The representative HRTEM images of the TiO2 nanoparticles prepared with various amount of NaAlg are shown in Fig. S3 a–c. As seen in these figures, the (1 0 1) plane is quite clear in these images. The XRD patterns of the TiO2-0.5, TiO2-1 and TiO2-3 are shown in Fig. S3d. The crystalline planes corresponding to the peaks for anatase TiO2 have been indexed. These XRD results reveal that all possess highly crystallized anatase structures without any impurity phase. Thus HRTEM and XRD analyses show the phase purity and crystallinity of TiO2 nanoparticles.
The BET surface area, pore size and pore volume of the as-prepared TiO2 nanoparticles are summarized in Table 1. The results show that the amount of NaAlg affects the texture of the products significantly. The photocatalytic activities of the as-prepared TiO2 nanoparticles with different NaAlg amount were evaluated by photocatalytic degradation of RhB. As shown in Table 1, all the samples can efficiently photodegrade RhB under UV light irradiation. By comparing the textural and photocatalytic properties of the TiO2 products, the TiO2 nanoparticles prepared by adding 2 wt% NaAlg as template perform better than others, which could be attributed to their hierarchically porous structures and broad pore size distribution. For that reason, the optimum concentration of NaAlg can be determined to be 2 wt%, and we studied the textural and photocatalytic performances of the hierarchical TiO2 nanomaterials using 2 wt% NaAlg as template in detail in the following.