low-toxic reagents through a relatively simple procedure. The coatings exhibit rather high photocatalytic activity with respect to persistent organic pollutants (such as phenolic compounds) even at low UV irradiation power," explained Aleksandr Gorshkov, the author of the patent and postgraduate student of the Department of Ecology and Chemical Engineering of the SUSU INSM.
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Photo: SUSU postgraduate Aleksandr Gorshkov
The existing analogues of the photocatalyst in the form of thermostable microporous coating have a common disadvantage: low thermal stability, which limits their use in many technological processes. When heated above 400 degrees Celsius in the substances based on titanium dioxide, crystals are often agglomerated (the larger their size, the worse their catalytic activity), and a transition of anatase to rutile (change of polymorphic modifications of titanium dioxide) is noted.
Unique coating properties
The method of obtaining a thermostable coating with photocatalytic properties suggested by Aleksandr Gorshkov helps prevent the reducing in the activity of the substance even when it is heated up to 700 degrees Celsius because anatase nanocrystals are stabilized in the silicate matrix.
The phase of hydrophilic mixed silicon-titanium oxide also provides high adhesion (adhesion of surfaces of heterogeneous bodies) and high mechanical strength of the coating with the substrate. The researchers used plates of etched sodium silicate glass, which are hydrophilic material, to create the coating.
The microporosity of the substance also increases the activity of the catalyst, because this property affects the high specific surface area.
"In addition, the adsorption mechanism in micropores differs from that in macro- and mesopores. In micropores, the substrate fills the entire pore volume, not just the inner surface. Adsorption of the substrate (in our case—persistent organic pollutants) on a photocatalyst is an important stage of the process of photodestruction, and in microporous materials it runs better," said Aleksandr Gorshkov.
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Photo: Sample plates with the innovative coating applied
From photocatalyst to water treatment plants
The developed coating (147 milligrams on one plate) showed good results during the tests on phenol, a model compound. Photodestruction occurred on 38% of the organic compound in 50 millilitres of solution at a concentration of 10 mg/l after one hour of ultraviolet irradiation. The wavelength was 405 nm, and the irradiation power was 600 W/m2.
When the laboratory tests are completed, the researchers want to test the patented coating on actual waste water samples. The next step is to design, build, and test a pilot water treatment plant.
Research in the field of new materials and ecology is among the priorities of the World-class Ural Interregional Research and Education Centre for Advanced Production Technologies and Materials, which is currently being created by the joint efforts of Ural Federal University, SUSU, KSU, and other regional higher education institutions, the Ural Branch of the Russian Academy of Sciences, industrial partners, and the administrations of the Chelyabinsk, Sverdlovsk, and Kurgan regions.
SUSU is a participant of Program 5-100, which is dedicated to enhancing the competitiveness of Russian universities among leading research and education centres around the world.