Nitrogen-doped TiO2 Thin Films Research Articles

Combined Analytical Study on Chemical Transformations and Detoxification of Model Phenolic Pollutants during Various Advanced Oxidation Treatment Processes.

Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO2 thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte.

Efficient removal of 2-chlorophenol from aqueous solution using TiO2 thin films/alumina disc as photocatalyst by pulsed laser deposition

Pulsed laser deposition facilitates the epitaxial deposition and growth of TiO2 at low temperature on hot substrate. In this study, nanosized nitrogen-doped TiO2 thin films were deposited on fabricated alumina disc-shaped and glass substrates. Textural properties of the fabricated disc and alumina disc-supported TiO2 were investigated using N2 adsorption–desorption isotherms, field emission scanning electron microscopy (FESEM), X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. FESEM showed the presence of single crystals of TiO2 on the alumina disc. FTIR showed the presence of octahedral TiO2 and different hydroxyl groups on the surface which is responsible for the photoactivity and also showed the functional groups adsorbed on the catalyst surface after the photocatalytic degradation. The concentration of 2-chlorophenol and the photo-redox intermediate products as a function of irradiation time was determined. The concentration of the produced chloride ion during the photocatalytic degradation was determined by an ion chromatography. The results showed that the photocatalytic activity of the catalyst decreased upon cycling. The obtained results were compared with nanostructured TiO2 supported on glass substrate. Higher efficiency of 100% degradation was achieved for TiO2/Al2O3 catalyst, whereas about 70% degradation of 2-CP was achieved using TiO2/glass. Different photointermediates of 2-CP degradation have been identified for each cycle. The difference of intermediates is supported by the adsorbed fragments on the catalyst surface.

Synthesis and characterization of sprayed nitrogen doped TiO2Thin films

Abstract Highly transparent undoped and nitrogen doped Titanium dioxide (N-TiO2) thin films were deposited onto glass/FTO substrates by chemical spray pyrolysis technique. The deposited thin films were characterized for their photoelectrochemical, structural, morphological, and optical properties using XRD, SEM, and UV–Vis spectrophotometer. X-ray diffraction studies showed that the films were polycrystalline with a tetragonal crystal structure. The scanning electron micrograph displayed that the films are uniform, compact, and with randomly distributedgrains of size varying from 40 nm to 60 nm. The observed direct bandgap was about 3.55 eV for undoped TiO2 films and 3.54 to 3.31 eV for N-TiO2 thin films.

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.

Effect of the nitrogen–oxygen ratio on the position of N atoms in the TiO2lattice of N-doped TiO2thin films prepared by DC magnetron sputtering

The nitrogen-doped TiO2thin films are deposited on the glass substrate by using a direct-current (DC) magnetron sputtering technique.

Photocatalytic Activity and Visible-Light Response of TiO2 Thin Film Doped with Nitrogen by Using Urea

TiO2 has become a widely investigated photocatalyst because of its low cost, low toxicity and high photocatalytic activity under UV irradiation that causes photocatalytic decomposition of organic compounds. Impurities dopant and metal are often used to acquire impurities doped or metal doped TiO2 powder by a sol-gel method. In this paper, we made nitrogen doped TiO2 by a simple process. TiO2 (P25) thin films with 80 % of anatase and 20 % of rutile were fabricated on FTO glass by electrophoretic deposition (EPD). These were then doped with nitrogen by using urea and sintered in electric furnace at 500 and 600 degrees Celsius. EPD was superior for film formation at dispersibility. We calculated absorbance spectra of nitrogen doped TiO2 thin film fabricated on FTO glass. As the result, 600 degrees Celsius is superior sintering temperature at absorbance under visible light than 500 degrees Celsius. Moreover, when the samples sintered at 600 degrees Celsius, each additive amount had different increment of absorbance in specific visible light range. This result indicates the improvement in visible-light response on TiO2 by the simple process. To further research, it is essential to make nitrogen doped TiO2 under pressure and measure the photodegradation reaction.

Thermal annealing effect on nitrogen-doped TiO2 thin films grown by high power impulse magnetron sputtering plasma power source

The work reports plasma assisted growth of nitrogen-doped titanium dioxide (N-TiO2) thin films using high power impulse magnetron sputtering (HiPIMS) power source and effect of post-deposition thermal annealing. The films were deposited at low pressure. The binding energies of elements of interest, the energy gap, crystallinity and morphology of the films were analyzed before and after annealing. The results showed an increase in binding energies, a fact attributed to enhanced oxidation, after the annealing process. Only nitrogen doped samples grown by HiPIMS exhibited the presence of substitutional nitrogen. The energy gap of the films was found to decrease after doping and annealing. Improvement in crystallinity with a small shift in the crystalline peaks indicating decrease in lattice parameter, which could be seen by surface smoothing, was observed after thermal annealing. As a result of the growth of films by HiPIMS, nitrogen doping and post-deposition thermal annealing, improvements in the properties of the films which have relevance for photocatalytic and energy applications were observed.

Enhanced visible light adsorption of heavily nitrogen doped TiO2 thin film via ion beam assisted deposition

Nitrogen doping is widely used to enhance the visible light absorption of TiO2 by narrowing the bandgap. It is recognized that this modification is sensitively affected by the spatial distribution of anion doping. In order to explore the effects of nitrogen distributions in TiO2, we synthesized nitrogen-doped TiO2 thin films via the ion-beam assisted deposition (IBAD) technique and calcinations in NH3 atmosphere. The morphology and crystal structure of these thin films were characterized by scanning electron microscope and X-ray diffraction respectively. The chemical states and spatial distributions of nitrogen in the TiO2 were investigated by X-ray photoelectron spectroscopy. The nitrogen can be heavily and uniformly doped in anatase thin film by the IBAD technique with the N/Ti atomic ratio ranging from 61.3 to 51.9 %, much higher than that calcinated at 500 °C under NH3 atmosphere, which fluctuated from 23.2 to 4.5 %. The time-dependent depth profile of the N 1s spectrum shows that the doped nitrogen in the TiON thin film synthesized via IBAD distributes from the surface to the inner layer. Compared to the traditional calcinations synthesized methods, the as-synthesized TiON thin film, shows a much higher absorption in the visible-light range. Its light absorbance spectrum extends to over 700 nm, covering most of the visible-light region.

Development of visible light activated TiO2 thin films on stainless steel via sol spraying with emphasis on microstructural evolution and photocatalytic activity

Visible light activated nitrogen doped TiO2 thin films were developed on 304 stainless steel by sol spraying method using a common painting airbrush. Thin films with different thickness were prepared and calcined at various temperatures from 400 to 600°C. The samples were studied using ellipsometry, XRD, GIXRD, XPS, DRS, SEM and FESEM. Photocatalytic activities of the films were investigated by measuring their ability to degrade methylene blue solution under visible light irradiation. Results revealed that uniform nanostructured films with a thickness range of 29–150nm were successfully prepared on stainless steel by sol spraying. Doping nitrogen into TiO2 structure restricted the crystallite growth of anatase phase and reduced the band gap energy to 2.85eV and therefore, activated TiO2 in visible light region. Increasing calcination temperature not only promoted crack formation in thin films, but also encouraged Fe diffusion from substrate into thin films structure. However, the N doped TiO2 film calcined at 500°C with a thickness of 150nm indicated a significant photocatalytic activity in visible light with 22% higher efficiency in comparison with undoped TiO2 film. Development of TiO2 based photocatalytic thin films by a simple method of airbrushing, builds up the hope for industrial scale applications in future.

Effect of nitrogen doped titanium dioxide (N-TiO2) thin films by jet nebulizer spray technique suitable for photoconductive study

The TiO2 and Nitrogen doped TiO2 thin films were effectively synthesized on glass substrate for different Nitrogen doping concentration (4, 6, 8, 10 at.%) by Jet nebulizer spray technique. The XRD patterns revealed that the films were in anatase phase with the tetragonal structure. On observing SEM images, the occurrences of apparent agglomeration pattern were found in 8 at.% N-TiO2 thin film. The presence of elements was confirmed from EDX analysis. A considerable reduction in band gap was attained on increasing nitrogen concentration using UV–Visible spectroscopy. By analyzing the PL spectra, it is found that nitrogen incorporation on TiO2 lattice reduces the band to band recombination in the surface state emission. N-TiO2 thin film shows high persistent photoconductivity with slow decay.

Undoped TiO2 and nitrogen-doped TiO2 thin films deposited by atomic layer deposition on planar and architectured surfaces for photovoltaic applications

Undoped and nitrogen doped TiO2 thin films were deposited by atomic layer deposition on planar substrates. Deposition on 3D-architecture substrates made of metallic foams was also investigated to propose architectured photovoltaic stack fabrication. All the films were deposited at 265 °C and nitrogen incorporation was achieved by using titanium isopropoxide, NH3 and/or N2O as precursors. The maximum nitrogen incorporation level obtained in this study was 2.9 at. %, resulting in films exhibiting a resistivity of 115 Ω cm (+/−10 Ω cm) combined with an average total transmittance of 60% in the 400–1000 nm wavelength range. Eventually, TiO2 thin films were deposited on the 3D metallic foam template.

Development of Dye-Sensitized Solar Cells with Sputtered N-DopedTiO2Thin Films: From Modeling the Growth Mechanism of the Films to Fabrication of the Solar Cells

In this paper, nitrogen-doped TiO2thin films were deposited by DC reactive sputtering at different doping levels for the development of dye-sensitized solar cells. The mechanism of film growth during the sputtering process and the effect of the nitrogen doping on the structural, optical, morphological, chemical, and electronic properties of the TiO2were investigated by numerical modeling and experimental methods. The influence of the nitrogen doping on the working principle of the prototypes was investigated by current-voltage relations measured under illuminated and dark conditions. The results indicate that, during the film deposition, the control of the oxidation processes of the nitride layers plays a fundamental role for an effective incorporation of substitutional nitrogen in the film structure and cells built with nitrogen-doped TiO2have higher short-circuit photocurrent in relation to that obtained with conventional DSSCs. On the other hand, DSSCs built with nondoped TiO2have higher open-circuit voltage. These experimental observations indicate that the incorporation of nitrogen in the TiO2lattice increases simultaneously the processes of generation and destruction of electric current.

Control of the visible and UV light water splitting and photocatalysis of nitrogen doped TiO2 thin films deposited by reactive magnetron sputtering

N-doped TiO2 thin films have been prepared by reactive RF magnetron sputtering at different pressures and with different compositions using a dual reactive gas mixture of nitrogen and oxygen. The morphological, optical, photo-electrochemical and photocatalytic properties have been studied in order to investigate the white light and visible light photoactivities of the films. Significant control over the band gap energy in the films was achieved by varying the deposition parameters. Photoelectrochemical characterization revealed improved white light photocurrent generation in nitrogen doped films prepared at low pressures. However, the visible light photocurrent generation showed improvement for all deposition pressures, and changed accordingly with the nitrogen incorporation. Photocatalytic measurements of a common chemical pollutant NMP (N-methyl-2-pyrrolidone) under different irradiation conditions provided evidence of improved photoactivity for samples prepared at high pressure, due to the increased active surface area and optimal nitrogen doping levels. Overall, this study showed a simple method to produce highly controllable nitrogen doping in different sites within TiO2 showing improved visible light photoactivity and photo induced pollutant degradation. More interestingly, by investigating the effect of different nitrogen sites in nitrogen doped TiO2, we have shown that the optimized conditions for photocatalysis do not correspond to those for water splitting.

Effect of Nitrogen Doping on Optical and Photocatalytic Properties of TiO2 Thin Film Prepared by Spin Coating Process

Nitrogen-doped TiO2 thin films were prepared by spin coating on glass substrate. Different amount of nitrogen doped in TiO2 matrix was 0, 3 and 10%. As-obtained films were annealed at 400°C for 2h. The optical and photocatalytic properties of N-doped TiO2 thin films were analyzed via UV-Vis spectrophotometry. The chemical properties were investigated by Fourier transform infrared spectrometer and Raman spectroscopy. When doping TiO2 with nitrogen, its absorption spectrum is shifted to visible region resulting to the enhancement of photocatalyst properties in dye photodegradation. Raman and FTIR patterns show that N-doped TiO2 pattern is still identical to undoped TiO2 pattern resulting to unsubstitutation of nitrogen atom in Ti-O bonding.

Photoelectrochemical degradation of azo dye over pulsed laser deposited nitrogen-doped TiO2 thin film

We investigated the synergetic effect of electrochemical and photocatalytic oxidation in photoelectrochemical (PEC) process for the degradation of hazardous organic compounds exemplified by methyl orange, an azo dye. Nitrogen doped TiO2 thin film (NTTF) synthesized by the pulsed laser deposition (PLD) method, was used as the working anode. The crystalline, optical properties, surface morphology, and structure of the NTTF were characterized by XRD, UV–vis absorbance edges, SEM, and XPS. Results showed that the NTTF was dominated by anatase phase after sintered at 600°C with significant visible light response at 595nm. XPS analyses indicated nitrogen doping was mainly responsible for reducing the band gap as evidence of 3% N doping into the structure via the linkage of TiON and NTiO bond. SEM images illustrated the nitrogen-doped TiO2 nanoparticles being attached firmly and spread evenly over the ITO glass surface, which is beneficial for PEC applications. The degradation efficiency of MO by photoelectrochemical, photocatalytic, electrochemical and photolysis methods were compared in terms of pseudo-first-order reaction rate. PEC was the most efficient in degrading MO at a bias potential of 2.0V (vs. SCE) under light at a wavelength of 325nm, which was consistent with results of IPCE (%) measurements. The synergetic effect was quantified at current/bias potential of 0.07mA/0.3V and 0.6mA/2.0V, respectively. Results demonstrated that the bias potential could separate photogenerated holes and electrons effectively and enhance the electrochemical-oxidation of MO. The mechanistic aspects of MO degradation by the PEC process were discussed.

Concurrent photoelectrochemical reduction of CO2 and oxidation of methyl orange using nitrogen-doped TiO2

This study employed a novel material, nitrogen-doped TiO2 thin film (NTTF), as a photoanode for the concurrent photoeletrochemical (PEC) reduction of CO2 and oxidation of methyl Orange (MO). Under illumination, the onset potential of the total current was approximately 1.5V (vs. SCE) and the maximum total current was around 0.65mA at 2V (vs. SCE). The photocurrent can be effectively driven to the counter electrode at this positive potential, which will decrease the recombination of photo-generated holes and electrons, leading to more electrons available for CO2 reduction in the cathodic chamber and more holes for the oxidation of hazardous chemicals in the anodic chamber simultaneously. Formic acid, formaldehyde, methanol and methane were detected as the CO2 reduction products at a Cu electrode in the KHCO3 electrolyte. The first-order kinetic model was successfully applied to simulate the NTTF PEC reduction of CO2. The reaction rate constant were 6.68×10−7, 2.18×10−4, 8.62×10−4 and 2.27×10−4s−1, for the formation of formic acid, formaldehyde, methanol, and methane, respectively. The maximum Faradaic efficiency was 5.01, 1.04, 5.41 and 7.83% for the generation of formic acid, formaldehyde, methanol, and methane, individually. In addition, the effect of initial CO2 concentration on CO2 reduction was also conducted in the presence of methanol (0, 20 and 40%). Results showed that methanol-containing electrolyte enhanced CO2 solubility thereby suppressing hydrogen generation and favoring CO2 reduction. Finally, the degradation of methyl orange was compared using PEC, photocatalytic (PC), electrochemical (EC) and direct photolysis (P) processes. The PEC process was able to achieve a 10-log versus less than 1-log of methyl orange degradation by all other methods studied within 60min under otherwise similar conditions of pH, temperature, intensity and wavelength of light source. Results clearly demonstrated the potential of a sustainable technology for the concurrent reduction of CO2 and oxidation of hazardous chemicals by the PEC process using solar energy.

Preparation and photocatalytic properties of nanometer TiO2 thin films by improved ultrasonic spray pyrolysis

The nitrogen-doped TiO2 thin films were prepared on glass substrate by an improved ultrasonic spray pyrolysis device with butyl titanate as the titanium source and ammonia as the nitrogen source. The surface morphology, crystal structure and optical properties of the resulting films were characterized by SEM, XRD and UV-VIS spectroscopy, respectively. The results show that N-doped TiO2 films have a more uniform and compact surface, the particle size trends to become smaller and then larger with the increasing amount of doping nitrogen. All the thin films belong to polycrystalline anatase structure and have a well visible light responsiveness with N doped. The photocatalytic activity and hydrophilic properties were investigated under ultraviolet irradiation. The degradation rate for methylene blue solution can reach 94.0% after 3 h under ultraviolet irradiation. The hydrophilic test shows that the hydrophilicity of TiO2 thin films can be improved by doping nitrogen to some extent.

Nitrogen-doped TiO2 films as drug-binding matrices for the preparation of drug-eluting stents

Nitrogen doped-TiO2 thin film was deposited by plasma enhanced chemical vapour deposition (PECVD) process and its applicability as a drug-binding matrix was investigated in the preparation of drug eluting stents. N–TiO2 film was deposited at 5 W and uniformly covered metallic stent surfaces. Films showed excellent mechanical stability and good adhesion. Alpha lipoic acid, heparin, and abciximab could then be grafted onto the N–TiO2 film through ester bond formation after water plasma modification of the films' surfaces. Drug-grafted N–TiO2 films showed smooth surfaces and good blood compatibility in in vitro platelet adhesion tests. The films maintained uniform coverings, without peeling, even after expansion by a balloon catheter. Grafted-heparin and abciximab could be released continuously for three weeks from drug-grafted N–TiO2 stents in in vitro drug release test. Such immunosuppressive and antiproliferative drug-grafted N–TiO2 film is expected to minimize potential problems related to organic polymers and the risk of direct contact of a bare metal surface with a blood vessel. Hence, the N–TiO2 films prepared in this study are promising alternatives to organic polymers for the preparation of drug-eluting stents.

A Comparative Study on the Photocatalytic and Gas Sensing Properties of Pure and N‐doped TiO2 thin Films

AbstractA correlation between the photocatalytic efficiency and gas sensitivity has been attempted on pure and N‐doped TiO2 thin films prepared by pulsed DC magnetron sputtering. The physical properties are studied. The gas sensing behavior in pure and nitrogen doped TiO2 thin films could be realized at low temperature. The measurements start at 130 °C. The nitrogen doped TiO2 (3 sccm) has no sensitivity for oxygen. All sensors have sensitivity to hydrogen. If the temperature is increased the sensitivity is increased. All samples show photocatalytic activity. The photocatalytic and gas sensing properties have no significant correlations.

The Visible Photocatalysis Properties of Nitrogen-doped TiO2 Thin Film

Titanium oxide films with different amounts of nitrogen doping have been deposited by the DC magnetron sputtering technique. The characteristics of the TiO2 films, such as crystal structures, chemical compositions, analyses, surface morphologies and photocatalyst effects were examined. The anatase phase of pure titanium oxide was observed to be deposited on the Al substrate at 250°C, while the mixed phase of anatase and rutile appeared as the temperature was increased to 350°C. The intensity of the anatase phase (101) was enhanced after nitrogen-doping the TiO2 films. A daylight lamp was used as the visible light source to analyze the IPA decomposition reaction on the surface of the TiO2 films. The nitrogen doped TiO2 films had good photocatalyst properties and followed the first-order kinetic model regarding decomposition of IPA. The apparent first-order rate constant of the TiO2 films with nitrogen doping was about 2.6 times larger than that of undoped TiO2 films. The results show that nitrogen doped TiO2 films can be active under visible light radiation.