Nitrogen-doped Anatase TiO2 Research Articles

X-ray Photoelectron Spectroscopy (XPS) Analysis of Ultrafine Au Nanoparticles Supported over Reactively Sputtered TiO2 Films.

The impact of a titania (TiO2) support film surface on the catalytic activity of gold nanoparticles (Au NP) was investigated. Using the reactive dc-magnetron sputtering technique, TiO2 films with an amorphous, anatase, and nitrogen-doped anatase crystal structure were produced for a subsequent role as a support material for Au NP. Raman spectra of these TiO2 films revealed that both vacuum and NH3 annealing treatments promoted amorphous to anatase phase transformation through the presence of a peak in the 513–519 cm−1 spectral regime. Furthermore, annealing under NH3 flux had an associated blue shift and broadening of the Raman active mode at 1430 cm−1, characteristic of an increase in the oxygen vacancies (VO). For a 3 to 15 s sputter deposition time, the Au NP over TiO2 support films were in the 6.7–17.1 nm size range. From X-ray photoelectron spectroscope (XPS) analysis, the absence of any shift in the Au 4f core level peak implied that there was no change in the electronic properties of Au NP. On the other hand, spontaneous hydroxyl (–OH) group adsorption to anatase TiO2 support was instantly detected, the magnitude of which was found to be enhanced upon increasing the Au NP loading. Nitrogen-doped anatase TiO2 supporting Au NP with ~21.8 nm exhibited a greater extent of molecular oxygen adsorption. The adsorption of both –OH and O2 species is believed to take place at the perimeter sites of the Au NP interfacing with the TiO2 film. XPS analyses and discussions about the tentative roles of O2 and –OH adsorbent species toward Au/TiO2 systems corroborate very well with interpretations of density functional theory simulations.

Correlation between optical and structural properties of nitrogen doped anatase TiO2 thin films

Raman spectroscopy, grazing incidence X-ray diffractometer (GIXRD), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and photoluminescence spectroscopy (PL) were performed on TiO2 thin films exposed to a nitrogen N2+ ion beam at different temperatures from 45 °C to 585 °C. The crystalline structure, the thickness, the dielectric functions, the band gap and the Urbach energies were studied. The obtained results show a strong change of physical properties of TiO2 after exposing to N2+ ion beam. Raman modes and diffracted peaks show the anatase structure for all the deposited N-doped films. The presence of nitrogen doping into the TiO2 layer is confirmed by XPS measurements. The substitutional nitrogen defects promote a decrease of the band gap for N-doped TiO2 by 150 meV at the doping temperature 585 °C. This reduction was explained by the increase in valence band extremity caused by the hybridization of the N 2p states and the O 2p states of the valence band of TiO2. The Raman, GIXRD, XPS, SE, AFM, and PL results are consistent and provide an invaluable complementary information about the nitrogen diffusion within the TiO2 lattice at different temperatures.

Carbon monoxide oxidation over copper and nitrogen modified titanium dioxide⋆

Copper-Titanium Dioxide (Cu-TiO2) catalysts have been widely used to catalyze small molecules through photo- and thermal-catalytic approaches. We report nitrogen doped titanium oxide (N-TiO2) improved catalytic performance of Cu-TiO2 in the carbon monoxide oxidation reaction. Anatase TiO2 and rutile TiO2 are chosen to investigate the effect of the TiO2 phase for nitrogen modification. XPS and DFT results showed both interstitial nitrogen and substitutional nitrogen exists over nitrogen doped anatase TiO2, N-TiO2 (A). Only substitutional nitrogen exists over nitrogen doped rutile TiO2, N-TiO2 (R). Compared with copper over titanium dioxide (Cu-TiO2) catalysts, copper over nitrogen doped titanium dioxide catalysts (Cu-N-TiO2) showed enhanced redox properties based on analysis of temperature programmed reactions including H2-TPR and CO-TPSR. IR studies using CO as a probe molecule as well as copper XPS results showed that surface copper concentration distributed differently with the addition of nitrogen. Therefore, correlation between the ratio of [Cu+]/[Osurf.] and the reaction rate is suggested, because this ratio represents contributions from both active and spectator species in the carbon monoxide oxidation reaction.

