Current advancements in CO2 capture using graphene-based materials European Journal of Chemistry 15 (3) (2024) 302-306 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2024 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.15.3.302-306.2561 European Journal of Chemistry View Journal Online View Article Online Current advancements in CO2 capture using graphene-based materials Madushan Dhammika Gunarathna 1,*, Nimeshi Aviddika Abeysinghe 1, Ashan Sithija Wickramaarachchi 1, and Polegodage Dilushi Sureka Ruwan Kumari 2 1 Department of Chemistry, Faculty of Science, University of Kelaniya, Kelaniya, 11300, Sri Lanka 2 Department of Microbiology, Faculty of Science, University of Kelaniya, Kelaniya, 11300, Sri Lanka * Corresponding author at: Department of Chemistry, Faculty of Science, University of Kelaniya, Kelaniya, 11300, Sri Lanka. e-mail: mdham191@kln.ac.lk (M.D. Gunarathna). 10.5155/eurjchem.15.3.302-306.2561 Received: 27 April 2024 Received in revised form: 28 June 2024 Accepted: 04 July 2024 Published online: 30 September 2024 Printed: 30 September 2024 In 2023, global CO2 emissions were 37.4 billion tonnes and a 1.1% increase compared to 2022. Although most countries try to decarbonize their economies, oil and gas supplied 52% of the world's energy needs in 2021, and by 2050 it will be 47%. Therefore, in the future, oil and gas will still account for a considerable percentage of the energy sector. However, the continuous release of CO2 into the atmosphere at this rate can result in severe environmental problems. One of the promising approaches to address this issue is CO2 capture. This captured CO2 can then be stored underground or used to produce commercially valuable products. In recent years, graphene-based materials have gained attention in CO2 capture due to their interesting properties, such as high thermal stability and durability. This review focuses mainly on recently published articles on carbon capture using graphene-based materials. Graphite Monoliths Mesopores Micropores Graphene oxide Reduced graphene oxide Cite this: Eur. J. Chem. 2024, 15(3), 302-306 Journal website: www.eurjchem.com 1. Introduction Graphite is one of the well-known carbon allotropes and consists of sp2 hybridized carbons arranged in six-membered hexagonal rings [1,2]. Graphite is a layered structure, and hundreds and thousands of carbon layers are arranged on top of each other [3]. A single layer of graphite is known as graphene. It was first extracted by Andre Geim and Konstantin Novoselov in 2004, and they won the Nobel Prize in 2010 for their discovery [4]. These two scientists removed some flakes from graphite using scotch tapes, and they observed that some of the flakes were thinner than the others, so they kept removing the flakes until they obtained flakes that were only one atom thick. Although graphite and graphene have the same atomic arrangement, changing the number of layers can change the properties of the material (i.e., it has been observed that decreasing the number of layers increases the electrical conductivity and thermal conductivity) [5-7]. Graphene has been emerging as a potential candidate for CO2 capture in recent years due to interesting properties such as high surface area, high thermal stability, higher mechanical strength, high chemical stability, high selectivity, etc. [8,9]. However, the production of single-layer graphene is difficult and expensive; therefore, most studies are conducted using graphene derivatives such as graphene oxide (GO) and reduced graphene oxide (RGO). In addition, it is well known that it is possible to incorporate other elements, such as nitrogen and sulfur, into graphene layers to synthesize different graphene derivatives. Researchers around the world have suggested different materials for CO2 capture, such as zeolites, alumina-based compounds, metal-organic frameworks, metal oxides, etc. [10]. However, most of these materials have several drawbacks, such as high cost, limited adsorption capacity, poor thermal stability, etc. [11,12]. Existing CO2 