Co-doped TiO2 Thin Films Research Articles

Structural, Morphological, Optical and Photocatalytic Properties of Y, N-Doped and Codoped TiO2 Thin Films

Pure TiO2, Y-N single-doped and codoped TiO2 powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state diffuse reflectance absorption and scanning electron microscopy (SEM). According to the GXRD patterns and micro-Raman spectra, only the anatase form of TiO2 was made evident. Ground state diffuse reflectance absorption studies showed that doping with N or codoping with N and Y led to an increase of the band gap. Laser induced luminescence analysis revealed a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic activity of supported catalysts, toward the degradation of toluidine, revealed a meaningful enhancement upon codoping samples at a level of 2% (atomic ratio). The photocatalytic activity of the material and its reactivity can be attributed to a reduced, but significant, direct photoexcitation of the semiconductor by the halogen lamp, together with a charge-transfer-complex mechanism, or with the formation of surface oxygen vacancies by the N dopant atoms.

Structural and wettability investigation of titanium dioxide coating: influence of dopant concentration (Si and Sr)

In this study, different samples of Si and Sr co-doped TiO2 thin films (5 mol% Si and 5-10-15-20 mol% Sr) were prepared via simple sol–gel synthesis method by using strontium acetate as strontium precursor, tetraethoxysilane as silicon precursor, and titanium (IV) isopropoxide (TTIP) as titanium precursor. The effects of co-doping process on the structural, optical, and wettability properties of thin films were studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and contact angle measurement. XRD results showed that, the anatase phase formation was promoted by Si+4 and Sr+2 co-doped TiO2 samples at higher percentage of Sr.Accordingly, the titania thin films showed various water contact angles, the water contact angles first decreased from 55.1° to 8.1° then increased to 40.7° by changing the content of Sr dopant from 5 to15 mol% and then to 20% mol.

N and F Codoped TiO2 Thin Films on Stainless Steel for Photoelectrocatalytic Removal of Cyanide Ions in Aqueous Solutions

N-F codoped TiO2 films were immobilized on stainless steel sheets through a combined approach involving a dip-coating technique and a hydrothermal treatment, followed by calcination at 400°C in the presence of air. Photocatalyst characterization was conducted using XRD, Raman and UV-VIS spectroscopy as well as SEM. The films were tested in a three-electrode cell for the photoelectrocatalytic degradation of CN-containing compounds. The results showed that the increase in the degradation rate of CN-containing compounds is both influenced by a synergistic effect of the doping agents and strongly dependent on the concentration of CN-containing compounds in the solution. Nitrogen contributed to the enhanced photoactivity under visible light due to the generation of localized states within the band gap of TiO2, whereas the presence of fluoride improved the superficial properties of the film, which resulted in higher amounts of CN-containing compounds that were degraded by direct charge transfer through the photogenerated holes.

Enhanced optical and hydrophilic properties of Si and Cd co-doped TiO2 thin films

In this study, preparation of Si and Cd co doped (5 mol% Si and 5–20 mol% Cd) TiO2 dip-coated thin films on glass substrates via sol–gel process have been investigated. The samples were characterized by X-ray diffraction (XRD) and Scanning electron microscopy analysis after heat treatments. XRD results suggested that adding dopants has a great effect on crystallinity and particle size of TiO2. Titania rutile phase formation was inhibited by Si4+ and promoted by Cd2+ doping. But the effect of Cd doped appeared at high concentration. Accordingly, the thin films showed various water contact angles. The water contact angles changed from 69.0° to 9.6° by changing the content of Cd doped.

Effect of Sn and La doping on optical and hydrophilic properties of TiO2 thin film

Sn and La co-doped TiO2 thin films were fabricated on surface of glass slide substrates. Co-doped titania thin films were prepared by a sol gel method using, TBT as a precursor. Morphology and crystallite size of the obtained co-doped thin films changed by changing the content of La. Accordingly, the doped titania thin films showed various water contact angles and optical band gaps. As, the optical band gap of the nanostructured doped titania thin films decreased with increasing in content of La from 3.4 to 2.32 eV. Moreover, the water contact angles changed from 69.0° to 13.5° by changing the content of La.

