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

Method for making transparent photocatalytic superhydrophilic glass materials activated by visible light

TECHNICAL FIELD

The present invention relates to titanium based photocatalytic materials based on UV and visible light, which can be used e.g. , odor removal and indoor disinfection.

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 levels is due to many factors that can be attributed to human activities, such as emissions from internal combustion engines, factories, etc.

Methyl terributyl ether (MTBE, (CH₃)₃COCH₃) is the most widely used motor fuel additive [2]. Petrol contains MTBE, so it is also found in the troposphere. MTBE concentrations in the troposphere are expected to increase further under high usage loads. This is directly related to human disease, as one of the major disadvantages of this substance is carcinogenicity [2-3]. The indoor concentration of MTBE is approximately the same as that of outdoor air.

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

Typically, the TiCl2 photocatalyst is used either as a powder or immobilized on a substrate. T1O2 nanopowders used as photocatalysts have been identified as safe substances, which in some cases have been used as dietary supplements. However, recent T1O2 toxicity studies have shown that TiCh nanoparticles smaller than 20-30 nm can pose major 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 they have less adhesion to the substrate than thin films [7]. Thus, T1O2 must be strongly immobilized on the substrate to prevent nanoparticles from entering the atmosphere.

The thin photoactive TiCh film must meet the following requirements in order to be used in the field: high photocatalytic activity, superhydrophilicity, high transparency, optimum mechanical properties for substrate adhesion and abrasion resistance. In addition, TiCh photocatalyst immobilized on the window glass has great potential as a micronutrient deaerator and self-cleaning material for air, as modified window glass has significant market potential and soda-lime glass is an inexpensive base material.

Various methods have been used to prepare thin TiCl 2 films, such as intestinal gel submersion [8], intestinal gel sputter coating [9], chemical vapor deposition (CVD) [10], atomic layer deposition (ALD) [11], etc. In addition to the above methods, chemical spray pyrolysis is simple, fast, and inexpensive, and is suitable for coating large areas. It has been established that the photocatalytic activity of a thin TiO2 film deposited on a substrate (e.g., window glass) depends on several probable factors: thickness, surface morphology, crystal size, diffused ions (e.g., Na⁺and Si⁴⁺), etc.

A solution is known from WO9613327, which describes a transparent window having excellent photocatalytic activity and light transmittance, whereby at least one, about 0.1 to 5 micrometer thick, titanium oxide with a photocatalytic effect is formed by a pyro-sol method on a light transmitting glass substrate, is at least 50%, and preferably, an opaque SiO 2 gel transparent film is formed between the light-permeable substrate and the titanium oxide film, about 0.02-0.2 micrometres thick. This can be considered as the closest solution known in the art.

A solution is known from WO9411092, which describes the use of a photocatalyst for cleaning a hospital bed contaminated with bacteria and for treating air containing a malodorous compound. A semiconductor (e.g., titanium dioxide) film of an optical catalyst is applied to the interior surface of a hospital bar or living room wall. The film of the photocatalyst, which is irradiated with light from a general light source such as a fluorescent lamp, is optically excited by the low ultraviolet radiation in the light of the fluorescent lamp. Bacteria and chemical compounds that fall on the optically excited film are degraded.

A solution is known from WO9629375 which describes a method of making the substrate surface ultrahydrophilic by covering the surface with a layer containing a photocatalytic semiconductor, e.g. When applied to the surface of a substrate, such as a mirror, lens or window glass, this method prevents the growth of water droplets and renders the substrate very fog-free. Items treated with this method do not contain contaminants and can be easily cleaned in the rain or washed with water.

A solution is known from WO2013106776, which describes photocatalytic compositions containing a photocatalyst and a co-catalyst, wherein the photocatalyst may be titanium-based and react in some embodiments with visible light. The photocatalyst may be titanium dioxide, titanium oxide impurities or a composite powder containing titanium oxide. The composition may form a transparent layer on the substrate. A method for preparing a dispersion of CeO2 and spraying this dispersion on a substrate, in particular glass and window glass, has also been described.