capture technologies can be classified into two types: (i) carbon capture and storage and (ii) carbon capture and utilization [13]. The first step of carbon capture is the separation of CO2 from gas streams. Several techniques are used, such as solid adsorbents, solvent absorption, cryogenic separation, and metal-organic frameworks [11]. The most commonly used technique is the use of amine solutions (i.e., monoethanolamine/MEA) to separate CO2 [14]. However, most of these techniques have not met the expected carbon capture efficiency and are energy-intensive and expensive [15,16]. Therefore, it is necessary to optimize existing carbon capture technologies to make this technology more feasible. This review focuses on recent advances in CO2 capture using graphene- based materials. ABSTRACT REVIEW ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.15.3.302-306.2561 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.15.3.302-306.2561 mailto:mdham191@kln.ac.lk http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.15.3.302-306.2561&domain=pdf&date_stamp=2024-09-30 Gunarathna et al. / European Journal of Chemistry 15 (3) (2024) 302-306 303 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.302-306.2561 Figure 1. Various liquid phase processes which are used to synthesize graphene oxide from raw graphite. 2. Synthesis of graphene and graphene derivatives Graphene can be synthesized using different methods such as chemical vapor deposition, electrochemical exfoliation, epi- taxial growth, liquid phase exfoliation, mechanical exfoliation, and chemical exfoliation [17]. Out of these techniques, the most popular technique is liquid phase exfoliation due to its cost- effectiveness [18]. In liquid-phase exfoliation, intercalating agents are introduced into the graphite sheets, and these sheets are exfoliated. One of the popular liquid-phase exfoliation techniques is the modified Hummers method [19]. In the modified Hummers method, graphite is oxidized using an oxidizing agent in an acidic medium, and as a result, it will intro- duce oxygen functional groups (i.e., epoxy groups, hydroxyl groups, and carboxylic acid groups) into the graphite layer. The introduction of oxygen functional groups increases the interlayer distance between graphite layers; hence, these graphite oxide layers can be separated by sonication, thermal shock, shearing, etc. [18]. Separated graphene oxide layers can be dissolved in water or any other suitable solvent due to the presence of functional oxygen groups [20]. Graphene oxide can be further reduced to form reduced graphene oxide using different reducing agents such as ascorbic acid (vitamin C), hydrazine hydrate, resveratrol, chitosan, polyethyleneimine, sodium borohydride, bovine serum albumin, green tea polyphenols, etc. [21,22]. As shown in Figure 1, there are some other liquid phase exfoliation methods, such as the Staudenmaier, Hofmann, and Tour methods [23]. Graphene oxide is commercially available now in different forms (i.e., paste, powder, films, etc.), and there are leading suppliers such as Matexcel, CD bioparticles, Alfa Chemistry, ACS material, etc. 3. Graphene-based materials for CO2 capture An, L. et al. synthesized different types of nitrogen-rich porous carbons derived from graphene and tested them for their CO2 adsorption capacity [24]. These nitrogen-rich porous carbons were synthesized using graphene oxide as the precursor. Graphene oxide was synthesized using the modified Hummers method and reacted with urea to incorporate nitrogen atoms, and this nitrogen-doped graphene was subjected to KOH activation [21]. Instead of urea, there are some other compounds that can be used as nitrogen doping agents, such as NH3, ammonium salts, and nitric acid. KOH activation was carried out at different KOH concentrations and different activation temperatures to form different N-rich porous carbons [24]. As shown in Equations 1-4, during the KOH activation process, carbon atoms in nitrogen-doped graphene oxide react with KOH to form CO2, CO, H2, and carbonates [25]. This will create new voids in the structure and, as a result, will give rise to new micropores and mesopores; hence, it will significantly increase the surface area of BET (Brunauer, Emmett, and Teller) [26]. Micropores have a pore size of up to 2 nm, and pores in the range of 2 to 50 nm are classified as mesopores [27]. 