Application of Rh/TiO2 Nanotube Array in Photocatalytic Hydrogen Production from Formic Acid Solution

Abstract

Titanium dioxide nanotubes (TNTs) were fabricated via electrochemical anodization process. Photocatalytic hydrogen generation from formic acid solution was investigated using TNTs with simultaneous Rh deposition. The effects of calcination temperature and time for TNTs on hydrogen generation were studied. The maximum hydrogen generation (54 µmol) was observed when using TNTs with a 500 °C calcination temperature and 10 h calcination time under 5 h of black light (352 nm) irradiation. The reusability tests indicated that the TNTs with photodeposited Rh metal (Rh/TNT) had excellent stability up to the fifth cycle for hydrogen generation from formic acid solution. The TNTs were characterized before and after photodeposition of Rh metal via X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), and diffuse reflectance spectroscopy (DRS). XRD revealed the presence of optimal anatase–rutile phase ratios in TNTs at 500 °C and 300 °C calcination temperatures. XRD and SEM revealed the deposition of Rh metal on the TNT surface at 300 °C and 500 °C calcination temperatures. It was observed that the light absorption ability of TNTs calcined at 500 °C was greater than that of TNTs calcined at 300 °C. The reaction mechanisms for the formation of TNTs and photocatalytic hydrogen production from formic acid solutions by TNTs with simultaneous Rh deposition were also proposed.