Krasnoyarsk scientists, together with colleagues from Taiwan, synthesized magnetite nanoparticles with silver that can effectively absorb organic dyes from water. After absorbing pollutants, the nanoparticles are easily removed from the water using a magnetic field. They can then be processed for reuse. The research results were published in the journal Applied Surface Science.

Organic dyes are an integral part of life. They are used in various industries and give bright and rich colors to products. When released into wastewater, they have a negative impact on the environment and aquatic ecosystems. Discharge of untreated wastewater into natural reservoirs leads to disruption of the natural processes of self-purification of water and to deterioration of the sanitary condition of reservoirs. Most organic dyes, having excellent solubility in water, are not amenable to traditional methods of purification and biodegradation, posing a serious threat to the environment even at low concentrations.

Scientists from the Krasnoyarsk Science Center SB RAS, together with colleagues, synthesized magnetite nanoparticles with silver and studied their structure and magnetic properties, as well as the ability to absorb or destroy organic dyes in water.

“Research into water purification methods and the search for new opportunities is increasingly in demand. The trend towards water purification using magnetic nanoparticles is becoming highly relevant. A huge advantage of magnetic nanoparticles is the possibility of their removal from the liquid being purified using a magnetic field and repeated subsequent use,” says Oksana Ivanova, Candidate of Physical and Mathematical Sciences, researcher at the L.V. Kirensky Institute of Physics SB RAS.

The main magnetic material used as an absorber of contaminants in liquids is magnetite. It is non-toxic and has good magnetic properties; it is easy to obtain and easy to modify. Scientists decided to modify nanoparticles with silver to improve their antibacterial, adsorption, catalytic and photocatalytic properties.

“The combination of magnetite and silver in nanoparticles gives them special properties, since silver has high catalytic activity, and magnetite is characterized by a large magnetic moment. This makes it possible to easily manipulate the particles using a magnetic field in a non-contact manner in a wide variety of environments,” explains Oksana Ivanova.

Since the method of nanoparticle synthesis plays an important role in determining their characteristics, researchers approached this issue with special attention. Magnetite nanoparticles with silver were obtained using a modified solvothermal method - placing reagents with a solvent in an autoclave under high pressure and temperature. This method is used to synthesize new compounds, because many substances dissolve better under such conditions. Scientists made changes to the process by using polyvinylpyrrolidone in the synthesis, which allowed them to obtain a porous surface of magnetite nanoparticles.

The nanostructures were kept in an autoclave for several hours at a temperature of 200°C. During this time, magnetite nanoparticles turned into nanocrystals and assembled into globules with a silver core. At the same time, heat treatment for six hours provided more porous formations with a larger number of adsorption centers on the surface of the nanoparticles. Increasing the heat treatment time led to “clogging” of the pores. The researchers noted that the developed materials had high magnetization and low coercivity. Thanks to these abilities, the developed nanoparticles can be easily removed from liquids using the magnetic field. These parameters are ideal for applying particles as adsorbents of contaminants from a liquid medium.

Another task was to determine the ability of the new particles to absorb dyes from water. The analysis was carried out using organic dyes, namely Congo red and methylene blue. The highly porous nanoparticles absorbed the blue dye almost instantly. The specialists also noted the possibility of regenerating nanoparticles for reuse after contact with dyes. The surface of the nanoparticles after adsorption of dyes was cleaned by simple washing in ethyl alcohol.

“The performance characteristics of nanoparticles strongly depend on the synthesis conditions. For example, the rate and amount of adsorbed dye depend on the conditions of nanoparticle synthesis and their resulting form, and the catalytic ability is determined by the composition of the particles. Our approach has significant advantages over existing adsorption methods, since it does not require additional surface treatment of nanoparticles or the addition of solvents. The synthesized system of nanoparticles demonstrated higher catalytic activity in the decomposition of Congo red and methyl orange dyes compared to those known in literature” says Oksana Ivanova.

Specialists from the National Pingtung University (Taiwan) also took part in the study. The research was supported by the Russian Science Foundation (project No. 23-22-10025) and the Krasnoyarsk Regional Science Foundation.

The information was prepared with the support of a grant from the Russian Ministry of Education and Science as part of the federal project “Popularization of Science and Technology.”