A Surface Photovoltage Study of Surface Defects on Co-Doped TiO2 Thin Films Deposited by Spray Pyrolysis

Surface photovoltage (SPV) spectroscopy is a powerful tool for studying electronic defects on semiconductor surfaces, at interfaces, and in bulk for a wide range of materials. Undoped and Cobalt-doped TiO2 (CTO) thin films were deposited on Crystalline Silicon (c-Si) and Flourine doped Tin oxide (SnO2:F) substrates by chemical spray pyrolysis at a substrate temperature of 400 °C. The concentration of the Co dopant in the films was determined by Rutherford backscattering spectrometry and ranged between 0 and 4.51 at %. The amplitude of the SPV signals increased proportionately with the amount of Co in the films, which was a result of the enhancement of the slow processes of charge separation and recombination. Photogenerated holes were trapped at the surface, slowing down the time response and relaxation of the samples. The surface states were effectively passivated by a thin In2S3 over-layer sprayed on top of the TiO2 and CTO films.

Comparison of structural, optical, photocatalytic behavior and hydrophilic properties of pure and Sn/La co-doped TiO2 thin films

In this study, a new method to enhance the hydrophilic properties of TiO2 thin films coated on the glass was developed by Sn and La co doped thin films. The effects of Sn (5–20 mol%) and La (5 mol%) co doped on the optical and hydrophilic were investigated. The optical, microstructure and hydrophilic properties of the thin film were studied using differential Uv–Vis spectroscopy, X-ray diffraction, scanning electron microscope and contact angle measurement. After 20 mol% Sn and 5 mol% La doped TiO2 thin film are superhydrophilic with water contact angle less than 19.2°. Also, the optical absorption spectrum indicates that the TiO2 have a direct band gap of 3.15 eV. But optical band gap of the doped TiO2 was found to be 3.0–1.8 eV.

Deposition of Co-doped TiO2 Thin Films by sol-gel method

Cobalt doped TiO2 thin films have been prepared by sol-gel method onto glass substrate at room temperature. in this present work, we are interesting to study the effect of Cobalt doped TiO2 thin films.the concentration of Co was varied from 0 to 6%at .The obtained films have been annealed at 500°C for 2 hours. X-ray diffraction patterns showed that Co: TiO2 films are polycrystalline with a tetragonal anatase and orthorhombic brookite types structures. The surface morphologies of the TiO2 doped with cobalt thin films were evaluated by Atomic Force Microscopy (AFM). The optical properties were studied by mean of UV-visible and near infrared spectroscopy.The calculated optical band gap decreases from 3.30 to 2.96 eV with increasing Co doping.

Photocatalytic degradation of paraquat herbicide in the presence TiO2 nanostructure thin films under visible and sun light irradiation using continuous flow photoreactor

Degradation of paraquat herbicide as a real sample was studied by photocatalytic process using N, S codoped TiO2 thin films. N, S/TiO2 thin films were successfully prepared via sol–gel dip coating method. UV–Vis spectroscopy and chemical oxygen demand (COD) have used for process performance. UV–Vis results indicated that at optimum pH 5.8, maximum decomposition of 84.39% in 5h has occurred under visible irradiation with initial concentration of 10ppm. Based on the COD results, after 8h, a reduction of the COD values from the paraquat of solution was evidently obtained in same condition. Moreover, our results indicated, which nanostructure of N, S/TiO2 thin films are recycled and stable, displaying a good potential of this technique in practical application. The immobilized TiO2 on the glass beads were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and fourier transform infrared (FT-IR).

