Researchers have developed a novel material that can capture the toxic air pollutant nitrogen dioxide which is produced during the combustion of fossil fuels, an advance that can lead to better air pollution control, and remediation technologies.
The study, published in the journal Nature Chemistry, describes the selective, fully reversible and repeatable process by which the new material can trap the noxious gas.
The researchers, including those from the Oak Ridge National Laboratory in the US, said the material -- a metal-organic framework, or MOF -- requires only water and air to convert the captured gas into nitric acid for industrial use.
They said the material -- denoted as MFM-520 -- can capture atmospheric nitrogen dioxide at normal pressures and temperatures even at low concentrations, and in the presence of moisture, and other gases like sulphur dioxide and carbon dioxide.
According to the researchers, the material can be developed into cost-effective technologies that can remove the toxic gas from the air, and convert it into nitric acid for use in producing fertilizer, rocket propellant, nylon, and other products.
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"To our knowledge, this is the first MOF to both capture and convert a toxic, gaseous air pollutant into a useful industrial commodity," said Sihai Yang, lead author of the study from the University of Manchester in the UK.
"It is also interesting that the highest rate of nitrogen dioxide uptake by this material occurs at around 45 degrees Celsius, which is about the temperature of automobile exhausts," he added.
The researchers said the global market for nitric acid in 2016 was USD 2.5 billion, adding that the new MOF technology can improve the profits of companies manufacturing the chemical, especially since the only additives required for the process are water and air.
As part of the study, the scientists used a chemical analysis technique called neutron spectroscopy, and computational techniques to precisely characterise how the new material captured 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 study co-author Timmy Ramirez-Cuesta from the Oak Ridge National Laboratory.
"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," he added.
According to the researchers, neutron vibrational spectroscopy is a unique tool to study how gases are absorbed by materials at the surface level, and for probing the reaction mechanisms at the molecular level, especially when combined with computer simulation.
"The interaction between the nitrogen dioxide molecules and MOF causes extremely small changes in their vibrational behaviour. Such changes can only be recognized when the computer model accurately predicts them," said study co-author Yongqiang Cheng from the Oak Ridge National Laboratory.
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