n-TiO2 Thin Films Research Articles

Multiphysics computational fluid dynamics (CFD) modelling of diclofenac amide removal by photocatalytic oxidation on Fe-TiO2/N-TiO2 thin films microreactor

An improved multiphysics computational fluid dynamics (CFD) model, which couples radiation field modeling, species transport, and kinetics was developed to determine the dark adsorption–desorption (kads,m kads,n, kdes,m, kdes,n) and apparent reaction rate (kapp) constants for the photocatalytic oxidation of diclofenac amide (DCFA) in a recirculating thin-film micro-slit reactor. The photocatalytic oxidation of DCFA under UV irradiation was investigated by changing the initial concentration (Co) (0.73–1.7 ppm) and recirculation flow rate (Q) (0.15–3.73 L h−1). The ratio of estimated adsorption–desorption rate constants by fitting the CFD model to experiments were kads,m/kads,n = 0.45, and kdes,m/kdes,n = 1.5, and kapp varied from 1.08 to 1.68 × 10-3 mmol m-3 h−1(W m−2)-0.5 with Q (0.15–3.73 L h−1). The CFD model unveiled the switch from mass transfer to kinetics-controlled oxidation of DCFA. The proposed CFD model can be employed as a rapid and flexible tool for the determination of intrinsic kinetic constants in photocatalytic thin-film MRs in the reaction kinetics regime.

Integral Algorithms to Evaluate TiO2 and N-TiO2 Thin Films’ Cytocompatibility

Titanium oxide (TiO2) and oxynitride (N-TiO2) coatings can increase nitinol stents' cytocompatibility with endothelial cells. Methods of TiO2 and N-TiO2 sputtering and cytocompatibility assessments vary significantly among different research groups, making it difficult to compare results. The aim of this work was to develop an integral cytocompatibility index (ICI) and a decision tree algorithm (DTA) using the "EA.hy926 cell/TiO2 or N-TiO2 coating" model and to determine the optimal cytocompatible coating. Magnetron sputtering was performed in a reaction gas medium with various N2:O2 ratios and bias voltages. The samples' morphology was studied by scanning electron microscopy (SEM) and Raman spectroscopy. The cytocompatibility of the coatings was evaluated in terms of their cytotoxicity, adhesion, viability, and NO production. The ICI and DTA were developed to assess the cytocompatibility of the samples. Both algorithms demonstrated the best cytocompatibility for the sample sputtered at Ubias = 0 V and a gas ratio of N2:O2 = 2:1, in which the rutile phase dominated. The DTA provided more detailed information about the cytocompatibility, which depended on the sputtering mode, surface morphology, and crystalline phase. The proposed mathematical models relate the cytocompatibility and the studied physical characteristics.

Nanostructured TiO2: Analysis and characterization

Nanostructured TiO2 thin films were deposited on quartz glass at room temperature by sol–gel dip coat-ing method. The effects of annealing temperature between 200◦C to 1100◦C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO2 thin film annealed at between 200◦C to 600◦C was amorphous trans- formed into the anatase phase at 700◦C, and further into rutile phase at 1000◦C. The crystallite size of TiO2 thin films was increased with increasing annealing temperature. From atomic force microscopy images, it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films in- creases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100◦C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO2 thin films were in- creased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO2 thin films were decreased.

Formation and structural features of nitrogen-doped titanium dioxide thin films grown by reactive magnetron sputtering

The structural features of N-doped titanium dioxide (N-TiO2) thin films deposited via reactive magnetron sputtering system with different nitrogen to oxygen ratio are analyzed. Bias voltage was used as a significant parameter involved in the deposition process. Grown films have two-phase structure consisting of anatase and rutile mixture. The analysis of structure and morphology of the films by SEM, TEM, XRD, FTIR and XPS techniques showed the changing of anatase to rutile ratio and grain size reduction in N-TiO2 thin films with increase of nitrogen content in the working gas at simultaneous bias applying. Nitrogen atoms in oxide form are located at the crystallites boundaries and this 2D quasi-layer of NOx species limits the epitaxial growth of TiO2 crystallites during film formation.

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.

