An insight into the influence of morphology on the photoelectrochemical activity of TiO2 nanotube arrays

In this study, we demonstrate the evolution of morphology and band gap tuning of TiO2 nanotube (TNT) arrays by an electrochemical anodization method. Both XRD and Raman spectra confirm the crystallinity of TNT arrays in a phase pure anatase form. The crystallinity of TNT increases up to the anodization time of 60 min and with further increase in time, the crystallinity decreases due to the destruction of tubular structures. By increasing the anodization time, the optical absorption of TiO2 is extended up to the visible region. The well defined visible light photoluminescence emissions reveal the structural defects, oxygen vacancies (F or F2+, F+) and radiative recombination sites created within the band gap. The nanotubes fabricated at an anodization time of 60 min show the highest photoconversion efficiency of 11.86% in the potassium hydroxide (KOH) electrolyte containing ethylene glycol.