TiO2-SiO2 Thin Films Research Articles

Coating of expanded polystyrene spheres by TiO2 and SiO2–TiO2 thin films

Expanded polystyrene spheres (EPS) were coated by SiO2–TiO2 or TiO2 for application as a fluidized bed in the photocatalytic reactor. Silica coating was realized by the sol–gel process carried out in a vacuum evaporator at 60–70 °C. The most uniform and thin layer of silica coating was obtained by the Stöber method based on the hydrolysis of tetraethyl orthosilicate (TEOS) catalysed by an ammonia solution. Effective TiO2 coating was obtained by the immersion of EPS in the titania aqueous suspension and evaporation of water in a vacuum evaporator. Heating of EPS spheres coated by SiO2, TiO2 or SiO2–TiO2 at the temperatures of 120–140 °C resulted in a shrinkage of their volume. For the thick layer coating, a strong corrugation of EPS surface was observed. The photocatalytic tests showed, that highly corrugated surface of coated EPS slowed down ethylene decomposition, whereas a thin layer coating of both, SiO2 and TiO2 was advantageous.Graphical abstract

Enhanced visible light photocatalytic activity of nanostructured SiO2-TiO2 thin films through optimizing thickness

Thin films of silicon dioxide-titanium dioxide (SiO2-TiO2) with different thicknesses were deposited by a simple dip-coating method in a repetition behavior followed by heating processes. Choosing the optimum thickness is accounted as an approach for improving photocatalytic and hydrophilicity properties of a thin film. The obtained results from FESEM and AFM characterizations showed that with increasing thickness, the surface roughness increases from 3.089 nm to 132.8 nm. The XRD patterns indicate the presence of anatase phase for the SiO2-TiO2 thin film. Optical measurements were used to calculate thickness, generation rate of photocarriers, band gap, and refractive index of the samples. Decrease of band gap with increasing thickness makes the layer more proper for photocatalytic activity under visible light. It is obtained that the generation rate of carriers has the highest value (17.16 × 1024 m−3s−1) for the thickness of 336 nm. PL spectra for the thickness of 336 nm confirmed the presence of defects which reduce the recombination rate and improve charge carrier separation. XPS was used to distinguish the chemical composition. Variation of defect concentrations, number of grain boundaries, and surface roughness with thickness were considered as the main parameters affecting the photocatalytic performance. The highest photodegradation was obtained for 336 nm thick film under illumination of visible light (100% degradation of 40 ml solution of 10 mg l−1 methylene blue (MB)). This research provides a systematic study on the structural and optical properties of the different thick SiO2-TiO2 films with goal of enhancing photocatalytic activity in the visible light region.

Investigation of TiO2 Deposit on SiO2 Films: Synthesis, Characterization, and Efficiency for the Photocatalytic Discoloration of Methylene Blue in Aqueous Solution.

TiO2-SiO2 thin films were created on Corning glass substrates using a simple method. Nine layers of SiO2 were deposited; later, several layers of TiO2 were deposited, and their influence was studied. Raman spectroscopy, high resolution transmission electron spectroscopy (HRTEM), an X-ray diffractometer (XRD), ultraviolet-visible spectroscopy (UV-Vis), a scanning electron microscope (SEM), and atomic force microscopy (AFM) were used to describe the sample's shape, size, composition, and optical characteristics. Photocatalysis was realized through an experiment involving the deterioration of methylene blue (MB) solution exposed to UV-Vis radiation. With the increase of TiO2 layers, the photocatalytic activity (PA) of the thin films showed an increasing trend, and the maximum degradation efficiency of MB by TiO2-SiO2 was 98%, which was significantly higher than that obtained by SiO2 thin films. It was found that an anatase structure was formed at a calcination temperature of 550 °C; phases of brookite or rutile were not observed. Each nanoparticle's size was 13-18 nm. Due to photo-excitation occurring in both the SiO2 and the TiO2, deep UV light (λ = 232 nm) had to be used as a light source to increase photocatalytic activity.

