Preparation of Nitrogen-Substituted TiO₂ Thin Film Photocatalysts by the Radio Frequency Magnetron Sputtering Deposition Method and Their Photocatalytic Reactivity under Visible Light Irradiation

Abstract

Nitrogen-substituted TiO2 (N-TiO2) thin film photocatalysts have been prepared by a radio frequency magnetron sputtering (RF-MS) deposition method using a N2/Ar mixture sputtering gas. The effect of the concentration of substituted nitrogen on the characteristics of the N-TiO2 thin films was investigated by UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The absorption band of the N-TiO2 thin film was found to shift smoothly to visible light regions up to 550 nm, its extent depending on the concentration of nitrogen substituted within the TiO2 lattice in a range of 2.0-16.5%. The N-TiO2 thin film photocatalyst with a nitrogen concentration of 6.0% exhibited the highest reactivity for the photocatalytic oxidation of 2-propanol diluted in water even under visible (lambda > or = 450 nm) or solar light irradiation. Moreover, N-TiO2 thin film photocatalysts prepared on conducting glass electrodes showed anodic photocurrents attributed to the photooxidation of water under visible light, its extent depending on wavelengths up to 550 nm. The absorbed photon to current conversion efficiencies reached 25.2% and 22.4% under UV (lambda = 360 nm) and visible light (lambda = 420 nm), respectively. UV-vis and photoelectrochemical investigations also confirmed that these thin films remain thermodynamically and mechanically stable even under heat treatment at 673 K. In addition, XPS and XRD studies revealed that a significantly high substitution of the lattice O atoms of the TiO2 with the N atoms plays a crucial role in the band gap narrowing of the TiO2 thin films, enabling them to absorb and operate under visible light irradiation as a highly reactive, effective photocatalyst.

Molecular Metal Oxide Cluster-Surface Modified Titanium(IV) Dioxide Photocatalysts

“…A similar spectroscopic feature was observed for TiO 2 doped with Cr and N prepared by physical methods such as ion implantation and magnetron sputtering. [10,35] In contrast, on chemically doping Cr and N ions into TiO 2 , fairly strong shoulders by the d-d transition appear in the visible region with the absorption edge almost invariant. [12] Fig.…”

“…For this purpose, doping of metal ions and anions into TiO 2 has been intensively studied. [6][7][8][9][10][11][12] However, the defects introduced into TiO 2 lead to a decrease in its crystallinity reducing the carrier mobility and increasing the recombination probability. Consequently, if visible-light activity is obtained, the UV-light activity decreases in most cases.…”

Evaluation of Photocatalytic Properties of Portland Cement Blended with Titanium Oxynitride (TiO2−xNy) Nanoparticles

“…This research found that the presence of nitrogen in the structure of TiO2 as substitution by oxygen creates Ti-N bonds and electronic states in forbidden energy levels [12,13]. This anionic partial substitution increases the range of the solar spectrum absorbed [14]. In this case, nanoparticles of TiOxNy can absorb wavelengths between 365 nm and 500 nm [15,16].…”

Photocatalytic Activity and RNO Dye Degradation of Nitrogen-doped TiO2 Prepared by Ionothermal Synthesis

“…11 Given the current state-of-art, 5,[12][13][14] it is highly desirable to identify new synthesis routes for TiO 2 doping in order to obtain visible light-active photocatalysts. TiO 2 , doped or not, has been synthesized using techniques such as sputtering, 15,16 chemical vapor deposition, 17,18 sol-gel process, 19,20 hydrothermal process, 7 electrochemical methods, 21,22 and, more recently, ionothermal synthesis. 23,24 Ionothermal synthesis was referred for the first time in 2004 by Cooper et al 25 to distinguish the synthesis carried out using solvents composed predominantly by ionic liquids (IL) or deep eutectic mixtures (EU) from hydrothermal preparations, which take place in a predominantly molecular solvent.…”