The smallest nanoscale particles synthesized to detect heavy metal ions in water

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Scientists from Saint Petersburg University, Sirius University of Science and Technology and Saint Petersburg University University synthesized the smallest nanoscale organometallic structures to detect metal ions heavy in water. The results and results of the experiments and the description of the properties of crystals are published in Nanomaterials.

Organometallic polymers, or organometallic frameworks (MOF), are crystals composed of metal ions interconnected by organic molecules, that is to say organic linkers. Various concentrations of metal ions and organic linkers can be used to synthesize materials with different structures and properties. MOFs are widely used to design electrochemical sensors as reaction catalysts in the chemical industry or as propellant additives.

Some of the MOFs are luminescent MOFs. They emit light caused by UV rays, an electromagnetic field, or other disturbances. Luminescent MOFs are actively used as LED components and luminescent thermometers. In addition, they are used in the diagnosis of cancer. Luminescent MOFs are also used as luminescent sensors for pollutants.

Chemists at the University of St. Petersburg have synthesized the smallest nanoscale crystals by the wet chemical method assisted by ultrasound. They were synthesized by a slow mixing of aqueous solutions of sodium terephthalate and europium chloride using the ultrasonic-assisted wet chemical method, precipitated as a polycrystalline solid. Ultrasound provided better mixing of the solution, slowed particle growth, prevented microparticle aggregation, and resulted in the formation of individual microparticles.

Scientists have synthesized particles of different sizes. The average particle size can be 8 nm up to hundreds of micrometers. Today, nanoparticles of metal-organic structures of europium (III) terephthalate tetrahydrate (Eu2bdc3 · 4H2O) are the smallest MOF crystals based on rare earths of nanometric size.

“We did not expect that a double decrease in reagent concentration would result in a reduction in the size of several orders. Presumably, this effect may be due to the europium-terephthalate complex 1: 1. This can speed up the process of particle growth. Previously, scientists could synthesize nano-sized terephthalate particles equal to 40nm or even larger. We managed to synthesize particles five times smaller in size, ”said Andrey Mereshchenko, director of research, associate professor in the department of laser chemistry at the University of St. Petersburg and doctor of chemistry.

The method developed to synthesize nanoparticles can make a positive contribution to nanotechnology and coordination chemistry. Using this method, we can synthesize nanoparticles from other MOFs. The experiments also reported the selective quenching of luminescence by heavy metal ions. As a result, the synthesized nanoparticles can be used as sensors to detect heavy metal ions in water.

“This discovery has the potential to develop effective sensors to monitor heavy metal ions in drinking water. Our luminescent MOFs demonstrate significantly lower detection limits on heavy metal ions. This will ensure more accurate measurements of pollutants in the water, even in small concentrations, ”said Viktor Nosov, co-author of the article and chemistry student at the University of St. Petersburg.

The reported nanoparticles can also be used as luminescent sensors to detect Cu2 +, Cr3 + and Fe3 + ions in water. The presence of these metals in water poses a threat to humans and animals. The accumulation of heavy metals in the body can affect the human metabolism and lead to diseases of the nervous system, vascular diseases and digestive disorders. The chemists plan to continue research and develop an express test to detect heavy metal ions in drinking water and waste.

Reference: Kolesnik SS, Nosov VG, Kolesnikov IE, et al. Ultrasonically assisted synthesis of luminescent micro- and nanocrystalline MOFs based on Eu as luminescent probes for heavy metal ions. Nanomaterials. 2021; 11 (9): 2448. do I: 10.3390 / nano11092448

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