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Scientists of St. Petersburg State University, together with specialists from Sirius University and the Academic University, have created the smallest nanoparticles of metal-organic polymers that will determine the content of heavy metals in water.

Metal-organic polymers, or metal-organic framework structures (MOX), are compounds in which metal ions are interconnected by organic linker molecules. Using different combinations of metals and linkers, it is possible to obtain materials with different structures and properties. Today, MOX-based compounds are used in the production of electrochemical sensors, in the chemical industry as reaction catalysts, as well as as an additive to rocket fuel.

Some compounds are phosphors, that is, they are capable of emitting light under the influence of ultraviolet, electromagnetic field or other disturbances. Fluorescent MOX are used to create monitor screens and fluorescent thermometers, as well as for the diagnosis of cancer. In addition, phosphors can be used as highly sensitive sensors to detect harmful substances due to their luminescent properties.

Chemists of St. Petersburg State University synthesized the smallest nanoparticles using ultrasound. To do this, scientists slowly — literally drop by drop — added a solution of sodium terephthalate to the solution of europium chloride in an ultrasonic bath, which led to the formation of a precipitate. Ultrasonic waves in this case help to mix the solution more thoroughly, slow down the growth of particles and prevent them from sticking together — all this makes the connection more stable.

As a result of the synthesis, scientists were able to obtain particles of different sizes: from eight nanometers to hundreds of microns. At the moment, eight-nanometer nanoparticles of europium terephthalate synthesized by chemists of St. Petersburg State University are the smallest particles of metal-organic skeleton structures of rare earth elements.

"We did not expect that reducing the concentration of reacting substances by just two times would lead to a reduction in the particle size by almost a thousand times. Probably, this effect is associated with the presence of the europium-terephthalate complex in the solution in a ratio of 1:1, which contributes to a faster increase in the number of crystal nuclei. Previously, researchers were able to obtain nanoparticles of europium terephthalate with a diameter of 40 nanometers or more. We synthesized particles five times smaller," said the head of the study, Associate professor of the Department of Laser Chemistry and Laser Materials Science of St. Petersburg State University, Doctor of Chemical Sciences Andrey Mereshchenko.

The method of synthesis of nanoparticles developed by chemists makes a great contribution to nanotechnology and coordination chemistry, since it makes it possible to synthesize nanoparticles from other metal-organic frame structures. During the study, St. Petersburg State University experts also found that heavy metal ions significantly extinguish the luminescence of the obtained nanoparticles, which allows them to be used as sensors for detecting heavy metal ions in water.

"This discovery will help to create effective sensors for monitoring the content of heavy metal ions in drinking water. The sensitivity of our phosphors is slightly lower than the maximum permissible concentrations, which will allow us to accurately determine the presence of hazardous substances in water, and in small concentrations, due to the size of nanoparticles," said Viktor Nosov, one of the authors of the work, a student of St. Petersburg State University in the field of Chemistry.

The nanoparticles obtained by scientists can also be used as luminescent sensors to detect iron, copper and chromium ions in water. The content of these metals in water can be dangerous for humans and animals, since their accumulation in body tissues affects metabolism and can subsequently lead to diseases of the nervous and circulatory systems, as well as the gastrointestinal tract. In the future, chemists plan to continue their research and create an express test for the determination of heavy metal ions in drinking water, as well as in wastewater.

The study supported by the Russian Foundation for Basic Research (project No. 20-33-70025 "The effect of solvent on the growth dynamics and structure of metal-organic frame structures") was conducted at the Department of Laser Chemistry and Laser Materials Science of St. Petersburg State University using the equipment of the resource centers of the St. Petersburg State University Science Park, as well as at the Sirius University of Science and Technology.

The article was published in the journal Nanomaterials
Photo of microparticles © Press service of SPBGU

Source: St. Petersburg State University Press Service, sci-dig.ru