6KOH + 2C → 2K + 3H2 + 2K2CO3 (1) K2CO3 + 2C → K2O + 2CO (2) K2CO3 → K2O + CO2 (3) 2K + CO2 → K2O + CO (4) Most of the studies have conducted BET surface area analysis (Brunauer-Emmett-Teller) and total pore volume analysis using nitrogen adsorption isotherms to study the textural properties of graphene-based materials. Nitrogen adsorption-desorption isotherms are graphs that are generated by measuring the volume of nitrogen adsorbed and desorbed onto a surface with respect to the relative pressure [28]. In the BET model, monolayer coverage is considered and uses the linear region of nitrogen isotherms, usually at relative pressures in the range of 0.05-0.35; this relative pressure range can also change depending on the type of adsorbent [29]. As shown in Figure 2, An, L. et al. measured the BET surface area of nitrogen-doped porous carbons derived from graphene in the relative pressure range P/P0 = 0.04–0.32 [22]. Equation 5 represents the BET equation arranged in the y = mx + c format: V is the adsorbed gas quantity, P0 is the saturation pressure of the adsorbate, P is the equilibrium pressure of the adsorbate, Vm is the monolayer adsorbed gas volume, C is the BET constant, E1 is the heat of adsorption for the first layer, and EL is the heat of vaporization. Equations 6-9 represent how to calculate the Vm using the slope and the intercept of the plot. 1 𝑉𝑉[�𝑃𝑃0𝑃𝑃 �−1] = 𝐶𝐶−1 𝑉𝑉𝑚𝑚𝐶𝐶 � 𝑃𝑃 𝑃𝑃0 � + 1 𝑉𝑉𝑚𝑚𝐶𝐶 (5) 𝐶𝐶 = exp(𝐸𝐸1−𝐸𝐸𝐿𝐿 𝑅𝑅𝑅𝑅 ) (6) 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 = 𝐶𝐶−1 𝑉𝑉𝑚𝑚𝐶𝐶 (7) 𝐼𝐼𝐼𝐼𝐼𝐼𝑆𝑆𝐼𝐼𝐼𝐼𝑆𝑆𝑆𝑆𝐼𝐼 = 1 𝑉𝑉𝑚𝑚𝐶𝐶 (8) 𝑉𝑉𝑚𝑚 = 1 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠+𝑖𝑖𝑖𝑖𝑖𝑖𝑠𝑠𝑖𝑖𝑖𝑖𝑠𝑠𝑠𝑠𝑖𝑖 (9) 304 Gunarathna et al. / European Journal of Chemistry 15 (3) (2024) 302-306 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.302-306.2561 Table 1. CO2 adsorption of T-GU-700-6, M90_0.5 and activated-RGO-950. Material Surface area (m2/g) Total pore volume (cm3/g) CO2 uptake at 1 atm (mmol/g) Isosteric heat of adsorption (kJ/mol) Reference 25 °C 0 °C T-GU-700-6 1032.00 0.82 2.40 3.24 -12-33 [24] M90_0.5 328.00 1.35 2.10 - - [31] Activated-RGO-950 1315.98 1.07 2.45 3.36 -27.42 [33] (a) (b) Figure 2. Nitrogen adsorption isotherms of nitrogen-doped porous carbons derived from graphene and the full green lines represent the approximate region that can be used for BET calculations (images are adapted with permission from An, L. et al. Copyright (2019) American Chemical Society) [24]. After evaluating the monolayer adsorbed gas volume (Vm), then Equations 10 and 11 can be used to get the BET surface area, where St is the total surface area of sample material, N is the Avogadro number, V is the molar volume of the adsorbed gas, s (0.162 nm2) is the cross-sectional area of an adsorbed nitrogen molecule and a is the mass of the sample [30]. 𝑆𝑆𝑖𝑖 = 𝑉𝑉𝑚𝑚𝑁𝑁𝑠𝑠 𝑉𝑉 (10) 𝑆𝑆𝐵𝐵𝐸𝐸𝑅𝑅 = 𝑆𝑆𝑡𝑡 𝑎𝑎 (𝑚𝑚2 𝑔𝑔)⁄ (11) An, L. et al. reported that the thermal shocking process and KOH activation can increase the surface area of graphene-based materials [22]. However, increasing the temperature above a certain threshold level and continuously increasing the KOH concentration can decrease the surface area of graphene-based materials [22]. Politakos, N. et al. synthesized monolithic nanostructures from graphene oxide and reported that reduction of graphene oxide to a certain threshold level can increase the BET surface area of monolithic nanostructures [31]. Monoliths are structures consisting of pores that resemble a honeycomb [32]. Chowdhury, S. et al. synthesized graphene- based adsorbents using graphite as the starting material [33]. Graphite powder was used to synthesize graphene oxide, and graphene oxide was thermally reduced to form reduced graphene oxide. The reduced graphene oxide was