Unravelling local environments in mixed TiO2–SiO2 thin films by XPS and ab initio calculations

Mixed TixSi1−xO2 oxide can exhibit a partial phase separation of the TiO2 and SiO2 phases at the atomic level. The quantification of TiO2–SiO2 mixing in the amorphous material is complicated and was so far done mostly by infrared spectroscopy. We developed a new approach to the fitting of X-ray photoelectron spectroscopy data for the quantification of partial phase separation in amorphous TixSi1−xO2 thin films deposited by plasma enhanced chemical vapour deposition. Several fitting constraints reducing the total number of degrees of freedom in the fits and thus the fit uncertainty were obtained by using core electron binding energies predicted by density functional theory calculations on TixSi1−xO2 amorphous supercells. Consequently, a decomposition of the O1s peak into TiO2, SiO2 and mixed components was possible. The component areas ratios were compared with the ratios predicted by older theoretical models based on the atomic environment statistics and we also developed several new models corresponding to more realistic atomic structure and partial mixing. Based on the comparison we conclude that the studied films are mostly disordered, with only a moderate phase separation.

Oxidation resistant TiO2–SiO2 coatings on mild steel by Sol–Gel

Single and multilayer titania–silica (TiO2–SiO2) oxidation resistant dry gel thin film was applied on mild steel (MS) through sol–gel based dip coating. The coated samples were fired at 410 °C for 30 min and the coating film thickness was found to be 200–400 nm using spectroscopic ellipsometry. The structural and chemical analysis of the films was carried out by XRD, SEM–EDS and TG–DTA. The oxidation resistance of coatings was evaluated by weight gain per unit area after exposing to 400 °C for 20 h in air. Uncoated specimens exhibited a weight gain of 0.72 mg/cm2. However, the weight gain was less by 6 times for single layer and 16 times for 3 layers of coatings (deposition). Further, oxidation kinetics study revealed a reduction of parabolic oxidization rate constant by 43 times (0.026 mg2 cm−4.h−1) for single layer and 325 times (8 × 10−5 mg2 cm−4.h−1) for 3 layer coatings, compared to bare MS exposed to identical conditions. Such a high reduction in oxidation with multilayer deposition is probably due to the effective coverage of micro–cracks, which may be induced due to the thermal mismatch between the coatings and MS. An improvement in adherence of coating was confirmed due to the formation of (Fe0. 927Ti0.073)2.O3 at the interface using XRD. The addition of SiO2 to TiO2 was found to minimise the coating defects associated with sol–gel and also inhibit the formation of anatase. Thus, the present work demonstrated the application of TiO2–SiO2 thin film coating on MS through sol–gel technique to form an impervious layer to substantially enhance the oxidation resistance at elevated temperatures.

Preparation and Optical Properties of TiO2-SiO2 thin films by Sol-gel Dipping Method

TiO2, SiO2 and TiO2-SiO2 thin films were prepared by sol-gel dipping method on glass substrates. The pyrolysis behavior of TiO2 and SiO2 dry gel were tested by differential thermal analysis (DTA). The microstructure and optical properties of the TiO2, SiO2 and TiO2- SiO2 were studied by X-ray diffraction (XRD) and ultraviolet and visible spectrophotometer. The results showed that the phase structure of the films was affected by the composition. All the films were transparent in the visible region. Meanwhile, the transparency of SiO2 was better than TiO2 and TiO2-SiO2 composite film. The ban-gap of the TiO2, SiO2 and TiO2-SiO2 thin films were 3.79, 4.01 and 3.91.

Laser irradiation synthesis and photocatalytic properties of TiO2-SiO2 hybrid thin films

In this study, we introduce a noble method for the fabrication of highly crystalline hybrid TiO2-SiO2 thin films using laser irradiation under ambient conditions. Upon light absorption at the interface between TiO2 sol-gel film and Si wafer during the laser irradiation process, the TiO2 gel film coated on the Si wafer is transformed into anatase TiO2 film, and the surface of underlying Si wafer is oxidized to a 20.63 μm thick SiO2 film composed of nano-spheres with average diameter of 24.12 nm. The photocatalytic characteristics of the TiO2-SiO2 hybrid film on methylene blue and its discriminated morphologies are compared with those of a TiO2 film fabricated by conventional thermal annealing. The TiO2-SiO2 hybrid film shows enhanced super-hydrophilicity and superior photocatalytic characteristics, while thermally annealed 0.16 μm thick TiO2 films exhibit hydrophobic and low photocatalytic properties. The laser assisting process is promising for the fabrication of highly crystalline TiO2-SiO2 hybrid film with super-hydrophilic and photocatalytic characteristics.

