A method of making a transparent visual light activated photocatalytic superhydrophilic glass material

Method for the production of transparent photocatalytic superhydrophilic glass material activated by visible light

TECHNICAL FIELD

The invention relates to titanium oxide-based photocatalytic materials activated by UV radiation and visible light, which can be used, for example, as self-cleaning surfaces, including glass walls, doors and windows both indoors and outdoors, as an indoor and outdoor air purifier, as an antifouling agent, as an antibacterial agent. to remove odor and disinfect the interior.

BACKGROUND OF THE INVENTION

According to the World Health Organization (WHO), air pollution causes three million premature deaths a year [1]. The increase in pollution is due to many factors that can be linked to human activities, such as emissions from internal combustion engines, factories, etc.

Methyl tert-butyl ether (MTBE, (CH₃)₃COCH₃) is the most widely used motor fuel additive [2]. Gasoline contains MTBE, so it is also found in the troposphere. MTBE concentrations in the troposphere are expected to increase further under heavy use. It is directly related to human disease, as one of the main disadvantages of this substance is carcinogenicity [2-3]. The concentration of MTBE indoors is about the same as in ambient air.

Titanium dioxide (T1O2) is an extremely promising material for the treatment of volatile organic compounds (VOCs), including MTBE, due to its relatively high photocatalytic activity under UV light. In addition, T1O2 is chemically inert, corrosion-resistant and inexpensive [4].

The TiO2 photocatalyst is generally used either as a powder or as an immobilized substrate. T1O2 nanopowders used as photocatalysts have been considered safe substances, in some cases used as food supplements. However, recent T1O2 toxicity studies have shown that TiO2 nanoparticles smaller than 20-30 nm can pose significant health risks [5]. In addition, coatings made from industrial T1O2 nanopowders are used in gas phase photooxidation systems [6]. However, coatings made of nanopowders are less mechanically stable, ie their adhesion to the substrate is weaker than that of thin films [7]. Thus, T1O2 must be strongly immobilized on the substrate to prevent nanoparticles from entering the atmosphere.

A thin photoactive TiO2 film must meet the following requirements to be useful in the field: high photocatalytic activity, superhydrophilicity, high transparency,

Optimum mechanical properties in terms of adhesion to the substrate and abrasion resistance. In addition, the TiO 2 photocatalyst immobilized on the window glass is seen as a great prospect as a decomposer and self-cleaning material for airborne micro-pollutants, as modified window glass has significant market potential and soda-lime glass is a cheap base material.

Various methods have been used to make thin TiO2 films, such as intestinal gel-dip coating [8], salt-gel spin coating [9], chemical vapor deposition (CVD) [10], atomic layer deposition (ALD) [11], and the like. In addition to the above-mentioned methods, chemical spray pyrolysis is simple, fast and inexpensive and is suitable for covering large surfaces. It has been found that the photocatalytic activity of a thin TiO2 film applied to a substrate (eg window glass) depends on several probable factors: thickness, surface morphology, crystal size, ions diffused from the substrate (eg Na⁺and Si⁴⁺), etc.

WO9613327 is known, which describes a transparent glass window and the like with excellent photocatalytic activity and light transmission, in which at least one photocatalytic titanium oxide film with a linear transmittance of at least 550 nm is formed on a light-transmitting glass plate substrate. , and preferably a light-transmitting SiO2 precoat is formed between the light-transmitting substrate and the titanium oxide film to be about 0.02-0.2 micrometers thick.

A solution is known from WO9411092, which describes the use of a photocatalyst for the purification of a hospital wound contaminated with bacteria and for the treatment of air containing a malodorous compound. A semiconductor (e.g., titanium dioxide) optical catalyst film is applied to the inner surface of a hospital ward or dwelling wall. A photocatalyst film irradiated with light from a general light source, such as a fluorescent lamp, is optically excited by low ultraviolet radiation from the fluorescent lamp. Bacteria and chemical compounds falling on the optically excited film are decomposed in the photo.

WO9629375 discloses a method for ultraphilophilizing a substrate surface comprising coating the surface with a layer comprising a photocatalytic semiconductor such as titanium dioxide and then excitationing the photocatalytic material with light so that the contact angle between said layer and water is about 10 ° or less. If this method is used on the surface of a substrate, such as a mirror, lens or window glass, it will prevent the growth of water droplets and the substrate will become very foggy. Objects treated with this method do not deposit contaminants on the surface and can be easily cleaned under rain or by washing with water.