Nitrogen-doped mixed-phase TiO2 with controllable phase junction as superior visible-light photocatalyst for selective oxidation of cyclohexane

Nitrogen-doped anatase/rutile mixed-phase TiO2 photocatalysts with carbonaceous species were successfully fabricated by pyrolyzing MIL-125 (Ti) and P25 composite as the precursor, and subsequently doping nitrogen into the pyrolysis product using urea as the dopant in a sealed reactor. Through varying the addition amount of P25 in the precursor, the ratios of anatase/rutile phases in the photocatalysts were conveniently adjusted. The photocatalysts showed excellent photocatalytic cyclohexane oxidation performances under visible light irradiation. The yield of the KA oil (cyclohexanol and cyclohexanone) reached 112.44 μmol after 5 h illumination for the photocatalyst with the optimal anatase/rutile ratio (N-TiO2-3), which was 5.66 and 39.87 times that of N-TiO2-0 (nitrogen-doped anatase TiO2) and N-P25 (nitrogen-doped P25), respectively. In the meantime, the selectivity toward cyclohexanone could reach 100%. The influences of pyrolysis temperature and atmosphere on the microstructure of catalysts and resulting catalytic performances for cyclohexane oxidation were also investigated. The improved photocatalytic properties were attributed to the combined effects of the high visible-light absorption caused by nitrogen doping, valid separation of photogenerated electron-hole pairs derived from the mixed-phase junction, unique auxiliary function of carbonaceous species and porous structure. A possible photocatalytic mechanism was proposed according to the active species determined by trapping experiments.

Adsorption Property of CS2 and COF2 on Nitrogen-Doped Anatase TiO2(101) Surfaces: A DFT Study.

SF6 has been utilized widely as an electrical insulation medium because of its excellent arc extinguishing performance and insulation characteristics. In this paper, the adsorption property of two kinds of key SF6 carbon-containing decomposition components (CS2 and COF2) on nitrogen-doped anatase TiO2(101) (N–TiO2) surfaces was simulated and analyzed based on density functional theory. The results demonstrated that N–TiO2 shows good gas sensitivity toward CS2 with the increase of conductivity but is insensitive toward COF2. In addition, the gas-sensing property of CS2 on N–TiO2 is stronger than that of COF2. This work provides the theoretical information on such a gas-sensitive material for key SF6 carbon-containing decomposition components, supporting its utilization as a chemical sensor applied in condition monitoring and defect diagnosis in SF6 gas-insulated equipment based on decomposition component analysis.

Enhancement of the photocatalytic activity of N-doped TiO2 nanograss array films by low-temperature sulfur doping

Moderate in-situ chemical oxidation of Ti meshes was used to prepare nitrogen-doped (N-doped) anatase TiO2 nano-grass array films with urea as the nitrogen source. Further sulfur doping through immersion of the films in a thiourea solution at a relatively low temperature of 353 K was subsequently performed to enhance the visible-light-driven photocatalytic activity of the films. SEM images confirmed that the loose microstructure of the nanograss arrays became compact after N-doping or N, S co-doping. N-doping and N, S co-doping decreased the band gap values of the TiO2 films and increased the effective visible light utilization. XPS analysis revealed that nitrogen mainly existed in interstitial form. Subsequent sulfur ions appeared as S6+, S4+, and S2−, with S6+ and S4+ replacing Ti4+, and S2− replacing O2−, respectively. With an increase in the urea treatment time, the sulfur ions were oxidized, achieving higher valence states. S6+ substitution resulted in a charge imbalance, which could only be neutralized by hydroxide ions. The imbalance made it easier for water that had settled on the TiO2 films to chemically dissociate, and thereby generating hydroxyl radicals. OH• radicals as well as Ο2•−radicals played a significant role in the degradation of RhB dye. The RhB decolorization activity achieved by the N, S co-doped samples was 48 times that of the undoped samples.

Modification of the Optical and Electronic Properties of TiO2 By N Anion-Doping for Augmentation of the Visible Light Assisted Photocatalytic Performance

In this work, a nitrogen-doped anatase TiO2 nanocrystal is prepared by a modified sol-gel preparation method using the nonionic surfactant (polyoxyethylene sorbitan monooleate) as a structural controller and a soft template. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, UVVis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy techniques. Then the photocatalytic activity of these samples is assessed by the photocatalytic oxidation of phenol under visible light irradiation. The phenol concentration is measured using a UV-Vis spectrometer. Experimental results show that N-doping leads to an excellent visible light photocatalytic activity of the TiO2 nanocatalyst. Furthermore, the formation energy and electronic structure of pure and N-doped anatase TiO2 are described by density functional theory (DFT) calculations. It is found that N-doping narrowed the band gap of bare TiO2, which leads to an excellent visible light photocatalytic activity of N–TiO2 nanocatalysts. Therefore, the prepared N–TiO2 photocatalyst is expected to find the use in organic pollutant degradation under solar light illumination.