Optical and mechanical properties of Sol-gel prepared Titania (TiO2) –Silica (SiO2) mixed thin films ‘as prepared at 300 K’ without any post heat treatment

The mixed metal oxide (MMO) thin films like titania-silica (TiO2–SiO2) prepared by sol-gel technology have shown a variety of interesting optical, mechanical and thermo-mechanical properties; these thin films are being used in a variety of applications. In the present investigation, the TiO2–SiO2 (TS) thin films (on glass substrates) are prepared at 300 K from non-aqueous individual sols of TiO2 and SiO2 of 0.1 molar (TS-1) and 0.3 molar (TS-3) concentrations; no post heat treatment has been conducted on these films. The thicknesses of the two layer (2 l) and four layer (4 L) thin films prepared by dip coating are in the range 27 nm to 170 nm. The optical and mechanical properties of these ‘as-deposited’ thin films have been evaluated. The ‘as-deposited’ TS thin films show an optical transparency (in the visible region) of ∼90% and optical band gaps are in the range 4.44 eV to 4.50 eV. The optical density has been calculated from the refractive index measurements. The refractive index of TS-1 thin films of thickness 27 nm is practically constant at 1.61 over the wavelength range 400–750 nm. Micro-cracks have been observed (Scanning electron micrographs) in TS-1-4L and TS-3-4L thin films. These micro cracks are more significant in TS-3-4L samples than those of TS-1-4L samples. These cracks are not seen in all other samples (TS-1-2L and TS-3-2L). These mixed titania-silica thin films show higher adherence and higher hardness compared to those of TiO2 thin films. The Raman spectroscopy measurements show the existence of multiple phases of Ti–O–Si. It is known that in the multi-phase structures, the phase boundaries hinder crack propagation and enhances the resistance to plastic deformation enhancing the mechanical hardness of these TS thin films.

Surfactant Effect on the Synthesis of Mesoporous TiO<sub>2</sub>-SiO<sub>2</sub> Coatings Using Sol-Gel Technology

The aim of the research was to develop the area of mesoporous thin films of a binary TiO2–SiO2 system. Sol was synthesized from tetraethylorthosilicate as the silica source and titanium isopropoxide solution as the TiO2 source, while triblock copolymer surfactant (Pluronic F 127 (10% solution in water, (P))) was used as the mesostructure-directing agent. In this paper we present sol-gel obtained TiO2–SiO2 with a mesoporous structure. The effects of added titanium on the mesostructure and on the porosity are presented and discussed. Four different molar percentage ratios of Ti: Si were used for the synthesis of mixed TiO2–SiO2 mesoporous thin films on glass substrate. The mesoporous structure of thin films was characterized by X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), scanning electron microscopy (SEM) and the water contact angle. These mesoporous TiO2–SiO2 thin films could have many potential applications in many areas such as separation membranes, catalysis, optics, and self-cleaning surfaces.

Light emission and atomic coordination structure of sol-gel derived erbium-doped SiO2-TiO2 thin films

Erbium-doped SiO2-TiO2 thin films were prepared by the sol-gel method, using erbium nitrate pentahydrate powder, tetraethyl-orthosilicate (TEOS), and titanium tetraisopropoxide (TTIP) as precursors. The Si/Ti ratios in the SiO2-TiO2 films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. Atomic coordination structure of erbium was defined by extended X-ray absorption fine structure spectrometry (EXAFS) and optical properties of the films were characterized by micro-photoluminescence (Micro-PL). The first-neighbor-shell coordination number of erbium in SiO2-TiO2 thin films would influence the optical properties. The 700°C-annealed 80%SiO2-20%TiO2:Er1.0% (mol%) film with the lowest coordination number exhibits the highest photoluminescence intensity. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis reveals that the main bonding structures of SiO2-TiO2 thin films are related to the erbium dopants. The modification of microstructure and chemical bonding configuration in the SiO2-TiO2 films by the Er-doping concentration and its influence on the optical properties are discussed.

Engineered TiO2 and SiO2‐TiO2 films on silica‐coated glass for increased thin film durability under abrasive conditions

Thin films durability is critical to retain its performance in real life applications. For automotive glass, further factors such as haze appearance developed under abrasive conditions become relevant to ensure the driver's visibility. Macroscopic abrasion resistance tests of TiO2/SiO2 and SiO2–TiO2/SiO2 thin films on soda‐lime silica (SLS) glass were performed according to an American standard for safety grazing. The purpose of this, was to increase the top active film durability in a bilayer system by understanding how film thickness and top film composition influence abrasion performance. In order to achieve this understanding, three approaches were considered: (a) determination of the influence of TiO2 top film thickness, (b) replacement of the TiO2 top film by SiO2–TiO2 films, and (c) determination of the influence of SiO2–TiO2 film thickness. Results showed that thinner top TiO2 film thickness leads to SiO2/TiO2 bilayers with lower haze value and improved abrasion resistance. It was also found that SiO2 addition to TiO2 top film composition promotes the thin film adhesion and sample durability against abrasive wear. Friction coefficient and micro‐hardness measurements support the abrasion results. Factors contributing to the improvement of the lifetime performance of TiO2 and SiO2–TiO2 thin films were identified.

