N-doped TiO2 Films Research Articles

Efficiency of cathodic arc-grown N-doped TiO2 films for the photocatalytic reduction of Cr(VI) under UV-Vis irradiation

The photocatalytic activity of undoped and N-doped TiO2 anatase films with different thicknesses prepared by cathodic arc deposition on glass substrates is reported. After TiO2 deposition, the doping of the films was carried out by plasma immersion ion implantation in a nitrogen environment. The composition of the films was studied by x-ray photoelectron spectroscopy, the surface morphology was analyzed by atomic force microscopy and the crystalline structure was examined by x-ray diffraction. The thickness was determined by observing the film cross section with scanning electron microscopy. The transmittance of the films in the UV-Vis range was studied as well. The photocatalytic activity of the films was evaluated through the efficiency in the reduction of Cr(VI) in the presence of ethylenediaminetetraacetic acid under UV-Vis irradiation. N-doped films presented a higher photocatalytic efficiency than undoped films: Cr(VI) reduction after 5 h irradiation augmented from 58% (pure TiO2) to 85% (N-doped TiO2) for films of 300 nm thickness, and from 69% to 85% for films with a thickness of 440 nm. On the other hand, pure TiO2 films of 790 nm thickness were more efficient (99% of Cr(VI) reduction) but the effect of doping on the photocatalytic activity was negligible.

Synergistic coupling {101}-{111} facet of N-doped TiO2 film enhance spatial charge separation for methylene blue photodegradation

The synthesis of N-doped TiO2 film with co-exposed {101} and {111} facets via a one-pot facile hydrothermal method had proven to enhance the photocatalytic activity of TiO2. The high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) data show the incorporation of N ions into the TiO2 accomplishes the facet modification. The shifting of the N-doped TiO2 photocatalyst adsorption bandgap toward a higher wavelength was identified as the TiO2 band gap was reduced. Up to 66 % methylene blue had successfully been degraded with the aid of N-doped TiO2 as an active photocatalyst. The enhanced photodegradation of N-doped TiO2 film is mainly attributed to the presence of {101} and {111} facets, leading to the efficient separation of carriers and lengthening the life of photogenerated carriers, consequently improving its photocatalysis potential.

Characterization of Nitrogen-Doped TiO2 Films Prepared by Arc Ion Plating without Substrate Heating in Various N2/O2 Gas Mixture Ratios

Nitrogen-doped TiO2 films exhibit good photocatalytic ability in the visible (VIS) light region. This study reports the fabrication of these films using arc ion plating (AIP) in different ratios of nitrogen partial pressure (PN2) to oxygen partial pressure (PO2) without substrate heating and/or applied bias. This approach allows a significant broadening of the range of possible substrates to be used. X-ray diffraction (XRD) patterns indicate that these films deposited at room temperature are amorphous, and surface electron microscope (SEM) and atomic force microscope (AFM) images show that they have rough surfaces. Their transmittance and optical properties are measured with a spectrometer and ellipsometer, respectively. In addition, the bandgap energies of these amorphous films are derived by the ellipsometer from the Tauc–Lorentz (TL) model. The results indicate that the N-doped TiO2 film with a PN2/PO2 ratio of 1/4 attains the narrowest bandgap and the highest absorbance in the visible region. It can be attributed to the prominent Ti–N peaks observed in the sample’s Ti and N X-ray photoelectron spectroscopy (XPS) spectra. In addition, verified with the methylene blue (MB) test, this sample exhibits the best photocatalytic performance for its narrowest energy gap.

The Preparation of N-Doped Titanium Dioxide Films and Their Degradation of Organic Pollutants.

N-doped TiO2 films supported by glass slides showed superior photocatalytic efficiency compared with naked TiO2 powder due to them being easier to separate and especially being responsive to visible light. The films in this study were prepared via the sol-gel method using TBOT hydrolyzed in an ethanol solution and the nitrogen was provided by cabamide. The N-doped TiO2 coatings were prepared via a dip-coating method on glass substrates (30 × 30 × 2 mm) and then annealed in air at 490 °C for 3 h. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis. The doping rate of N ranged from 0.1 to 0.9 (molar ratio), which caused redshifts to a longer wavelength as seen in the UV-vis analysis. The photocatalytic activity was investigated in terms of the degradation of phenol under both UV light and visible light over 4 h. Under UV light, the degradation rate of phenol ranged from 86% to 94% for all the samples because of the sufficient photon energy from the UV light. Meanwhile, under visible light, a peak appeared at the N-doping rate of 0.5, which had a degrading efficiency that reached 79.2%, and the lowest degradation rate was 32.9%. The SEM, XRD and UV-vis experimental results were consistent with each other.

Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD

Abstract Nitrogen-doped TiO2 films were grown on borosilicate glass substrates at 400 °C by the metallorganic chemical vapor deposition (MOCVD) for removing dye from water under visible light. The effect of N-doping on the structural, surface, and photocatalytic properties of films was evaluated. X-ray photoelectron spectroscopy (XPS) analyses revealed that 1.56 and 2.44 at% of nitrogen were incorporated into the films by varying the NH3 flux during the growth. Methyl orange dye degradation experiments showed that the N-doped films presented photoactivity under visible light. The film containing 2.44 at% of nitrogen exhibited the best photocatalytic behavior, with 55% of efficiency. Recyclability tests under visible light showed that the film efficiency dropped gradually after each test. N-TiO2 films grown by MOCVD have the potential to be used in environmental applications by removing pollutants using a green method under sunlight or even under internal illumination, although its reuse is limited.

Synthesis of N-Doped TiO2 with good photocatalytic property

N-doped TiO2 (N–TiO2) films with different surface topography were synthesized by the Hydrothermal method in three group solutions. Analyzed results indicate that the ratio of anatase phase to rutile phase in the N–TiO2 film stands at 2.1:1. Brookite phase of TiO2 is also found in result material, which was characterized by Raman spectroscopy. Effects of the doping on optical absorption properties of the N–TiO2 were investigated. The optical absorption edge is red shifts and long tail occurs in the presence of N doping. Thereby the N–TiO2 film may exhibit improved absorption properties for UV and visible light. By in-situ method, nanomaterials with target structures can be obtained by simple methods, and the nanostructures are much more stable.

The structure and self-regeneration performance of Salix psammophila-activated carbon modified by Ag and N co-doped TiO2.

In this study, Salix psammophila activated carbon (AC) was modified by immersing it in an AgNO3 solution and coating it with an N-doped TiO2 film to improve its self-regeneration performance in visible light. Ag+ was adsorbed and reduced to Ag nanoparticles by AC. Ti element only existed as Ti4+, and N element was incorporated into TiO2 mainly in the form of interstitial nitrogen. The photodegradation of Ag-N-TiO2-AC (AC coated with Ag and N co-modified TiO2) was enhanced under visible light irradiation because of its three inherent structures: (1) Ag and N co-modified TiO2 had a smaller average crystal size; (2) with a low bandgap (1.59 eV), the photoresponse region of Ag and N co-modified TiO2 was greatly extended; (3) the lifetime of the photogenerated holes was increased. With the increase in the AgNO3 dosage, the Ag-N-TiO2-AC photodegradation increased, while its adsorption decreased. Because of these synergistic effects, 0.05Ag-0.1N-TiO2-AC (where 0.05 is the dosage of AgNO3, g) presented the best self-regeneration performance under visible light irradiation.

Effect of nitrogen-doping on the surface chemistry and corrosion stability of TiO2 films

TiO2 and N-doped TiO2 films were grown on AISI 316 stainless steel substrates and on Si (100) by metallorganic chemical vapor deposition (MOCVD) at 400°C and 500°C. X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle techniques were used to characterize de films. The corrosion behavior was assessed by monitoring the open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization tests in 3.5wt% NaCl solution at room temperature. The results show that 6.18 at% of nitrogen was introduced in the films grown at 400°C and 8.23 at% at 500°C, and that besides TiO2, nitrogen phases were identified. All the films are hydrophilic and the contact angles varied from 48° to 72°. The films presented good homogeneity, low porosity and rounded grains in the range of 40–90nm. The RMS roughness varied between 5.5 and 18.5nm. Titanium dioxide films grown at 400°C showed better corrosion resistance than those grown at 500°C due to its compact morphology. Nitrogen-doping was not efficient to protect the substrate from corrosion.

