Influence of Aspect Ratio of TiO2 Nanorods on the Photocatalytic Decomposition of Formic Acid

A variety of shape-controlled TiO2 nanoparticles, such as spheres, short ellipsoidal rods with a low aspect ratio (low AR), and long ellipsoidal rods with a high aspect ratio (high AR), were synthesized by a gel-sol method. X-ray diffractometer and ultraviolet diffuse reflectance spectroscopy analyses revealed that the synthesized TiO2 nanoparticles have the same anatase structure with a band-gap energy (E-g) of 3.2 eV regardless of nanoparticle shape. Electrochemical impedance spectroscopy (EIS) results showed that the increasing aspect ratio of TiO2 nanoparticles was accompanied by increases in the charge-transfer rate between nanoparticle surfaces and electrolyte, the space charge capacitance on the surface of TiO2 nanoparticles, and electrochemical double-layer capacitance at the interfacial region of the electrolyte. The amount of electron donors in the nanoparticles increased with increasing aspect ratio of nanoparticles, which is in good agreement with EIS results. Use of high-AR ellipsoidal TiO2 nanoparticles as photocatalysts resulted in enhanced current density and, consequently, an increase in the photocataiytic decomposition rate of formic acid.