Univariate Lattice Parameter Modulation of Single-Crystal-like Anatase TiO₂ Hierarchical Nanowire Arrays to Improve Photoactivity

Strain engineering is a highly effective tool for tuning the lattice parameter and in turn optimizing the optical, electronic, and chemical properties of numerous functional materials. In conventional methods, the strain is imposed from an additional heterogeneous substrate, bringing extra composition/phase that disturbs the mechanism investigations of the effects of lattice parameters on material properties. Here, we report a convertible-precursor-induced growing method to fulfill the elongation of the uniaxial lattice parameter of anatase TiO2 with a complex structure of single-crystal-like hierarchical arrays, without changing the composition, morphology, phase, and surface states. This methodology relies on a precursor-induced oriented growth and lattice parameter modulation on the basis of the lattice mismatch from the precursor. Unlike conventional substrate-manipulating methods, the employed precursor can be converted to the final materials (i.e., anatase TiO2), which can eliminate the effects of the additional substrate. It is found that for anatase TiO2, the elongation of lattice parameter a leads to the shift-up of the conduction band bottom and can thus accelerate the reduction reactions of O2. The elongation of lattice parameter a and unique structural features make the TiO2 arrays highly active for photocatalytic degradation of toluene in air, with a turnover frequency (TOF) 3.8 times and 2.1 times, respectively, that of the normal TiO2 arrays and P25 powder under ultraviolet irradiation. The enhanced reduction capability is further confirmed by the much-improved efficiency to assist the photoreduction of Cr(VI) in water.