*2.3. N2-Physorption Analysis*

Specific surface area, surface texture, and pore size distribution were acquired via the N2-physisorption technique. N2 adsorption–desorption isotherms, Barrett, Joyner, and Halenda method (BJH) for calculating pore size distribution, and t-plot of the prepared composites are shown in Figure 7. As it can be seen, all the obtained isotherms are of Type III. The reversible Type III isotherm is represented as a convex to the x-axis over its entire range. It also reveals the multilayer formation process. It forms because of strong lateral interactions between adsorbed molecules in comparison to interactions between adsorbate and the adsorbent surface.

The BJH pore size distribution indicates that all samples are mesoporous in nature with an average pore radius of ca. 5 nm as shown in Table 3. Moreover, the t-plot method is a widely used procedure to estimate the total surface area and the external surface area of materials. For mesoporous materials, the adsorbed volume (V) varies linearly with the film thickness (t) and passes through the origin. The total surface area (Stot) is directly given by the slope of the first linear fit at low pressure. Once all pores are filled, adsorption occurs only on the external surface of the material and leads to a second linear fit at high pressure, the slope of which allows the determination of the external surface (Sext). The external surface area obtained for our samples was similar to the value of the BET surface area because of the mesoporous nature of the prepared composites. The values of BET-specific surface area, total pore volume and average pore radius are given in Table 3.

**Figure 7.** (**a**) N2 adsorption–desorption isotherm, (**b**) t-plot of the as-prepared samples, and (**c**) BJH pore size.


