Synthesis and Structure of Nanocrystalline TiO₂ with Lower Band Gap Showing High Photocatalytic Activity

Abstract

Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**.

Photocatalytic CO oxidation with water over Pt/TiO2 catalysts

“…Another issue is the process of creation of hole-electron pairs over Pt/TiO 2 catalysts. The energy gap of TiO 2 is 3.2 eV (anatase), which allows the electron to be transferred from the valence band to the conduction band under UV [35]. It was earlier mentioned that in the case of the light used in this work, UV constitutes only a few percent of the total radiation.…”

Review of the anatase to rutile phase transformation

“…However, doping inevitably affects the semiconducting properties of materials, which may be disadvantageous to the photocatalytic performance. Alternatively, as discussed subsequently, doping also may act advantageously through reduction in the band gap and improvement in the charge carrier separation and associated extended exciton lifetime [18,68,73,151].…”

“…• Reduction of the band gap in titania [18,151] • Introduction of mid-gap states [56,163] • Improvement in charge carrier separation [68,73] • Increase in the levels of surface-adsorbed species (e.g., hydroxyl radicals) [43] It often is not appreciated that all titania is contaminated with some levels of impurities. The presence of unintentional impurities or intentional dopants has a strong effect on the kinetics of the anatase to rutile transition [170].…”

"HYDROTHERMAL SYNTHESIS OF ULTRA VIOLET-VISIBLE LIGHT RESPONSIVE RUTHENIUM DOPED TITANIA (RuXTi1-XO2) NANOSHEET AND ITS EFFECT ON PHOTOCATALYTIC DEGRADATION OF REACTIVE RED DYES "

“…Previous studies showed that anatase phase of titania has a higher photocatalytic activity than rutile phase and it can be attributed to the presence of a higher degree of surface hydroxyl groups. 29,30 Though the shape-controlled synthesis of TiO2 and RuXTi1-XO2 resulted in anatase and rutile type phases, the significantly higher concentration of anatase type revealed that surface hydroxyl group catalyzed photocatalytic degradation mechanism proposed by Nagaveni et al 30 is quite valid in the present systems. However, higher degradation rate exhibited by RuXTi1-XO2 UV-VISIBLE LIGHT RESPONSIVE RUTHENIUM DOPED TITANIA Ashwini Ashok et al…”