New design improves plasma jet water decontamination

Plasma is an ionized gas, that is, a gas containing electrons, ions, atoms, molecules, radicals and photons. It is often called the fourth state of matter and, surprisingly, it permeates everything. Plasmas, generated artificially by transmitting energy to a gas, are found in fluorescent tubes that light kitchens, but they have also allowed cell phones to become smaller and smaller.

Plasma has been a true revolution in the world of technology. Previously, to etch circuits on silicon wafers used in electronic devices such as mobile phones, it was necessary to use polluting chemicals. Today, the use of plasma has made it possible to do this in a cleaner and more precise way, making it possible to make the slits smaller and smaller, and with them, the devices.

But plasma also has other applications, such as water treatment. The groups FQM-136 Physics of Plasmas and FQM-346 Organic Catalysis and Nanostructured Materials of the University of Córdoba collaborated in a study whose aim was the elimination of contaminants present in water by applying plasma to promote processes chemicals.

Their study is published in the journal Chemosphere.

In order to tackle the problem of the growing presence of organic pollutants in water, such as dyes and other compounds resulting from agricultural and industrial activity in water and which destabilize ecosystems, these researchers opted for application of plasma.

In 2017, they demonstrated for the first time that argon plasmas induced by microwaves open to air, by acting on water, generated reactive species in it containing oxygen and nitrogen (such as hydroxyl radicals, water peroxide, nitrogen radicals) capable of decontaminating it.

Today, researchers Juan Amaro Gahete, Francisco J. Romero Salguero and María C. García have succeeded in designing a reactor of this type of plasma and in considerably increasing the quantities of these active species generated in water, thus allowing the destruction of high concentrations. of dyes (in this case, methylene blue) in just a few minutes.

They achieved this by modifying the design of the surfatron, the metal device that mixes the energy of a microwave generator with the plasma to maintain it.

“What we did was place a small piece of silicon in the quartz discharge tube, making it possible to generate a different plasma, non-filamentary and more effective in creating active species when interacting with water “, explained Professor María. C. Garcia.

The aforementioned plasma components, when interacting with water, generate oxidizing species capable of degrading organic compounds and killing microorganisms, which allows this plasma reactor to be used in applications related to sanitation. the water.

This new configuration therefore extends the applicability of this type of plasma.

“The design completely changes the configuration of the electromagnetic field generated by the surfatron to create the plasma, resulting in a plasma with different and more efficient properties, also eliminating the problem of filamentation (the division of the plasma column into multiple filaments) , which destabilizes,” explained Professor García.

And then… decontamination. “These oxidizing species generated by the action of the plasma are very reactive and make it possible to destroy the organic matter present in the water,” continued Professor Francisco J. Romero.

For this to happen, the plasma is not introduced into the water. It is rather made to act at a distance, so that between the water and the plasma there is a zone of air where numerous reactions occur due to collisions between the excited species and the molecules of oxygen, nitrogen and water vapor, and “reactive species that diffuse”. in the liquid and end up with the contaminants” are generated.

The decontaminating potential of this type of plasma, generated with this new design, “has been tested to reduce high concentrations of methylene blue dye in water, with very efficient results in terms of energy, achieving the elimination complete coloring with reduced processing times. “, said researcher Juan Amaro.

Thus, with this work, we are making progress on one of the applications of plasma, this “fourth state of matter” created by providing energy to a stable gas and transforming it into ionized gas, and this applies to almost everything: making microchips, disinfecting surfaces, healing wounds, putting anti-reflective coatings on glasses, improving seed germination, recovering waste, activating the surface of plastics to achieve better paint adhesion, and countless other applications.