## 3 Results and Discussion
### Relationships between CO2 Adsorption Capacity and Nanopore Structure  
It is shown in Figure 8 that 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. In the order of undeformed coal, cataclastic coal, and granulitic coal, the absolute adsorption capacity of coal specimens presents obviously linear positive correlation with the pore volume and specific surface area of macropores (black lines in Figure 8a,e); as it changes from granulitic coal to crumple coal, the pore volume and specific surface area of macropores decreases obviously, and the absolute adsorption capacity increases slightly (red lines in Figure 8a,e). The absolute adsorption capacity of tectonically deformed coals is obviously controlled by mesopores; the volume and specific surface area of mesopores both present good linear positive correlation with the absolute adsorption capacity (Figure 8b,f). Figure 6: Relationships between incremental pore volume (**a**), incremental pore specific surface area, (**b**) and average pore diameter. Figure 7: Various types of pore volume (**a**–**d**) and specific surface area (**e**–**h**): (**a**) Pore volume of total pore; (**b**) Pore volume of micropore; (**c**) Pore volume of mesopore; (**d**) Pore volume of macropore; (**e**) Pore area of total pore; (**f**) Pore area of micropore; (**g**) Pore area of mesopore; (**h**) Pore area of macro pore. Increases in micropores mainly contribute to increases in the total pore volume and specific surface area. Therefore, the relationships between total pore volume and specific surface area of tectonically deformed coals and absolute adsorption capacity are consistent with those of micropores. In the order of undeformed coal, cataclastic coal, and granulitic coal, the absolute adsorption capacity of the coal specimens presents obviously linear positive relationships with pore volume, specific surface area of micropores, total pore volume, and specific surface area of the coals (black lines in Figure 8c,d,g,h). As it changes from granulitic to crumple coal, there are obvious increases in the pore volume and specific surface area of micropores and total pores; however, the absolute adsorption capacity increases more gently (red lines in Figure 8c,d,g,h). Therefore, during coal deformation, tectonic stress causes damage of the coal matrix block from the undeformed coal to cataclastic coal and granulitic coal. The volume and specific surface area of all types of pores exhibit obvious increases, especially for macropores and mesopores, which causes the increase in the CO\({}_{2}\) adsorption capacity of the coal. As the tectonic deformation increases gradually (crumple coal), the coal structure is more broken; the tectonic stress has affected the smaller nanopores with newly formed, large numbers of micropores, as well as micropores formed due to damages of existing macropores and mesopores [21]. Therefore, in the case of crumple coal, an increase of tectonic deformation causes obvious decreases in the pore volume and specific surface area of macropores, slight increases in the pore volume and specific surface area of mesopores, and sharp increases in pore volume and specific surface area of micropores. However, the absolute adsorption capacity of crumple coal presents a slight increase, which coincides with the change trend of mesopores, and does not increase or decrease obviously with changes of macropores and micropores. The above analyses indicate that 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. Those also reveal that curves of excess adsorption and absolute adsorption of granulitic coal and crumple coal present intersection points.