Effect of nitrogen-doping and post annealing on wettability and band gap energy of TiO2 thin film

Titanium dioxide film is one of the most promising self-cleaning materials. The self-cleaning performance is directly related to the photocatalytic activity and surface wettability, which, in turn, depends on the TiO2 film structure parameters. Nitrogen-doping and post annealing are commonly used for TiO2 film treatment. The present paper addresses the mechanisms of N-doping and annealing induced TiO2 film structure transition, band gap narrowing and wettability transition. It is shown that N-doping combined with annealing leads to anatase → rutile phase transition, formation of hierarchical topography, change of surface chemical composition, and consequently results in reduction of band gap energy and water contact angle. N-doping level and N-linkages are found to significantly affect the structure/properties of annealed TiO2 and N-doped TiO2 films. The proposed mechanisms might help optimize TiO2 film synthesis and post treatment procedures. Moreover, annealed N-doped TiO2 film with highest N-content, simultaneously exhibiting anatase-rutile polycrystalline structure, high roughness, as well as lowest band gap energy and water contact angle, is supposed to present optimal self-cleaning performance.

Low-temperature S-doping on N-doped TiO2 films and remarkable enhancement on visible-light performance

Sulfur doping of nitrogen-doped TiO2 nanograss array films was realized through facile thiourea solution immersion at a low temperature of 353 K. Doped nitrogen and sulfur atoms were found mainly in the interstitial form. Nitrogen doping (N-doping) and sulfur doping (S-doping) enhanced visible light absorption and decreased the band gap of undoped TiO2 films from 3.10 to 3.01 and 2.81 eV, respectively. Furthermore, N-doped and N, S co-doping made the water absorbed on TiO2 was easier to chemically dissociate and generate hydroxide groups. N-doping favored to produce more O2•− radicals and S-doping benefit to generate more OH• radicals. Both OH• and O2•− active radicals played a significant role in the degradation of RhB. The photocatalytic activity of undoped TiO2 films was increased by 2.5 times by N-doping through urea treatment. By further S-doping, the photocatalytic performance of N-doped TiO2 films was enhanced by 4.0 times again.

Effect of post annealing on properties of N-doped TiO2 films deposited by reactive magnetron sputtering

The paper studies the effect of annealing on the structure and properties of N-doped TiO2 films, deposited by reactive magnetron sputtering. An increase in the annealing temperature results in a reduction of the film thickness and a rise of the refractive index. The post annealing induces the anatase-rutile phase transition and also leads to band gap narrowing and wettability transition.

Difference of visible-light photocatalytic activity behaviors between nitrogen- and phosphorus-doped titanium(IV) oxide films

The property of phosphorus (P)-doped titanium(IV) oxide (TiO2) films prepared using phosphide was compared with that of nitrogen (N)-doped TiO2 films prepared using nitride. X-ray diffraction analysis showed that the crystallite size of P-doped TiO2 film was larger than that of N-doped TiO2 film. The data also indicated the low crystallinity of P-doped TiO2 film. Optimal calcination temperatures for phenol photodegradation were observed at 475 °C for P-doped TiO2 films and 550 °C for N-doped TiO2 films. The difference in the optimal temperature is discussed in terms of the change in crystallinity and crystallite size. Phenol degradation experiments in the repeated use of P- and N-doped TiO2 films revealed the feature of the stability.

Photocatalytic antibacterial study of N-doped TiO2 thin films synthesized by ICP assisted plasma sputtering method

Specific plasma engineering based synthesis can induce interesting photocatalytic antibacterial activities in TiO2 films. This work presents the combination of pulsed DC (PDC) plasma with inductively coupled plasma (ICP) to synthesize undoped and nitrogen doped (N-doped) TiO2 thin films using magnetron sputtering. The surface properties of resulting films were systematically analyzed in detail and correlated to the photocatalytic antibacterial activity against Gram negative Escherichia coli (E.coli). The addition of ICP source to PDC discharge generated TiO2 films with enriched surface roughness due to the bombardment of highly activated species on the substrate. The ICP assisted films exhibited the morphology of nanoclusters with clear defined boundaries, higher O content and higher surface wettability. It was found that the films deposited with N-doping and addition of ICP source significantly increased the eradication of bacteria both in dark as well as in white light (artificial indoor light). Higher antibacterial activity of N-doped TiO2 films in white light has been explained by photocatalytic degradation mechanism.