Effect of plasma power on the semiconducting behavior of low-frequency PECVD TiO2 and nitrogen-doped TiO2 anodic thin coatings: photo-electrochemical studies in a single compartment cell for hydrogen generation by solar water splitting

Previously optimized anatase and nitrogen-doped anatase TiO2 coatings have been grown by low-frequency plasma-enhanced chemical vapor deposition (PECVD) on different kinds of substrates at low plasma power (64 W) and high plasma power (100 W) for photo-electrochemical studies. Nitrogen-doped TiO2 layers exhibit better photoactivity and also higher electronic conductivity under UV and visible irradiations than non-doped materials. The main reason is that nitrogen introduction induces TiO2 band gap tailoring towards higher wavelengths. In addition, films prepared at low plasma power present a ‘typical photo-material’ behavior (whose activity depends directly on the presence of light) while layers synthesized at higher plasma power contain an initial conductive phase giving them an activity that exists in the dark yet and can be slightly enhanced by illumination. Such conclusions are prominent in the field of photo-anodic thin films; indeed PECVD could constitute a promising approach for tailoring the efficiency of photo-electrochemical cells for hydrogen production under solar light.

Conductive TiN thin layer-coated nitrogen-doped anatase TiO2 as high-performance anode materials for sodium-ion batteries

Nitrogen-doped anatase titanium oxide (N-TiO2) with enhanced electronic conductivity induced by titanium nitride (TiN) thin layer coating was employed as high-performance anode material for sodium-ion batteries. The TiN thin layer can not only dramatically increase the electronic conductivity among crystal grains but also alleviate the volume expansion to consolidate the structure during long-term sodiation and desodiation process. The composite exhibits an excellent electrochemical performance, delivering a high specific capacity of 226.9 mA h g−1 at 0.1 C and owning excellent rate capability of 158.3 mA h g−1 at 10 C high rate. Moreover, the composite has no obvious capacity decay after 500 cycles at 1 C, showing its superior cycling performance. The enhancement of electrochemical performance may be attributed to the faster kinetics of sodium ion sodiation/desodiation, which could be a result of enhanced electronic conductivity due to the formation of TiN thin layer coating.

A first principle simulation of competitive adsorption of SF6 decomposition components on nitrogen-doped anatase TiO2 (101) surface

Gas insulated switchgear has been widely used in modern electric systems due to its significantly excellent performances such as compact structure and low land occupation as well as the security stability. However, inside defects caused during manufacture process can lead to partial discharge which might develop into serious insulation failure. Online monitoring method on basis of gas sensors is considered a promising way of detecting partial discharge for alarm ahead of time. Research has found that TiO2 nanotubes sensors show good response to SO2, SOF2, SO2F2, the decomposition components as a result of partial discharge. In order to investigate the gas-sensing mechanism of nitrogen-doped TiO2 prepared via plasma treatment methods to SO2, SOF2, and SO2F2, the adsorption structures of both three gas molecules and anatase TiO2 (101) surface were built, and DFT calculations were then carried out for calculation and analysis of adsorption parameters. Adsorption property comparison of anatase TiO2 (101) surface after nitrogen doping with Au doping and without doping shows that nitrogen doping can obviously enhance the adsorption energy for SO2 and SOF2 adsorption and no charge transfer for SO2F2 adsorption, further explaining the adsorption mechanism and doping influence of different doping elements.

Novel nitrogen-doped anatase TiO2 mesoporous bead photocatalysts for enhanced visible light response

Abstract This work reports the synthesis and characterization of a novel, high surface area N-doped anatase TiO 2 mesoporous bead as a photocatalyst for visible light photodegradation. The beads were prepared using a two-cycle microwave-assisted hydrothermal method using three different types of nitrogen dopants: diaminohexane, triethylamine, and urea. In the first cycle, TiO 2 mesoporous beads with controlled structures were synthesized at 200 °C without further calcination. The obtained beads were then subjected to a second cycle of microwave -assisted hydrothermal process for nitrogen doping. The photocatalytic activity of the N-doped mesoporous TiO 2 beads was determined by measuring the decomposition of a methyl blue aqueous solution under UV and visible light. It was found that different precursors lead to different degrees of doping which enhances the light absorption primarily in the visible light region. We demonstrate that the photocatalytic activity or photodegradation is enhanced in the visible light region.