Photoelectrocatalytic degradation of Rhodamine B using N doped TiO2 thin Films

Highly transparent Nitrogen doped Titanium dioxide (N-TiO2) thin films are deposited onto glass/FTO substrates at optimized substrate temperature 450°C by using a simple chemical spray pyrolysis technique. The N-TiO2 thin films are characterized for their photoelectrochemical, structural, morphological and optical properties using PEC, XRD, SEM, and UV-Vis. spectrophotometer. The PEC study shows that both short circuit current (Isc) and open circuit voltage (Voc) for the doping concentration at 1.5 at. % are relatively maximum (Isc = 0.72 mA and Voc = 520 mV). X-ray diffraction studies show that films are polycrystalline with a tetragonal crystal structure. The scanning electron micrograph shows that the films are uniform, compact and with randomly distributedgrain size varying from 20 to 60 nm. The observed direct band gapsare about 3.4 and 3.37 eV for typical TiO2 and N-TiO2 thin films respectively.

Influence of annealing on structural and optical properties of n-TiO2 thin films grown by sol-gel spin coating

The influence of thermal annealing to the properties of n-TiO2 thin films fabricated by sol-gel spin coating has been investigated using X-ray diffraction (X-RD) and UV-Vis optical transmittance measurements. TiO2 thin films were prepared by dissolving TiO2 Nano-powders into a solvent of ethanol and it becomes sol-gel. The sol-gel of TiO2 was deposited on indium tin oxide (ITO) substrate. Then, the TiO2 the thin films were inserted into tube furnace for annealing in the temperature range of 3000C to 5000C during 60 minutes. Based on the xray diffraction results, the crystal structure of TiO2 is anatase phase structures. The crystalline size of TiO2 films after annealing at 300°C was 46.6 nm and it slightly decreased to 46.2 nm after annealing at 500°C. The optical transmittance value of TiO2 film increased after annealing in comparison before annealing the TiO2 film.

Nano-wall like visible-light active carbon modified n-TiO2 thin films for efficient photoelectrochemical oxygen separation from water

Efficient photoelectrochemical oxygen separation from water was demonstrated using a nano-wall like carbon modified n-type titanium oxide (CM-n-TiO2) electrode during water splitting reaction. The CM-n-TiO2 electrode was synthesized by flame-oxidation of Ti metal sample. The combustion products of natural gas flame acted as the carbon source. The oxygen separation rate during water splitting was evaluated in terms of anodic photocurrent density, Jp, under solar simulated light illumination of 1 sun. Upon incorporation of carbon within the titanium oxide, the photocurrent density was enhanced to 4.97 mA cm−2 at CM-n-TiO2 electrode compared to 0.66 mA cm−2 at regular of n-TiO2 both at the same measured potential of - 0.6 V/SCE. Such a multiple-fold increase in photocurrent density at CM-n-TiO2 thin film electrode was attributed to its enhanced absorption in the UV region, red-shift to visible region due to carbon incorporation and as well as due to pronounced nano-wall like surface morphology generated under the harsh conditions of flame oxidation. CM-n-TiO2 photoelectrodes were characterized in terms of photocurrent measurements under white light and as well as under monochromatic light illuminations, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), the valence band X-ray photoelectron spectroscopy (XPS) and the AC-impedance measurements.

Heterogeneous photocatalytic degradation of toluene in static environment employing thin films of nitrogen-doped nano-titanium dioxide

Photocatalytic semiconductor thin films have the ability to degrade volatile organic compounds (VOCs) causing numerous health problems. The group of VOCs called “BTEX” is abundant in houses and indoor of automobiles. Anatase phase of TiO2 has a band gap of 3.2 eV and UV radiation is required for photogeneration of electrons and holes in TiO2 particles. This band gap can be decreased significantly when TiO2 is doped with nitrogen (N-TiO2). Dopants like Pd, Cd, and Ag are hazardous to human health but N-doped TiO2 can be used in indoor pollutant remediation. In this research, N-doped TiO2 nano-powder was prepared and characterized using various analytical techniques. N-TiO2 was made in sol–gel method and triethylamine (N(CH2CH3)3) was used as the N-precursor. Modified quartz cell was used to measure the photocatalytic degradation of toluene. N-doped TiO2 nano-powder was illuminated with visible light (xenon lamp 200 W, λ = 330–800 nm, intensity = 1 Sun) to cause the degradation of VOCs present in static air. Photocatalyst was coated on a thin glass plate, using the doctor-blade method, was inserted into a quartz cell containing 2.00 µL of toluene and 35 min was allowed for evaporation/condensation equilibrium and then illuminated for 2 h. Remarkably, the highest value of efficiency 85% was observed in the 1 μm thick N-TiO2 thin film. The kinetics of photocatalytic degradation of toluene by N-TiO2 and P25-TiO2 has been compared. Surface topology was studied by varying the thickness of the N-TiO2 thin films. The surface nanostructures were analysed and studied with atomic force microscopy with various thin film thicknesses.

