Surfactant-additive-free synthesis of 3D anatase TiO2 hierarchical architectures with enhanced photocatalytic activity

Crystalline morphology-adjusting and facet-controlling of TiO2 has attracted extensive attention recently, and the growth of titania (TiO2) is generally related to either Ostwald ripening (OR) or orientation attachment (OA). However, few works about solvothermal crystallization of TiO2 have involved both OR and OA. Here, the crystallization and evolution of anatase TiO2 assemblies in acetic acid was studied systematically. Anatase TiO2 hierarchical architectures, such as flower-like assemblies composed of leaf-like sheets and spindle shaped assembly exposing (101) facets, were synthesized via a template-free approach combined with calcination. It is shown that acetic acid and the original concentration of titanium isopropyloxide (TTIP) play crucial roles in the architectures of the obtained assemblies: the acetic acid acted as reactant, solvent, and bonding reagent. The formation mechanism of the products was proposed according to the experimental results as a surfactant-free self-assembly procedure. The photocatalytic activities of the photocatalysts were evaluated by hydrogen production under ultraviolet irradiation in the absence of molecular oxygen, and the flower-like assemblies exhibited the highest photocatalytic activity compared with those of the TiO2 nanoparticles and spindle shaped assemblies. The enhanced photocatalytic activities could be attributed to the synergetic effect of the architecture, high crystallinity, and the large surface areas of the photocatalysts.