## 3 Results and Discussion
The distribution function \(D_{v}(R)\) of the NC2 sample contains a narrow isolated peak with a maximum of \(\approx\)2.6 nm. Thus, the pores R \(\approx\) 2.6 nm make the main contribution to the formation of the porous structure of NC2 sample. The height of the peak \(D_{v}(R)\) of NC2 sample shows a more than two-fold increase in the concentration of micropores compared with NC1_10 and NC1_5 samples. At the same time, the concentration of mesopores with radii from 5 to 50 nm is approximately twice as low. As a result, a decrease in the average pore radius is observed in a number of samples NC1_10\(\rightarrow\)NC1_5\(\rightarrow\)NC2 from \(R_{\rm c}\) = 7.5 nm to \(R_{\rm c}\) = 3.7 nm (Table 4). Figure 8: Volume functions of pore distribution in samples NC1_10 (1), NC1_5 (2), NC2 (3). Another important characteristic of a porous structure is the specific surface area and pore volume. To calculate the specific surface area, the asymptotic behavior of scattering intensity was used, since the relation known as the Porod's law is satisfied for \(s\rightarrow\infty\)[29]:  
\[I(s)=I_{p}+\frac{K_{p}}{s^{4}}, \tag{3}\]  
where \(I_{p}\) is a constant value characterizing the contribution of atomic scattering to the small-angle scattering intensity, and the Porod constant \(K_{p}\) is proportional to the total pore surface area [29]. The calculation of the parameters \(I_{p}\) and \(K_{p}\) is performed by creating dependency graphs \(s^{4}I(s)=f\big{(}s^{4}\big{)}\). Then, having selected the linear sections on the graphs when \(s\rightarrow\infty\), \(I_{p}\) and \(K_{p}\) parameters can be determined using the least squares method. Having determined the Porod constant, the Porod invariant can be calculated:  
\[Q_{p}=\int_{0}^{s_{\max}}s^{2}I(s)\mathrm{d}s+\frac{K_{p}}{s_{\max}}, \tag{4}\]  
where \(s_{\max}\) is the maximum value of the wave vector. The specific surface area of pores is calculated by the formula:  
\[S_{p}=\frac{S}{m}=\pi w\frac{K_{p}}{\rho_{m}Q_{p}}, \tag{5}\]  
where \(w=1-\frac{\rho_{m}}{\rho_{x}}\) is the pore volume fraction, \(\rho_{m}\) is the real density, and \(\rho_{x}\) is the structural density. Table 4 presents the obtained results of calculating the integral invariants of the scattering curves for the studied NC. As seen in Table 4, a decrease in the integral intensity (the Porod invariant \(Q_{p}\)) is observed in NC2 sample, which can be explained by a decrease in the fraction of large inhomogeneities (mesopores). However, the total area of pores increases, as indicated by the value of the Porod constant \(K_{p}\). As a result, almost a two-fold increase in the specific surface area of pores is observed in the NC2 sample compared with other synthesized NC. The peculiarity of the small-angle X-ray scattering method described above is that it is sensitive to both closed and open pores. However, the presence of closed pores in the nanocomposite makes it unsuitable for use as an adsorbent or catalyst. In this case, it is important to study other adsorption methods that would provide information about open pores. One of the simple and reliable methods is the method of adsorption/desorption of gases, such as nitrogen. The gas molecules will interact only with the surface of the porous material accessible to them, and this will give information about the presence and distribution by the size of open pores in it. At the first stage of this study, adsorption/desorption isotherms are obtained, which are shown for the synthesized biocarbon nanocomposites in Figure 9. All isotherms can be classified by the isotherm shapes as type I according to the IUPAC classification, which are typical of microporous solids. All isotherms are characterized by the discrepancy of adsorption and desorption branches, especially in the area of low relative pressure. Such isotherm behavior is called low pressure hysteresis, and it can be caused, according to [30], by:  
1. Irreversible retention of gas molecules in pores, the size of which is close to the size of these molecules;
2.