Topic: EnvironmentGlobal Warming

Last updated: May 27, 2019

The emission of gaseous pollutants in the atmosphere, industrial and houseenvironments are of a great concern due to the risk that these pollutants exert1. Althoughthe natural production of most atmospheric pollutants is much higher than artificial andindustrial production, the problem of the latter is that it usually occurs in a much localizedway, so that in places close to the emission source concentrations can be very high2.Carbon dioxide (CO2) capture is of interest due to its environmental and economicrelevance. Likewise, carbon monoxide (CO) and hydrogen sulfide (H2S) are considered as4suffocating agents for humans, even in reduced concentrations; as well as sulfur oxides(SOX), which has a negative contribution to the environment and human health1, 2.These gases are also recognized to contribute to the global warming through the greenhouseeffect, cause acid rain and photochemical smog, and several respiratory diseases due to itschronic exposure3-8. Therefore the sensing of these gases to avoid chronic exposure is ofa great interest, in addition to the development of materials allowing its collection andcapture before the release of burning or industrial gases to the environment.An alternative of environmental monitoring to this problem is the emergingapplication of graphene as gas sensing or capture material due to its low cost, low powerconsumption and high surface area9, 10. Graphene is highly stable, causes lowcontamination and bind gas molecules by intermolecular interactions to its surface,reaching high molecular adsorption and storage9-13.

For instance, the adsorption abilitiesof graphene towards toxic gaseous species (such as CO2, CO, NO2, NH3) have been welldescribed9, 11, 14-19. In this regard, most of the recent developments are focused onmaterials enhancing the adsorption stability of adsorbates onto graphene. In this sense, thelocal reactivity of graphene can be tailored via doping, which creates more reactiveadsorption sites20-26. Metals such as Cu, Ag, Au, Ti, Cr, Mn and Pd have beentheoretically considered as dopants in graphene to enhance its adsorption, storage capacityand sensing properties towards CO, CO2, NO2, NO, H2S and other harmful molecules27-31. Moreover, doping of graphene oxide has been also reported to form stable andexcellent sorbents for gas collection and filtration, even with low interference of O2molecules32.

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Thus, the application of metal-doped graphene for gas collection/sensingapplications is expected to emerge as these materials will be experimentally available.Theoretical studies based on the Density Functional Theory (DFT) framework haveshown the excellent sorption properties of Fe-embedded graphene (FeG) for a wide class ofair and water pollutants, significantly enhancing the adsorption with respect to intrinsicgraphene through strong Lewis-acid-base interactions25, 26, 33-36. Among theadvantages of iron as dopant are its low cost, low environmental toxicity compared to noblemetals, and its high acceptor character, making it an excellent candidate in terms ofimproving the sensitivity of graphene at environmental levels. In addition, iron is bonded to5graphene with high binding energies (?7.0 eV) and high diffusion barriers (?6.8 eV)37,38, then forming high stable adsorbents. In this sense, synthesized FeG through aberrationcorrectedtransmission electron microscopy technique shows high stability at the air andresistance to oxidants and corrosive species, where the dopants are able to disperse andbind to defective graphene with low cluster formation39.

Additionally, the bandgap ofgraphene is opened by Fe-doping, which turns it useful for sensing applications25; forexample, the CO2 detection onto FeG nanoribbons has been proved40, 41. Furthermore,we recently have theoretically studied the adsorption and sensing properties of FeG towardnitrogen oxides and formaldehyde25, 26, indicating that FeG is highly sensitive to thesegas molecules even in the presence of oxygen.Taking into consideration that FeG emerges as a promising material for adsorption,filtration, collection and/or sensing of harmful gas molecules, a DFT study was performedto study the gas adsorption of harmful gas molecules (CO, CO2, SO2 and H2S) as targetgases onto FeG nanosheets, characterizing also the role of O2 interference in the adsorptionmechanism. The FeG-Gas systems were characterized from its geometrical, energetic,electronic and binding properties. Molecular dynamics studies were performed to analyzethe FeG-Gas interaction stability at ambient conditions, and the adsorption stability wasalso characterized in aerobic conditions. As a reference, the gas adsorption was also studiedonto pristine graphene. Through this study, FeG is suggested to enhance the gas adsorptionprocess of toxic gaseous pollutants with negative effects on human health and on theenvironment.


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