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WO1997007069A1 - Verre autonettoyant et procede pour le realiser - Google Patents

Verre autonettoyant et procede pour le realiser Download PDF

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Publication number
WO1997007069A1
WO1997007069A1 PCT/US1996/012792 US9612792W WO9707069A1 WO 1997007069 A1 WO1997007069 A1 WO 1997007069A1 US 9612792 W US9612792 W US 9612792W WO 9707069 A1 WO9707069 A1 WO 9707069A1
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WO
WIPO (PCT)
Prior art keywords
glass
precursor
photocatalyst
self
film
Prior art date
Application number
PCT/US1996/012792
Other languages
English (en)
Inventor
Adam Heller
Yaron Paz
Yair Haruvy
Original Assignee
Adam Heller
Yaron Paz
Yair Haruvy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Adam Heller, Yaron Paz, Yair Haruvy filed Critical Adam Heller
Priority to JP9509342A priority Critical patent/JPH11511109A/ja
Priority to EP96928813A priority patent/EP0844985A1/fr
Priority to AU68432/96A priority patent/AU6843296A/en
Publication of WO1997007069A1 publication Critical patent/WO1997007069A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
    • C03C17/23—Oxides
    • C03C17/25—Oxides by deposition from the liquid phase
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/34—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions
    • C03C17/3411—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions with at least two coatings of inorganic materials
    • C03C17/3417—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions with at least two coatings of inorganic materials all coatings being oxide coatings
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C23/00—Other surface treatment of glass not in the form of fibres or filaments
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2217/00—Coatings on glass
    • C03C2217/20—Materials for coating a single layer on glass
    • C03C2217/21—Oxides
    • C03C2217/212—TiO2
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2217/00—Coatings on glass
    • C03C2217/70—Properties of coatings
    • C03C2217/71—Photocatalytic coatings
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2218/00—Methods for coating glass
    • C03C2218/10—Deposition methods
    • C03C2218/11—Deposition methods from solutions or suspensions
    • C03C2218/113—Deposition methods from solutions or suspensions by sol-gel processes

Definitions

  • This invention relates to the photocatalytic oxidative stripping of organic contaminants from the surface of glass and the process of making such photocatalytic glass.
  • TiO 2 TiO 2 coated glass mesh and TiO 2 coated glass tube-based photoreactors.
  • Another reactor with a TiO 2 coated glass tube is described by T. Ibusuki et al. on page 376.
  • the photocatalytic films described were all light scattering, as they were made of photocatalysts such as Degussa P25, e.g., with an abundance of titanium dioxide particles approximately 0.1-0.3 microns in diameter. This particle size, even in the thinnest films, produces a milky appearance. Such light scattering films are not efficient or useful in applications such as clear, self-cleaning glass surfaces for windows and mirrors.
  • Such known films are applied to optical lenses of optical instruments to provide scratch resistance and are also applied in anti-reflective optical coatings, usually by reactive evaporation or by reactive sputtering of titanium in an oxygen-containing atmosphere.
  • Such coatings can also be made by applying a solution containing a precursor of a photocatalyst, e.g., TiO 2 , to a glass surface, forming a precursor film and heating to a high temperature where organic matter in the precursor film is oxidized and TiO 2 is crystallized.
  • a good photocatalyst strips a film of stearic acid at a rate of about 20nm per hour or more, i.e., reduces the thickness ofthe stearic acid film by about 20 nm per hour (or more).
  • the preferred barrier is formed by first introducing into the near surface region ofthe glass to be coated, protons, i.e. hydrogen ions, by exchanging alkali metal ions with protons of an acid and/or by hydrolytic cleavage of silicon-oxygen-silicon bonds with an acid, in a process called "acid etching" or simply "etching".
  • the hydrogen or proton-containing glass layer is then reacted with a precursor of an oxide ofa four-valent element, preferably a precursor of crystalline titania or zirconia comprising inorganic oxide.
  • a thin, sodium-migration blocking layer comprising titanium, silicon and oxygen and/or zirconium, silicon and oxygen is formed.
  • a sodium migration blocking layer is also formed when the proton or hydrogen-containing glass (acid glass), is reacted with a precursor of silica.
  • a preferred process of forming the acid glass layer includes etching with acid, most preferably boiling in 9 M sulfuric acid.
  • the sodium migration reducing barrier layer is preferably formed upon heating the acid glass with a precursor of titania, and/or zirconia to a temperature in excess of about 300°C and less than about 500°C and preferably about 400°C.
  • the photocatalytic activity of a formed, optically clear TiO 2 layer on glass is also enhanced by treating the TiO 2 coated glass with a material that reacts with sodium oxide, particularly with a dilute acid that does not dissolve TiO 2 in the form in which it is included in the coating.
  • a material that reacts with sodium oxide particularly with a dilute acid that does not dissolve TiO 2 in the form in which it is included in the coating.
  • the anion of an acid that does not dissolve TiO 2 does not form a strong complex with four valent titanium.
  • These types of acids include protic acid, Lewis acid and Bronsted acid, and can be in liquid or gas form.
  • nitric, perchloric, and tetrylfluorboric acids are useable in the invention, as they are not known to form complexes with four valent titanium.
  • Chlorides, fluorides and sulfates are generally not useable in the invention because they are known to strongly complex with titanium (TV).
  • a particularly useful sodium migration blocking layer is formed by applying a film of an organotitanate that decomposes upon heating in air, a nascent, yet non-crystalline precursor of anatase TiO 2 , and reacting the precursor with the sodium-depleted acid glass prior to final calcining of the coated glass and at an elevated temperature, preferably about 450°C. After final calcination, a transparent, non-scattering, adherent nanocrystalline photocatalytic oxide film is produced, with a distinct, sodium migration-blocking interface between the glass and the photocatalytic film.