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A solution is known WO2013106776, which describes photocatalytic compositions comprising a photocatalyst and a co-catalyst, wherein the photocatalyst may be titanium-based and react to visible light in some embodiments. The photocatalyst may be titanium dioxide, titanium oxide with additives, or a powdered composite material containing titanium oxide. The composition may form a transparent layer on the substrate. CeO has also been described₂ a method of preparing the dispersion and spraying the dispersion on a substrate, in particular on glass and window glass.

A solution is known from WO2010064225, which describes the synthesis of an additive titanium dioxide photocatalyst active in the visible light and in the high-temperature stable anatase phase, which comprises reacting hydrated titanium dioxide with hydrogen peroxide in aqueous solution and forming a salt. Also described is active light-free titanium dioxide in the free anatase phase that is stable at temperatures up to about 900-1000 ° C.

US2003167878 discloses a process for preparing a solution of crystalline titanium dioxide-containing colloidal particles, wherein one or more titanium-containing hydrolysable compounds are stabilized with oxalic acid in the reaction medium. The reaction is the basis for the preparation of titanium dioxide-based materials in the anatase phase suitable for titanium dioxide-based materials, including photocatalytic applications.

EP1205243 is known, which describes a method for applying an thin film of titanium dioxide with photocatalytic activity in a crystalline form to a transparent inorganic base, in particular Pyrex glass. The film is formed by precipitation (spinning, spraying, dipping) of a stable liquid precursor containing an inorganic or organometallic titanium (IV) compound which is partially or completely hydrolysed in the presence of acids, surfactants and finally s-triazine derivatives. The latter increase the photocatalytic activity of the film. Areas of application include air purification and deodorization, indoor disinfection and self-cleaning clear glass. The thickness of the film is 50 nm to 10 micrometers. The material is weather- and wear-resistant, homogeneous and transmits more than 80% of the visible light spectrum.

EP0737513 is known, which describes the preparation of photocatalytic and transparent films by the sol-gel method from a solution of TiO applied to a soda-lime glass heated to 500 ° C.₂ from a layer annealed at 400 ° C (Examples 1 and 15), the solution being prepared from titanium (IV) isopropoxide and acetylacetone (solvent). Concentration of Ti (IV) alkoxide

The acetylacetone in the acetylacetone was 0.5 mol / L, which converts to a molar ratio of about 1:20. This can be considered as the closest solution known in the art.

Films deposited on ordinary window glass have been found to have low photocatalytic activity because the film contaminates the Na diffused from the substrate upon annealing.⁺ and Si⁴⁺with ions [17].

There is a need for an easier method of applying titanium dioxide film with photocatalytic properties to glass, such as window glass and borosilicate glass, compared to the closest solution known in the art, the film being activatable by UV light and visible light. with superhydrophilic properties and the ability to efficiently decompose volatile organic compounds (VOCs) such as MTBE, acetone and benzene. This material is suitable for self-cleaning windows and containers and for cleaning the air. Such material can also be used in crop production.

SUMMARY OF THE INVENTION

The invention relates to a process for the preparation of a transparent, photocatalytic and superhydrophilic thin layer of titanium dioxide, comprising the following steps:

preparing a solution of a metal alkoxide, a gelling agent and a solvent;

the resulting solution is applied to a substrate heated by ultrasonic spray pyrolysis, e.g. window glass, borosilicate glass, soda lime, quartz, at a substrate temperature of 250-450 ° C, most preferably about 350 ° C; and annealing the product at an ambient temperature of about 400-700 ° C, preferably about 500 ° C. For window glass and soda-lime glass, the specified temperature may be up to about 550600 ° C; for borosilicate glass, quartz and silicon, the temperature can be up to about 700 ° C.

Said metal alkoxide is preferably a Ti (IV) alkoxide, such as titanium (IV) isopropoxide, titanium butoxide or titanium (IV) ethoxide.

Said gelling agent is any suitable gelling agent, e.g. acetylacetone.

The molar ratio of said Ti (IV) alkoxide gelling agent is 1: 1 to 1: 6, preferably 1: 4.

Said solvent is preferably an alcohol (e.g. ethanol, methanol, 2-propanol, 2-butanol), wherein the concentration of the solution - the concentration of the titanium oxide precursor - is 0.05-1.0 mol / l, preferably 0.2 mol / l.

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Most preferably, the TiCl 2 film / coating is precipitated at 350 ° C, followed by annealing in air at 500 ° C. The thickness of the TiO2 film / coating is preferably in the range of about 110 to 330 nm.