Reactive pulsed laser deposited N–C codoped TiO2 thin films

TiO2 is a large bandgap chemically stable oxide useful for several applications that involve photo-activated processes, including photocatalysis, photovoltaics, photoelectrolysis, etc. However, the large band gap renders this material not a very efficient absorber of the solar spectrum. Various schemes of cation and anion doping have been utilized that reduce this deficiency to a certain extent. In this paper we present the results of N–C codoping of TiO2 thin films deposited by a reactive pulsed laser deposition technique. These films were compared for their optical and structural properties with undoped, N doped and C doped TiO2 films prepared by the same technique. While all samples contained polycrystalline anatase phase, varying N2 and CH4 partial pressures resulted in change in TiO2 lattice parameters due to codoping. X-ray diffraction high-resolution scans show the evidence of C incorporation into TiO2 lattice by 2θ shift in (101) reflections due to large ionic radius of C. N doping was confirmed by XPS analyses. Direct relationship between oxygen vacancies and doping concentration was established by the deconvolution of XPS peaks. Considerable bandgap reduction occurred that was measured by using UV–vis diffuse reflectance spectroscopy. Results show that reactive pulsed laser deposition is indeed a useful method for the synthesis of codoped TiO2 thin films as bandgap reduction of ~1.00eV via N–C codoping was successfully achieved.

Evolution of structural and magnetic properties of Co-doped TiO2 thin films irradiated with 100 MeV Ag7+ ions

In continuation to our earlier studies where we have shown room temperature ferromagnetism observed in TiO2 and Co-doped TiO2 (CTO) thin films independent of their phase (Mohanty et al 2012 J. Phys. D: Appl. Phys. 45 325301), here the modifications in structure and magnetic properties in CTO thin films using 100 MeV Ag7+ ion irradiation are reported. Owing to the important role of defects in tailoring the magnetic properties of the material, we vary the ion fluence from 5 × 1011 to 1 × 1012 ions cm−2 to create post-deposition defects. While the film deposited under 0.1 mTorr oxygen partial pressure retains its crystallinity showing radiation-resistant behaviour even at a fluence of 1 × 1012 ions cm−2, films deposited under 1 to 300 mTorr oxygen partial pressure becomes almost amorphous at the same fluence. Using Poisson's law, the diameter of the amorphized region surrounding the ion path is calculated to be ∼4.2 nm from the x-ray diffraction peak intensity ((1 1 0) for rutile phase) as a function of ion fluence. The saturation magnetization (Ms) decreases exponentially similar to the decrease in x-ray peak intensity with fluence, indicating magnetic disordered region surrounding the ion path. The diameter of the magnetic disordered region is found to be ∼6.6 nm which is larger than the diameter of the amorphized latent track. Therefore, it is confirmed that swift heavy ion irradiation induces a more significant magnetic disorder than the structural disorder.

The Research of N/C-Codoped TiO<sub>2</sub> Films Deposited by Arc Ion Plating

The N/C co-doped TiO2thin films were successfully deposited on medical glass slide by pulsed negative bias arc ion plating. The influence of pulsed negative bias, annealing temperature on films properties was investigated. Film structure, surface morphologies and optical properties were measured with XRD, SEM and UV-VIS transmittance spectroscope. The results show that the most absorption edges of the as-deposited films increase with the rising of the pulse negative bias, and the maximum of 540 nm is achieved under-600V bias. The films absorption edges increase in different degree after annealing at 400°Cfor 2h and 4h, and the best extension can increase 46nm after annealing. The interaction of the annealing treatment and bias functions enhance the N and C reaction activities and extend absorption edge. The greatest absorption edge dater of the co-doped TiO2films under the negative pulse bias for 0V can reach 550nm after the annealing at 400°Cfor 2h. The crystal morphology become inconspicuously with the bias increasing from 0V to-300V, which is corresponding to the XRD result, the anatase diffraction peaks weaken obviously.

