## 3 Results
### Nanoring Analysis  
The development degree of nanopores determines the adsorption capacity of coal for gases, and studying the nanoring structure in coal plays a significant role in understanding the pore structure on the coal surface. The nanoring parameters of the samples refer to the characteristics of annular pores in the sample dataset obtained through Nano Ring Analysis in AFM. By setting relevant parameters such as the expected diameter, threshold height, pitch, and type of height threshold, parameters such as the number of nanorings, roughness, and confidence score were obtained. The confidence score represents the degree of reliability of the analytical method for the obtained results. During nanoring analysis, nanoring structures with low confidence scores may be non-target particles resulting from image noise or scratches and should be excluded. In contrast, nanoring structures with high confidence scores are more likely to be the desired sample annular characteristics for the study. Therefore, this study only retains nanoring structures with confidence scores greater than 0.5 to enhance the reliability of the research results. Since nanoring analysis focuses on pore structures with an expected diameter of more than 10 nm, nanoring structural analysis was conducted on six different volatile matter samples at various expected diameters, ranging from 10, 20, 30,..., to 500 nm. The threshold height was set at 1 nm, the pitch in both X and Y directions was 600 nm, and the type of height threshold was set to the entire image. The results of the nanoring analysis are shown in Table 4.  
The number of nano-rings at different expected diameters in the samples varied with the volatile matter content of the coal samples. As shown in Table 3, the total number of nano-rings in samples AH-1 to SX-4 ranged from 49 to 102. Additionally, the study plotted the distribution of nano-rings within each expected diameter range of the samples, as shown in Figure 4.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Sample Number**} & \multirow{2}{*}{\(\mathbf{V_{\text{daf}}}\)} & \multicolumn{6}{c}{**Expected Diameter**} & \multirow{2}{*}{**Total Number of Nanorings**} & \multirow{2}{*}{\(\mathbf{R_{r}}\)} \\ \cline{3-4} \cline{6-7}  & & **10–100** & **110–200** & **210–300** & **310–400** & **400–500** \\ \hline AH-1 & 33.17 & 1 & 21 & 13 & 8 & 6 & 49 & 4.82 \\ \hline HB-1 & 27.96 & 7 & 34 & 23 & 10 & 8 & 82 & 4.903 \\ \hline SX-1 & 14.51 & 5 & 30 & 18 & 10 & 5 & 68 & 4.504 \\ \hline SX-2 & 13.53 & 24 & 40 & 18 & 3 & 5 & 90 & 2.162 \\ \hline SX-3 & 12.67 & 29 & 30 & 19 & 5 & 2 & 85 & 2.046 \\ \hline SX-4 & 9.61 & 37 & 49 & 3 & 5 & 8 & 102 & 1.639 \\ \hline \end{tabular}
\end{table}
Table 4: Number and Roughness of Nanorings in Samples at Different Expected Diameters.  
Figure 4: Distribution of Nanorings in Various Expected Diameter Ranges for the Samples.  
The study found that the number of nanorings with expected diameters between 10 and 200 nm is significantly greater in low-volatile coal samples compared to high-volatile coal samples. The number of nanorings with diameters in the 210-300 nm range decreases compared to high-volatile coal samples, and a further decline is observed for nanorings with expected diameters in the 310-500 nm range. This is attributed to the fact that high-volatile coal has not undergone sufficient condensation polymerization, resulting in a coarser pore structure. The formation of nanorings is closely related to nanoscale pore structures. Low-volatile coal, with its developed pore structure, provides the space and necessary conditions for the formation of nanorings, leading to a significant increase in the number of smaller-diameter nanorings in low-volatile coal.