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

Abstract

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.