Influence of silver nanoparticles on titanium oxide and nitrogen doped titanium oxide thin films for sun light photocatalysis

Decreasing recombination of photogenerated charge carriers in photocatalysts is a critical issue for enhancing the efficiency of dye degradation. It is one of the greatest challenges to reduce the recombination of photo generated charge carriers in semiconductor. In this paper, we report that there is an enhancement of photocatalytic activity in presence of Sun light, by introducing Plasmon (silver nanoparticles (Ag)) onto the titanium oxide (TiO2) and nitrogen incorporated titanium oxide (N-TiO2) films. These silver nanoparticles facilitate the charge transport and separation of charge carriers. In this paper we find that the phase transformation accurse from rutile to anatase with increase of nitrogen flow rates. The FE-SEM analysis showed the micro structure changes to dense columnar growth with increase of nitrogen flow rates. XPS studies of the N-TiO2 thin films revealed that the substitution of N atoms within the O sites plays a crucial role in narrowing the band gap of the TiO2. This enables the absorption of visible light radiation and leads to operation of the film as a highly reactive and effective photocatalysis. The synergetic effect of silver nanoparticles on TiO2 and N-TiO2 films tailored the photocatalytic acitivity, charge transfer mechanism, and photocurrent studies. The silver nanoparticle loaded N-TiO2 films showed highest degradation of 95% compare to the N-TiO2 films. The photo degradation rate constant of Ag/N-TiO2 film was larger than the N-TiO2 films.

Structural features of N-containing titanium dioxide thin films deposited by magnetron sputtering

N-containing titanium dioxide (N-TiO2) thin films have been obtained by the midrange magnetron sputtering with two-component N2/O2 reactive working gas. Complex analysis of the films structure and phase composition demonstrates its significant changes due to nitrogen content. X-ray diffraction data show the anatase-rutile phase transition and crystallites size reduction in N-TiO2 thin films with increase of nitrogen content in the reactive atmosphere. The investigation has been focused on phase transition, zeta potential, chemical bonds and UV-light influence on the wettability of the films versus nitrogen concentration. Hydrophilization of N-TiO2 films surface under UV-light has an irreversible character.

Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer

In this work, we investigate the broad-band photoabsorption of an n-TiO2 thin film and its hole-blocking properties when a heterostructure is grown on a chemically textured p-Si substrate. We demonstrate that average specular reflectance of conformally grown TiO2 thin films on chemically prepared pyramidally textured Si substrates can be brought down to ∼0.2% (in the wavelength range of 300–1200nm), which increases up to ∼0.53% after annealing at 673K in air for 1h. X-ray diffraction data reveal the amorphous nature of as-grown TiO2 thin films which undergoes a transition to a crystalline one after annealing. In addition, bulk current-voltage characteristics show that the leakage current increases after annealing which corroborates well a with change in the band gap, as is measured from the optical absorption spectra, due to a transition from amorphous to crystalline (anatase phase) of TiO2. Moreover, TiO2/Si heterojunction allows the transport of electrons but blocks the transport of holes. The present results are not only important for the fundamental understanding of the charge transport across TiO2/Si heterostructures but also to design hole-blocking solar cells.

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.

Electrical and Ultraviolet-A Detection Properties of E-Beam Evaporated n-TiO2 Capped p-Si Nanowires Heterojunction Photodiodes

