Rodríguez-Garcia, S.; Santiago, R.; López-Díaz, D.; Merchan, MD; Velázquez, MM; Fierro, JLG; Palomar, J. (2019). Role of the Structure of Graphene Oxide Sheets on the CO2 Adsorption Properties of Nanocomposites Based on Graphene Oxide and Polyaniline or Fe3O4 – Nanoparticles, ACS Sustainable Chemistry & Engineering, 7 (14), pp. 12464-12473. https://doi.org/10.1021/acssuschemeng.9b02035
Before discussing the properties of graphene oxide with respect to CO2, the terms “adsorption” and “absorption” should be clarified.
As will be explained later, graphene oxide can adsorb and absorb CO2 in various nanomaterial configurations.
Absorption is often confused with “adsorption”.
This is the ability of a material to bind atoms, ions, or molecules of a gas, liquid, or solid.
In this case, the ability to attract CO2 to the surface of graphene oxide and keep it stuck, adhered, or fixed.
This attraction is similar to the “surface tension” that causes water droplets to coalesce into larger droplets when the distance between them is small enough.
Absorption is the property of a material to absorb, integrate, or combine with atoms, ions, or molecules of a gas, liquid, or solid.
In this case, graphene oxide has the ability to integrate CO2, although it should be noted that it does not do this on its own, as it requires nanocomposites and polymers from third parties.
Analyzed facts
The article analyzed here presents relevant information that would explain the role of graphene oxide in the fight against climate change.
The study by (Rodríguez-García, S.; Santiago, R.; López-Díaz, D.; Merchán, M.D.; Velázquez, M.M.; Fierro, J.L.G.; Palomar, J. 2019) demonstrates the “adsorptive” properties of graphene oxide in combination with Fe3O4 nanoparticles to reduce CO2 emissions into the atmosphere.
The combination of graphene oxide with Fe3O4 nanoparticles is directly related to the development of cancer drugs and DNA vaccines (Shah, MAA; He, N.; Li, Z.; Ali, Z.; Zhang, L. 2014), biocide fertilizers for agricultural use (Zhang, M .; Gao, B .; Chen, J .; Li, Y .; Creamer, AE; Chen, H. 2014), and 5G electromagnetic wave absorption tests (Ma, E . ; Li, J.; Zhao, N.; Liu, E.; He, C.; Shi, C. 2013), administration of vaccines with genetic reformulations using the CRISPR technique (Abbott, TR; Dhamdhere, G. ; Liu, Y. ; Lin, X.; Goudy, L.; Zeng, L.; Qi, LS 2020 | Ding, R.; Long, J.; Yuan, M.; Jin, Y.; Yang, H.; Chen, M.; Duan, G. 2021 | Teng, M.; Yao, Y.; Nair, V. Luo, J. 2021).
In other words, it is always the same highly versatile compound in all cases and applications.
Figure 1. Schematic diagram of the CO2 adsorption reaction on graphene oxide
Although graphene oxide has special properties that make it an ideal material for atmospheric filtration and air decontamination, it is paradoxical and contradictory at the same time.
It should not be forgotten that inhaled graphene oxide (in suspended particles) is harmful to health (Ou, L.; Song, B.; Liang, H.; Liu, J.; Feng, X.; Deng, B.; Shao, L. 2016) and can cause significant damage, as already described in previous contributions, see graphene oxide in blood (Palmieri, V.; Perini, G.; De Spirito, M.; Papi, M. 2019), graphene oxide interaction with brain cells (Rauti, R .; Lozano, N .; León, V .; Scaini, D .; Musto, M .; Rago, I .; Ballerini, L. 2016), graphene oxide disrupts mitochondrial homeostasis (Xiaoli, F . ; Yaqing, Z .; Ruhui, L .; Xuan, L .; Aijie, C .; Yanli, Z .; Longquan, S. 2021), among other articles that can be retrieved via the query “graphene toxicity” .
Returning to the analysis of the article, it states that graphene oxide nanocomposites with polyaniline (PANI) or Fe3O4 nanoparticles are capable of adsorbing and retaining CO2.
This particular capacity “increases linearly with the volume of the micropores“.
