Materials Today Communications 33 (2022) 104776 Available online 28 October 2022 2352-4928/© 2022 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Materials Today Communications journal homepage: www.elsevier.com/locate/mtcomm CO 2 adsorption by coal-based activated carbon modified with sodium hydroxide Seyed Saeed Rokni Dehkordi, Qasem Delavar, Habib Ale Ebrahim ∗ , Seyed Sahand Partash Department of Chemical Engineering, Amirkabir University (Tehran Polytechnic), Tehran, Iran ARTICLE INFO Keywords: CO 2 Adsorption NaOH Modified activated carbon ABSTRACT This paper used sodium hydroxide to improve the CO 2 adsorption capacity of coal-based activated carbon. The effect of several modification parameters, including sodium hydroxide concentration (0.01–8 M), impregnation time (4–7 h), drying duration (4–7 h), the effect of washing, and the impact of fixed bed operating conditions such as inlet flow rate, the height of the adsorption column, and operating pressure on CO 2 adsorption capacity were investigated. The plain and impregnated adsorbents were thoroughly characterized by several instrumental analyses. With increasing NaOH loading, CO 2 adsorption capacity improved until its maximum value at 1 M NaOH concentration. Washing the samples was an important parameter on CO 2 uptake in the fixed bed when samples were impregnated with high concentration NaOH solution. The mechanisms of modification and CO 2 adsorption process on the modified activated carbon were carefully studied. The dynamic adsorption capacity for the plain and impregnated AC at optimum conditions were 21.20 and 51.41 mg/g, respectively, which indicates that the capacity for CO 2 adsorption increased by more than 142%. According to the findings, NaOH-modified activated carbon can efficiently capture CO 2 . 1. Introduction According to the 1998 Kyoto Protocol, carbon dioxide, methane, nitrous oxides, hydrofluorocarbons, perfluorocarbons, and sulfur hex- afluoride are greenhouse gases [1,2]. Even though the warming po- tential of greenhouse gases like methane and nitrous oxide is more significant than carbon dioxide, CO 2 is the primary greenhouse gas emitted by anthropological activities. Also, it is long-living in the earth’s atmosphere [3]. Greenhouse gases have sustained the earth’s temperature, which is crucial for living beings, especially humans. If they had not existed in the atmosphere, the earth’s temperature would have been several degrees lower, making it unsuitable for human life [4]. However, with the industrialization of societies and the increase in fossil fuel consumption, the amount of carbon dioxide in the atmosphere has been increasing, causing global warming [5]. As a result, the carbon dioxide global average concentration has now reached 419 ppm, whereas it was 280 ppm before the industrial revolution [6,7]. Thus, there has been a worldwide effort to conduct studies for elim- inating this harmful gas from stacks of various industries [8,9]. Overall, 78 percent of the world’s carbon dioxide is produced by human activity. The primary production sources are power plants (25%), transportation (29%) and industries (23%) [10]. ∗ Corresponding author. E-mail address: alebrm@aut.ac.ir (H.A. Ebrahim). In general, there are three techniques for capturing carbon: pre- combustion, oxy-fuel, and post-combustion [11]. Post-combustion method for carbon capture is the most widely used technology. This method could be added to the existing processes and removes the pro- duced carbon dioxide without much modification to existing plants [12]. Chemical absorption, physical adsorption, lime carbonation, mem- brane separation, and cryogenic separation are some of the separation technologies that use the post-combustion technique to capture CO 2 from flue gases. However, all existing techniques have advantages and disadvantages. For example, chemical absorption with alkanolamines is very popular, but it has disadvantages, such as its corrosive nature [9, 12,13]. Among these various techniques, adsorption with porous ma- terials has more advantages, such as low energy consumption, ease of operation, and low investment cost [14–16]. Many adsorbents have been used for the carbon dioxide separa- tion process, such as MOFs, zeolites, and activated carbons [17,18]. Activated carbon can be used to adsorb carbon dioxide due to its high porosity and low moisture sensitivity. It is also economically affordable [19]. It has been established that the surface chemistry of activated carbon has a significant impact on its adsorption capacity. Thus, it is hypothesized that introducing Lewis bases to the activated carbon https://doi.org/10.1016/j.mtcomm.2022.104776 Received 9 July 2022; Received in revised form 12 October 2022; Accepted 24 October 2022