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

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

EP1205243 is known which describes a method of applying a thin film of titanium dioxide with a photocatalytic activity on a transparent inorganic base, in particular a Pyrex glass, in crystalline anatase. The film is formed by precipitation (sputtering, spraying, immersion coating) of a stable liquid precursor containing an inorganic or organometallic titanium (IV) compound which has been partially or completely hydrolyzed in the presence of acids, surfactants and, ultimately, s-triazine derivatives. The latter increase the photocatalytic activity of the film. Applications include air purification and deodorization, interior disinfection and self-cleaning clear glass. The film has a thickness of 50 nm to 10 micrometers. The material is weather and abrasion resistant, homogeneous and transmits more than 80% of the visible light spectrum. It has been established that films deposited on ordinary window glass have low photocatalytic activity because the film contaminates the diffused Na⁺and Si⁴⁺ with ions [17],

There is a need for a simple method of applying thin film of titanium dioxide with photocatalytic properties to glass such as window glass and borosilicate glass, which must be UV and visible light, have superhydrophilic properties and be able to efficiently degrade volatile organic compounds (VOCs, benzene. Such material is suitable for self-cleaning windows and containers and for air purification. Such material can also be used in plant cultivation.

SUMMARY OF THE INVENTION

The invention relates to a process for the preparation of a transparent, photocatalytic and superhydrophilic thin film 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 by ultrasonic spray pyrolysis to a heated substrate, e.g., window glass, borosilicate glass, soda lime glass, quartz,, substrate temperature, e.g. 150-500 ° C, preferably 250-450 ° C, most preferably about 350 ° C; and the product is annealed in an atmosphere at a temperature of about 400-700 ° C, preferably about 500 ° C. In the case of window glass and soda-lime glass, the temperature may be up to about 550-600 ° C; the temperature may be up to about 700 ° C for borosilicate glass and quartz.

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

Said gelling agent is any suitable gelling agent such as acetylacetone.

The molar ratio of said Ti (IV) alkoxide to 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 titanium oxide precursor - is 0.05-1.0 mol / l, preferably 0.2 mol / l.

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

The films are transparent, have a smooth and smooth surface, firmly adhered to the substrate, and superhydrophilic even at 3 months (without prior UV treatment), and decompose acetone and MTBE 100% to HaO and CO 3. The TiCh film on the glass substrate degrades 31% of MTBE under visible light, while the TiCh film on the borosilicate substrate degrades 62% of MTBE under visible light.

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

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

Yet 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, prepared by the method described above.

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

Another object of the present invention is a self-cleaning glass and / or air-cleaning glass and / or a glass container for growing plants consisting of a glass layer and a TiO2 layer deposited on said glass layer by chemical spray pyrolysis.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

Figure 2 shows X-ray diffraction patterns of TiCl2 films deposited on soda-lime glass and borosilicate substrates at 250 ° C, 350 ° C and 450 ° C.

Figure 3a shows soda lime glass at various temperatures (250, 350 and 450 ° C) and 450 ⁰ Raman spectra of TiCl 2 films deposited on a borosilicate support. Figure 3b shows the effect of deposition temperature on 144 cm Raman spectroscopy of TiCh films deposited on a surface¹ peak position and half-width. All samples were annealed in air for 1 hour at 500 ° C.

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

Figure 5 shows XPS spectra of thin TiCl2 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 TiCl2 films deposited on soda lube glass at 250 and 450 ° C and on borosilicate glass at 450 ° C. All samples were annealed in air for 1 hour at 500 ° C.

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

Figure 8 is a table summarizing XPS studies and contact angle measurements of thin TiCh films deposited on soda-lime glass and borosilicate substrates at various temperatures. All XPS study specimens and specimens retained for three months for wetting tests are included. All samples were annealed at 500 ° C for 1 hour.

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

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

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

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

Figure 13 is a schematic diagram of the ultrasonic spray pyrolysis process.

EXAMPLES OF THE INVENTION

Thin films of TiO3 were deposited on a typical industrial window glass (soda lube) and borosilicate glass substrate by ultrasonic spray pyrolysis (USP). A schematic diagram 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 1: 4 molar ratio. The carrier gas was compressed air at a flow rate of 8 L / min and the spray rate was set at 2.5 mL / min. The ultrasonic mist transport tube was located at a fixed distance of 7 cm from the heating plate (on which the trays were placed). There were six spray cycles. The temperatures of the hot plate were 250 ° C, 350 ° C and 450 ° C for the layers deposited on the baking soda lime glass and 450 ° C for the film sprayed on the borosilicate glass. All precipitated samples were annealed in the air for 1 hour at 500 ° C in a Nabertherm L5 / 11 / 06D oven and are referred to throughout the article as prepared samples.

