No abstract

Purpose Over the past decades, intense efforts have been devoted to design and synthesize efficient photocatalysts which are active under sunlight for environmental and energy applications. Titanium dioxide (TiO2) has attracted much attention over many years for organic contaminant degradation in air or water due to its strong optical absorptivity, chemical stability and low cost. However, TiO2 has a very low photo quantum yield which prompts the easy recombination of photogeneration electron/hole pairs. In addition, bandgap of 3.2 eV restrains application of this photocatalyst mainly to the UV range. Design/methodology/approach Vertically oriented one-dimensional TiO2 nanostructures remarkably improve electron transport by creating a direct conduction pathway, decreasing intercrystalline contacts and stretching grown structure with the specified directionality. In this research, to enhance the visible light absorbance of TiO2, prearranged hydrogenated titanium dioxide nanorods (H-TNRs) in the presence of H2/N2 gas flow are hydrothermally synthesized. Findings The X-ray diffraction patterns illustrated the characteristic peaks of tetragonal rutile TiO2 and confirmed that there is no phase change after hydrogenation. Trivalent titanium ions surface defects and oxygen vacancies were considered as major reasons for redshift of absorption edge toward visible region and subsequently narrowing the bandgap to 2.27 eV. The optimized photocatalysts exhibited high visible-light-driven photocatalytic activity for degradation of methylene blue in water within 210. The synthesized H-TNRs established themselves as promising photocatalysts for organic compounds degradation in the aqueous solution. Originality/value To the best of the authors’ knowledge, this work is original and has not been published elsewhere nor is it currently under consideration for publication elsewhere.

We report the influence of pH on the hydrothermal growth of TiO2 nanostructures, observing variations in photocatalytic activity. Using comprehensive characterization techniques, we find that nanorod growth significantly depends on the synthesis conditions and that TiO2 mainly crystallizes in the rutile phase. A red shift in the absorption edge towards the visible region was observed by changing the initial HCl : H2O molar ratio, resulting in a tangible shift in the energy band gap from 3.54 eV to 2.95 eV. The highest photocatalytic degradation efficiency of methylene blue in aqueous solution under UV irradiation was achieved with an initial HCl : H2O molar ratio of 1 : 1 (86.5 % after 210 min). In parallel to the experimental results, the crystal structure, optical and electronic structure of the rutile TiO2 system and subsequently their influence on the photocatalytic activity were modeled using density functional theory calculations. The photocatalytic enhancement is attributed to higher density of states and expanded energy bands around the Fermi level, leading to a prolonged lifetime of photoinduced charge carriers and the higher charge transfer which is also measured by electrochemical impedance spectroscopy. Our results are promising towards the judicious design and synthesis of TiO2‐based photocatalysts.