The structural studies of Ag containing TiO2–SiO2 gels and thin films deposited on steel

FTIR spectroscopic structural studies of titania-silica monolith samples as well as thin films deposited on steel were described in this work. Thin films were synthesized by the sol–gel method applying the dip coating as separate one-component TiO2 and/or SiO2 layers or as two-component TiO2–SiO2 thin films. Silver nanoparticles were incorporated into the structure from pure SiO2 sol, deposited then as an additional layer in those hybrid multilayers systems. Except the spectroscopic studies, XRD diffraction, SEM microscopy with EDX analysis and AFM microscopy were applied. The structural studies allow to describe and compare the structure and the morphology of thin films, as well those Ag free as Ag containing ones, also by the comparison with the structure of bulk samples. In FTIR spectra, the band observed at about 613 cm−1 can be connected with the presence of the non-tetrahedral cation in the structure and is observed only in the spectra of Ag containing bulk samples and thin films. The bands at 435–467 cm−1 are due to the stretching vibrations of Ti–O bonds or as well to the bending vibrations of O–Si–O one. In the ranges of 779–799 cm−1 and 1027–1098 cm−1, the bands ascribed to the symmetric stretching vibrations and asymmetric vibrations of Si–O–Si connections, respectively, are observed. SEM and AFM images gave the information on the microstructure and the topography of samples surface. XRD measurements confirmed the presence of only amorphous phase in samples up to 500 °C and allowed to observe the tendency of their crystallization.

Synthesis and characterization of erbium-doped SiO2-TiO2 thin films prepared by sol-gel and dip-coating techniques onto commercial glass substrates as a route for obtaining active GRadient-INdex materials

Abstract In this work, SiO 2 -TiO 2 films doped with erbium were prepared by dip-coating sol-gel process onto commercial glass substrates. The surface morphology of the films was characterized using atomic force microscopy, while thickness, refractive index, extinction coefficient and porosity of the films were determined by ellipsometric measurements in a wavelength region of 400–1000 nm. Optical constants and porosity were found to vary with erbium concentration. The proof of principle presented in this paper is applicable to systems of different nature by tailoring the sol-gel precursors in such a way that active GRadient-INdex media described by a complex, parabolic-like refractive index distribution for beam shaping purposes is obtained.

Microstructure and optical dispersion characterization of nanocomposite sol–gel TiO2–SiO2 thin films with different compositions

Nanocomposite TiO2–SiO2 thin films with different compositions (from 0 to 100mol% TiO2) were deposited by sol–gel dip-coating method on silicon substrate. Crystal structure, chemical bonding configuration, composition and morphology evolutions with composition were followed by Raman scattering, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy respectively. The refractive index and the extinction coefficient were derived in a broad band wavelength (250–900nm) from spectroscopic ellipsometry data with high accuracy and correlated with composition and microstructure. Results showed an anatase structure for 100% TiO2 with a grain size in 6–10nm range. Whereas, the inclusion of SiO2 enlarges the optical band gap and suppresses the grain growth up to 4nm in size. High TiO2 dispersion in SiO2 matrix was observed for all mixed materials. The refractive index (at λ=600nm) increases linearly with composition from 1.48 (in 100% SiO2) to 2.22 (in 100% TiO2) leading to lower dense material, its dispersion being discussed in terms of the Wemple-DiDomenico single oscillator model. Hence, the optical parameters, such optical dispersion energies E0 and Ed, the average oscillators, strength S0 and wavelength λ0 and the ratio of the carrier concentration to the effective mass N/m∗ have been derived. The analysis revealed a strong dependence on composition and structure. The optical response was also investigated in term of complex optical conductivity (σ) and both volume and surface energy loss functions (VELF and SELF).

Si Substrate as a SiO2 Source for the Preparation of Mesoporous SiO2–TiO2 Thin Films

Abstract A Si substrate has been proved to be used as a SiO2 source for the preparation of mesoporous silica–titania thin films with cylindrical mesochannels. Exposing mesostructured titania–surfactant thin films to aqueous NH3 vapor reinforces the pore walls with uniformly distributed silicate species, which retain the mesostructure after calcination.