Optical Properties and UV Sensing Response of Nitrogen-doped TiO2 Thin Film by CVD

This work was demonstrated a cold-wall chemical vapour deposition (CVD) setup to prepare nitrogen (N)-doped titanium dioxide (TiO2) thin film on glass substrates, which presents semi-transparent yellowish surface. The prepared N-doped TiO2 film is homogeneous and possesses polycrystalline anatase structure. The transmittance measurement was carried out in the ultraviolet-visible spectral region to evaluate the film thickness, optical constants, and the optical band gap was determined by Tauc plot. A metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector by the Pt/N-doped TiO2 film has shown a positive response towards UV illumination.

Study on the chemical bond structure and chemical stability of N doped into TiO 2 film by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by DC pulse magnetron sputtering technique. The surface of TiO2 film was implanted by N ion beam at room temperature and N doped TiO2 (N-TiO2) film was obtained. X-ray diffractometer result showed that with the increase of sputtering power, the crystal structure of TiO2 film changed from amorphous to anatase polycrystalline structure. Transmission electron microscopy result revealed that nanoscale clusters existed in amorphous TiO2 film. The bandgap of TiO2 film was about 3.28 ± 0.05 eV. X-ray photoelectron spectroscopy results revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. With increasing TiO2 film crystallinity, N atom-percent and ratio of Ti–N to Ti–NO decreased and increased, respectively. TiO2 film deposited with 900 W in sputtering power, N atom-percent decreased to 6.6 at.% and ratio of Ti–N to Ti–NO increased to 0.81:1. The bandgap of N-TiO2 film was about 3.02 ± 0.07 eV. N atom-percent and ratio of Ti–N to Ti–NO kept at 2.73 ± 0.26 at.% and (0.87 ± 0.03):1 for all annealed N-TiO2 films. The bandgap of annealed N-TiO2 film was about 3.16 ± 0.03 eV. So, the crystallinity of TiO2 film was one of most important parameters, which influenced the chemical bond structure and chemical stability of N in TiO2 films.

Best compromise for photocatalytic activity and hydrophilicity: N-doped TiO2 films under UV light

This study seeks to determine the best compromised parameters for photoluminescence performance and hydrophilicity of nitrogen-doped titanium dioxide coatings deposited on glass substrates using radio frequency reactive magnetron sputtering. Rf power (W), process pressure (mtorr), Ar/O2/N2 flow ratios and substrate temperature (°C) were optimized with reference to the structure and photocatalytic characteristics of TiO2. An L9 (34) orthogonal array, the signal-to-noise ratio and analysis of variance were employed for determination of the compromise deposition settings of nitrogen-doped titanium dioxide thin films, annealed in Ar ambient (10 mtorr) at temperatures of 250, 350 and 450 °C, for a period of 30 min. The results demonstrate that for Ar/O2/N2 flow ratios of 80/20/0, 75/20/5, 70/20/10, and 65/20/15, the respective corresponding methylene blue absorbance is 0.412, 0.406, 0.385, and 0.355, which depicts a greater photocatalytic activity with a larger N2 flow ratio. For the morphological properties, the nitrogen-doped titanium dioxide films with a larger N2 flow ratio show a homogenous structure, smaller grain sizes and more spherical particles with Ra roughness of 1.394–0.362 nm. The effects of annealing temperature, duration of ultraviolet and visible light irradiation were also analyzed. The films annealed at higher temperature (450 °C) under ultraviolet and visible light irradiation of 240 min exhibit coexistence of the anatase (101) and rutile (004) structures, which appears to imbue the nitrogen-doped titanium dioxide film with greater photocatalytic activity and photo-induced hydrophilicity. Novelty Statement 1. This study seeks to determine the best compromised parameters for photoluminescence performance and hydrophilicity. 2. The ANOVA results show that the rf power has the major effect on methylene blue (MB) absorbance and the process pressure ranks the second. 3. This study determines the effect of Ar/O2/N2 flow ratios and post annealing treatment on the morphology, hydrophilicity and photocatalytic activity of N-TiO2 thin films. The results demonstrate that a greater photocatalytic activity for N-TiO2 thin films can be achieved by using a greater N2 flow ratio. 4. The film that is annealed at 450 °C exhibits the coexistence of the anatase (101) and rutile (004) structures, which appears to imbue the N-doped TiO2 film with greater photocatalytic activity and photoinduced hydrophilicity under UV and visible light illumination.

The investigation of band gap and N chemical bond structure of N–TiO2 film prepared by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by the direct current pulse magnetron sputtering technique. Then the surface of TiO2 film was implanted by the N ion beam at room temperature. Through this way, N-doped TiO2 (N–TiO2) film was obtained and the band gap of N–TiO2 film was decreased to 2.97 eV. XPS result revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. N ion was substitutionally/interstitially doped into TiO2 crystal lattice and Ti–N bond was formed. N ion was doped into amorphous TiO2 and Ti–ON bond was formed. The polycrystal TiO2 film could result in that more N ion was substitutionally/interstitially doped into TiO2 crystal lattice, which could effectively narrow the band gap of N–TiO2 film. This work provides a potential N doping method which could be applied commercially.

Carbamazepine degradation using a N-doped TiO2 coated photocatalytic membrane reactor: Influence of physical parameters

Commercial α-Al2O3 photocatalytic membranes with a pore size of 200 and 800-nm were coated with N-doped TiO2 photocatalytic film using a sol-gel technique for concurrent bottom-up filtration and photocatalytic oxidation. X-ray diffraction confirmed that the deposited N-doped TiO2 films are in the form of anatase with 78–84% coverage of the membrane surface. The concentration of N found by X-ray photoelectron spectroscopy was in the range of 0.3–0.9 atomic percentage. Membrane permeability after coating decreased by 50% and 12% for the 200- and 800-nm membrane substrates, respectively. The impact of operational parameters on the photocatalytic activity (PCA) of the N-doped TiO2-coated membranes was examined in a laboratory flow cell based on degradation of the model micropollutant carbamazepine, using a solar simulator as the light source. The significant gap in degradation rate between flow through the membrane and flow on the surface of the membrane was attributed both to the hydraulic effect and in-pore PCA. N-doped TiO2-coated membranes showed enhanced activity for UV wavelengths, in addition to activity under visible light. Experiments of PCA under varying flow rates concluded that the process is in the mass-transfer control regime. Carbamazepine removal rate increased with temperature, despite the decrease in dissolved oxygen concentration.

Influence of N-doping and air annealing on the structural and optical properties of TiO2 thin films deposited by reactive DC sputtering at room temperature

N-doped TiO2 thin films have been grown over glass substrates without intentional heating by DC sputtering of a metallic Ti target immersed in a reactive gas mixture of argon, oxygen and nitrogen. The oxygen partial pressure has been adjusted to achieve effective N-doping, intended to decrease the band gap energy with respect to analogous undoped layers. These N-doped TiO2 films are found amorphous by X-ray analysis, even after post-deposition heating in air up to 550 °C, whereas the analogous intrinsic TiO2 layers exhibit rutile crystalline structure before and after heating. The obtained results agree with the localized level model that has been developed for titania crystals and applies here for amorphous TiO2:N layers, which show an effective redshift of 0.88 eV with respect to the undoped samples. Nevertheless, the widest gap value of 3.22 eV is achieved for the several TiO2 and TiO2:N thin films after annealing in air at the highest temperature. This is attributed to the suppression of oxygen vacancies and Ti3+ oxidation states during such thermal treatment.

N-doped TiO2 based visible light activated label-free photoelectrochemical biosensor for detection of Hg(2+) through quenching of photogenerated electrons.

A novel photoelectrochemical (PEC) biosensor was fabricated based on N-doped TiO2 for the detection of Hg(2+) through the quenching of photogenerated electrons. The N-doped TiO2 was synthesized by a sol-gel method with urea and tetrabutyl titanate as the N and Ti sources. Compared with the undoped TiO2, the N-doped TiO2 showed an enhanced photocurrent response under visible light (λ > 420 nm). The sensing surface was functionalized with 5'-amino-modified T-rich oligonucleotides. The photoelectrochemical biosensor bound Hg(2+) on the surface by a highly specific T-Hg(2+)-T recognition. Hg(2+) on the surface of the N-doped TiO2 film withdrew the photogenerated electrons and decreased the recorded current signal. The dynamic linear range for Hg(2+) has been determined to be as low as 2-6 μM.