  • the photocatalyst coated glass ofthe invention when exposed to ultraviolet light, efficiently cleans itself of organic contaminants.
  • This photocatalyst coated glass ofthe invention is particularly useful in applications such as photocatalytically self-cleaning windows, windshields and mirrors.
  • Figure 1 is a graph showing the UV absorption spectra of TiO 2 films on fused silica.
  • Figure 2 is FTIR spectra of stearic acid coated on clear TiO 2 film on fused silica prior to (dotted line) and after (solid line) exposure to UVA light for 7.5 minutes.
  • Figure 3 is a graph showing the UV absorption spectra of TiO 2 films on etched (dashed line) and on non-etched soda lime glass (solid line).
  • Figure 4 is a graph showing the effect ofthe calcination temperature on UVA, i.e., near UV, photoactivity of clear films of titanium dioxide:(A) Two layers of TiO 2 on fused silica, (B) Two layers of TiO 2 on etched glass, (C) One layer of TiO 2 on etched glass, (D) One layer of TiO 2 on one layer of ZrO 2 on etched glass.
  • Figure 5 is a graph showing the effect of etching duration on the photoefficiency of clear TiO 2 films on soda lime glass.
  • Photocatalytic films can form the basis for self-cleaning or photooxidatively cleaning glass, useful, for example, as self-cleaning windows, mirrors, optical components, eyeglass lenses, and automotive windshields.
  • photocatalyst films e.g. TiO 2
  • the coated self-cleaning glasses ofthe invention provide an abrasion resistant, photoefficient, optically clear, self-cleaning glass.
  • Deposition of organic contaminants on glass usually reduces visibility. Furthermore, light particularly from headlights of oncoming cars and from the sun when the sun is low on the horizon, interferes with driving when the windshield is contaminated. Films of organic contaminants smeared on the windshield by wipers operating in rain also add to the hazard of driving. Light scattered from contaminants on outside or inside rearview mirrors of cars impairs visibility in these mirrors. Dirt or fingerprints on lenses or eyeglasses impair vision.
  • the inventive films maintain surfaces clean of organic contaminants. Inorganic, non-oxidizable contaminants are readily removed by being blown or washed off, once the organic matter that makes them stick to the glass surface is oxidized.
  • the most preferred method for preparing photocatalytic glass is by acid etching the glass followed by application ofthe photocatalyst composition and then calcination.
  • the photocatalytic film coated glasses ofthe invention e.g. containing photocatalytic particles and adherent to glass, are optically clear. They may have a tint or color, but do not absorb or scatter visible light so as to impair visibility through the glass or cause severe glare.
  • the photocatalytic films also adhere to glass and resist abrasion.
  • An inventive film adhering to glass cannot be removed by pressing adhesive tape against it, as discussed below in Example 1 , and rapidly pulling on it (Tape Test).
  • An abrasion resistant film ofthe invention is not damaged when cleaned with wet or dry paper or cloth, and it typically is not scribed by a pencil of H2 hardness or softer.
  • the photocatalytic film is formed of photocatalytic particles, e.g., TiO 2 , cast onto acid glass and calcined for specific adherence to the glass.
  • the photocatalyst-containing films ofthe invention contain a material that, upon exposure to light, particularly UV light, accelerates the oxidation in air of organic compounds absorbed or deposited on the film.
  • One example of such a film is a film containing crystalline, preferably anatase, titanium dioxide.
  • the film is well bound to glass in the present invention, generally through an intermediate barrier layer that prevents migration of alkali metal oxides, e.g. sodium, yet is transparent to visible light.
  • the glasses useful in the present invention have varied compositions.
  • the most commercially important and most common glasses comprise sodium and calcium ions and have a network formed of bonds of silicon and oxygen atoms.
  • the self-cleaning glasses of this invention are usually photocatalytic films cast on common glass, which is formed of silicon dioxide, alkali metal oxides (oxides of Column I metals ofthe periodic table), particularly sodium and potassium, and oxides of alkaline earth metals (oxides of Column 2 metals ofthe periodic table), particularly calcium.
  • the ratio ofthe number of oxygen atoms to the number of silicon atoms is between 2.2 and 2.7 in the glasses ofthe invention. In the preferred glasses, the ratio of oxygen atoms to silicon atoms is between 2.2 and 2.5.
  • the glasses may contain other oxides, such as oxides of trivalent or tetravalent rare earths or oxides of aluminum, boron, antimony, germanium, lead and tin.
  • the glasses are transparent, meaning that they can be seen through and are useful as windows, mirrors, windshields, and the like.
  • An example of glass commonly used in such applications and useful in the invention is soda lime glass.
  • the method ofthe invention is intended to prevent migration of alkali metal oxides from glass, particularly of sodium and/or potassium, into the precursor ofthe photocatalytic film and/or into the photocatalyst film by creating a barrier to the migration.
  • the photocatalytic film formed upon calcining of its precursor can efficiently clean its surface of oxidizable contaminants such as carbon-rich organic films.
  • Glass that is commercially used in windows, mirrors, and optical lenses typically contains significant amounts of alkali metal oxides, such as sodium oxide and potassium oxide (usually at least about 10% by weight).
  • alkali metal oxides such as sodium oxide and potassium oxide (usually at least about 10% by weight).
  • Photocatalysts useful in this invention are generally photoconductors or semiconductors having band gaps greater than 2.5eV and smaller than 4.5eV.
  • the photocatalytic films are generally less than one micron thick, preferably about 40-80 nm thick, and consist of sufficiently small particles to avoid scattering of visible light.
  • the crystallites ofthe photocatalytic particles are densely packed and oriented so that they do not scatter visible light.
  • the preferred photocatalysts are crystalline oxides, particularly crystalline oxides comprising titanium, tin, tungsten or molybdenum.
  • a particularly useful photocatalyst is titanium dioxide in the anatase phase.