The films are transparent, with a flat and smooth surface, firmly adhered to the substrate and superhydrophilic even at 3 months of age (without prior UV treatment) and decompose acetone and MTBE 100% to HsO and CCh. The TiCl 2 film on the glass decomposes 31% of MTBE in visible light, the TiOs film on borosilicate decomposes 62% of MTBE in visible light.

Surprisingly, in addition to UV-A radiation, visible light also activates the glass. In addition, such a film has a high photocatalytic activity even on window glass, although it is known from the prior art that its photocatalytic activity should be low. One of the most pronounced experiments with a film applied on borosilicate glass (350 ° C) was that the degradation of MTBE at 6% and 40% relative humidity was almost the same, ie the increase in humidity did not impair performance.

Another object of the invention is to provide a self-cleaning glass made by the methods described above.

Another object of the present invention is to provide an air purifying material for the decomposition of volatile organic compounds by UV-A and visible light, which is prepared by the method described above.

Another object of the invention is a glass vessel for growing plants.

Another object of the invention is to provide self-cleaning glass and / or air-cleaning glass and / or a glass vessel for growing plants, which comprises a layer of glass and TiO2 applied to said glass layer by chemical spray pyrolysis. layer.

LIST OF DRAWINGS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 is a scanning electron micrograph of a T1O2 layer deposited on soda-lime glass at 250 ° C (Figure 1a), 350 ° C (Figure 1b) and 450 ° C (Figure Ic) and T1O2 deposited on a borosilicate glass substrate at 450 ° C. layer (Figure Id). All samples are annealed for 1 hour at 500 ° C. The thumbnails in Figures 1a to 1d are cross-sectional photographs of T1O2 films taken with a scanning electron microscope.

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Figure 2 shows X-ray diffractograms of TiCl 2 films deposited on soda-lime glass and borosilicate substrates at 250 ° C, 350 ° C and 450 ° C.

Figure 3a shows the soda-lime glass at different temperatures (250, 350 and 450 ° C) and the temperature at 450⁰ Raman spectra of TiO2 films deposited on a borosilicate support. Figure 3b shows the effect of deposition temperature on 144 cm Raman spectroscopy of TiCh films applied to a surface.^{- 1} peak location and half-width. All samples were annealed in air at 500 ° C for 1 hour.

Figure 4a shows the transmittance spectra of thin TiCl 2 films applied to soda-lime glass at 250, 350 and 450 ° C, and Figure 4b shows similarly deposited thin films on a borosilicate glass support. All samples were annealed at 500 ° C for 1 hour.

Figure 5 shows the XPS spectra of thin TiCl 2 films deposited on soda-lime glass and borosilicate substrates at different temperatures in the Ols binding energy region.

Figure 6 shows the XPS spectra of the Nals region of thin TiO2 films deposited on soda-lime glass at 250 and 450 ° C and on borosilicate glass at 450 ° C. All samples were annealed in air at 500 ° C for 1 hour.

Figure 7 shows the photocatalytic conversion of MTBE to (a) 350 ° C and (b) 450 ° C to thin glass TiO 2 films deposited on borosilicate glass at 450 ° C. All samples were annealed at 500 ° C; The MTBE concentration at the inlet was 10ppm; relative humidity 6%; reactor temperature 30 ° C.

Figure 8 is a table summarizing XPS studies and contact angle measurements of thin Ti (h-films deposited on soda-lime glass and borosilicate substrates at different temperatures. All samples from XPS studies and samples stored for three months for wetting experiments are included. All samples were annealed at 500 ° C.

Figure 9a shows the effect of MTBE residence time (photocatalytic surface used) on MTBE conversion and Figure 9b shows the formation of MTBE intermediate TBF (relative humidity 6%, exposure duration 15.6 s per section, UV-A radiation).

Figures 10a and 10b show the conversion of MTBE by visible light and UV-A radiation (5 ppm MTBE, relative humidity 6%, exposure duration 15.6 s per section) on soda-lime glass and borosilicate glass articles, respectively.

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Figures 11a and 11b show the formation of the MTFE intermediate TBF by visible light and UV-A radiation (5 ppm MTBE, relative humidity 6%, exposure duration 15.6 s per section).

Figure 12 shows the effect of humidity (6% and 40% relative humidity) on MTBE conversion (10 ppm MTBE, exposure duration 15.6 s per section).

Figure 13 is a diagram of an ultrasonic spray pyrolysis process.