The structure of the samples was examined 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 Ä, 40 kV at 40 mA). Measurements were made in a 2-theta configuration with a scan range of 20-60 ° in 0.02 ° steps and a scan speed of 27mm¹. The average crystal size was calculated by the Scherrer's method from the half width of the T1O2 anatase phase reflection diffraction line (101). Raman spectra were obtained with a HORIBA Jobin Yvon HR800 micro-Raman spectrometer in the 100-1200 cm range¹, 532 nm laser beam was used for excitation.

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

Surface morphology and film thickness for energy dispersion spectroscopic analysis were measured using a Zeiss HR FESEM Ultra 55 scanning electron microscope at accelerating voltages of 4.0 kV and 7.0 kV. X-ray photoelectron spectroscopy (XPS) was performed on a Kratos Analytical AXIS ULTRA DLD spectrometer equipped with an Al Ka ​​monochromatic X-ray source and an Mg / Κα dual-channel achromatic X-ray source. TiCl 2 binding energy values ​​were calculated from the C 5s peak (285.0 eV). Transmittance and reflectance spectra of the films were obtained in the spectral range 200-1200 nm with a Jasco V-670 spectrophotometer.

TiCh films are smooth, dense, without cracks and firmly attached to the substrate. The surface roughness measured from a surface of 1 x 1 itm is about 0.4-1.25 nm.

The photocatalytic activity of the thin films was investigated by the photocatalytic degradation of the model air pollutant methyl tert-butyl ether (MTBE, C5H12O) in the gas phase. The inlet concentration of the gaseous pollutant was 10ppm. The photocatalytic activity of the thin films was studied in a multi-section continuous photocatalytic reactor. The multi-compartment reactor consists of five compartments each with a volume of 130 ml and one compartment with a photocatalytic coating of 120 cm², so the total area of ​​the reactor is 600 cm²(see [27]). A Fourier transform infrared analyzer (FT-IR, Interspec 200-X) with a Specac Tornado gas cell (8 m, 1.33 L) and a flow-through nozzle were connected to the reactor. A 15 W fluorescent lamp (Actinic BL, Philips) with a UV-A irradiance of 3.3 mW / cm was placed above each section of the reactor² (integrated between 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, which was maintained by lamp heat and controlled by a temperature controller (Omega CN9000A).

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

The MTBE peaks were measured in the infrared band 1063-1124 cm '¹. The intermediate terributyl formate (TBF) formed (or formed) by MTBE gas-phase photocatalytic oxidation was also monitored quantitatively (in the infrared band 1138-1190 cm¹) by analyzing the effluent gas by FT-IR using a quantitative spectral collection in FDM VPFTIR HiRes. No gaseous products other than carbon dioxide and water were observed.

The photocatalytic thin film coatings of 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. In the dark, it was found that MTBE TiCh was not adsorbed on the surface of the catalyst by a thin film. In the absence of a catalyst, no photochemical degradation of MTBE was observed under UV irradiation. In both comparisons, contaminant content (no difference between reactor inlet and outlet values) remained unchanged when contaminated air was passed through five sections of the reactor for 30 minutes.

Surface morphology

Photographs of TiO2 films deposited on glass panes and borosilicate glass at temperatures of 250 to 450 ° C and annealed at 500 ° C by scanning electron microscope are shown in Figure 1. TiCl 2 films are smooth, dense, non-cracked and firmly attached to the substrate. The results show that the surface morphology of the layers deposited on the glass substrate changes when the deposition temperature is increased from 250 ° C to 450 ° C (Figure 1a, b, c). The TiCl2 film deposited on the 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-defined grains having a size of about 50 nm. The TiCh film sprayed at 350 ° C has an intermediate surface morphology which includes the surface morphology of both the film deposited at 250 ° C and 450 ° C.

The thickness of each prepared thin film was determined from cross sections obtained by scanning electron microscopy. We observed that the thin TiCl2 films deposited on the window glass had a thickness of 110, 180 and 240 nm at deposition temperatures of 250, 350 and 450 ° C, respectively. The TKh film deposited on a borosylate glass substrate at 450 ° C has a thickness of 330 nm. The observed changes in thickness and morphology of TiCb deposited on different substrates may be accounted for by the difference in growth rate, since the substrate glass pane (2 mm) is thicker than borosilicate glass (1 mm) and therefore the temperature of the borosylate substrate could be higher.