Photocatalytic antibacterial activity of TiO2–SiO2 thin films: The effect of composition on cell adhesion and antibacterial activity

• The effect of composition of TiO 2 –SiO 2 thin films on cell adhesion was studied. • The effect of surface composition on surface free energy was studied. • SiO 2 addition favors for cell adhesion. • Strong relation was found between the bacterial adhesion and antibacterial activity. Colloidal solutions of SiO 2 –TiO 2 mixed oxides having different SiO 2 contents were synthesized by sol–gel technique and thin films were deposited over glass slides by using dip coating technique. The samples were characterized by XRD, SEM, AFM and methylene blue adsorption methods. The surface free energy of thin films was measured by sessile drop method by using diiodomethane, glycerol and water as probe liquids. The photocatalytic antibacterial activity of the samples was determined for Escherichia coli XL1-blue by using artificial solar irradiation. The surface characterization studies revealed the presence of small crystallites of anatase phase, enhanced dispersion of TiO 2 particles and increasing surface free energy at elevated SiO 2 content. Highest photocatalytic antibacterial activity was obtained over 92 wt% SiO 2 containing sample and strong correlation was found between the bacterial adhesion and antibacterial activity. Surface-adhered E. coli cells having direct contact with TiO 2 particles were inactivated at a higher rate than suspended cells.

Effect of SiO<sub>2</sub> Particle Size on Optical Properties of TiO<sub>2</sub>-SiO<sub>2</sub> Nanocomposite Thin Films

TiO2-SiO2thin film system is known to be very attractive to use for photocatalytic and display applications. In this study, TiO2-SiO2nano-composite solutions were prepared by adding colloidal solutions consisted of different SiO2nano-particle sizes (7-50 nm) into TiO2powder-dispersed solutions. TiO2-SiO2thin films on glass substrates were fabricated by the dip-coating technique and their crystal structure, surface morphology and photocatalytic properties were investigated as a function of SiO2particle size. While the SiO2particle size had little influence on the crystal structure of thin films, the photocatalytic activity and anti-reflectance (anti-glare) characteristics were found to be dependent on the SiO2particle size. This result could be explained in terms of surface characteristics and the order of degradation of methylene blue under UV light irradiation.

Super-hydrophilic property of vanadium doped TiO2–SiO2 sol–gel derived thin film

In this work, vanadium doped TiO2–SiO2 thin films were deposited on glass substrates using the sol–gel dip coating method. Fourier transform infrared spectroscopy was used to investigate the film characteristics. Field Emission Scanning Electron Microscopy and UV–vis spectrophotometer were used to evaluate the film thickness and the optical properties of the thin film. In addition, surface morphology and surface roughness of films were measured with atomic force microscopy analysis. The optical results indicated that vanadium dopant in TiO2–SiO2 changed the absorption edge from ultraviolet to visible light. Water contact angle on the film surfaces was measured by a contact angle analyzer under UV and visible light irradiation. The results indicated that vanadium as a dopant ion had a significant effect on the hydrophilicity property of TiO2–SiO2 thin films.

Atmospheric pressure chemical vapor deposition of high silica SiO2–TiO2 antireflective thin films for glass based solar panels

The atmospheric pressure chemical vapor deposition (APCVD) of SiO2–TiO2 thin films on glass by employing a [[(tBuO)3SiO]2–Ti(OiPr)2] single-source precursor, which can be prepared from commercially available materials, results in antireflective thin films with high silica SiO2 : TiO2 ratio (i.e. SiO2 > 1) on float glass under industrially relevant manufacturing conditions.

Investigation of phase separation of nano-crystalline anatase from TiO2SiO2 thin film

In this work, a set of SiO2–TiO2 mixed oxides was prepared by the polymeric sol–gel route and deposited on glass substrate through the dip coating technique. Then, the effect of different important preparation parameters (sol–gel stabilizers, Ti content, and heat treatment) on the phase separation was investigated. The developed films were heat treated at 500°C and characterized using TGA/DTA, FTIR, XRD, SEM, and AFM. The results showed that TiO2 segregation can be controlled by selecting an appropriate composition of diethanolamine (DEA) and methyl methacrylate (MMA) for preparation of polymeric silica–titania sol. Besides, anatase phase in the samples were crystallized without any stabilizers within heat treatment procedure at 500°C; however, using appropriate composition of DEA and MMA crystallization rate significantly decreased.