EXAMPLE OF EMBODIMENT OF THE INVENTION

TiO 2 thin films were deposited on a typical industrial window glass (soda-lime glass) and a borosilicate glass substrate by ultrasonic spray pyrolysis (USP). A schematic of the USP process is shown in Figure 13.

The spray solution consisted of titanium (IV) isopropoxide (0.2 mol / l) and acetylacetone in ethanol in a molar ratio of 1: 4. Compressed air with a flow rate of 81 / min was used as the carrier gas, the spray rate was set at 2.5 ml / min. The tube transporting the ultrasonic mist was fixed at a distance of 7 cm from the hotplate (where the trays were placed). There were six spray cycles. The temperature of the heating plate was 250 ° C, 350 ° C and 450 ° C for the layers deposited on the soda-lime glass, and 450 ° C for the film sprayed on the borosilicate glass. All precipitated samples were annealed in air for 1 hour at 500 ° C in a Nabertherm L5 / 11 / 06D oven and are referred to as prepared samples throughout the article.

The structure of the samples was studied by X-ray diffraction and Raman spectroscopy. X-ray diffraction patterns were recorded on a Rigaku Ultima IV diffractometer (Cu Ka radiation, λ = 1.5406 Å, 40 kV at 40 mA). Measurements were made in a 2-theta configuration in the scanning range of 20-60 ° in 0.02 ° increments and at a scanning speed of Z ^ min '¹. The average crystal size was calculated by the Scherrer method from the half-width of the diffraction line of the T1O2 anatase phase reflection (101), and Raman spectra were obtained on a HORIBA Jobin Yvon HR800 micro-Raman spectrometer¹, a 532 nm laser beam was used for excitation.

The wetting of the films was studied by measuring the contact angle of water with a DSA 25 (KRÜSS Instrument) using the surface drop method. The result was the average of the four points on the substrate. In the surface wetting experiments, irradiation with UV-A was performed with a 15 W fluorescent lamp (Actinic BL 15W, Philips) in the range of 180-400 nm and a maximum irradiance at 365 nm.

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Surface morphology and film thickness for energy dispersion spectroscopic analysis were measured with a Zeiss HR FESEM Ultra 55 accelerating voltage of 4.0 kV and 7.0 kV with a scanning electron microscope. X-ray photoelectron spectroscopy (XPS) was performed on a Kratos Analytical AXIS ULTRA DLD spectrometer with an Al Ka ​​monochromatic X-ray source and an Mg / Κα dual-anode achromatic X-ray source. T1O2 binding energy values ​​were calculated from the Cls peak (285.0 eV). Transmittance and reflectance spectra of the films were obtained with a Jasco V-670 spectrophotometer in the range of 200-1200 nm.

TiOa films are smooth, dense, free of cracks and firmly adhered to the substrate. The surface roughness measured on a surface of 1 x 1 μm is about 0.4-1.25 nm.

The photocatalytic activity of the thin films was investigated by photocatalytic decomposition of methyl teributyl ether (MTBE, C5H12O), a model air pollutant, in the gas phase. The inlet concentration of the gaseous pollutant was 10 ppm. The photocatalytic activity of the thin films was studied in a multi-section photocatalytic continuous flow reactor. The multi-section reactor consists of five sections, each with a volume of 130 ml and a photocatalytic coating area of ​​120 cm in one section of the reactor.², the total area of ​​the reactor is thus 600 cm² (see [27]). A Fourier transform infrared analyzer (FTIR, Interspec 200-X) with a Specac Tornado gas cell (8 m, 1.33 L) and a flow humidifier was connected to the reactor. A 15 W fluorescent lamp (Actinic BL, Philips) with a UV-A intensity of 3.3 mW / cm was placed above each section of the reactor.² (integrated in the range 180-400 nm, maximum radiation at 365 nm, UV-B / UV-A ratio <0.2%). The relative humidity of the gas stream at 20 ° C was 6% or 40% and the temperature in the reactor was 30 ° C, maintained by the heat of the lamp and controlled by a temperature controller (Omega CN9000A).

Contaminated air was generated in the LOU supply tank by evacuating the tank and injecting a defined amount of MTBE through the inlet. After evaporation for 20 minutes, the tank was filled to 3 bar and allowed to equilibrate for 90 minutes. The gas flow regulator ensured a gas flow rate of 0.5 l / min, so that the contact residence time in the reactor section was 15.6 s.