Structural properties determined by X-ray diffraction

Figure 2 shows X-ray diffractograms of TiO2 films deposited on a tray of glass and borosylate glass at 250, 350 and 450 ° C and annealed at 500 ° C for 1 hour. As can be seen in Figure 2, X-ray diffraction patterns of TiCl 2 films exhibit 2-theta peaks belonging to the T1O2 anatase structure at 25.5 °, 37.8 °, 48.2 °, 53.9 ° and 55 ° [12]. In addition, 2-theta diffraction peaks appeared at 22.9 ° and 43.3 °, respectively, on the silica-containing substrate. No diffraction peaks of the rutile or brucite phase of T1O2 are seen. The average size of the T1.O2 crystals was calculated from the peak of the anatase phase (101) according to the Scherrer formula. The average size of crystals on the baking soda glass increases with the deposition temperature and is 20-35 nm. The TiCh film deposited on a borosylate glass substrate has an average crystal size of 26 nm at 450 ° C and 40 nm at 350 ° C. Thus, it was confirmed that TiCh films deposited on glass and borosylate glass substrates are in the crystalline phase of the anatase but have different crystal size, thickness and surface morphology as determined by scanning electron microscopy (Figure 1). One reason for this may be the different thicknesses of the substrates used, as evidenced by the difference in the rate of film formation between the soda-lime and borosylate glass substrates.

Structural properties determined by Raman spectroscopy

Figure 3a shows the Raman spectra of TiO 2 films deposited on various types of soda lime glass and borosilicate substrates at different temperatures (250, 350 and 450 ° C) and subsequently annealed at 500 ° C for 1 hour.^-1. Vibration peaks in Raman spectra 143 (Eg) cm '¹, 197 (Eg) cm '¹, 396 (Big) cm '¹ and 637 (Eg) cm-1¹which are characteristic of the T1O2 anatase phase and no peak belongs to the rutile or brucidic phase of T1O2.

Raman peaks were solved by Fityk software on Gaussian curves and examined for changes in their half-width as well as the major peak of the anatase phase (144 cm '¹) Raman shift (Figure 3b). You can see that 144 cm '¹ at a peak wavelength shifts to films of maximum wavelength for soda lime at 250 ° C, with a slight difference between films deposited on soda lime at 350 and 450 ° C. For the film sprayed on the borosilicate glass at 450 ° C, no shift towards higher energy was observed. 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.

Shift of Raman peaks towards higher energy and increase in half-width have been explained by a decrease in crystal size [13]. However, the locations and half-widths of Raman peaks behave differently when raising the deposition temperature of samples from soda lime glass 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 wave number while the half-width decreases. Such a discrepancy between half-width and Raman shift has also been observed for T1O2 thin films deposited at 400 ° C on an atomic layer, and this discrepancy is explained by the temperature-dependent change in crystal size, which is accompanied by stresses [13]. However, it should also be noted that E_g The Raman-like evolution has also been attributed to non-harmonic effects of phonon retention, stresses, non-stoichiometric defects and crystal lattice potentials due to differences in deposition temperatures [14].

Optical properties

The optical transmittance spectra of T1O2 thin films annealed on baking soda lime and borosilicate glass at 500 ° C are measured in the wavelength range 200-800 nm. In the 400-800 nm spectral region, the total permeability of TiCh films is about 85% and the permeability increases with the increase of the precipitation temperature (Figure 4a).

Prohibited zone width found (ahu)² and extrapolating the linear portion of the photon energy binding graph, assuming it is an indirect exclusion zone. As the precipitation temperature increases, a decrease in the optical barrier width of the TiCh films is observed. At π

The TiCh thin films deposited on 250, 350 and 450 ° C soda-lime glass have a size of 3.71 eV, 3.58 eV and 3.56 eV, respectively. For T1O2 deposited on a borosilicate glass at 450 ° C, Eg is 3.54 eV.