  • photocatalysts include TiO 2 with co-catalysts such as Pt, Pd, Au, Ag, Cu, W, Mo, or their sulfides and oxides; compound oxides such as (SrTiO 3 ) or CaTiO 3 , and TiO 2 in the rutile phase or in the mixed anatase and rutile phases. While a preferred photocatalyst, titanium dioxide, is exemplified herein, it is understood that other photocatalysts, e.g., those described above, forming clear films on glass may also be used. Titanium dioxide in the anatase or the rutile phases has an index of refraction of visible (yellow) light greater than about 2.4.
  • Coating of photocatalyst films on glass having a low refractive index causes an increase in the refractive index.
  • a low refractive index e.g., soda lime glass which has a refractive index below 1.6
  • Coating of photocatalyst films on glass having a low refractive index causes an increase in the refractive index.
  • such an increase can be undesirable, because as the angle between the dashboard and the windshield is reduced or the index of refraction ofthe windshield is raised, the reflected image ofthe dashboard becomes visible to the driver looking through the windshield.
  • Such reflection is reduced by forming the photocatalytic film ofa combination ofthe photocatalyst and a material having a lower refractive index than that ofthe photocatalyst.
  • Such a film is one comprising non-crystalline silicon dioxide (SiO 2 ) and anatase or rutile TiO 2 .
  • SiO 2 non-crystalline silicon dioxide
  • TiO 2 anatase or rutile TiO 2
  • the index of refraction, in the visible is only about 1.46. (As compared with 2.4-2.7 in the absence of SiO 2 .)
  • a photocatalyst precursor is generally a film formed of a non-crystalline, three, four, or five- valent element, preferably of an oxide of such an element, which film forms an active photocatalytic film, eg., on calcining in air.
  • the oxide is non-volatile at about 600°C, and the preferred three, four, or five-valent elements are titanium, tin, tungsten, or molybdenum. Most preferred is Ti + .
  • the photocatalyst-precursor films can be formed by their deposition from a liquid phase, or from a vapor phase.
  • Useful photocatalytic precursor compositions include alkoxides, halides and oxyhalides of titanium, tin, tungsten, or molybdenum, e.g., a titanium tetralkoxide.
  • a most preferred photocatalyst precursor is a film formed upon partial hydrolysis of titanium tetraalkoxide, followed by polymerization by condensation ofthe hydrolysate.
  • the sol of which the photocatalysts precursor film is cast in addition to the photocatalyst precursor, also contains a precursor ofa lower refractive index film.
  • a preferred second component or precursor sol is a precursor of silicon dioxide, e.g., formed by co-hydrolyzing a silicon alkoxide, such as a silicon te raalkoxide silicon, alkyltrialkoxide or dialkyldialkoxide, co-dissolved with titanium alkoxide acetylacetonate.
  • the ratio ofthe amounts ofthe silicon and titanium oxide precursors in the sol are adjusted as needed to obtain the desired refractive index.
  • the photocatalytic film compositions range from pure titanium dioxide to compositions having a 1 : 10 titanium dioxide:silicon dioxide molar ratio.
  • Preferred low-refractive index films comprise vitreous silicon dioxide and crystalline titanium dioxide phases.
  • a barrier layer is defined as a barrier that slows or stops the diffusion or migration of alkali metal ions (e.g., sodium ions) and or alkali metal oxides (e.g., sodium oxide) into the photocatalyst precursor film or into the photocatalyst film.
  • alkali metal ions e.g., sodium ions
  • alkali metal oxides e.g., sodium oxide
  • the barrier layer operates at the termperatures that the inventive photocatalyst precursor and photocatalyst films experience, and for the duration ofthe films.
  • the barrier ofthe invention is the product ofthe reaction between hydrogen glass and a photocatalyst precursor as defined above.
  • the most preferred three, four, or five-valent elements are Ti 4+ , Zr 4+ , Ge 4+ , Sn + , and Si 4+ .
  • the most preferred barrier film is the reaction product between acid glass and the precursor of TiO 2 , and includes the elements silicon, titanium, and oxygen.
  • a photocatalyst containing layer can be formed on the surface ofthe glass from a vapor phase or from a precursor dissolved or dispersed in a liquid.
  • the preferred liquids containing the precursor are long lived sols. An example of these is described in Example 1.
  • Stable sols can be formed, for example, of titanium tetraalkoxides, by reacting these first with acetylacetone, then with water.
  • the sols contain polymers ofthe precursor species or crystallites ofthe photocatalyst that do not have a longest dimension greater than about 30nm and most preferably not greater than about 20 nm, and are preferably smaller than about 5nm in their larger dimension.
  • the preferred liquid phase in which the sol is dissolved or dispersed comprises alcohol in excess. Alcohols such as n-propanol, methanol, and butanol are useable.
  • a film of this liquid is applied to the glass surface, preferably to acid or etched glass, formed by acid etching (boiling in 9M sulfuric acid).
  • the volume applied and the concentration ofthe precursor are selected so that the final thickness ofthe photocatalyst-containing layer will not be less than lOnm nor more than 500nm.
  • the preferred final thickness is 20-200nm.
  • the film can be formed by known methods, such as spraying microdroplets while the glass is cold or hot; dipping the glass in the liquid then removing it; pouring the liquid onto the glass and leveling the liquid layer mechanically or by spinning.
  • the film can also be formed by other methods, including a dry process, such as sputtering or evaporating a metal and then oxidizing it; or by reacting a low molecular weight molecular or metallic precursor in the gas phase prior to its deposition on the glass.
  • a dry process such as sputtering or evaporating a metal and then oxidizing it; or by reacting a low molecular weight molecular or metallic precursor in the gas phase prior to its deposition on the glass.
  • a titanium tetraalkoxide can be evaporated and decomposed either en route to or on the surface ofthe glass.
  • TiCl 4 can be reacted with water to form
  • TiO 2 en route to the surface.
