## 3 Results and Discussion
It can be seen that the pores of the sample are mainly micropores, with a certain amount of macropores. However, we cannot observe macropores in the TEM image (Figure 3b) of the outer surface of the as-synthesized sample. Therefore, such macropores are located inside the cube-like particles, suggesting that the as-synthesized sample is of hollow structure. After the calcination at 723 K, the sample shows a transitional type isotherm between the Type IV (a) and Type II. A distinct hysteresis loop can be observed between P/P\({}_{0}\)= 0.4-0.75, suggesting the existence of the mesopores. Like the as-synthesized sample, the sample calcined at 723 K also shows steep uptake between P/P\({}_{0}\) = 0.9-1.0, revealing that the sample also has macropores. As shown in Figure 5b, due to the increase of crystal size by calcination, the pore size of the calcined sample increases from microporous to mesoporous range, mainly centering at 3.6 nm. In addition, there are a few macropores distributions in the range of 50-100 nm. When the calcination temperature increases to 923 K, the sample shows an isotherm of Type III. A hysteresis loop can be observed between P/P\({}_{0}\) = 0.75-1.0, suggesting that the sample has a broad pore size distribution in the range of large-sized mesopores and macropores. As can be seen in Figure 5c, the pore channels of the sample are not well developed and the pore size is widely distributed in the range of 10-100 nm. At this time, the pore channels of the sample are only a simple accumulation of enlarged crystals by calcination at 923 K. The textural properties of as-synthesized and calcined zirconia are shown in Table 1. The as-synthesized sample shows big surface area of 146.78 m\({}^{2}\)/g and large pore volume of 0.23 cm\({}^{3}\)/g. With the increase of calcination temperature, the surface area and pore volume of the samples decrease significantly, and the pore size increases accordingly. Figure 3: TEM images (**a–c**,**e–g**,**i–k**) and electron diffraction patterns (**d**,**h**,**l**) of as-synthesized (**a–d**) and calcined zirconia (**e–h**) calcined at 723 K; (**i–l**): calcined at 923 K.  
The TG-DTG curve of the as-synthesized sample is shown in Figure 6. The first weight loss of 5.2% below 444 K can be related to the removal of the physisorbed water. The second weight loss of 4.03% between the 444 K and 545 K corresponds to the decomposition of DTAB. The third weight loss of 10.8% in the range of 545 K to 840 K is due to the further decomposition of DTAB and the elimination of absorbed hydroxyl group, as well as non-structural carbonate group. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Surface Area (m2/g)** & **Pore Volume (cm3/g)** & **Average Pore Size (nm)** \\ \hline a & 146.78 & 0.23 & 6.24 \\ b & 66.72 & 0.19 & 8.89 \\ c & 20.03 & 0.10 & 18.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The textural properties of as-synthesized (a,b) and calcined zirconia (b) calcined at 923 K.  
Figure 4: N\({}_{2}\) adsorption–desorption isotherms of as-synthesized (**a,b**) and calcined zirconia (**b**) calcined at 723 K; (**c**): calcined at 923 K.  
Figure 5: Pore size distributions of as-synthesized (**a,b**) and calcined zirconia (**b**) calcined at 723 K; (**c**): calcined at 923 K.