Synthesis and characterization of co-doped TiO2 thin films on glass-ceramic

In this research, an attempt was made to improve TiO2 photo-catalyst properties, thus pure, N–Ce co-doped TiO2 thin films were prepared on glass-ceramic substrate using a sol–gel dip-coating technique. The samples were calcinated in air at 475°C, 550°C, and 650°C for 2h. The result of simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the presence of Ce in TiO2 could inhibit the phase transformation from anatase to rutile and enhance the thermal stability, and anatase was the dominant phase in N–Ce co-doped TiO2 samples. Also based on the results, the doping results in decreasing the size of TiO2 crystallite. The results of ultra violet-visible light diffuse reflectance spectra (UV–vis DRS) presented that cerium doping results in a shift in the absorption spectra of N–Ce co-doped TiO2 to the visible region. The photo-induced hydrophilicity and photo-catalytic activity of the films were evaluated by the water contact angle measurement and photo-catalytic degradation of aqueous methyl orange, respectively. It was found that N–Ce co-doped TiO2 thin films showed a higher photo-catalytic activity, and better photo-induced hydrophilicity than the pure TiO2 thin films. However, too much doping did not improve properties of N–Ce co-doped TiO2. The results of the experiments showed that doping with Ce content of Ce/Ti% equal to 3% and N content of urea/tetra n-butyl ortho titanate equal to 0.25 can improve N, Ce co-doped TiO2 properties.

Magnetic Properties of Co-Doped TiO2 Films Grown on TiN Buffered Silicon Substrates

Co-doped TiO2 thin films are grown on TiN buffered silicon substrates by the pulsed laser deposition method and then hydrogenated. Transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy measurements have shown that the TiN buffer layer can suffer a 400°C deposition temperature and prevent the growth of silicon dioxide on silicon. After that, the room temperature ferromagnetism behaviors are observed in the hydrogenated samples, which are measured by the alternating gradient magnetometer. X-ray photoelectron spectroscopy and x-ray absorption fine structure measurements have revealed the existence of cobalt clusters. According to the material analysis, the magnetic behavior after hydrogenation is suggested to be induced by the enhancement of cobalt clusters.

Realizing high visible-light-induced carriers mobility in TiO2-based photoanodes

Increasing the quantum conversion efficiency in visible-light region is a key issue for the efficient usage of solar energy in the process of photoelectrochemical (PEC) water splitting. Here, based on the N anion and S cation codoped TiO2 thin film photoanodes, we find experimentally and theoretically that the transport ability of visible-light-induced carriers can be notably enhanced by engineering the dopant electronic energy states. The hole transport resistivity is decreased from 6.8 × 104 to 1.3 × 104 Ω m via delocalizing the introduced bands, leading to an evident increase of the internal quantum efficiency from 5% to 20% at the visible-light region of 450–550 nm. Further DFT calculations exhibit that the split of the isolated band is induced by a strong N and S hybridization, which favors to decrease the hole effective mass and to improve the hole mobility by three times. The photocurrent of N − S codoped TiO2 thin film is thus twice that of monodoping cases, the best value for doping modified TiO2 thin film photoanodes. This work may provide not only a design principle but also a candidate for tailoring and optimizing TiO2 towards high PEC activity.

Efficient photocatalytic degradation of organic water pollutants using V–N-codoped TiO2 thin films

TiO2, N-doped TiO2, V-doped TiO2, and V–N-codoped TiO2 thin films have been prepared using RF-magnetron sputtering and their photocatalytic activities have been investigated. The codoping strategy was adopted to decrease both the band gap of TiO2 and the recombination rate of the photo-generated electron–hole pairs. Low concentration doping with single element (V or N) preserves the anatase dominated phase in TiO2 film while codoping with V and N produces a mixed phase of nearly equal amount of rutile and anatase as inferred from the XRD and Raman spectroscopy studies. XPS studies reveal that, for N-doped TiO2 elemental N resides at interstitial lattice positions but codoping with V permits N to reside in both substitutional and interstitial sites in TiO2 lattice. UV–vis studies indicate that the band gap of TiO2 (3.2eV) reduced to 3.0eV, 2.8eV and 2.5eV, by N-doping, V-doping and V–N codoping, respectively. The photocatalytic activity of pure, N-doped, V-doped, and V–N codoped TiO2 thin films were tested by examining the degradation of methylene blue, chlorophenol and nitrophenol as a function of time. It was observed that the codoped TiO2 gave the highest photocatalytic activity in comparison to the mono-doped and undoped TiO2 because of high visible light absorption and possible reduction in the recombination of photo-generated charges. Density of states calculated using density functional theory (DFT) showed that the narrowing of band-gap for the codoped TiO2 is obtained by the formation of isolated energy levels of V 3d and N 2p states below the conduction band and above the valence band of pure TiO2, respectively. While for the mono-doped TiO2 the narrowing of the band gap is only contributed by impurity levels formed near any one of the band edges. It is concluded that for the codoped TiO2, high visible light absorption is caused by the formation of impurity energy states near both the band edges which also act as the trapping sites for both the photo-generated charges to reduce the recombination process.