MTBE peaks were measured in the infrared band 1063-1124 cm '¹. The intermediate tert-butyl formate (TBF) formed (or formed) due to gas-phase photocatalytic oxidation of MTBE was also monitored quantitatively (infrared band 1138-1190 cm -1).¹) by analyzing the exhaust gas by FT-IR using a quantitative spectral library FDM VPFTIR HiRes. Apart from carbon dioxide and water, no gas phase products were observed.

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Photocatalytic thin film coatings on all samples were irradiated with UV-A for 24 hours prior to each photocatalytic experiment. Comparative experiments were performed to evaluate MTBE adsorption and photochemical degradation. MTBE T1O2 was not found to adsorb to the catalyst surface in the dark. In the absence of catalyst, no photochemical degradation of MTBE was observed under UV light. In both comparative experiments, the pollutant content did not change (there was no difference between the reactor inlet and outlet values) when the polluted air was passed through the five sections of the reactor for 30 minutes.

Surface morphology

Scanning electron micrographs of TiO2 films deposited on window glass and borosilicate glass at 250 to 450 ° C and annealed at 500 ° C are shown in Figure 1. TiCL films are smooth, dense, free of cracks and firmly adhered to the substrate. The experimental results show that the surface morphology of the layers deposited on the glass substrate changes as the deposition temperature is increased from 250 ° C to 450 ° C (Figure 1a, b, c). The TiCl 2 film deposited on the window glass at 250 ° C has a flat surface structure and a grain size of about 20 nm. Films deposited at 450 ° C have larger, well-separated grains with a size of about 50 nm. TiO2 film sprayed at 350 ° C has an intermediate surface morphology that includes the surface morphology of films deposited at both 250 ° C and 450 ° C.

The thickness of all prepared thin films was determined from the cross-sections obtained by scanning electron microscopy. We observed that the thickness of the thin TiO2 films deposited on the window glass was 110, 180 and 240 nm, respectively, at deposition temperatures of 250, 350 and 450 ° C. The thickness of the TiO 5 film applied to the borosilicate glass substrate at 450 ° C is 330 nm. The observed changes in the thickness and morphology of T1O2 deposited on different substrates can be attributed to the difference in growth rate, as the window glass substrate (2 mm) is thicker than the borosilicate glass (1 mm), so the borosilicate glass substrate temperature may be higher than the window glass.

Structural properties determined by X - ray diffraction

Figure 2 shows X-ray diffractograms of TiO2 films deposited on a glass and borosilicate glass substrate at 250, 350 and 450 ° C and annealed at 500 ° C for 1 hour. As shown in Figure 2, the X-ray diffractograms of the TiO2 films show 2-theta peaks at 25.5 °, 37.8 °, 48.2 °, 53.9 ° and 55 °, which belong to the T1O2 anatase structure [12]. In addition, 2-theta diffraction peaks appeared at 22.9 ° and

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Above 43.3 ° belonging to the silicon-containing substrate. No diffraction peaks in the rutile or brucid phase of T1O2 are visible. The average size of T1O2 crystals was calculated from the anatase phase (101) peak according to Scherrer's formula. The average size of the crystals on the soda-lime glass increases with the precipitation temperature and is 20-35 nm. The average size of the TiOs film crystals supported on the borosilicate glass support is 26 nm for precipitation at 450 ° C and 40 nm for precipitation at 350 ° C. Thus, it was confirmed that the TiCC films deposited on the glass and borosilicate glass substrate are in the crystalline phase of anatase, but their crystal size, thickness and surface morphology differ according to scanning electron microscopy (Figure 1). One reason for this may be the different thicknesses of the substrates used, which is confirmed by the difference in the rate of film formation on soda-lime and borosilicate glass substrates.

Structural properties determined by Raman spectroscopy

Figure 3a shows the Raman spectra of TiO2 films between 100 and 800 cm deposited on soda-lime glass and borosilicate substrates at different temperatures (250, 350 and 450 ° C) and then annealed at 500 ° C for 1 hour. '¹. Vibration peaks in Raman spectra 143 (Eg) cm '¹, 197 (Eg) cm '^!, 396 (Bjg) cm '^! and 637 (E_g) cm '¹ at which the TiCl 2 anatase phase is characteristic and no peak belongs to the rutile or brucide phase of T1O2.

The Raman peaks were approximated to Gaussian curves using Fityk software and the changes in their half-width as well as the Raman shift of the main anatase phase peak (144 cm ') were examined (Figure 3b). It can be seen that 144 cm^! The peak at is shifted to the highest wavelength for films deposited on soda-lime glass at 250 ° C, with a small difference between films deposited on soda-lime glass at 350 and 450 ° C. No shift towards higher energy was observed for the film sprayed on borosilicate glass at 450 ° C. At the same time, it can be seen that the largest half-width belongs to the film deposited at the lowest temperature, but the films deposited at higher temperatures have the smallest half-width, which changes little.

