3.2. Textural and photocatalytic performances
Nitrogen physisorption studies were conducted to determine the specific surface area of TiO2 nanomaterials through the application of the BET theory and to access their pore size distribution. Fig. 6a depicts the nitrogen adsorption-desorption isotherm of the hierarchically porous TiO2 nanomaterials. According to the IUPAC classification, the isotherm and hysteresis loop belong to the type II isotherm and H3-type loop [26]. The isotherm and hysteresis loop indicate that the majority of pores belong to the family of mesopores, resulting from the aggregates of nanoparticles with slit-shaped pores, which is consistent with the SEM and TEM observation. The specific surface area of the mesoporous TiO2 nanoparticles is calculated to be 57.3 m2·g−1 by the Brunauer-Emmett-Teller (BET) equation. By using nonlocal density functional theory (NLDFT) method, the pore sizes of the sample exhibit a broad distribution ranging from 3 to 28 nm with the main characteristic pore size of ∼20 nm, as illustrated in Fig. 6b.