Enhancement of visible-light photo-activity of TiO₂ arrays for environmental water purification

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.

Role of pH in the Hydrothermal Synthesis of TiO2 Nanorod Photocatalysts

“…Eventually, the autoclave was cooled to the room temperature. The synthesized photocatalysts were collected by filtration and washed three times with distilled water and then dried at 60 °C in air for 12 h [23,62] . The initial HCl : H 2 O molar ratio was proportionally changed to attain various pH levels.…”

“…Eventually, the autoclave was cooled to the room temperature. The synthesized photocatalysts were collected by filtration and washed three times with distilled water and then dried at 60 °C in air for 12 [23,62] The initial HCl : H 2 O molar ratio was proportionally changed to attain various pH levels. To achieve pH = 1.5, 15 ml DI water and 45 ml HCl and also for pH = 3.5, 50 ml DI water and 10 ml HCl were mixed and the subsequent procedure was the same.…”