Chemical composition and wetting

The chemical composition and bond structure of the thin TiCl2 films were studied by XPS. Figure 5 shows XPS spectra of the electron (Ols) oxygen layers of the TiCh films surface analysis. After precipitation at various temperatures, the TiCl 2 films were annealed at 500 ° C for 1 hour.

The peaks of the XPS spectra of the electrons of the Ols inner layers were asymmetric and the peaks were deconvoluted using Lorentz-Gaussian (pseudo-Voigt) fitting analysis. Shirley-type matching was used to subtract the background.

The coupling energy peaks above the -530 eV and -531 eV electrons of the Ols inner layers are caused by the Me-0 bond [16]. Thus, we can assign the main peak (-530 eV) to Ti-O. The lower peak at -531 eV is due to T12O3 (Ti⁺³) associated with the occurrence of oxygen atoms (Vo). The link energy above -532 eV shows that the TiO2 film also has hydroxyl groups (OH-) on its surface. The atomic concentrations of the components found in the Ols spectra of thin TiO2 films, such as Ti-O, Vo and OH-, were determined using the Snowfields cross-sections according to the area of ​​the respective Ols spectral peaks. The atomic ratios of OH / Ti-O and Vo / Ti-O in the components are shown in Figure 8. These can be used to evaluate the content of oxygen vacancies and hydroxyl groups on the surface of T1O2. As can be seen, the ratio [OH] / [Ti-O] increases from 0.06 to 0.30 with an increase in precipitation temperature, while the highest [Vo] / [Ti-O] ratio (0.23 atom%) occurs at 350 ° C in TiOi film applied to soda-lime glass.

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

Figure 6 shows that TiO2 film deposited on a borosilicate glass substrate is still contaminated with a small amount of sodium. As can be seen, Na decreases⁺ content with increasing precipitation temperature, which can be attributed to increasing film thickness as the precipitation temperature increases, slowing down the diffusion of Na-ions to the surface

Chen et al., Explain ΊΪ2Ο3 and OH^- correlated with the presence of 2Ti upon the occurrence of oxygen vacancy³⁺ this effect removes 2 electrons from the crystal lattice, which in turn is replaced by 2OH. Thus, as more oxygen is removed from the TiCh.v grid, the concentration of oxygen vacancies increases and OH^- content which promotes wetting [18].

The surface wettability of TiO 2 films deposited at various temperatures was determined by measuring the water contact angle. Figure 8 shows the mean contact angles of newly deposited, UV-treated and aged T1O2 thin films. After 1 hour annealing at 500 ° C, all samples were stored in plastic boxes for three months. The results show that the surface wettability of the prepared T1O2 thin films deposited on the baking soda glass depends on the deposition temperature. The water contact angle of the samples deposited on the baking glass at 350 and 450 ° C is <10 °, confirming the superhydrophilicity of the samples [19]. The contact water of the sample precipitated at 250 ° C is approximately 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 established that a large number of hydroxyl groups on the film surface promotes wetting [19].

Interestingly, the XPS study shows that the sample deposited on the borosilicate glass at 450 ° C has a larger contact angle than the sample deposited on the soda lube glass and has a (OH) / (Ti-O) ratio twice that of the TiCl film. However, it has been established that surface morphology can play an important role in wettability [19]. Therefore, a significant amount of OH could be precipitated on the borosilicate glass^- amount of sample with relatively low wettability may be 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 deposited at 350 and 450 ° C, independently of the deposition temperature and substrate, was approximately 0 °. Various mechanisms have been proposed for this process, initiated by Fujishima et al. [20]. This is due to the proposed displacement of surface hydroxyl groups [21] and light-induced surface edges.

After the UV irradiated samples were kept in a plastic box for 3 months, the water contact angle increased independent of the precipitation temperature and substrate compared to the UV irradiated samples (Figure 8). Such wetting can be attributed to the substitution of oxygen atoms for chemically sorbed hydroxyl groups [22] and the adsorption of organic pollutants on TiCk films in the air [23]. As can be seen, the increase in water contact angle with aging of TiCh films is much slower. The TiCl 2 films deposited on the soda-lime glass at 350 ° C maintained their superhydrophilicity, i.e. a water contact angle of 10 °. In addition, TiCh film deposited at 450 ° C has a faster water contact angle change than other TiCh films.