Nitrogen-doped TiO2 nanospheres for advanced sodium-ion battery and sodium-ion capacitor applications

We synthesized nitrogen-doped anatase TiO2 nanospheres, and then used them as high-performance anode materials for NIBs and NICs, which were found to display enhanced electrochemical performances.

Nitrogen-doped TiO2 microsheets with enhanced visible light photocatalytic activity for CO2 reduction

Nitrogen-doped anatase TiO2 microsheets with 65% (001) and 35% (101) exposed faces were fabricated by the hydrothermal method using TiN as precursor in the presence of HF and HCl. The samples were characterized by scanning electron microscopy, X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy, UV-visible spectroscopy, and electrochemical impedance spectroscopy. Their photocatalytic activity was evaluated using the photocatalytic reduction of CO2. The N-doped TiO2 sample exhibited a much higher visible light photocatalytic activity for CO2 reduction than its precursor TiN and commercial TiO2 (P25). This was due to the synergistic effect of the formation of surface heterojunctions on the TiO2 microsheet surface, enhanced visible light absorption by nitrogen-doping, and surface fluorination.

Nature of Nitrogen-Doped Anatase TiO2 and the Origin of Its Visible-Light Activity

Nitrogen doped anatase TiO2 is studied using hybrid density functional theory (DFT) calculations. It is shown that under typical experimental conditions nitrogen prefers to substitute at a Ti-site and bond to two or three neighboring oxygen ions, forming nitrite or nitrate molecules. This leaves one Ti-vacancy and under-coordinated oxygen ions that produce a large electron density of states at the valence band edge, with localized characters slightly extending into the pristine TiO2 band gap, due to an altered local electrostatic potential and orbital interactions. We suggest that this large electronic density of states at the valence band edge is responsible for the enhanced subgap tail absorption observed in N-doped anatase TiO2 and hence the visible-light photocatalytic activity.

Photocatalytic degradation of endosulfan in contaminated soil with the elution of surfactants

Microbial degradation has been commonly used to remedy endosulfan-contaminated soil. However, this technique is limited by low degradation efficiency with high toxic metabolite. This work investigated the photodegradation efficiencies of endosulfan in soil with the elution of surfactants and revealed the kinetic characteristics of photocatalytic degradation with two strategies, i.e., surfactant elution followed with photocatalytic degradation, and simultaneous elution and photocatalytic degradation. The endosulfan-contaminated soil, photocatalyst (nitrogen-doped anatase TiO2), and three eluents composed of Tween 80, SDS, and Na2SiO3 were prepared, respectively. The degradation efficiencies of endosulfan in soil were examined by the photocatalyst under visible-light irradiation with two strategies, i.e., surfactant elution followed with photocatalytic degradation, and simultaneous elution and photocatalytic degradation. The kinetic characteristics of photocatalytic degradation of endosulfan in soil were studied at certain time intervals. The XRD, X-ray photoelectron spectroscopy, and UV–vis diffuse reflection spectra revealed that nitrogen was doped into TiO2 lattice, and the optical absorption of nitrogen-doped TiO2 shifted toward visible-light region. The residual ratios of α-, β-endosulfan in soil eluates obviously decreased with the irradiation time increasing and could not be detected at 240 min; this process could be well described by first-order kinetic model, and the half-lives of α-, β-endosulfan were 43.0–71.7 and 51.1–85.3 min, respectively; the concentrations of endosulfan sulfate showed a trend of increase, decrease, and till complete degradation. For simultaneous elution and photocatalytic degradation, the residual ratios of α-, β-endosulfan in soil were 0.21–0.25, 0.41–0.43 at 120 h with eluent 1 to eluent 3 treatments, respectively; the degradation process of endosulfan in soil-aqueous systems could be well described by four-parameter biphasic first-order kinetic model. Endosulfan in the soil eluates could be completely degraded at 240 min under visible-light irradiation and could be described by pseudo first-order kinetic equation. The degradation process of endosulfan in soil-aqueous systems obeyed four-parameter biphasic first-order kinetic model. As an intermediate of photocatalytic degradation, endosulfan sulfate could be rapidly degraded. It was concluded that surfactant elution followed with photocatalytic degradation was more effective than simultaneous elution and photocatalytic degradation.

