## 4 Conclusions  
This study presents evolutions of CO\({}_{2}\) adsorption and nanopore structure characteristics with coal structure deformation, and reveals the effects of nanopore structure on CO\({}_{2}\) adsorption in tectonically deformed coals.  
Isotherms of excess and absolute adsorption of four coal specimens exhibit an increase at first, and then a decrease with increasing pressure. There exist maximum values of excess and absolute adsorption capacity increasing with increasing coal deformation degree. Maximum values of excess adsorption capacity of undeformed coal, cataclastic coal, granulitic coal, and crumple coal are 9.48 m\({}^{3}\)-g\({}^{-1}\), 12.04 m\({}^{3}\)-g\({}^{-1}\), 15.83 m\({}^{3}\)-g\({}^{-1}\), and 16.74 m\({}^{3}\)-g\({}^{-1}\), respectively. The maximum excess adsorption capacity is present at a pressure ranging from 4 MPa to 5 MPa, and with increasing coal deformation degree the pressure corresponding to the maximum excess adsorption amount shifts to the higher pressure. The error analysis indicates that an increase of pressure causes the rapid increase in the error between excess adsorption and absolute adsorption.  
In addition, as the degree of coal deformation increases, the pore volume and specific surface area present an obviously increasing trend in the case of micropores, exhibiting an increase at first (cataclastic coal and granulitic coal) and then stabilization (crumple coal), in the case of mesopores, and showing the gradual decrease in the case of macropores. The effects of pore volume and specific surface area on the absolute adsorption capacity of tectonically deformed coals is relatively consistent at the pressure stage of 0-7 MPa. The mesopores are the key factor of CO\({}_{2}\) adsorption of tectonically deformed coals at the pressure stage of 0-7 MPa, followed by the micropores and the limited effect of macropores at the strong coal deformation stage. The volume and specific surface area of mesopores both present good linear positive correlation with the absolute adsorption capacity. Differences in  
Figure 9: Adsorption space distributions at higher and lower pressure stages: (**a**) Division of higher and lower pressure adsorption space of pore volume distribution curve; (**b**) Division of higher and lower pressure adsorption space of pore area distribution curve; (**c**) Division of higher pressure and lower pressure stage of isothermal excess adsorption curve; (**d**) Division of higher pressure and lower pressure stage of isothermal absolute adsorption curve.  
mesopore development result in the intersection of curves of excess adsorption and absolute adsorption in granulitic coal and crumple coal.  
Specimen preparation, macro- and microstructure analysis, Z.L.; isotherm adsorption experiment and liquid nitrogen adsorption, L.W. All authors discussed the results and contributed to the final manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, grant numbers 41702169 and 41572138, and China Postdoctoral Foundation, grant number 2019M662013.  
The authors declare no conflict of interest.