The shift of the Raman peaks towards higher energy and the increase in half-width have been explained by a decrease in crystal size [13]. However, the locations and half-widths of the Raman peaks behave differently when the precipitation temperature of the samples on soda-lime glass is raised from 350 ° C to 450 ° C. The locations and half-widths of the Raman peaks in the samples behave differently as the Raman peaks shift towards a higher wavenumber while the half-width decreases. There is such a discrepancy between the half-width and the Raman shift

TiO applied to the surface by atomic layer deposition at 400 ° C was also observed₂ in the case of thin films, and this discrepancy is explained by the temperature-dependent change in crystal size with stress [13]. However, it should also be noted that the development of EgRaman has also been attributed to the non-harmonic effects of phonon retention, stresses, non-stoichiometric defects and crystal lattice potentials due to differences in deposition temperatures [14].

Optical properties

TiO annealed on soda-lime glass and borosilicate glass at 500 ° C₂ The optical transmittance spectra of thin films are measured in the wavelength range 200 to 800 nm. TiO is in the 400800 nm spectral range₂-the total permeability of the films is about 85% and the permeability increases with increasing precipitation temperature (Figure 4a).

Prohibited zone width found (greedy)² and extrapolating the linear portion of the photon energy binding plot, provided that it is an indirect exclusion zone. TiO is observed as the precipitation temperature increases₂-reduction of the optical band gap of the films. TiO precipitated on soda-lime glass at 250, 350 and 450 ° C₂ the Eg sizes of the thin films are 3.71 eV, 3.58 eV and 3.56 eV, respectively. TiO precipitated on borosilicate glass at 450 ° C₂ in which case Eg is 3.54 eV.

Chemical composition and wettability

Thin TiO₂The chemical composition and bond structure of the films were studied by XPS. Figure 5 shows TiO₂XPS spectra of the electrons of the oxygen inner layers (Ols) obtained from the surface analysis of the fibers. After precipitation at different temperatures, the TiO was annealed₂films at 500 ° C for 1 hour.

The peaks in the electron XPS spectra of the ols inner layers were asymmetric and the peaks were deconvolved using Lorentz-Gaussian (pseudo-Voigt) fit analysis. Shirley type matching was used to subtract the background.

The binding energy peaks above 5530 eV and −531 eV in the electrons of the inner layers are due to the Me-0 bond [16]. Thus we can attribute the main peak (-530 eV) to Ti-O.

The sub-peak at -531 eV is caused by Ti₂Os (Ti⁺³) from the vacancy of oxygen atoms (Vo). The arm above the binding energy of -532 eV indicates that TiO₂There are also hydroxyl groups (OH-) on the surface. Thin TiO₂The atomic concentrations of the components found in the Ols spectrum of the films, such as Ti-O, Vo and OH-, were determined by Snowfields

Using cross-sections according to the area of ​​the corresponding Ols spectral peaks. The atomic ratios of OH / Ti-O and Vo / Ti-0 in the components are shown in Figure 8. These can be used to estimate the content of oxygen vacancies and hydroxyl groups on the surface of TiCl 2. As can be seen, the [OH] / [Ti-O] ratio increases from 0.06 to 0.30 with increasing precipitation temperature, while the highest [Vo] / [Ti-O] ratio (0.23 atom%) occurs at 350 ° C in TiO2 film applied to soda-lime glass.

Films deposited on ordinary window glass have been found to have low photocatalytic activity because the film contaminates the Na diffused from the substrate upon annealing.⁺ and Si⁴⁺with ions [17]. Na diffused from the substrate to the film surface⁺ion content was analyzed by XPS (Figure 8).

It can be seen in Figure 6 that the TiOa film deposited on the borosilicate glass support is still contaminated with a small amount of sodium. As can be seen, Na decreases⁺ content with an increase in the deposition temperature, which can be attributed to an increase in the film thickness as the deposition temperature increases, which slows down the diffusion of Na ions to the surface.

Chen et al. explain T12O3 and OH^- associated with the formation of an oxygen vacancy of 2Ti³⁺ 2 electrons are removed from the crystal lattice, which in turn is replaced by 2OH^-. Thus, as more oxygen is removed from the T1O2-X lattice, the concentration of oxygen vacancies increases and OH^- content which promotes wetting [18].