  • metallic Ti can be reactively sputtered in an O 2 containing atmosphere to form a TiO 2 film.
  • Reactants that are useful in exchanging sodium ions or other alkali metal ions ofthe glass at or near its surface (by protons) and thus increase the photocatalytic activity ofthe coated glass are generally acids.
  • the acid glass reacts with a precursor ofthe crystalline TiO 2 , ZrO 2 or SiO 2 film, a sodium migration reducing barrier layer is formed. Even in the presence of this barrier layer, some photoactivity of the crystalline titanium dioxide-comprising films on glass is still lost when sodium oxide from the glass diffuses into part ofthe titanium dioxide layer near the glass. Photoactivity can be partially restored by subsequent acid treatment.
  • Acid Etching Glass-Pretreatment Etching is the process whereby the reactive acid glass is formed.
  • etching may involve one or both ofthe following processes: Exchange of alkali metal (e.g., sodium) ions ofthe glass with protons; and scission, through hydrolysis, of Si-O-Si bonds. In both processes, a glass having SiOH junctions is produced.
  • An enxample of an etchant is boiling 9M aqueous sulfuric acid. This is the preferred etchant.
  • the glass is first exposed to acid so that sodium ions are extracted from its surface, being exchanged by protons and thereby forming an acid glass with silicon-bound OH-groups.
  • the treatment with acid can be at ambient or, preferably, at higher temperatures, e.g., at the boiling temperatures ofthe acid.
  • the glass surface can be rinsed following exposure to the acid with water, preferably deionized water, so as to remove any water soluble sodium salt. It has been noticed that treating ofthe glass with an acid prior to applying the photocatalytic coating to the glass leads to a higher photoefficiency.
  • the rinsing solution can be deionized water, or it can also contain a volatile base or ion such as ammonium hydroxide or an ammonium salt.
  • Preferred acids for etching glass include those which form a hydrogen glass upon reaction with the glass. An example of such an acid is 9M (50%) sulfuric acid. Most preferably, the glass is reacted with boiling 9M H 2 SO 4 .
  • the photocatalyst precursor or photocatalyst containing film is then deposited on the acid-treated surface.
  • the acid treated glass should not be calcined prior to application ofthe catalytic film, as such calcining lowers the photocatalytic activity. It is suggested that reaction between the acid-treated glass and the photocatalyst crystalline precursor establishes a sodium-migration barrier at the interface ofthe glass and the film.
  • the acid-treated and optionally rinsed glass is coated with the photocatalyst precursor.
  • the precursor be in the form of a sol having an ambient temperature shelf life longer than a day.
  • the sol can be formed, for example, from a titanium tetraalkoxide, such as titanium tetraisopropoxide.
  • the tetraalkoxide is first reacted in an alcohol solution, preferably in an excess alcohol, and preferably in an alcohol solution where the alcohol differs from the one that is evolved from the tetraalkoxide upon its hydrolysis.
  • the sol can be formed by adding water to the titanium tetraalkoxide solution, in the preferred process the titanium tetraalkoxide is first reacted with a bifunctional Ti 4+ complexing agent, such as acetylacetonate, to form a complex where the titanium to acetylacetonate ratio is 1 : 1.
  • This complex is then hydrolyzed, preferably at room temperature, by adding water (preferably dissolved in alcohol), preferably at a molar ratio of 10 moles of water per 1 mole of titanium.
  • the resulting precursor sol is generally stable, meaning that when stored for at least a day at a temperature between 5°C and 35°C the solution remains substantially clear.
  • a uniform film ofthe photocatalyst-containing compounds is cast on the glass through a process such as spinning, dipping, painting, spraying or applying an excess of solution then spreading it with a blade.
  • the cast film is then allowed to dry.
  • the dried-film coated-glass is next calcined, e.g., heated at a temperature to form photocatalytic crystallites and cause the photocatalyst layer to adhere to the glass. Calcination is preferably by heating in air at a rate resulting in a temperature increase of
  • this glass is photocatalytically self-cleaning within the scope ofthe invention.
  • the calcination temperature is generally in excess of 275°C and less than 650°C, and preferably is in the range of 400°C - 650°C.
  • the most preferred temperature is in the range of 400-550°C; for films on silica, the most preferred range is 550-600°C.
  • the photocatalytic activity (i.e. the rate at which the glass cleans itself of an organic contaminant) ofthe already photocatalyst-coated glass can be further increased by a second treatment, termed "post-treatment", with acid.
  • Post-treatment even in the absence of initial acid etching to form the acid glass, increases the low photocatalytic activity, though only to a lesser level than that observed when the glass was acid etched prior to deposition ofthe photocatalyst precursor. Applicants have found that multiple acid treatments can increase the self-cleaning glass's photoefficiency.
  • the photocatalytic-film- coated glass is again exposed to an acid that reacts with or neutralizes sodium oxide or calcium oxide or a product of these.
  • the preferred acids for this process step are strong mineral acids, the ions of which do not form strong complexes with four valent ions such as titanium ions (Ti 4+ ).
  • Dilute aqueous nitric acid, and particularly nitric acid of O.IM to 3M concentration, with a preferred concentration of 0.2M is useful for this process step.
  • Other useful acids include tetra fluoboric acid and dilute perchloric acid.
  • acids examples include 6M aqueous hydrochloric acid and 6M aqueous sulfuric acid, both of which dissolve or damage the photocatalytic titanium dioxide film on the glass.
  • the glass may be rinsed, preferably with water, then dried.
  • the inventive self cleaning glasses include a substrate glass, barrier and a photocatalyst, as described above.
  • Self-cleaning glasses ofthe invention prepared as described above have coatings that strongly adhere to the glass and are abrasion resistant. These self-cleaning glasses have a photoefficiency, as defined in Example 1, when a film stearic acid is photoreacted, of at least 3.5 X lO " .