Photocatalytic activity

TiO₂ The photocatalytic activity of the thin film catalysts was tested for MTBE degradation in the gas phase under the following conditions: residence time of 15.6 s per section, relative humidity of about 6% and reactor temperature of 30 ° C. The concentration of MTBE at the reactor inlet was 5 and 10 ppm.

In various studies, besides the oxidation end products (CCh and H2O), acetone, terributyl formate (TBF, C5H10O2), isobutene and ferributyl alcohol are intermediates in the photocatalytic decomposition of MTBE in the gas phase [2, 27]. The only intermediate observed in the gas phase was TBF when MTBE was degraded on the surface of TiCl 2 films obtained by spray pyrolysis. Other intermediates expected to be formed in the gas phase upon further degradation of MTBE or TBF were either not adsorbed and degraded on the catalytic surface, or desorbed below the detection limit of the analytical apparatus (<500 ppb).

MTBE conversion ((C_Sisse - C_V(yeah) / C_S(%), the photocatalytic oxidation of MTBE and the formation of TBF are shown in Fig. 7 as a function of increasing contact duration with successive addition of reactor sections. MTBE degradation of precipitated TiCl 2 films, except films deposited at 250 ° C, was investigated for five contact durations (15.6, 31.2, 46.8, 62.4, and 78.0 s) using one, two, three reactors, respectively. , four or all five sections. The photocatalytic activity of the thin films was first investigated in a section of the reactor containing 120 cm² photocatalytic surface, with the film deposited at 250 ° C having the lowest MTBE conversion (about 4%) and was no longer synthesized for further study. For the photocatalytic activity of films deposited at 350 and 450 ° C, 600 cm MTBE conversion was used.² the size of the covered area. Figure 7 shows the conversion expected to be higher at longer exposure times.

The highest MTBE conversion (over 80%) occurred at 350 ° C for T1O2 thin film deposited on soda-lime glass. Compared to films deposited at 450 ° C, the variation can be attributed to the varying surface morphology and maximum amount of oxygen vacancies that produce hydroxyl radicals (Table 1). These hydroxyl radicals then oxidize the absorbed VOC molecules.

TiCh films deposited on a borosilicate substrate at 450 ° C exhibit slightly higher MTBE conversion than films deposited on window panes, due to the significantly lower Na⁺ions (0.80 and 11 atomic%, respectively). Many studies have shown that diffused W-ions from the substrate act as recombination centers for electron-hole light [24-25].

TiO2 film deposited on a borosilicate substrate at a temperature of 350 ° C and having a photocatalytic surface area of ​​480 cm², 100% MTBE conversion was sufficient at a specific exposure duration of 0.13 s / cm² (Specific Exposure Time is defined 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 size of the surface was sufficient to completely decompose TBF (10 ppm MTBE) with an exposure duration of 15.6 s per reactor section (see Figure 9).

TiO on soda lime glass? the photocatalytic activity under visible light is lower than that of the thin film (2-5 sections) applied to the borosilicate glass. For example, Figure 10 shows that when the exposure time to visible light was 78 s (5 sections, 600 cm²), the MTBE conversion was 62% for borosilicate glass thin film and only 31% for soda lime glass thin film. Despite its lower conversion rate, it can still be used in many applications, especially when the working surface area of ​​the material is not a limiting factor.

Typical generation and disappearance of intermediate TBF can be seen in Figure 7c. As the duration of exposure increases, the TBF content also reaches its maximum (1.9 ppm TBF, 48% of theoretical maximum with about 40% MTBE degraded at 4 ppm) when the exposure duration is 48.8 s. Further prolongation of the exposure duration to 78 seconds results in an intermediate where the rate of degradation of the intermediate exceeds its rate of formation (only 15% of MTBE is degraded to TBF (1.9ppm at 7.5 ppm), 85% of MTBE is oxidized to other products or mineralized). For other photocatalytic thin TiCl 2 films, different stages of the typical formation profile of intermediates have been observed. For TiCl 3 film deposited at 350 ° C, TBF formation is consistently reduced (for 78 seconds, TBF is only 5% of MTBE). Thus, the rate of degradation of the by-product exceeds the rate of formation (Figure 7a). For a film deposited on a soda-lime glass at 450 ° C, the tendency for TBF to decompose is greater than s (exposure for 78 s is about 13% of the decomposed MTBE), although not as clear as the borosilicate glass. at once. Many studies have shown that the formation of intermediates in photocatalytic degradation can be influenced by many factors, such as type and amount of catalyst, method used, etc. [2, 26].