The surface wettability of TXh films deposited at different temperatures was determined by measuring the contact angle of water. Figure 8 shows the average contact angles of freshly deposited, UV-treated and aged T1O2 thin films. After annealing at 500 ° C for 1 hour, all samples were kept in plastic boxes for three months. The results show that the surface wettability of the prepared TKX thin films deposited on soda-lime glass depends on the deposition temperature. The water contact angle of the samples precipitated on soda-lime glass at 350 and 450 ° C is <10 °, which confirms the superhydrophilicity of the samples [19]. The water contact angle of the sample precipitated at 250 ° C is about 33 °. This sample also has the lowest (OH) / (Ti-O) ratio by XPS analysis (Figure 8). This highlights the importance of hydroxyl groups on the film surface, as it has been found that the large number of hydroxyl groups on the film surface promotes wetting [19].

Interestingly, according to the XPS study, a sample precipitated on borosilicate glass at 450 ° C has a larger contact angle than a sample precipitated on soda-lime glass and has a (OH) / (TiO) ratio twice as high as that deposited on soda-lime glass at 450 ° C. kilel. However, it has been identified that surface morphology may play an important role in wettability [19]. Therefore, borosilicate glass could precipitate and significant OH^- relatively low wettability of the sample due to differences in surface morphology.

After 30 minutes of UV treatment, the water contact angle of all samples drops below 10 °, indicating superhydrophilicity. In addition, the water contact angle of the samples precipitated at 350 and 450 ° C was about 0 °, regardless of the precipitation temperature and the substrate. Various mechanisms have been proposed for this process, initiated by Fujishima et al. [20]. This is due to displacements of surface hydroxyl groups [21] and light-induced surface vacancies.

After storing the UV-irradiated samples for 3 months in a plastic box, the contact angle of the water increased regardless of the precipitation temperature and the substrate compared to the UV-irradiated samples (Figure 8). Such degradation can be attributed to the replacement of chemically sorbed hydroxyl groups by oxygen atoms [22] and the absorption of organic pollutants into TiO2 films in the air [23]. TiCl 2 films deposited on soda-lime glass at 350 ° C retained their superhydrophilicity, i.e. a water contact angle of 10 °. In addition, a faster change in water contact angle has been observed for the TiCl 2 film deposited at 450 ° C than for other TiO2 films.

Photocatalytic activity

T1O2 The photocatalytic activity of thin film catalysts was tested in the gas phase decomposition of MTBE under the following conditions: residence time 15.6 s per section, relative humidity ca. 6% and reactor temperature 30 ° C. The MTBE concentration at the reactor inlet was 5 and 10 ppm.

Various studies have found that in addition to the final oxidation products (CO2 and H2O), the intermediates in the photocatalytic decomposition of MTBE in the gas phase are acetone, tert-butyl formate (TBF, CsFFoCh), isobutene and tert-butyl alcohol [2, 27]. The only intermediate observed in the gas phase for the decomposition of MTBE on the surface of TiCh films obtained by spray pyrolysis was TBF. No other intermediates expected to be formed in the gas phase upon further degradation of MTBE or TBF were either adsorbed and degraded on the catalytic surface or desorbed below the detection limit of the analytical apparatus (<500 ppb).

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MTBE conversion ((Csisse - Cväija) / C_sThe photocatalytic oxidation of MTBE and the formation of TBF as a function of prolonged contact time are shown in Figure 7. The MTBE degradation of the precipitated TiO 2 films, except for those deposited at 250 ° C, was studied for five exposure durations (15.6, 31.2, 46.8, 62.4 and 78.0 s) using one, two, three reactor reactors, respectively. , four or all five sections. The photocatalytic activity of the thin films was first studied in a section of the reactor with a 120 cm² photocatalytic surface, with the film deposited at 250 ° C having the lowest MTBE conversion (approximately 4%) and no further synthesis for a larger study. For testing the photocatalytic activity of films deposited at 350 and 450 ° C, 600 cm MTBE was used for conversion.² the size of the area covered. Figure 7 shows the conversion, which is expected to be higher with a longer duration of exposure.

The highest (over 80%) MTBE conversion was observed for the TiCE thin film applied to soda-lime glass at 350 ° C. Compared to films deposited at 450 ° C, the change can be attributed to the varying surface morphology and the highest amount of hydroxyl radical-generating oxygen vacancies (Table 1). These hydroxyl radicals then oxidize the adsorbed VOC molecules.