  • the glasses ofthe invention have a photooxidation rate sufficient to oxidize daily, in direct sunlight, organic contaminant films at a rate of 50 nm per day or more. At this rate, impaired vision due to a dirty windshield or lens of an eyeglass is minimized. 50 nm thick spots of contaminants interfere with vision, for example, by scattering light and causing glare.
  • the glasses ofthe invention can also withstand successive applications and removals of scotch tape on their coated surfaces (tape test). Glasses of the invention can withstand being scribed with pencils of hardness H2 or softer as described in Example 1.
  • the sol was made of a precursor solution prepared by mixing 4.5 mL Ti(OCH(CH 3 ) 2 ) 4 , (97% in propanol) with 10.0 mL n-propanol and 1.6 mL acetylacetone (acac) to provide a stock solution having Ti:propanol:acac molar ratio of about 1 :9: 1.05.
  • a casting solution was prepared by mixing 1.0 ml ofthe precursor solution with a 1.8 ml water/n- propanol solution (1:9 v/v), the resulting water to titanium ratio being about 11:1.
  • the fused silica slides Prior to casting, the fused silica slides were rinsed in a cleaning solution (usually methanol), washed thoroughly with de-ionized water, and dried in a stream of air. The casting solution was then spread on the substrate (0.03 mL per 2.5x2.5 cm slide) which was spun, after the application, for 2 minutes at 4000 rpm to dryness. In the next stage, the coated silica slides were heated in air to 500°C at a rate of 50°C min " and were calcined at this temperature for 30 minutes. The calcination transformed the product of the hydrolytic reaction into a microcrystalline oxide, stripped all organic residues, and bound the TiO 2 film to the substrate. Multiple TiO 2 layers were produced by applying a layer, drying in an oven (90°C, 10 minutes), applying another layer and finally calcining.
  • a cleaning solution usually methanol
  • the thickness ofthe films 60 ⁇ 15 nm for a one layer film, was determined with an Alpha step 200 profilometer (Tencor Instruments). Transmission electron diffraction patterns and images ofthe thin films were obtained using JEOL- 1200EX and JEOL-2010 microscopes. For these measurements, the films were detached from their supports by pressing 200 mesh copper grids against the films while boiling in potassium hydroxide solution (6 M), following by thorough washing ofthe grids with water to remove any potassium residues. The electron diffraction ring patterns obtained by this method were indexed as that of T1O2 in the anatase phase and the dark field imaging suggested that the crystallites were segmented, with a typical segment being approximately 3 nm in diameter.
  • the resultant films were not damaged when wiped aggressively with any of several types of paper, including "Kimwipe", office copying machine paper, and newsprint, whether dry or wet. Furthermore, the films could not be removed by 20 successive applications and removals of Scotch® adhesive tape (3M-810), nor damaged when scribed with pencils of hardness H2 or softer.
  • the photoactivity ofthe various coated slides was tested by casting thin films of stearic acid (CH 3 (CH 2 ) 16 COOH) on the TiO 2 -coated substrates and measuring at a defined irradiance the rate of decrease in the integrated absorbance ofthe ensemble ofthe C-H stretching vibrations between 2700 cm “1 and 3000 cm “1 .
  • stearic acid CH 3 (CH 2 ) 16 COOH
  • the measurements were performed on batches of 8-12 slides.
  • the organic films were cast by applying 3x10"2 ml of 8.8x10"- ⁇ M stearic acid in methanol per slide and spinning at 1000 rpm for 2 minutes to dryness.
  • the integrated IR absorbance ofthe stearic acid films was measured by a Nicolet Magna IR-750 FTIR.
  • the actual number of stearic acid molecules on the surface was calculated based on the integrated absorbance of densely packed monolayers of homologs having a known area per molecule (such as octadecyl trichlorosilane, arachidic acid and behenic acid).
  • a typical stearic acid film had, prior to illumination, an integrated absorbance of 0.6 cm" 1 corresponding to ⁇ 1.9xl0 ⁇ molecules cm"2 .
  • the UV light source for the photoefficiency measurements was either a UVA wide band lamp, the peak emission being at 365 nm (Hideaway 6000 Solarium, Helitron Ltd.) or a 254 nm line-emitting mercury lamp (Sylvania G30T3).
  • the irradiance, measured at the slide surface, was 2.4 ⁇ 0.4 mW cm"2 for the UVA source and 0.8 ⁇ 0.15 mW cm ⁇ 2 for the 254 nm source, corresponding to respective fluxes of 4.4x1015 photons sec" cm"2 and 1.0x10 IS photons sec"-- cm"2.
  • the photoefficiency is defined as the number of carbon - hydrogen bonds of stearic acid stripped from the photocatalyst surface per incident photon, dAxKxN/f, where dA is the change in the integrated IR absorbance ofthe C-H vibrations ofthe stearic acid per minute; K is the number of C-H bonds in a stearic acid molecule (35); N is the number of stearic acid molecules per cm ⁇ per integrated absorbance unit, having a value of 3.17x101-5; and f is the irradiance
  • FIG. 1 presents the integrated absorbance of the organic contaminant's infrared C-H stretching vibrations.
  • Figure 2 presents the FTIR spectra ofa Ti ⁇ 2 film on silica contaminated with stearic acid prior to and after exposure to the UVA light for 7.5 minutes.
  • the rate at which the stearic acid film was stripped remained constant during the exposure, as long as a continuous stearic acid film remained on the surface ofthe photocatalyst.
  • the efficiency ofthe photoreaction was generally independent of time, remaining constant throughout the reaction period.
  • Table 1 presents the integrated absorbance of stearic acid on silica coated with the photoactive Ti ⁇ 2 films following illumination with the UVA light. The efficiency in the table was calculated based on the change following 7.5 minutes of illumination.
