## 3 Results
### Characterization of Brick Composite
#### 3.1.3 Porosity and Specific Surface Area  
To characterize the specific surface area and porosity of the brick-based composite, N\({}_{2}\) adsorption analysis was carried out. Figure 3 displays the N\({}_{2}\) adsorption-desorption isotherm and the corresponding pore size distribution curve for the studied material. The obtained N\({}_{2}\) adsorption-desorption isotherm corresponded to a type-IV isothermal profile, according to the International Union of Pure and Applied Chemistry (IUPAC) classification [78]. The adsorption of P/P\({}_{0}\) increased abruptly between 0 and 0.01 (Figure 3a), which confirmed the existence of micropores in the modified brick. The appearance of the hysteresis loop at the medium pressure area (0.2 \(<\) P/P\({}_{0}\)\(<\) 0.8; see Figure 3a) proved the abundance of mesopores, and the steep increase in the N\({}_{2}\) capacity in the high-pressure area (P/P\({}_{0}\)\(>\) 0.8; see Figure 3a) indicated the presence of macropores. The shape of this hysteresis loop resembled an H3-type hysteresis loop [78], indicating that the brick composite was mainly composed of mesopores and macropores [79; 80]. The pore size distribution shown in Figure 3(b1) agreed with the analysis described above, and revealed that the final composite had hierarchical pores with micropores, mesopores, and macropores. Figure 2: Morphological aspects of treated brick pellets observed using ESEM at different magnifications (**a–c**). ESEM micrograph of raw brick (**d**). Spherical and ellipsoidal surface zones targeted on alkali-activated brick grains for ESEM/EDS analysis (**e**). ESEM micrograph of alkali-activated brick surface on which the lengths of cube edges and sphere diameters of zeolitic specimens were measured (**f**). Note  
that, in image (**e**) circles represent the surface zones targeted for ESEM/EDS analysis, and in image (**f**) numbers represent lengths of cube edges and sphere diameters of zeolitic specimens. The analysis of N\({}_{2}\) adsorption-desorption isotherms was undertaken in the following range of pore sizes: 17-3100 A. This analysis permitted us to determine the average pore diameter (94.5-112.4 A), BET surface area (19.3 m\({}^{2}\).g\({}^{-1}\)), and pore volume (0.036 cm\({}^{3}\).g\({}^{-1}\)). Overall, the porosity analysis revealed the generation of hierarchical mesopores with \"bimodal\" pore size distribution at 29 A and \(\sim\)70-150 A. Compared to the pore distribution of raw brick (see Figure 3(b2)), the profile changes in the pore size distribution of the treated brick were intimately related to the significant increase in mesopores, which appeared mostly at low diameters, <50 A, and reached a maximum pore volume for pore diameters around 28 \(\pm\) 1 A. New mesopores were generated through zeolitization of brick-metakaolinite by alkaline treatment. Disordered hollow-like mesoporous frameworks were created by aggregated zeolitic crystals. As for the macroporous structure of the brick (i.e., pores with diameters of about \(\geq\)500 A), it could be directly observed from the ESEM images of a raw brick sample (see Figure 2d), and above  
Figure 3: N\({}_{2}\) adsorption (in blue) and desorption (in red) isotherm (**a**) and corresponding pore size distribution curves for brick composite (in blue; **b1**) and raw brick (in red; **b2**). Log differential pore volume dV/d(log d) versus pore diameter (**c**). all, on ESEM images of treated brick samples taken at higher magnifications (Figure 2b,c), particularly revealing numerous macropores on the surfaces of zeolitic aggregates (Na-P) with \"sponge\" morphologies (see Figure 2c). Although the values of average pore diameter, BET surface area, and pore volume obtained for the activated brick were somewhat low, our recent research has revealed that the generated \"hierarchical\" mesoporous structure of activated brick was well suited for adsorbing inorganic pollutants into the interior space of the alkaline brick under large-scale dynamic conditions [12, 81, 82].