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Clean Air Research Helps Convert Toxic Pollutant Into Useful Chemical

An international team of scientists has developed new technology to clear the air by converting toxic air pollutants produced from the burning of fossil fuels into a helpful industrial chemical.

(CN) – An international team of scientists has developed new technology to clear the air by converting toxic air pollutants produced from the burning of fossil fuels into a helpful industrial chemical.

The burning of fossil fuels such as oil, coal, and gasoline releases a plethora of toxic substances into the atmosphere, contributing to the greenhouse gas effect and climate change. Among these toxic products is nitrogen dioxide, which is produced specifically by diesel and biofuels and one of the most widespread contributors to unhealthy air quality.

Nitrogen dioxide is produced from vehicle emissions, power plants, and is most concentrated near big cities. It has damaging effects on our lungs and has been the focus of blame for the increase of asthma in children. In fact, vast amounts of it can lead to acid rain events.

In new study by The University of Manchester, scientists present a metal-organic framework (MOF) material that provides a selective, fully reversible, and repeatable way to capture nitrogen dioxide (NO2) and convert it into nitric acid. In addition to cleaning the air, but nitric acid created by the process is a multibillion-dollar product used in agricultural fertilizer for crops, rocket propellant and nylon.

MOFs are known for their ability to store gas, purify it, and even alter its composition. They are tiny three-dimensional structures of crystalline materials, but they can have vast, empty insides. Just one gram of material can have a surface area equivalent to a soccer field, making it the perfect vessel for this purpose.

The scientists, however, have developed no ordinary MOF. It contains a material called MFM-520 and can capture nitrogen dioxide at ambient pressures and temperatures – even when at low concentrations or during flow – in the presence of moisture, sulfur dioxide and carbon dioxide. Using only water and air, this material can convert this highly reactive pollutant into nitric acid and regenerate itself by degassing or by treatment with water in the air.

The technology could eventually help control air pollution and correct nitrogen dioxide’s effects on the environment.

"This is the first MOF to both capture and convert a toxic, gaseous air pollutant into a useful industrial commodity." said Dr Sihai Yang, a lead author and a senior lecturer at The University of Manchester's Department of Chemistry, in a statement. "It is also interesting that the highest rate of NO2 uptake by this MOF occurs at around 45 degrees Centigrade (113 degrees Fahrenheit), which is about the temperature of automobile exhausts."

Scientists in the past struggled to find ways to capture greenhouse and toxic gases from the air, given their relatively low concentrations and the presence of water in the atmosphere which negatively affects the separation of targeted gases from other gases. The MFM-520 material offers solutions to many of these challenges – and creates a valuable product in the process.

"The global market for nitric acid in 2016 was USD $2.5 billion, so there is a lot of potential for manufacturers of this MOF technology to recoup their costs and profit from the resulting nitric acid production,” said Martin Schröder, lead author and vice president and dean of the faculty of Science and Engineering at The University of Manchester, in a statement. “Especially since the only additives required are water and air."

A large part of the research came from scientists using neutron spectroscopy and computational techniques at Oak Ridge National Laboratory to precisely characterize how MFM-520 captures nitrogen dioxide molecules.

"This project is an excellent example of using neutron science to study the structure and activity of molecules inside porous materials," said Timmy Ramirez-Cuesta, co-author and coordinator for the chemistry and catalysis initiative at ORNL's Neutron Sciences Directorate. "Thanks to the penetrating power of neutrons, we tracked how the nitrogen dioxide molecules arranged and moved inside the pores of the material, and studied the effects they had on the entire MOF structure."

Jiangnan Li, a co-author and doctoral student at the University of Manchester, struck an optimistic tone.

"The characterization of the mechanism responsible for the high, rapid uptake of NO2 will inform future designs of improved materials to capture air pollutants,” Jiangnan Li said.

The scientists published their work in the journal Nature Chemistry.

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