  • the photoefficiency of a fused silica substrate coated with a single layer of Ti ⁇ 2 film was between 14xl0"3 and 21xl0"3 upon illumination with the UVA light and between 45x10 ⁇ 3 and 81xl0"3 upon illumination with the 254 nm light, the ratio between efficiencies being scaled with the ratio in the number of photons absorbed per cm-2 per second at each wavelength. Values, averaged over more than 25 slides are presented in table 2.
  • Table 1 Changes in the integrated absorbance ofthe FTIR C-H stretch band of stearic acid on silica slides coated with clear and photoactive Ti ⁇ 2 upon illumination with UVA light. The efficiency given in the table was calculated based on the change after 7.5 minutes of exposure.
  • Example 2 the same organotitanate coating solution described in Example 1 was applied onto the surface (0.04 ml per 3.75x2.5x1 mm slide) which was spun, as described for Example 1.
  • the coated glass substrates were calcined usually at a temperature of 400 °C, thus producing clear and homogeneous films, denoted as GE films.
  • Ti ⁇ 2 films on non-etched glass slides denoted as GN
  • Ti ⁇ 2 films on etched and on non-etched silica denoted SE, SN respectively
  • Thicker films were produced either by applying a first layer ofthe titanate precursor solution, oven drying (90 °C, 10 minutes), applying a second layer and calcination or by repeating the single layer preparation process.
  • the former class is denoted as (2), whereas the latter is denoted as (1+1).
  • GN type films on etched glass
  • Type GE films were found to be identical to the SN films described in Example 1 (i.e. consisted of segmented nanocrystallites having the anatase phase) whereas the type GN films were typical for materials having no long range order, with a diffused ring in their selected area diffraction pattern corresponding to an interplanar distance of 2.6 -3.6 A.
  • compositions ofthe supported films, as well as ofthe glass substrates, were measured by x-ray photoelectron spectroseopy (VG-ESCALAB).
  • VG-ESCALAB x-ray photoelectron spectroseopy
  • the samples were sputtered with an argon gun (Varian 981-2043, 3 kV, 25 mA) and re-measured.
  • the estimated sputtering rate was 0.15 nm min.” 1.
  • the samples were cut into 8 mm x 8 mm slides, that were attached to their pedestals by a conducting adhesive tape to reduce charging during the sputtering process.
  • a high atomic fraction of sodium was measured not only at the interface between the Ti ⁇ 2 and the glass but also at the air interface.
  • the concentration of sodium at the air interface was actually higher than in the bulk ofthe films.
  • the sodium diffusion length exceeded the film thickness and sodium segregated at the surface ofthe titanium dioxide film.
  • the effect of etching the glass prior to coating with the Ti ⁇ 2 precursor on the sodium concentration at the Ti ⁇ 2 film surface is evident, the atomic percentage of sodium in the GE films being 2-3 times lower than that in the GN films.
  • the atomic percentage of sodium exceeded that in the bulk ofthe soda lime glass (10 atom%), showing that the film was not only contaminated with sodium, but actually extracted sodium from the glass.
  • the photoefficiency ofthe photocatalytic stearic acid stripping process was between 5xl0 ⁇ 3 and 12xl0"3 for the GE slides illuminated with the UVA light whereas for the Ti ⁇ 2 films made on non-etched glass (the GN films) it was at least 7 times less.
  • the photoefficiency results obtained for a batch containing 12 slides, half of which were GE type while the other half were GN type are given as an example in Table 4.
  • Table 2 the average photoefficiencies obtained for Ti ⁇ 2 clear films on fused silica, on glass etched by H2SO4 prior to coating with the titanium precursor, and on non-treated glass are presented. Each value listed in the table represents an average for more than 25 samples.
  • Batch Film Type As is Double NaN0 3 NaN0 3 NaOH NaOH -number and wave ⁇ calcination treatment treatment + soaking soaking + and (# of length calcination calcination samples)
  • Table 5 Photoefficiency of Ti0 2 films, expressed as the number of C-H bonds in a steric acid film consumed per impinging photon.
  • a-Dipping in NaN0 3 (1 M, 10 minutes, 20°C).
  • b-Dipping in NaOH (1 M, 10 minutes, 20°C).
  • c-Batch 4 obtained by washing batch 3 slides with methanol to remove stearic acid residues, immersion in water and drying.
  • d-Dipping in NaN0 3 (0.2 M, 10 minutes, 20°C).
  • Table 5 demonstrates the deleterious effect of sodium contamination on the efficiency of titanium dioxide films on glass. Dipping ofthe clear Ti ⁇ 2 films in NaOH (IM, 20°C) reduced their efficiency under 365 nm light to nil (Table 5, batch 3), and subsequent washing with de-ionized water led to recovery ofthe efficiency (Table 5, batch 4). However, when the NaOH treated slides were calcined, the loss of their efficiency could not be reversed (Table 5, batches 3,4). Double calcination of GE films (Table 5, batches 3-5) did not increase or decrease their efficiency. Films made of Degussa P-25 that were immersed in NaOH were 10 fold less efficient than untreated films, under 365 nm light (Table 5, batch 1).
  • the XPS results show that sodium migrates from the soda lime glass substrate into the titanium dioxide layer during the calcination step.
  • the sodium was extracted from the surface of the soda lime glass, and when the extracted glass was overcoated with the organo-titanate precursor and calcined, then the sodium content in the titania films was significantly lower. Such lowering affected the titanium containing phase that formed and thereby the photocatalytic behavior. It is known that at temperatures below 550°C, the extraction of sodium from glass is governed by an ion exchange mechanism and is limited by the rate ofthe diffusion of sodium ions rather than by the rate of diffusion of protons.