Fabrication and Ultraviolet (UV) detection properties of p-Si Nanowires (NWs)/n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film-based heterojunction photodiodes have been reported in this paper. The highly oriented, uniform and vertically aligned p-type single crystalline silicon nanowire (SiNW) arrays have been synthesized by the two-step process of electroless metal deposition and etching technique. A thin layer (~120 nm) of anatase phase titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is then deposited on the top of p-SiNWs using electron-beam evaporation technique. The surface morphology and crystallinity of p-SiNWs and n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> capped SiNWs have been characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The optical properties of the as-deposited n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film grown on p-SiNWs were analyzed using the photoluminescence measurements. The UV detection properties of the p-SiNWs/n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> heterojunction was studied by measuring the room temperature current-voltage (I - V ) characteristics under dark and UV illumination conditions with incident optical power(P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> ) ≈ 650 μW at wavelength (λ) ≈ 365 nm. The as-fabricated p-SiNWs/n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film heterojunction photodiode showed an excellent value of Detectivity ~ 8.66 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> mHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the external quantum efficiency (EQE) ~ 79.33%, responsivity~ 0.234 A/W, and contrast ratio ~ 113.82 at -11 V bias. Other parameters such as rectification ratio (~ 519.82), Turn-on voltage (~0.732 V) and effective barrier height (~0.7924 eV) under dark condition were also calculated. The proposed p-SiNWs/n-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) thin film hetrojunction can thus be explored for UV-A detection.detection.

Role of Junction Geometry in Determining the Rectification Performance of Nanostructured TiO&lt;sub&gt;2&lt;/sub&gt;-Based p-n Junctions

This paper reports on the influence of junction geometry on the determination of the rectification performance of nanostructured titanium dioxide (TiO2)-based p-n homojunctions. Two types of p-n junction devices with different junction area/geometry were fabricated. Sol–gel grown undoped TiO2 nanoparticle layer was employed as the p-type side in both the cases. Electrochemically grown TiO2 nanotube array was used as the n-type side in one junction, while thermally grown n-TiO2 thin film was used in another. It was found that, due to unique advantage of excessively large junction area, p-TiO2/n-TiO2 nanotube device offered a dramatically improved ideality factor (4) and a rectification factor (1093) compared with its p-TiO2/n-TiO2 (thermally grown) counterpart (17 and 34, respectively). The 2-D distribution probability of the depletion region in the case of the first device was empirically correlated with the experimental findings and was supported by the corresponding $C$ – $V$ measurement results.

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.

Effect of Cathodic Polarization of n-TiO2 Thin Films on Their Photoresponse towards Water Splitting Reactions

Cathodic reduction of Titanium oxide (n-TiO_2) thin films was investigated as an alternative approach to customary hydrogen modification of n-TiO_2 under hydrogen gas stream at high temperature. Hydrogen modification of n-TiO_2 was carried out electrochemically under cathodic polarization. The photo-response of the electrochemically hydrogen modified n-TiO_2 (HM-n-TiO_2) exhibited a four-fold enhancement in their photoresponse compared to n-TiO_2 during water splitting under solar simulated light. The photoactivity of HM-n-TiO_2 suffers a substantial decrease after heat-treatment at 200°C, remarkably the photoactivity of these samples was fully repaired after re-hydrogenation under similar conditions. The electrodes were characterized using electrochemical and spectroscopic techniques.

Fabrication and photovoltaic characteristics of Cu2O/TiO2 thin film heterojunction solar cell

A p-Cu2O/n-TiO2 thin film heterojunction solar cell has been fabricated by electrodeposition of Cu2O on radio-frequency sputtered n-TiO2 thin film. The heterojunction solar cell was characterized by X-ray diffraction, scanning electron microscopy and UV spectroscopy. Capacitance–voltage (C–V) and current–voltage measurements were performed. The values of barrier height and carrier concentration were estimated from the reverse bias C–V. The transport mechanism is related to space charge limited current and a trapped charge limited current having slope values of 1.95 and 3.5. Impedance measurement showed that electrical resistance decreases when the voltage is increased. The energy band diagram shows that the main-band discontinuity forms in the valence band. The ideality factor, barrier height and series resistance, fill factor and efficiency were also measured. The heterojunction solar cell exhibits a maximum fill factor and a power conversion efficiency of about 0.35 and 0.15% respectively.

Phase transformation of nanostructured titanium dioxide thin films grown by sol–gel method

Nanostructured TiO2 thin films were deposited on quartz glass at room temperature by sol–gel dip coating method. The effects of annealing temperature between 200∘C to 1100∘C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO2 thin film annealed at between 200∘C to 600∘C was amorphous transformed into the anatase phase at 700∘C, and further into rutile phase at 1000∘C. The crystallite size of TiO2 thin films was increased with increasing annealing temperature. From atomic force microscopy images it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films increases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100∘C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO2 thin films were increased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO2 thin films were decreased.

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.