With TiCH film deposited on a borosilicate glass at 350 ° C, it can be seen that 480 cm of the photocatalyst² size of the surface was sufficient for 100% acetone conversion at a specific exposure duration of 0.13 s / cm² (Specific Exposure Time is defined as the exposure duration per unit photocatalytic surface, ie 15.6 s / 120 cm²) and an initial acetone concentration of 5 ppm.

TiCh film deposited on a borosilicate glass at a temperature of 350 ° C and having a photocatalytic surface area of ​​600 cm², decomposed 100% of MTBE at relative humidity of 6% and 40% (Figure 12).

Summary

Transparent TiCl2 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 without cracks. The film thickness increases with the increase of the 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 on the TiO2 precipitated on both the window glass and the borosilicate glass. in thin film. In addition, TiCh films deposited on borosilicate glass and soda-lime glass at 450 ° C have an average crystal size of 26 and 32 nm, respectively, indicating that Na⁺diffusion of ions has not reduced the average crystal size. The prepared thin TiCl2 films deposited on the soda lime glass at 350 and 450 ° C are super hydrophilic [contact angle <10 °, 14]. without UV treatment, their contact angles are 7 ° and 6 ° respectively. The surface wettability test showed that the water contact angle of the prepared TiCl2 films after 30 minutes of UV treatment is less than 10 °. Optical measurement showed that the films were very transparent (~ 80%). The photocatalytic activity of TiOs thin film catalysts was tested for the photocatalytic degradation of MTBE in the gas phase. The T1O2 thin film deposited on the borosilicate glass at 350 ° C decomposed 100% MTBE and, in the presence of acetone and ozone, decomposed the toluene.

References [1] http://www.who.int/mediacentre'l / factsheets / fs313 / en / [2] AK Boulamanti, CJ Philippopoulos, Photocatalytic degradation of methyl tert-butyl ether in the gas phase: A kinetic study, Journal of Hazardous Materials 160 (20 08) 83-87, [3] E. Galanos, S. Poulopoulos, C. Philippopoulos, Photocatalytic Destruction of Methyl Tert-Butyl Ether in a Gas Phase Using Titanium Dioxide, Journal of Environmental Science and Health, Part A, 37: 9,1665-1675 [4] G. Varshney, SR Kanel, DM Kempisty, V. Varshney, A. Agrawal, E. Sahle-Demessie, RS Varma, Μ. N. Nadagouda, Nanoscale TiCh Films and Their Application in Remediation of Organic Pollutants, Coordination Chemistry Reviews 306 (2016) 43-64.

[5] M. Skocaj, M. Filipic, J. Petkovic, S. Novak, Titanium dioxide in our daily lives; is it safe ?, TiCh in everyday life [227-247].

[6] Sammy W. Verbruggen, TiO2 Photocatalysis for Degradation of Pollutants in the Gas Phase: From Morphological Design to Plasmonic Enhancement, J. Photo C. and Photo. B. C: Photochemistry Reviews 24 (2015) 64-82.

[7] M. Addamo, V. Augugliaro, A. Di Paola, E. Garcia-Lopez, V. Loddo, G. Marci, L. Palmisano, Photocatalytic thin films of TiO2 formed by a sol-gel process using titanium tetraisopropoxide as. precursor, Thin Solid films 516 (2008) 3802-3807.

[8] S. Suarez, N. Arconada, Y. Castro, J. M. Coronado, R. Portela, A. Durän, B. Sanchez, Photocatalytic degradation of TCE in dry and wet air conditions with TiCh porous thin films, Applied Catalysis B: Environmental 108-109 (2011) 14-21.

[9] HO Seo, TG Woo, EJ Park, BJ Cha, H. Kim, SW Han, YD Kim, Enhanced photocatalytic activity of TiCE films by surface carbon impurities removal; the role of water vapor, Applied Surface Science 420 (2017) 808-816.

[10] D. Byun, Y. Jin, B. Kim, J. K. Lee, D. Park, Photocatalytic deposition of TiCh by chemical vapor deposition, Journal of Hazardous Materials B 73 (2000) 199-206.