The role of oxygen pressure in nitrogen and carbon co-doped TiO2 thin films prepared by pulsed laser deposition method

TiO2 absorbs mostly the UV part of the solar spectrum, which results in low efficiency of absorption for visible light applications. Using pulsed laser deposition technique, we introduce defect states in the band gap of TiO2 by co-doping with N and C under different oxygen pressures (4, 50 and 100mTorr) to tune the band gap towards visible region. This process yields anatase–rutile mixed phase films. As control samples, we deposit undoped TiO2 films with the above mentioned oxygen pressures. Several characterization techniques are used to examine thin film properties such as X-ray diffraction for crystal structure, Raman spectroscopy for phase analysis, X-ray photoelectron spectroscopy for electronic structure, scanning electron microscopy for planar and columnar morphology and ultraviolet–visible diffuse reflectance spectroscopy for photo absorption. While undoped TiO2 samples show only anatase phase, N and C co-doped TiO2 samples exhibit transition from rutile to anatase with increasing oxygen pressure. Oxygen pressure also affects the surface morphology and columnar structure of the films such that columnar structure is favored under oxygen-rich conditions. Finally, visible absorption around 550nm was obtained.

Li–Y doped and codoped TiO2 thin films: Enhancement of photocatalytic activity under visible light irradiation

Sol−gel synthesis based on the self-assembling template method has been applied to synthesize Li–Y doped and co-doped TiO2 not only to improve simultaneously the structural and electronic properties of TiO2 nanomaterials but also to achieve Li–Y doping of titania with high photocatalytic reactivity. The characterization of the samples was performed by GXRD, GSDR, FT-IR, and Raman spectroscopy. According to the GXRD patterns, all the observed reflections can be indexed using the anatase form of TiO2, Which is confirmed by ground state diffuse reflectance and micro-Raman spectra. The Li–Y doped titania materials immobilized as nanostructured thin films on glass substrates exhibit high photocatalytic efficiency for the degradation of toluidine and benzoic acid under visible light irradiation. The development of these visible light-activated nanocatalysts has the potential of providing environmentally benign routes for water treatment.

Photoluminescence study of carbon doped and hydrogen co-doped TiO2 thin films

Photoluminescence (PL) spectroscopy was used to study the charge carrier recombination processes in the C-doped and H-co-doped TiO2 thin films produced by magnetron sputtering. The radiative recombinations evident from the PL emission spectra (at about 470nm, 600nm and 850nm) were associated primarily with defects intrinsic to most thin films. Doping with C was found to promote the non-radiative recombination of charge carriers. This was due the filling of the band gap with C-induced energy states, as well as defect-rich microstructure formed also a result of C doping. This effect of C doping is lost upon annealing which eliminates the C dopant from of the thin films. Doping with H on the other hand permanently modifies the band gap structure of rutile by introducing a luminescence centre/s emitting at about 600nm, while suppressing the less desirable centre in the middle of the rutile band gap responsible for the characteristic PL at 850nm.

An experimental and first-principles study of the effect of B/N doping in TiO2 thin films for visible light photo-catalysis

Abstract Thin films of TiO2 and boron–nitrogen (B/N) co-doped TiO2 on glass substrates have been prepared by a simple sol–gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV–vis spectroscopy. The TiO2 thin films with co-doping of different B/N atomic ratios (0.27–20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV–vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results.