Preparation and characterization of chemically activated carbon materials for CO₂capture

Atmospheric carbon dioxide (CO 2 ) exists as a gas at standard temperature and pressure, and it occurs in Earth's atmosphere in this state [1,2].Rising levels of CO 2 , a greenhouse gas, are a major environmental problem [3].The main source of CO 2 emissions is the burning of fossil fuels, such as natural gas and coal.The combustion of these fossil fuels, such as natural gas, coal, and oil, is one of the major emission sources of CO 2 [4].In addition to outdoor levels of CO 2 , indoor levels of CO 2 have been extensively investigated because they have a direct impact on human health.Certain levels of CO 2 in indoor spaces cause symptoms such as headaches, vomiting, drowsiness, and dyspnea.Certain indoor spaces, such as automobiles, subways, and aircraft, have high concentrations of CO 2 , which can cause serious health hazards.Thus, an increased CO2 concentration in these types of spaces is considered by many researchers to be a serious problem [5,6].Recently, CO 2 capture and storage technology, including adsorption, absorption, cryogenics, and membranes, has received increased attention motivated by environmental concerns [7][8][9].Absorption into an alkanolamine solution is a conventional and mature technology; however, this method has major drawbacks, such as high regeneration energy requirements and significant waste.However, adsorption using solid sorbents has attracted widespread interest over recent years because of its low energy consumption, lower regeneration requirements, and ease of conservation and recycling [10].A wide range of solid adsorbents are currently under investigation, including zeolites, metal organic frameworks, porous carbon materials, macro-porous silica, and certain metal oxides [11][12][13][14][15].Among the solid adsorbents for CO 2 capture, carbon materials, such as activated carbon (AC), carbon aerogels, graphene, and carbon nanotubes, have shown significant advantages because of their highly developed porosities and extended specific surface areas [16][17][18][19][20][21][22][23][24].AC is of considerable interest because it is inexpensive, readily available, easily tuned, and thermally stable [25][26][27].Surface modification can be performed via a range of treatments, such as chemical or electrochemical oxidation, chemical activation, and thermal treatment [28][29][30].Chemical activation by ZnCl 2 , NaOH, or KOH is an effective method of controlling the poresize distributions and specific surface areas of carbon supports [31][32][33][34][35].In particular, the chemical activation method using KOH has been the most widely studied.Researchers have reported that high specific surface areas and well-developed microporous structures can be obtained.Also, KOH activation is the most effective method in terms of the degree of activation.In this study, we investigated the effects of KOH activation at various ratios on the surface of AC.Samples were prepared to evaluate highly efficient CO 2 capture capacities.The KOH impregnation process was initiated by mixing 1 g of AC with 4 g of KOH in a water and ethanol solution (1:1).The resulting solution was stirred to ensure even mixing and vaporized for 48 h at 90C.Then, the products were placed in a drying oven at 80C overnight.The activation process was performed in a tube furnace under N 2 flow (200 mL/ min); it involved heating the sample at a rate of 3 C/min up to 900C and maintaining this