TiO 2 films deposited on a borosilicate substrate at 450 ° C show a slightly higher conversion of MTBE than those deposited on window glass due to significantly lower Na⁺ion content (0.80% and 11 atomic%, respectively). Many studies have shown that Na diffused from the substrate is likely to act⁺-ions as recombination centers for electrons and holes formed by light [24-25].

TiO2 film with a photocatalytic surface size of 480 cm deposited on a borosilicate support at 350 ° C², 100% MTBE was sufficient for a specific exposure duration of 0.13 s / cm² (specific exposure duration is defined here as the exposure duration per unit photocatalytic surface, ie 15.6 s / 120 cm²) and an initial MTBE concentration of 10 ppm. 480 cm² The surface area was sufficient to completely degrade TBF (10 ppm MTBE) when the exposure duration was 15.6 s per reactor section (see Figure 9).

TiO on soda-lime glass? the photocatalytic activity is lower in visible light than that of the thin film (2 to 5 sections) applied to the borosilicate glass. For example, Figure 10 shows that when the duration of exposure to visible light was 78 s (5 sections, 600 cm²), the MTBE conversion was 62% for thin film applied to borosilicate glass and 62% for soda-lime glass.

In the case of a thin film only 31%. However, despite its lower conversion rate, it can be used in many applications, especially if the working surface area of ​​the material is not a limiting factor.

A typical formation and disappearance of the intermediate TBF can be seen in Figure 7c. As the duration of exposure increases, the TBF content also increases, reaching a maximum (1.9 ppm TBF, 48% of theory, where about 40% of MTBE is degraded, ie 4 ppm) when the exposure duration is 48.8 s. Further prolongation of the exposure time to 78 seconds results in a situation where the rate of degradation of the intermediate exceeds the rate of its formation (only 15% of MTBE decomposes into TBF (1.9 ppm out of 7.5 ppm), 85% of MTBE is oxidized to other products or mineralized). For other photocatalytic thin TiCl 4 films, different steps in the typical profile of intermediate formation have been observed. In the case of TiCl 2 film deposited at 350 ° C, the formation of TBF decreases continuously (only 5% of MTBE was formed in TB for 78 seconds). Thus, the rate of degradation of the by-product exceeds the rate of formation (Figure 7a). In the case of a film deposited on soda-lime glass at 450 ° C, the tendency for TBF to degrade tends to exceed 62 s (in 78 s TBF formed about 13% of the degraded MTBE), although this is less pronounced than in borosilicate glass. in the case of a film. Many studies have shown that the formation of intermediates by photocatalytic decomposition can be influenced by a number of factors, such as the type and amount of catalyst, the method used, etc. [2, 26].² the surface area was sufficient for 100% acetone conversion at a specific exposure time of 0.13 s / cm² (specific exposure duration is defined here as the exposure duration per unit photocatalytic surface, ie 15.6 s / 120 cm²) and the initial acetone concentration was 5 ppm.

TiO2 film with a photocatalytic surface area of ​​600 cm deposited on borosilicate glass at 350 ° C², decomposed 100% of MTBE at 6% and 40% relative humidity (Figure 12).

Summary

Transparent TiCF thin films were deposited on a conventional window glass and borosilicate glass substrate by ultrasonic spray pyrolysis at 250-450 ° C, followed by annealing at 500 ° C for 1 hour. Analysis by scanning electron microscopy showed that the films were smooth, dense and free of cracks. Film thickness

EE 05840 B1 increases with increasing precipitation temperature in the range of 110-330 nm. Measurements by X-ray diffraction and Raman spectroscopy confirmed the presence of the T1O2 anatase phase in the T1O2 thin film deposited on both the window glass and the borosilicate glass. In addition, the average size of the crystals of TiO2 films deposited on borosilicate glass and soda glass at 450 ° C is 26 and 32 nm, respectively, indicating that Na⁺diffusion of ions has not reduced the average crystal size. The prepared thin TiO2 films deposited on soda glass at * 350 and 450 ° C are superhydrophilic [contact angle <10 °, 14], without UV treatment their contact angles are 7 ° and 6 °, respectively. The surface wettability test showed that after 30 minutes of UV treatment, the water contact angle of the prepared TiO2 films is less than 10 °. Optical measurement showed that the films are very transparent (~ 80%). The photocatalytic activity of T1O2 thin film catalysts was tested by the gas phase photocatalytic decomposition of MTBE. A thin film of T1O2 precipitated on borosilicate glass at 350 ° C decomposed 100% MTBE and decomposed toluene in the presence of acetone and ozone.

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