Next, to investigate the structural feature of mesopores, the surface area and pore size distribution of eSVA/N5 are determined by using N2 sorption technique. The surface areas of mesopores can be calculated using the Brunauer-Emmett-Teller (BET) theory. The BET surface area of eSVA/N5 is measured as 52.2 m 2 /g, that is higher than that of eSVA/N0 (46.6%) and eSV/N40 (7.7 m 2 /g) (Figure ). The results indicate that mesopores with a disorder bicontinuous morphology have a larger surface area compared to cylinder mesopores in eSVA/N0. The relatively lower surface area of eSV/N40 is attributed to the collapse of the lamellar structure after etching. Also, the N2 sorption isotherm of eSVA/N5 exhibits a type IV isotherm characteristic, indicating the formation of a mesoporous structure (Figure ). Furthermore, the abrupt increase in nitrogen adsorption at P/P 0 = 0.88 indicates the presence of a significant outer surface. While the adsorption isotherm exhibits an H1-type hysteresis loop, indicating a relatively narrow pore size distribution. The average pore diameter of eSVA/N5 was calculated using the Barrett-Joyner-Halenda (BJH) method and found to be around 20 nm (inset in Figure ). Insert: pore size distribution.