  • the nanocrystalline Ti ⁇ 2 film has a greater affinity for sodium than the silicate network of soda lime glass, particularly when the surface ofthe crystallites is hydrated and the protons are sodium exchangeable, H2Ti n O2n+l being a stronger acid than H2Sin ⁇ 2n+l •
  • silicate glasses but not necessarily in Ti ⁇ 2 films on glass, sodium also accumulated at the surface upon hydration ofthe silicate network, sodium segregation at the surface being coupled with depletion of sodium from the layer below.
  • the sodium depleted .layer observed in silicate glasses was not observed in the GE films, showing that Na + accumulated throughout the film, not only at its air interface. It was particularly noteworthy that the concentration of sodium in the GN films was higher than in the soda lime glass itself. This higher concentration can be rationalized by Ti-OH being a stronger acid than Si-OH, because ofthe more electropositive nature of Ti + 4 relative to Si + 4 , combined with fast sodium diffusion across the film.
  • the sodium concentration in the titanium dioxide film was not related to its final concentration at the glass-titania interface, but to its concentration at this interface at the start ofthe calcination, when the unique sodium diffusion limiting layer was formed.
  • Sodium extraction followed by a first calcination, then by coating with the Ti ⁇ 2 precursor and by a final calcination did not provide films as photoactive as those obtained when in the first calcination the Ti ⁇ 2 precursor was already present. Therefore, dehydration and compacting ofthe glass accounted only for part ofthe sodium transport characteristics ofthe layer.
  • the unique sodium transport limiting characteristics are explained by reaction ofthe decomposing anatase Ti ⁇ 2 precursor and the dehydrating hydrogen glass, and/or by fast nucleation and growth at the interface between the glass and the Ti ⁇ 2 precursor layer.
  • the photoefficiency invariably decreased when the Na + concentration increased in the Ti ⁇ 2 films. Furthermore, the photoactive GE films lost efficiency when soaked in NaNO3 and calcined at temperatures where the NaNO3 decomposed to sodium oxide.
  • the lesser efficiency of films on soda lime glass relative to films on fused silica presented in Example 1 could have resulted either ofthe presence of non- anatase phases or the presence of sodium oxide at the air interface, where it would have raised the local pH.
  • films on non etched glass the sodium fraction exceeded 10 atom% and, as a result, formation of an ordered anatase, brookite or sodium titanate phase was inhibited. This reduced the efficiency practically to nil for 365 nm illumination.
  • on etched glass there were only crystalline anatase domains, even though their sodium atom percentage was as high as 8%.
  • the Ti ⁇ 2 films have a higher affinity for sodium ions than the soda lime glass itself and extract the sodium ions from the glass during the calcination step.
  • Sodium transport to the Ti ⁇ 2 layer can be retarded by forming a blocking layer. Such a layer forms upon calcining the Ti ⁇ 2 precursor film on the hydrogen glass, formed upon extraction ofthe sodium with hot acids such as sulfuric acid.
  • Table 6 presents the efficiency (as defined in Example 1) measured for a batch of slides containing GN and GE slides, with and without post -treatment, upon illumination with the UVA source.
  • pretreatment means boiling the uncoated glass in 9M sulfuric acid for 30 minutes
  • without water wash means that the slide was dried with a residue of nitric acid.
  • With water wash means that any residual nitric acid was removed by washing with de-ionized water.
  • Table 7 “treated with HNO3 " means soaked in HNO3 0.2 M for 15 minutes, followed by a water wash.
  • HNO3 post-treatment significantly increased the photoefficiency of non- etched glass (GN type) Ti ⁇ 2 films although their photoefficiency remained much smaller than that ofthe standard etched glass (GE) Ti ⁇ 2 films.
  • GE type films the improvement was slighter.
  • post-treatment was not an effective substitute for pre-etching ofthe glass.
  • the gain efficiency upon HNO3 post treatment was partially lost with time, as observed in repeated measurements.
  • No increase in efficiency was observed upon HNO3 treatment of films prepared according to Example 1 on fused silica (Table 8), manifesting that the observed increase in efficiency in the Ti ⁇ 2 coated glass was not due to a lowered surface pH.
  • the cause ofthe improvement was reaction or neutralization of sodium oxide or its products that migrated to the titanium dioxide layer's surface during the calcination process.
  • the acid chosen was nitric acid.
  • the anion of this acid in contrast to with the anions of sulfuric and hydrochloric acid does not complex the four valent titanium ion.
  • the rate of dissolution ofthe photoactive film in nitric acid was consequently much slower than its rate of dissolution in sulfuric or hydrochloric acid at the same normalities.
  • GE films were more resistant to soaking in concentrated acids than the GN films.
  • the coating solution prepared in the manner described in Example 1, (denoted as "Ti” solution in this example) was mixed with various non-interacting organic solvents such as hexane, methylene chloride, chloroform, thus obtaining coating solutions, their viscosities depending upon the volumetric ratio between the coating solution and the non-interacting solvent.
  • films made from the "Ti” solution, as well as from a mixture ofthe "Ti” solution with methanol which may interact, like other alcohols, with the titanium dioxide precursor were prepared.
  • the mixed solutions were spread on acid - etched glass substrates (40 ml per 3.75x2.5 cm) which were spun, after the application, in N2 environment, for 2 minutes at 1000, 2500 or 4000 rpm to dryness.
  • the slides were then calcined at 400°C for 35 minutes, in air. Clear, homogenous, well adhered films, were obtained.
  • Table 9 Efficiency values of slides prepared by spin coating of mixtures ofthe Ti ⁇ 2 precursor coating solution with various non-interacting solvents.
  • Ti represents the regular coating solution, its preparation being described in example 1. It can be concluded that photoactive clear and homogenous films can be formed on glass by means of diluting the coating solution with solvents that do not interact with the titanium dioxide precursor and that this method is especially viable for cases in which relatively low rates of spinning are required.
  • Coating solutions of controlled viscosities prepared in the manner described in example 4, were used to produce clear, photoactive and homogeneous films of Ti ⁇ 2 on glass.