physically activated by heating it to temperatures of 750, 850, and 950 °C in the presence of CO2 flow (1000 mL/min) [30]. This physical activation process works in the same way as KOH activation, where CO2 reacts with carbons in reduced graphene oxide sheets and produces gaseous species, as shown in Equation 12 [30]. As a result, it will increase the porosity of the material. C + CO2 → 2CO ΔH = 172 kJ/mol (12) An, L. et al., measured the CO2 adsorption of different types of nitrogen-doped graphene synthesized under various conditions, and the highest CO2 adsorption was observed in T- GU-700-6 [22]. T-GU represents the graphene oxide that reacted with urea after the thermal shock process, 700 is the activation temperature in Celsius during the KOH activation process, and 6 represents the ratio of KOH/T-GU [22]. Politakos, N. et al., synthesized different monolithic nanostructures under various conditions and found that the highest CO2 adsorption was seen in M90_0.5 [28]. M represents the monolithic nanostructure, 90 represents the temperature in Celsius at which the monolith was synthesized, and 0.5 represents the ratio of GO/ASA (Ascorbic acid/Vitamin C) ratio [28]. Studies by Chowdhury, S. et al. have shown that the highest CO2 adsorption was seen for activated-RGO-950 [30]. 950 represents the temperature in Celsius at which the reduced graphene oxide was activated. Table 1 shows the CO2 adsorption capacity, surface area, and isosteric heat of adsorption of these materials [24,31,33]. By comparing the values of CO2 uptake of all materials in Table 1, it is clear that increasing the surface area does not significantly affect the CO2 uptake. The highest total pore volume was observed for M90_0.5; however, CO2 adsorption was lowest in M90_0.5; therefore, it is not possible to suggest that increasing porosity increases CO2 adsorption. Comparing the textural properties of different materials from different studies on CO2 adsorption is complex; therefore, evaluating the effect of surface area and total pore volume on CO2 adsorption needs more studies. It is well known that gas adsorption decreases with increasing temperature; this can be seen here by comparing CO2 uptake values at 25 and 0 °C; with increasing temperature, CO2 adsorption has decreased [34]. The isosteric heat of adsorption is another important property that needs to be considered when studying gas adsorption because if an adsorbent has a very high isosteric heat of adsorption, it is difficult to desorb the adsorbed gas. If it has a very low isosteric heat of adsorption, it will decrease the CO2 adsorption; therefore, moderate values are preferred. For physisorption processes, the isosteric values are generally between 5-40 kJ/mol [35]. The isosteric heat of adsorption values of T-GU- 700-6 and activated-RGO-950 suggest that this is a physisorption process; however, no isosteric heat of adsorption values were given for M90_0.5. An, L. et al., N. et al., and Chowdhury, S. et al. all have tested for the selectivity of CO2 in the presence of N2. T-GU-700-6, M90_0.5, and activated-RGO-950 had higher selectivity for CO2 in the presence of nitrogen, as shown in Figure 3. However, none of these studies measured the selectivity of CO2 in real flue gas conditions because the flue gas contains other species, such as O2, SO2, NOx, and H2O [36]. Gunarathna et al. / European Journal of Chemistry 15 (3) (2024) 302-306 305 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.302-306.2561 (a) (b) (c) Figure 3. (a) CO2 and N2 adsorption of T-GU-700-6, (b) CO2 and N2 adsorption desorption of M90_0.5, and (c) CO2 and N2 adsorption of activated-RGO-950 (Images are adapted with permission from An, L. et al. Copyright (2019) American Chemical Society Politakos, N. et al. Copyright (2020) American Chemical Society and Chowdhury, S. et al Copyright (2016) American Chemical Society) [24,31,33]. In order to use these materials in the industry, their stability and recyclability must be tested. An, L. et al., studied the cycle stability of T-GU-700-6 for five cycles