Synthesis of N-doped TiO2 with Different Nitrogen Concentrations by Mild Hydrothermal Method

Nitrogen-doped nanocrystalline anatase TiO2 powders with different nitrogen-doping concentrations were synthesized at 150°C and held for 2 h under an initial pressure of 3 MPa by the mild hydrothermal method with no postheat treatment. The X-ray photoelectron spectroscopy results confirmed that substitutional and interstitial nitrogen coexisted in the TiO2 lattice and formed Ti–N and Ti–O–N linkages, respectively. The visible light absorption of nitrogen-doped TiO2 in the wavelength 400 ∼ 550 nm was greatly enhanced compared with that of un-doped TiO2. Both optical absorption and photocatalytic efficiency were elevated with increased nitrogen-doping concentration.

Nitrogen doped anatase TiO2 sheets with dominant {001} facets for enhancing visible-light photocatalytic activity

The photocatalytic activity of TiO2 can be mainly improved from three approaches: (1) enhancing surface energy; (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain nitrogen (N) doped TiO2 sheets with dominant {001} facets by a hydrothermal process. The XRD patterns confirm the better crystallinity. XPS spectrums show nitrogen acting as interstitial N or an O–Ti–N structure in TiO2 sheets. Compared with that of TiO2 sheets, the N doped TiO2 sheets not only absorb visible light, but also have a large percentage of high reactive {001} facets, so the photocatalytic activities are greatly enhanced, as confirmed by the decomposition of methylene orange.

The composite of nitrogen-doped anatase titania plates with exposed {0 0 1} facets/graphene nanosheets for enhanced visible-light photocatalytic activity

Composite photocatalysts composed of nitrogen-doped anatase TiO2 plates with exposed {001} facets (NTS) and graphene nanosheets (G) were firstly synthesized by a facile one-pot hydrothermal process. The morphologies, structural properties, and photocatalytic activities of the resultant NTS/G composites were investigated in detail. Graphene nanosheets were demonstrated play three important roles in the NTS/G composites, as transporter of photo-excited electrons, extender of light absorption range and enhancer of adsorptive capacity, respectively. Due to the effective charge anti-recombination, the efficient utilization of the visible light and the high adsorptive capacity to target pollutants, the composites exhibited significant improvement in photocatalytic degradation of methylene blue under visible light irradiation. Based on the results, the mechanism of enhanced visible-light photocatalytic activity on NTS/G composites was proposed.

Preparation of nitrogen-doped anatase TiO2 nanoworm/nanotube hierarchical structures and its photocatalytic effect

As-anodized amorphous TiO2 nanotube arrays (TNAs) are immersed in hot ammonia solution (90 °C), which can both spontaneously reconstruct the amorphous TNAs to be anatase nanoworm/nanotube hierarchical structures in situ and simultaneously implant nitrogen into them. These hierarchical structures, having larger surface area, higher electrical conductivity and broader light absorption range than the original TNAs, possess dramatically enhanced photocatalytic activity for degradation of methyl orange (MO) under visible light irradiation. The optimized nitrogen doped hierarchical structures exhibit a best photodegradation rate (K) of 0.722 h−1, which greatly exceeds the degradation rate of the original TNAs annealed in ambient air at 500 °C for 2.5 h. This simple technique would enable us conveniently to design and fabricate highly photoactive one-dimensional TNAs-based functional materials applicable to photocatalysis and solar energy conversion.

Enhanced photocatalytic activity of nitrogen doped TiO2 photocatalysts sensitized by metallo Co, Ni-porphyrins

Nitrogen doped anatase TiO2 powders (N-TiO2) were sensitized by four kinds of metalloporphyrins (CoTHPP, CoTPP, NiTHPP, and NiTPP). The resulting materials were characterized by XRD, TEM, XPS, DRS and N2 adsorption. The results showed that the crystal structure and morphology of N-TiO2 were not affected by the existence of porphyrin on its surface, but the surface area increased after the N-TiO2 sensitized by metalloporphyrins. The photocatalytic degradation of methyl blue (MB) experiments showed that the metalporphyrins sensitized N-TiO2 composite catalysts, especially the CoTHPP/N-TiO2 and CoTPP/N-TiO2, exhibited higher degradation efficiency than the unsentisized N-TiO2 powders. In addition, the photocatalytic degradations of MB using the composite catalysts were all demonstrated to follow first-order kinetic model. The composite catalysts can be recycled four times without significant loss of photocatalytic activity.