4. Conclusions
In conclusion, hierarchically porous structures assembling by TiO2 nanoparticles with the diameter of 20 nm were produced. In this synthetic procedure, alginate template was used as sacrificial template and dripped into a Ti(SO4)2 solution to initiate gelation reaction. The porous architecture of the alginate templates were successfully transferred to the TiO2 nanomaterials after freezing drying and burning off the templates. The concentration of NaAlg at a given Ti4+ concentration had a great influence on the morphology of the final TiO2 materials. Generally, the volumes of the pores increased gradually along with the increment of the concentration of NaAlg solution, while the sizes of the TiO2 nanoparticles assembling into hierarchical structures had an opposite trend. An investigation of the photocatalytic activity shows that the hierarchically porous TiO2 nanomaterials are more effective as a photocatalyst for RhB degradation under UV illumination than the commercial available TiO2.