Researchers at NUST MISIS have synthesized mesoporous cobalt ferrite nanoparticles capable of absorbing different organic dyes depending on the size of their pores. The development opens up new possibilities for treating industrial wastewater without the need for additional chemical modification of the sorbent. One of the material’s key advantages is that it retains its effectiveness even after repeated cycles of use.
Organic dyes are among the most widespread classes of water pollutants. They enter wastewater from textile, pharmaceutical, and chemical manufacturing and are difficult to remove using conventional treatment methods. Existing magnetic nano-adsorbents typically require chemical surface treatment of the nanoparticles to effectively bind pollutants. Such coatings limit the range of substances that can be captured, complicate the operation of purification systems, and make regeneration of the sorbent more difficult.
Scientists from NUST MISIS and Pirogov Russian National Research Medical University demonstrated that surface modification of nanoparticles is not necessary. Instead, the key is in designing their internal structure correctly, since it determines which dye will be absorbed and by what mechanism.
The researchers synthesized rod-shaped cobalt ferrite nanoparticles — tiny magnetic rods permeated with two types of pores: small pores (up to 10 nm) and large pores (up to 50 nm). The ratio of pore sizes was controlled by adjusting the heating rate during calcination of the matrix from which the nanoparticles were later formed: the slower the heating, the greater the number of small pores. After water purification, the nanoparticles can be instantly removed from the water using an ordinary magnet.
To understand how the pores affect absorption, the researchers added the nanoparticles to solutions containing three dyes: methylene blue, methyl orange, and eriochrome blue.
“These three dyes were chosen deliberately — all of them are widely used in industry and regularly end up in wastewater. Methylene blue is used in medicine as well as for dyeing cotton, wool, and silk. As a byproduct of aniline production, it can heavily contaminate water resources in regions with chemical industries. Methyl orange is used in the chemical and textile industries. It is a toxic substance that is hazardous if inhaled, swallowed, or absorbed through the skin. Eriochrome blue is used in the textile industry for fabric dyeing. What all of them have in common is that they decompose extremely slowly in the natural environment and are poorly removed by standard purification methods. That is why, once they enter water systems, they remain there for a very long time. However, our development successfully dealt with each of them,” Alexey Nikitin, Candidate of Chemical Sciences and Associate Professor at the Department of Physical Materials Science at NUST MISIS.
Eriochrome blue produced an unexpected result: upon contact with the nanoparticles, it clumped together into large aggregates measuring several hundred nanometers. At low concentrations, the dye was absorbed effectively, but at high concentrations the aggregates returned to the solution. Such behavior has never before been documented for this class of dyes. The detailed findings were published in Journal of Colloid and Interface Science (Q1).
“This development changes the conventional view that surface chemistry is the most important feature of a sorbent. Pore architecture plays an equally important role. In the future, industries will be able to use sorbents tailored to specific pollutants, making them simpler, cheaper, and more reliable under real production conditions. In addition, dyes have different molecular structures and acquire different charges when dissolved in water, making them a convenient platform for studying adsorption processes,” Maxim Abakumov, Doctor of Chemical Sciences and Head of the “Biomedical Nanomaterials” Laboratory at NUST MISIS.
The study was carried out as part of the strategic technological project “Biomedical Engineering and Biomaterials” at NUST MISIS under the Russian Ministry of Science and Higher Education’s “Priority 2030” program.
