## 1 Introduction  
It is well known that the amount of CO\({}_{2}\) discharged into the atmosphere increases with the rapid development of industry and population growth. In addition, deforestation, the large amount of CO\({}_{2}\) and other gases generated by the burning of fossil fuels such as coal, oil, and natural gas directly discharged into the atmosphere, and the emission of limestone roasting to produce cement have resulted in global carbon dioxide emissions increasing by 3.8% [1]. All of the above factors have aggravated carbon dioxide emissions, thereby increasing the urgency of counteracting the greenhouse effect and its associated global warming. The Kyoto Protocol and the Paris Agreement aim to control greenhouse gas emissions under the United Nations Framework Convention on Climate Change (UNFCCC), in which CO\({}_{2}\) is listed as a major greenhouse gas that needs to be mitigated or recycled [2]. The greenhouse gases include more than CO\({}_{2}\), however; in fact, the global warming potentials of CH\({}_{4}\) and N\({}_{2}\)O are 25 times and 298 times that of CO\({}_{2}\), respectively. Nevertheless, due to its relatively large emission levels, CO\({}_{2}\) accounts for approximately 55% of the total greenhouse gas contribution [3, 4]. Thus, it is obvious that the adsorption and separation of carbon dioxide from the air is particularly important. In addition, the successful capture of CO\({}_{2}\) could have multifaceted practical values: first, oil recovery could be improved through appropriate reservoir engineering; second, the captured CO\({}_{2}\) could be used to produce industrial chemicals, including concrete, paint, and fertilizer; third, the CO\({}_{2}\) in the atmosphere could be captured and combined with hydrogen for direct synthesis into liquid hydrocarbons, which could then be utilized in fuel synthesis and supply, including gasoline and diesel. The use of raw materials can reduce the proportion of fossil energy to further control CO\({}_{2}\) emissions, ultimately achieving carbon neutrality or even net negative carbon emissions [5]. Recently, carbon engineering has developed a series of capture technologies that remove carbon dioxide directly from the air. Carbon dioxide can be removed from the atmosphere using biological, chemical, or physical processes [6]. These methods have certain limitations, however. For example, biological processes are very economical, but they are usually very slow and ineffective. As for chemical processes, the waste of carbon resources and volatilization of organic solvents during these actions lead to further environmental pollution, equipment corrosion, and complex post-treatment issues. The traditional technique for separating carbon dioxide is solvent washing, such as the use of an alcohol amine solution [7; 8; 9; 10]. Although this conventional method can reduce the concentration of carbon dioxide in the air, it is extremely expensive, the solvent is difficult to regenerate, the operation is complicated, and it consumes a great deal of energy [11]. In fact, the energy consumption of solvent washing is 3 to 4 times that of CO\({}_{2}\) captured from exhaust gas [12]. Given these drawbacks, there is an urgent need to find a more efficient, convenient, and energy-saving technique to replace the traditional carbon dioxide capture method. Adsorption separation is a potential technique. It is not only inexpensive, but also simple in terms of operation and equipment, and relatively low in energy consumption when the adsorbent is regenerated (the regeneration process of adsorbents is to desorb the adsorbed substances). Conventional adsorbents, however, including activated carbon, zeolite, silica gel, and metal oxides have poor scavenging effects on carbon dioxide in the air due to inferior separation selectivity and regeneration difficulty. For example, silica gel, which has amorphous properties, does not have a continuous uniform porous structure and exhibits unfavorable diffusion properties [11].