  • Ti ⁇ 2 precursor coated films were than calcined at 400 - 450 °C for 35 minutes. A clear, homogeneous, well adhered film of Ti ⁇ 2, was obtained. Best results, in terms of clarity and homogeneity, were obtained by performing the process under N2 atmosphere, enriched with the solvents' vapor. The photoefficiencies of several dip-coated films, as measured by the stearic acid test described in example 1, are presented in table 10.
  • Table 10 Efficiency values of slides prepared by dip-coating in mixtures hexane and the Ti ⁇ 2 precursor coating solution.
  • Ti represents the regular coating solution, the water to titanium ratio being 11:1, while Ti# represents a coating solution where the water to titanium ratio was app. 4: 1
  • Silica films were produced on soda lime glass by the same manner described in Examples 1 and 2, using silicon tetrapropoxide instead of titanium tetra-i- propoxide.
  • the silicate precursor solution consisted of 10 ml n-propanol, 1.6 ml acetylacetonate (acac) and 4.9 ml ofa Si(OPr) 4 solution (Aldrich Cat. No. 23,574, 95%) by weight).
  • the coating solution was made from 1.0 ml ofthe silicate precursor solution and 1.8 ml of 1:10 (v:v) water in n-propanol.
  • soda lime glass slides were then etched in boiling sulfuric acid for 30 minutes as described in Example 2, and coated by spin coating as described therein. Following drying at 80°C for 20 minutes, a second layer, made ofthe same coating solution described in Example 1 (denoted as "overlayer”), was applied by spin coating as described therein. The slides were then calcined at 450°C for 30 minutes to produce clear films comprised ofa silica layer (denoted as "underlayer") between the glass substrate and the photoefficient titanium dioxide overlayer. Glass slides coated with a film containing a first layer of zirconia and a second, photoactive layer of titania were obtained in the same manner.
  • the zirconia coating solution was made of zirconium tetra n-propoxide (Aldrich 33,397 -2, 70% in 1-propanol) with the same molar ratios between zirconium, acac, water and propanol as described for the titania precursor coating solution in Example 1. No post-treatment with nitric acid was used.
  • the efficiency ofthe slides was measured in the manner described in Example 1.
  • films containing one and two layers of TiO 2 on glass were made from the same batch of etched glass slides and with the same TiO precursor coating solution.
  • the efficiency of these slides was measured simultaneously with that ofthe glass-silica-titania films.
  • Table 11 the efficiency ofthe two layered structure, containing a silica underlayer and TiO 2 overlayer, was higher than that ofa single layer of titanium dioxide by a factor of between 1.4 and 2.0, but less than that ofa film containing two layers of TiO 2 .
  • a two-layered structure consisting of a zirconia underlayer and one TiO 2 overlayer coated on glass, had higher efficiency than that of a glass coated with a single film of TiO 2 , when made at calcination temperatures higher than 500°C, where the diffusion of sodium into the forming TiO 2 film is fast enough to reduce its efficiency even in acid etched glass substrates ( Figure 4).
  • a layer composed of a mixture of TiO 2 and SiO 2 (1:1) molar ratio was produced on soda lime glass and on fused silica by preparing the appropriate coating solution and applying it onto the substrate by spin coating as described in examples 1 and 2.
  • a precursor solution was made of 10 ml n-propanol, 2.25 ml titanium-tetra-i- propoxide (98% in propanol, density: 1.033 gr. cm “3 ), 1.6 ml acetylacetonate (acac) and 2.43 ml of silicon tetrapropoxide (Aldrich 23,574-1, 95% in propanol, density:0.916 gr. cm " ).
  • the coating solution was made by mixing 1.0 ml ofthe mixed precursor solution with 1.8 ml of a water/ n-propanol solution (1:10 v/v). The coating solution was then spread by spin coating at 4000 rpm on H 2 SO 4 etched glass slides (40 ⁇ l per 3.75 x 2.5 cm slide) and on non-etched fused silica slides (30 ⁇ l per 2.5 x 2.5 cm slide). The slides were then dried in an oven at 100°C for 10 minutes. On part ofthe slides, a second layer, consisting ofthe TiO 2 precursor coating solution, mentioned in Example 1 , was applied in the same manner described in Examples 1,2.
  • Table 12 The photoefficiencies of films composed of one TiO 2 layer on a silica/ titania underlayer in comparison to films made of one TiO 2 layer, two TiO 2 layers, and a mixture of TiO 2 /SiO 2 .

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Abstract

Un verre autonettoyant utile, par exemple, pour les vitrages et les pare-brise, est réalisé par l'application d'un film de revêtement optiquement clair et résistant à l'abrasion, contenant un photocatalyseur. Dans ce procédé, on provoquer une déplétion des oxydes de métaux alcalins dans un verre ordinaire et/ou on forme une barrière contre la migration de ces oxydes depuis le verre, et ensuite on applique le film de revêtement contenant le photocatalyseur. L'exposition à l'air et à la lumière qui est absorbée par le photocatalyseur, produit un film de revêtement qui empêche les salissures et les contaminations d'adhérer au verre.
PCT/US1996/012792 1995-08-18 1996-08-06 Verre autonettoyant et procede pour le realiser WO1997007069A1 (fr)

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AU68432/96A AU6843296A (en) 1995-08-18 1996-08-06 Self-cleaning glass and method of making thereof

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PATENT ABSTRACTS OF JAPAN vol. 018, no. 625 (C - 1279) 29 November 1994 (1994-11-29) *
ZELAZOWSKA: "Study of metal oxide and titanium oxynitride coatings on soda-lime glass", SZKLO I CERAMIKA, vol. 43, no. 6, 1992, POLAND, pages 2 - 7, XP002018688 *

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JPH11511109A (ja) 1999-09-28
AU6843296A (en) 1997-03-12
EP0844985A1 (fr) 1998-06-03

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