and observed that there was only a 5% decrease in CO2 adsorption compared to the first cycle [22]. Politakos, N. et al. studied the cycle stability of M90_0.5 for five cycles and reported that after each cycle there was a decrease in CO2 adsorption; however, this decrease in CO2 adsorption has slowly reduced with each cycle, suggesting that these monoliths are slowly stabilizing with respect to CO2 adsorption [28]. Chowdhury, S. et al., tested activated-RGO-950 for ten cycles and observed that there was no loss in CO2 adsorption after ten cycles. Despite recent advances in developing novel materials derived from graphene for CO2 capture, none of these materials have been commer- cially used so far. Therefore, more testing and research is needed to commercialize these graphene-based materials for CO2 capture. 4. Conclusion Different types of graphene-based materials were synthesized by An, L. et al., Politakos, N. et al., and Chowdhury, S. et al., and CO2 adsorption of all these materials was measured. Out of these studies, the highest CO2 adsorption was seen for activated-RGO-950 at 25 °C and 0 °C. T-GU-700-6, M90_0.5 and activated-RGO-950 had higher CO2 selectivity in the presence of nitrogen; however, all of these materials must be tested in real flue gas conditions. T-GU-700-6, M90_0.5, and activated-RGO- 950 have shown the cycle stability and isosteric heat of adsorption values of T-GU-700-6 and activated-RGO-950 have shown that CO2 adsorption is a physisorption process. Acknowledgements The authors would like to thank the Department of Chemistry, University of Kelaniya, for funding the publication of this paper. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered. CRediT authorship contribution statement Conceptualization: Madushan Dhammika Gunarathna; Methodology: Madushan Dhammika Gunarathna, Nimeshi Aviddika Abeysinghe; Investigation: Madushan Dhammika Gunarathna, Ashan Sithija Wickramaarachchi; Resources: Madushan Dhammika Gunarathna, Ashan Sithija Wickramaarachchi, Nimeshi Aviddika Abeysinghe; Data Curation: Madushan Dhammika Gunarathna, Ashan Sithija Wickramaarachchi, Nimeshi Aviddika Abeysinghe, Polegodage Dilushi Sureka Ruwan Kumari; Writing - Original Draft: Madushan Dhammika Gunarathna; Writing - Review and Editing: Madushan Dhammika Gunarathna, Ashan Sithija Wickramaarachchi, Nimeshi Aviddika Abeysinghe, Polegodage Dilushi Sureka Ruwan Kumari; Visualization: Madushan Dhammika Gunarathna, Ashan Sithija Wickramaarachchi, Nimeshi Aviddika Abeysinghe, Polegodage Dilushi Sureka Ruwan Kumari; Supervision: Madushan Dhammika Gunarathna; Project Administration: Madushan Dhammika Gunarathna. ORCID and Email Madushan Dhammika Gunarathna mdham191@kln.ac.lk https://orcid.org/0009-0007-0262-0405 Nimeshi Aviddika Abeysinghe nimeshiabeysinghe838@gmail.com https://orcid.org/0009-0002-8526-9166 mailto:mdham191@kln.ac.lk https://orcid.org/0009-0007-0262-0405 mailto:nimeshiabeysinghe838@gmail.com https://orcid.org/0009-0002-8526-9166 306 Gunarathna et al. / European Journal of Chemistry 15 (3) (2024) 302-306 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.302-306.2561 Ashan Sithija Wickramaarachchi siwic1997@gmail.com https://orcid.org/0000-0003-1654-2341 Polegodage Dilushi Sureka Ruwan Kumari surekadilushi@gmail.com https://orcid.org/0000-0001-6632-9034 References [1]. Kharisov, B. I.; Kharissova, O. V. Carbon allotropes: Metal-complex chemistry, properties and applications; 1st ed.; Springer International Publishing: Basel, Switzerland, 2019. [2]. 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Permissions for commercial use of this work beyond the scope of the License (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). mailto:siwic1997@gmail.com https://orcid.org/0000-0003-1654-2341 mailto:surekadilushi@gmail.com https://orcid.org/0000-0001-6632-9034 https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Synthesis of graphene and graphene derivatives 3. Graphene-based materials for CO2 capture 4. Conclusion Acknowledgements Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: