N-doped Titania Research Articles

Photocatalytic Degradation of Phenolics by N-Doped Mesoporous Titania under Solar Radiation

In this study, nitrogen-doped mesoporous titania was synthesized by templating method using chitosan. This biopolymer chitosan plays the dual role of acting as a template (which imparts mesoporosity) and precursor for nitrogen. BET-SA, XRD, UV-DRS, SEM, and FTIR were used to characterize the photocatalyst. The doping of nitrogen into TiO2lattice and its state was substantiated and measured by XPS. The photocatalytic activity of the prepared N-doped mesoporous titania for phenol ando-chlorophenol degradation was investigated under solar and artificial radiation. The rate of photocatalytic degradation was observed to be higher foro-chlorophenol than that of phenol. The photodegradation ofo-chlorophenol was 98.62% and 72.2%, while in case of phenol, degradation to the tune of 69.25% and 30.58% was achieved in solar and artificial radiation. The effect of various operating parameters, namely, catalyst loading, pH, initial concentration and the effect of coexisting ions on the rate of photocatalytic degradation were studied in detail.

Electrical and Proton Conduction Properties of Amorphous TiO2 Nanotubes Fabricated by Electrochemical Anodization

Electrolyte contacts were used to investigate the properties of pure and N-doped titania nanotubes (ntTiO2). Mott-Schottky analysis gave a flat-band potential Efb = -0.57V vs. Ag/AgCl for pure ntTiO2 and Efb = -0.22V vs. Ag/AgCl for N-doped ntTiO2. The charge carrier density was ND = 6.7 1020 cm-3 for pure ntTiO2 and ND = 3.9 1020 for N-doped ntTiO2. This investigation also allowed estimation of the apparent diffusion coefficient of H+ in ntTiO2. Following the Randles-Sevcik method, the effective proton diffusion coefficient in ntTiO2 is (2±1)•10-11 cm2s-1 while in N-doped ntTiO2 it is (4±1)•10-11 cm2s-1. Using the Warburg diffusion element determined by electrochemical impedance spectroscopy, the proton diffusion coefficient is (2±1)•10-11 cm2 s-1 for pure ntTiO2 while for nitrogen-doped ntTiO2 a value of (7±3)•10-11 cm2 s-1 is found. These values are consistent with those of the Randles-Sevcik method.

N-doped anodic titania nanotube arrays for hydrogen production

Titanium dioxide (TiO2) nanotube arrays are grown in a mixed electrolyte by anodizing process. The anodic nanotubes for N-doping were calcinated at 773 K in a tube furnace with a mixture of NH3 and Ar gas. The photocatalytic activity of N-doped TiO2 nanotubes was carried out in a water-splitting reaction under UV and visible light irradiation. Various characterization techniques (Scanning electron microscopy, X-ray diffractometry, X-ray photo-electron spectroscopy, etc.) are used to study the surface morphology, phase of structure, and binding energy.

Electronic Structure of Pure and N-Doped TiO2 Nanocrystals by Electrochemical Experiments and First Principles Calculations

Optical and electrochemical characterizations are carried out in conjunction with first-principles calculations on pure and N-doped titania nanocrystals. These are prepared in laboratory with initial doping concentrations of triethylamine in the range of 0.1−0.5 N/Ti molar ratio. Diffuse reflectance UV−vis spectra of N-doped samples present a significant absorption in the visible region. The flatband potential (Efb) of pure and nitrogen-doped TiO2 (−0.6 ± 0.2 V vs NHE) is determined by impedance spectroscopy (Mott−Schottky plots) and the quasi-Fermi level, nEF* (−0.67V vs NHE) by photovoltage measurements as a function of the suspension pH in the presence of an electrochemical probe (methylviologen, MV2+). Theoretical density of electronic states calculations, where several N doping versus vacancy combinations are taken into consideration, together with the optical and electrochemical experiments allow us to draw a detailed picture of the electronic features of the doped samples.

Photocatalytic Degradation of Reactive Green KE-4BD in Aqueous Solutions over N-Doped Titania

The photodegradation of reactive green KE-4BD solution is investigated using N-doped titania (N-TiO2) under visible light irradiation. N-TiO2 is prepared using ammonia or urea as a nitrogen source and characterized by X-ray diffraction, Brunauer-Emmett-Teller methods, and UV-visible diffuse reflectance spectra. The effects of the initial dye concentration and pH on photocatalytic degradation are studied, and the direct correlation between pH, dye concentration, and the rate of degradation are determined. Experimental results show that aqueous solutions of KE-4BD degrade easily in weakly acidic conditions in the presence of N-doped TiO2 (1 g/L) as a photocatalyst. The optimized dye concentration for photolysis is 150 mg/L. The complete degradation of KE-4BD could be achieved under visible light irradiation, and the dye molecules could be partly decomposed into inorganic substances.

Visible light photocatalysts—N-doped TiO2 by sol–gel, enhanced with surface bound silver nanoparticle islands

Antimicrobial thin film photocatalysts consisting of N-doped titania have been prepared by sol–gel methods and further enhanced using silver nanoparticles formed in situ on the surface of the films. The films have been characterised using XRD, SEM, XPS, UV-Visible spectroscopy and functionally tested using measurements for the photoinduced superhydrophilicity, stearic acid destruction and anti-microbial measurements using both E. coli and an epidemic strain of MRSA, EMRSA-16. The N-doped TiO2 films were seen to have interstitially doped nitrogen with the N 1s peak appearing at 400.0 eV in the XPS and as such showed good photocatalytic activity under white light. The photoactivity was then further enhanced by silver nanoparticle formations on the surface. The highly active photocatalytic films were seen to be effective agents against both bacteria and stearic acid using a white light source that is commonly found in UK hospitals.

Influence of the Nitrogen Concentration on the Photoinduced Hydrophilicity of N-doped Titanium Dioxide Thin Films Deposited by Plasma Sputtering

This work reports the influence of the nitrogen concentration (in the gas discharge) on the hydrophilicity properties of N-TiO2 thin films, deposited at low temperature using DC magnetron sputtering on p-Si [100] substrates at different nitrogen flow rates for a fixed electrical power and working pressure. The photoinduced hydrophilicity effect was evaluated by the surface wettability measured through the contact angle between de-ionized water drop and the film surface. Results show that the photoinduced hydrophilicity effect occurs preferentially in thin films with surfaces more irregular and predominantly anatase [101] crystalline orientation. Moreover, further observed phenomena were analyzed, investigated and discussed.

Photocatalytic degradation of C.I. Reactive Blue 19 with nitrogen-doped TiO 2 catalysts thin films under UV/visible light

Nitrogen-doped titania semiconductor thin films, with photocatalytic properties and a high transmittance in the visible range, have been deposited by unbalanced reactive magnetron sputtering on glass substrates, using d.c. pulsed power supplies. In order to increase the photocatalytic efficiency of the titania coatings the authors optimized the sputtering process, namely by using d.c. pulsed currents for better optimization of reactive gas consumption, and doped the coatings with nitrogen. With this combined and synergistic effect it was possible to enhance the catalysts absorption of visible light, by reducing its semiconductor indirect band-gap. By slightly doping the titania films with 0.7–0.9 at.% nitrogen the photocatalytic performance is ameliorated with almost one order of magnitude. This has been achieved by using nitrogen as a co-reactive gas, together with oxygen, when sputtering from a pure titanium target. The as-deposited thin films on glass are mostly amorphous; however, upon a thermal annealing in vacuum at 500 °C, the crystalline phases of anatase and rutile are developed, being anatase the most prominent polymorph. The photocatalytic performance of the N-doped titania films was evaluated by the decomposition of an organic dye (C.I. Reactive Blue 19) with combined UV/visible light irradiation. Furthermore, a mechanism for the degradation of this dye is proposed. The hydrophilic properties of these films have also been studied by means of water contact angle measurements after varied illumination periods; a minimum contact angle of ∼10° was achieved for optimized wettability conditions.

Comparison of the Photocatalytic Activity of N-Doped, P-Doped Titania under Solar Light Irradiation

P-, N-doped titania were synthesized by the direct hydrothermal method, which phosphorus from phosphoric acid and the following nitridation from urea solution. The resulting materials were characterized by XRD, XPS analysis, and their photocatalytic activities were tested by the solar light irradiation. N-doping titania resulted in the band-gap narrowing with improved photocatalytic activity. However, the phosphated titania exhibited higher photocatalytic activity than the N-doped one, but with larger band-gap energy.

Preparation and optical properties of TiO2−x N x /Ni0.5Zn0.5Fe2O4 core–shell nanocatalyst from sol–gel-hydrothermal process

A nitrogen doped TiO2/Ni0.5Zn0.5Fe2O4 core–shell structure nanoparticles was prepared by low temperature sol–gel-hydrothermal process. The characterizations of the catalyst indicate that the Ni0.5Zn0.5Fe2O4 nanocrystals of about 25 nm are well-coated with crystalline N-doped titania. The absorption edges in the diffusion reflectance spectra of TiO0.98N1.02 and TiO1.37N0.63/Ni0.5Zn0.5Fe2O4 shift to visible light region. The core–shell nanocatalysts can effectively photodegrade organic pollutants in the dispersion system and can be recycled easily by an external magnetic field.

N-doped ZrO2/TiO2 bimetallic materials synthesized in supercritical CO2: Morphology and photocatalytic activity

A series of N- and N/Zr-doped titanium nanomaterials were synthesized via an acetic acid modified sol–gel route using supercritical carbon dioxide (scCO2) as both the synthesis and drying medium. Titanium isopropoxide (TIP), and triethylamine (TEA) w/wo zirconium propoxide precursors were reacted with acetic acid in a polycondensation reaction in scCO2. The effects of N and N/Zr doping on the morphology, phase structure, mean crystallite size, textural properties, thermal and crystallization behavior, and photocatalytic degradation of methylene blue was investigated. SEM and TEM analysis showed that pure titania formed nanofibers from TIP and acetic acid whereas the doped samples gave a flake-like structure. The SEM and TEM images showed that a porous material consisting of ca. 10–15nm crystals were formed. XPS spectra indicated that the N1s peak for both N-doped titania and Ti–Zr binary metal oxide were centered at 400eV, indicating effective doping of nitrogen in the TiO2 matrix. From the XRD analysis, it was observed that a small amount of nitrogen and zirconia inhibited the crystal growth, resulting in smaller crystallite materials. The BET analysis of the N2 isotherm data revealed that small amount of zirconia and nitrogen (0.4at%) increased the surface area. All synthesized doped samples gave superior photocatalytic degradation of methylene blue compared to P25. These results show that scCO2 is a new promising route to provide N- and N/Zr-doped advanced photocatalytic nanomaterials.

Preparation and Visible Light Photocatalytic Activity of N-Doped Titania

N-doped titania powders were prepared with titanium tetraisopropoxide (TTIP) as the titanium source and urea as the nitrogen source by the sol-gel method. The samples were characterized using X-ray diffraction (XRD), diffuse reflectance spectrum (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The XRD and TEM results indicated that urea played an important role in controlling the size and aggregation process of titania nanoparticles. As an appropriate amount of urea was added into the titania sol, the size of the particles decreased. However, the excess urea reduced the dispersion of the particles and resulted in the aggregation. At the same time, the size of particle increased, and the size distribution broadened. The XPS and DRS results showed that the nitrogen was incorporated into titania lattice successfully, which brought about the redshift of the absorption edge and induced the photocatalytic activity in the visible light region. The photocatalytic experiments showed that the N-doped titania nanoparticles could effectively photodegrade methyl orange (MO) aqueous solution under visible light irradiation. The photocatalytic activity increased with the increase of the nitrogen doping level in the titania lattice, but decreased with the increase of the particle size and the organic surface residues caused by excess urea.

Photocatalytic degradation of selected herbicides in aqueous suspensions of doped titania under visible light irradiation

The aim of this work was to study the efficiency of Fe- and N-doped titania suspensions in the photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop, MCPP), (4-chloro-2-methylphenoxy)acetic acid (MCPA), and 3,6-dichloropyridine-2-carboxylic acid (clopyralid, CP) under the visible light ( λ ≥ 400 nm) irradiation. The obtained results were compared with those of the corresponding undoped TiO 2 (rutile/anatase) and of the most frequently used TiO 2 Degussa P25. Computational modeling procedures were used to optimize geometry and molecular electrostatic potentials of MCPP, MCPA and CP and discuss the obtained results. The results indicate that the efficiency of photocatalytic degradation is greatly influenced by the molecular structure of the compound. Lowering of the band gap of titanium dioxide by doping is not always favorable for increasing photocatalytic efficiency of degradation.

N-Doped Photocatalytic Titania Thin Films on Active Polymer Substrates

Active polymer substrates have found their way in the semiconductor industry as a base layer for flexible electronics, as well as in sensor and actuator applications. The optimum performance of these systems may be affected by dirt adsorbed on its surface, which can also originate mechanisms for the degradation of the polymer. Titanium dioxide (titania) semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron sputtering on one of the most applied and investigated electroactive polymer: poly(vinilidene fluoride), PVDF. In order to increase the photocatalytic efficiency of the titania coatings, a reduction of the semiconductor band-gap has been attempted by using a nitrogen doping. Rutherford Backscattering Spectroscopy was used in order to assess the composition of the titania thin films, whereas Heavy Ion Elastic Recoil Detection Analysis provided the evaluation of the doping level of nitrogen. X-ray Photoelectron Spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The photocatalytic performance of the titania films have been characterized by decomposing an organic dye illuminated with combined UV/visible light.

Nanoparticle Route for the Preparation in Aqueous Medium of Mesoporous TiO2 with Controlled Porosity and Crystalline Framework

Mesoporous TiO2 with tunable pore size and mono-, bi-, and tricrystalline frameworks was prepared from titania nanoparticles synthesized by a sol−gel method. The synthesis was performed by using an amphiphilic triblock copolymer, Pluronic F127, as a structure-directing agent and titanium isopropoxide as a precursor. The structure-directing agent was added in a presynthesized colloidal suspension composed of bicrystalline titania nanoparticles dispersed in an aqueous medium. By varying the ratio between the number of ethoxy units and the number of titanium atoms (EO/Ti), mesoporous TiO2 materials with controlled pore size were synthesized. Materials were characterized by TG/DTA, XRD, SEM, TEM, and N2 adsorption−desorption analysis. In the absence of copolymer, the porosity was low, indicating efficiently packed TiO2 nanoparticles. As the EO/Ti ratio was increased, the average pore size and the specific surface area became larger, whereas the crystallite size of anatase and brookite became smaller. The addition of copolymer induced the enrichment of the brookite polymorph, prevented particle growth, and delayed the formation of rutile. Bimodal (mesoporous−macroporous) N-doped titania with a pure anatase framework was obtained by using diethanolamine (DEA) as the source of nitrogen.

Superhydrophilicity-assisted preparation of transparent and visible light activated N-doped titania film

A novel and environmental friendly method was developed to prepare transparent, uniform, crack-free and visible light activated nitrogen doped (N-doped) titania thin films without the use of organic Ti precursors and organic solvents. The N-doped titania films were prepared from heating aqueous peroxotitanate thin films deposited uniformly on superhydrophilic uncoated glass substrates. The pure glass substrates were superhydrophilic after being heated at 500 degrees C for 1 h. Nitrogen concentrations in the titania films were adjusted by changing the amount of ammonia solution. The optimal photocatalytic activity of the N-doped titania films was about 14 times higher than that of a commercial self-cleaning glass under the same visible light illumination. The current reported preparative technique is generally applicable for the preparation of other thin films.

Continuous one-step synthesis of N-doped titania under supercritical and subcritical water conditions for photocatalytic reaction under visible light

N-doped titania was prepared continuously by one-step synthetic method under supercritical and subcritical water conditions using titanium(IV)tetraisopropoxide (TTIP) and nitric acid as a titania precursor and nitrogen source, respectively. The synthesized N-doped titania particles were characterized by XRD, N 2-adsorption, TEM, XPS, UV–vis diffuse reflectance spectroscopy. N-doped titania was successfully synthesized and its crystalline structure was homogenous anatase phase with high surface area. The absorption edge of synthesized N-doped titania shifted into the visible light region compared with commercial titania P25. All synthesized N-doped titania have higher photocatalytic activity than P25 under visible light irradiation. The photocatalytic activity of N-doped titania synthesized under supercritical water condition was the highest for the degradation of methyl orange under visible light due to the larger crystallite size compared with the N-doped titania synthesized under subcritical water condition.

A one-pot method to prepare N-doped titania hollow spheres with high photocatalytic activity under visible light

N-doped titania hollow spheres (NTHS) were prepared by a one-pot hydrothermal method using urea as precursor of nitrogen. The prepared hollow spheres were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectrum (DRS). The photocatalytic activity of as-prepared titania hollow spheres was determined by degradation of Reactive Brilliant Red dye X-3B (C.I. reactive red 2) under visible light irradiation, and was compared to non-doped titania hollow spheres and commercial P25 titania. Results indicated that the as-prepared NTHS showed highest photocatalytic activity.

N-doped Titania Thin Films, Prepared by Atmospheric Pressure Chemical Vapour Deposition: Enhanced Visible Light Photocatalytic Activity and Anti-microbial Effects

Titanium dioxide (TiO2) films have been highly commercialized as photocatalyst coatings with applications in technologies such as self-cleaning glass. There is however interest in developing superior coatings that operate under domestic lighting conditions for cleaning and anti-microbial applications in healthcare environments. One such approach to improve on TiO2 is to shift the band-gap from UV into the visible region of the spectrum, thus harvesting a greater proportion of solar energy and allowing the films to work under indoor-lighting conditions. This paper shows an example of the selective doping of TiO2 with beneficial results in the quest for visible light photocatalyst with anti-microbial properties.

Enhanced photocatalytic activity under visible light in N-doped TiO 2 thin films produced by APCVD preparations using t-butylamine as a nitrogen source and their potential for antibacterial films

Atmospheric pressure chemical vapour deposition (APCVD) of N-doped titania thin films has been achieved from titanium (IV) chloride, ethyl acetate and t-butylamine at a deposition temperature of 500 °C and the films characterised by XRD, Raman spectroscopy, XPS, SEM, UV–visible–NIR spectroscopy, contact angle measurements and stearic acid degradation. The films were compared to two industrial self-cleaning products: Activ™ and BIOCLEAN™ and shown to be significantly better in both photocatalysis and superhydrophilicity, two preferential properties of effective self-cleaning coatings. X-ray diffraction showed the films have the anatase TiO 2 structure. High resolution X-ray photoelectron spectroscopy was consistent with small quantities of nitrogen (0.15–0.7 at.%) occupying an interstitial site (N 1s ionisation at ∼400 eV). This work sheds light on the current confusion within the literature as to the role of nitrogen in the enhancement of the photocatalytic properties of thin films with direct evidence that selective doping at the interstitial site (ionisation ∼400 eV by XPS) has a pronounced effect on enhancing photocatalysis. Surprisingly in the majority of films no XPS peak for N for O substitution was observed (ionisation ∼396 eV by XPS). This is to our knowledge the first example of an N-doped titania film with only interstitial doping. These films showed significant photocatalysis with visible light. The best films were tested for their antimicrobial properties and found to be an effective agent for the destruction of Escherichia coli using lighting conditions commonly found in UK hospitals.