This detail is relevant because it matches the type of material used in ice nucleation, which also had to be porous to achieve better performance in nanocrystal formation (Liang, H.; Möhler, O.; Griffiths, S.; Zou, L. 2019).
The porous property is also appreciated in chemical fertilizers and, interestingly, in nanoparticles targeting RNA interference therapies in the brain (Joo, J.; Kwon, EJ; Kang, J.; Skalak, M.; Anglin, EJ; Mann, AP; Sailor, MJ 2016).
Indeed, porous graphene is used as an atmospheric nanofilter, as also reported by other authors (Blankenburg, S.; Bieri, M.; Fasel, R.; Müllen, K.; Pignedoli, C. A.; Passerone, D. 2010), in the form of 2D graphene oxide membranes adsorbing ammonia, CO2 and argon.
Reviewing the introduction of the article, other interesting statements can be observed.
Specifically, the justification for the research is summarized in the problem of global warming, which is “a serious problem for the planet. The increasing concentration of greenhouse gases, especially CO₂, makes it necessary to develop processes for their elimination“.
In this sense, graphene oxide presents itself as an “efficient and economical solution” to mitigate the effects that this “pollutant” can cause.
Among the different options studied in the scientific literature (membrane adsorption and absorption or chemical adsorption in liquid amines), none stands out as having a good balance between performance, energy efficiency and impact.
However, graphene oxide in the form of hydrogels, aerogels, nanospheres and nanotubes seems to triple the CO2 capture capacity when functionalized with Fe3O4.
The experiment performed aims to simulate a realistic scenario of CO2 adsorption, specifically that produced by a combustion gas.
This suggests that one of the obvious applications of graphene oxide could be in the exhaust pipes of combustion engines or any other industrial combustion process.
In fact, the authors point out that in a more realistic scenario corresponding to a post-combustion gas (pCO2 = 0.15 bar and pN2 = 0.85 bar), the IAST CO2/N2 selectivity values obtained from nanocomposites prepared with graphene oxide need to be improved to ensure effective retention.
The IAST (Ideal Adsorbed Solution Theory) is determined by several factors, the most important of which are the atmospheric pressure expressed in “bar” (pressure unit), the atomic weight per gram in mmol/g of the graphene oxide catalyst, the temperature, the CO2 concentration and the adsorption time.
The researchers conclude that graphene oxide coated with the PANI polymer offers better adsorption results at operating temperatures, as well as recyclability properties that allow its modulable behavior for higher efficiency.
Other studies have also focused on CO2 “adsorption” with graphene oxide.
For example, the study by (Wu, X.; Zhao, B.; Wang, L.; Zhang, Z.; Zhang, H.; Zhao, X.; Guo, X. 2016) tested the behavior of PVDF (polyvinylidene fluoride) and graphene oxide at different concentrations to create membranes by observing CO2 adsorption under room temperature conditions.
It was concluded that increasing the percentage of graphene resulted in an increase in the adsorption capacity of the membrane.
This result was influenced by the porosity factor (82% in the experiment), which was also responsible for the crystallization or nucleation of PVDF, which caused a change in the shape of the membrane, with increased roughness and contact surface with graphene oxide, and consequently increased adsorption capacity.
Interestingly, the membrane did not lose CO2 even when wet due to the hydrophobic properties of PVDF.
(Irani, V.; Maleki, A.; Tavasoli, A., 2019) also studied CO2 adsorption with nanofluidized graphene oxide combined with MDEA, also known as “mehyldiethanolamine amine,” confirming the capabilities of the material.
For example, the addition of 0.2 percent graphene oxide to MDEA was shown to increase its CO2 adsorption capacity by more than 10 percent at different temperatures, with little increase in the weight of the mixture.
Final thoughts
Graphene oxide can be used to adsorb CO₂ from the atmosphere and contribute to the reduction of greenhouse gases.
In this sense, it would not be surprising if it is already being used for this purpose, since, according to (Pöschl U,. 2005), graphene oxide is found in the analysis of aerosols in the atmosphere, together with soot resulting from pyrolysis and incomplete combustion of jet aircraft, in a small but unquantified amount.
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