[11] M. Buchalska, M. Surowka, J. Hämäläinen, T. Livonen, Photocatalytic activity of TiCh films on Si support prepared by atomic layer deposition, Catalysis Today 252 (2015) 14-19.

[12] Powder Diffraction File (PDF), (PDF-2 / Release 2013 RDB) (01-070-7348).

[13] L. Aarik, T. Arroval, R. Rammula, H. Mändar, V. Sammelselg, J. Aarik, Atomic layer deposition of TiCh from TiCk and Os, Thin Solid Films 542 (2013) 100-107.

[14] E. Uyanga, A. Gibaud, P. Daniel, D. Sangaa, G. Sevjidsuren, P. Altantsog, T. Beuvier, Chih Hao Lee, A. M. Balagurov, Structural and vibrational investigations of Nb-doped TiO2 thin films, Materials Research Bulletin, (2014), Vol.60 pp. (222-231).

[15] NC Rauta, T. Mathewsa, P. Chandramohanb, MP Srinivasanb, S. Dasha, AK Tyagi, Effect of temperature on growth of T1O2 thin films by spray pyrolysis: Structural, compositional and optical properties, Materials Research Bulletin 46 (2011) 2057-2063.

[16] I. Gromyko, M. Krunks, T. Dedova, A. Katerski, D. Klauson, I. Oja Acik, Surface properties of sprayed and electrodeposited ZnO rod layers, Applied Surface Science 405 (2017) 521-528.

[17] H. Xie, B. Liu, X. Zhao, Facile process to greatly improve photocatalytic activity of T1O2 thin film on window glass for photodegradation of acetone and benzene, Journal of Chemical Engineering 284 (2016) 1156-1164.

[18] W. Chen, P. Koshy, C. Christopher Sorrel, Effects of film topology and contamination as a function of thickness on photo-induced hydrophilicity of transparent T1O2 thin films deposited on glass substrates by spin coating, J. Mater. Sci (2016) 51 2465–2480.

[19] S. Banerjee, DD Dionysiou, SC Pillai, Self-cleaning applications of T1O2 by photoinduced hydrophilicity and photocatalysis, Applied Catalysis B: Environmental 176-177 (2015) 396-428.

[20] R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Light-induced amphiphilic surfaces, Nature 388 (1997) 431-432.

[21] N. Sakai, A. Fujishima T. Watanabe, K. Hashimoto, Enhancement of Photoinduced Hydrophilic Conversion Rate of T1O2 Film Electrode Surfaces by Anodic Polarization, J. Phys. Chem. B 105 (2001) 3023-3026.

[22] L. Yang, M. Zhang, S. Shi, J. Lv, X. Song, G. He, Z. Sun, Effect of annealing temperature on wettability of TiO2 nanotube array films, Nanoscale Research Letters (2014), 9, 621.

[23] C. Holtzinger, L. Rapenne. Mr. Chaudouet. G. Berthome, M. Langlet, Thickness effects in naturally superhydrophilic TiO2-SiO2 nanocomposite films deposited via a multilayer sol-gel route, J Sol-Gel Sci Technol (2012) 64: 465-479.

[24] P. Novotna, J. Krysa, J. Maixner, P. Kluson, P. Novak, Photocatalytic activity of sol-gel.

TiO2 thin films deposited on soda lime glass and soda lime glass precoated with a SiO2 layer, Surface & Coatings Technology 204 (2010) 2570-2575.

[25] H.-J. Nam, T. Amemiya, M. Murabayashi, K. Itoh, Photocatalytic Activity of Sol-Gel TiO2 Thin Films on Various Kinds of Glass Substrates: Effects of Na + and Primary Particle Size, J. Phys. Chem. B 2004,108,8254-8259.

[26] ZS Seddigi, SA Ahmed, SP Ansari, NH Yarkandi, E. Danish, MDY Oteef, M.

Cohelan, Shakeel Ahmed, AM Abulkibash, Photocatalytic Degradation of Methyl tertButyl Ether (MTBE): A Review, Advances in Environmental Research, Vol. 3, No. 1 (2014) 11-28.

[27] M. Krichevskaya, S. Preis, Gas-Phase Photocatalytic Oxidation of Styrene in a Simple 15 Tubular T1O2 Reactor, Journal of Advanced Oxidation Technology, Vol. 6, No. 2 (2003), 150-157.