WO2019234463A1 - Composition and process for the preparation of bifunctional thin layers with superhydrophobic and photocatalytic effects - Google Patents

Composition and process for the preparation of bifunctional thin layers with superhydrophobic and photocatalytic effects Download PDF

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WO2019234463A1
WO2019234463A1 PCT/HU2019/050028 HU2019050028W WO2019234463A1 WO 2019234463 A1 WO2019234463 A1 WO 2019234463A1 HU 2019050028 W HU2019050028 W HU 2019050028W WO 2019234463 A1 WO2019234463 A1 WO 2019234463A1
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weight
composition
substrate
bifunctional
amount
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PCT/HU2019/050028
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French (fr)
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László JANOVÁK
Imre DÉKÁNY
Ágota DEÁK
Norbert Varga
László MÉRAI
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Szegedi Tudományegyetem
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Priority to HUP2100009A priority Critical patent/HU231386B1/en
Publication of WO2019234463A1 publication Critical patent/WO2019234463A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/18—Materials not provided for elsewhere for application to surfaces to minimize adherence of ice, mist or water thereto; Thawing or antifreeze materials for application to surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
    • B05D5/083—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface involving the use of fluoropolymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40—Additives
    • C09D7/60—Additives non-macromolecular
    • C09D7/61—Additives non-macromolecular inorganic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2601/00—Inorganic fillers
    • B05D2601/20—Inorganic fillers used for non-pigmentation effect
    • B05D2601/24—Titanium dioxide, e.g. rutile
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/02—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain a matt or rough surface
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/0806—Silver
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/0831—Gold
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/221—Oxides; Hydroxides of metals of rare earth metal
    • C08K2003/2213—Oxides; Hydroxides of metals of rare earth metal of cerium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2237—Oxides; Hydroxides of metals of titanium
    • C08K2003/2241—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2296—Oxides; Hydroxides of metals of zinc
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
    • C08K2003/3009—Sulfides
    • C08K2003/3027—Sulfides of cadmium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals

Definitions

  • the present invention provides a novel solution in the field of coating materials and functional coatings and layers in that the thin layer simultaneously exhibits water-repellent and, using visible light illumination, photocatalytic self-cleaning properties.
  • a practical application of this type of catalysts is wastewater treatment: when light-excited species are bound to the surrounding water molecules or dissolved oxygen in an aqueous solution, for example, hydroxyl or superoxide radicals are formed which, due to their oxidative effect makes able converting, the carbon content of pollutants to C0 2 gas in the so-called mineralization besides peroxide, aldehyde and carboxylic acid intermediates.
  • One of the most widely used semiconductor photocatalysts for this purpose - among others - is the type n titanium dioxide, whose popularity is, among others, due to its relatively low cost, high chemical stability and the resulting non-toxic nature.
  • the three best-known crystalline modifications of Ti0 2 include rutile and anatase of the tetragonal structure, and rhombic brookite, but the latter does not deserve mention of photocatalytic applicability.
  • the size of the prohibited band of pure anatase Ti0 2 is ⁇ 3.2 eV, thus absorption of UV photons is needed to excite the electrons to the conducting band. Since only a fraction of the light emitted by the sun can be used to generate electron-hole pairs, a much more economical photocatalysis of visible light with Ti0 2 can only be achieved by reducing the size of the prohibited band practically: this may be achieved by minimizing the particle size, by reducing the oxygen content of the catalyst surface [Dette, C.; Perez-Osorio, M. A.; Kley, C. S. Nano Lett.
  • Contaminating transition metal nanoparticles in addition to modifying the size of the prohibited band, reduce the charge recombination by electron trapping, and are able to concentrate the energy of entering photons due to their local plasmonic properties.
  • nanoparticulate modified semiconductor photocatalysts there are several possibilities for producing nanoparticulate modified semiconductor photocatalysts, but perhaps the least complicated are photodeposition methods [Chan, S.C., Barteau, M. A. Langmuir 2005, 21, 5588-5595; Wenderich, K.; Mul, G. C hem. Rev. 2016, 116, 14587-14619], and methods for deposition from solution phase using conventional chemical reducing agents (e.g. Na-citrate, NaBH 4 ).
  • conventional chemical reducing agents e.g. Na-citrate, NaBH 4
  • silver nanoparticles have been efficiently accumulated by on Evonik P25 Ti0 2 in 0.5 % by weight amount by these methods [Veres, A.; Menesi, J.; Juhasz, A. Colloid Polym. Sci. 2014, 292, 207-217].
  • the obvious advantage of the small particle size catalysts produced by the above methods is the increased photocatalytic activity provided by the high specific surface area, however, the particle size may also impose significant limitations on applicability (greater chemical and mechanical degradation, accumulation in the product, and the like).
  • a practical solution to this problem can be to fix the catalyst particles on a solid support.
  • One of the large groups of catalyst carriers is polymers whose application has the advantage that when used, they can be functionalized (influencing the catalyst-carrier interaction), they have relatively low reactivity, and that their physical parameters can be modified to fit the purpose with minor manufacturing technology changes.
  • their drawbacks are their poor thermal conductivity, as well as the often inadequately controlled contamination of industrial polymers and polymeric raw materials by their manufacturers.
  • the polymer in catalytic processes its chemical degradation must also be taken into account, but this phenomenon can be utilized, for example, in waste treatment: faster decomposition of plastic products systemically contaminated by Ti0 2 seems to be a practical way to reduce our ecological footprint.
  • Polymer carriers have been successfully used, inter alia, to fix the previously mentioned Ag-Ti0 2 and also Ag-ZnO photocatalyst particles for producing photocatalytic and especially antibacterial thin layers [Veres, A.; Menesi, J.; Juhasz, A. Colloid Polym. Sci. 2014, 292, 207-217; Tallosy, Sz. P.; Janovak, L.; Menesi J. Environ. Sci. Pollut Res.
  • Kamegawa T. et ah, Adv. Mater 2012, 24, 3697-3700 investigates the superhydrophobic and photocatalytic behavior of a coating containing Ti0 2 photocatalyst and poly(tetrafluoroethylene) (PTFE) polymer on quartz substrates.
  • the coating is generated by a radiofrequency magnetron spray method (RF-MS) in an appropriate RF-MS device under argon.
  • RF-MS radiofrequency magnetron spray method
  • the applied coating is washed with acetone, ethanol, then water, dried at l00°C for 1 hour, and finally the surface is structured by hydrothermal treatment with aqueous NaOH solution.
  • the resulting composite layer provides a rough surface at the nano- and micro-level, which gives the surface lotus-like water-repellent properties in addition to the photocatalytic properties.
  • the present invention relates to a composition for forming a bifunctional thin layer on a substrate having superhydrophobic and photocatalytic activity, said composition comprising the following components:
  • the invention further relates to a composition according to the invention for use on a substrate to form a bifunctional thin layer having superhydrophobic and photocatalytic activity.
  • the invention also relates to a process for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, comprising the step of applying a composition according to the invention to the substrate.
  • the present invention further relates to a super-hydrophobic and photocatalytic bifunctional thin layer coated substrate wherein the coating is formed by applying the composition of the invention to the substrate.
  • Figure 1 shows the thin layer surface structures of (r-pPFDAc) containing 80 % by weight photocatalyst, and the pure poly(perfluorodecyl acrylate) (pPFDAc) at different magnifications.
  • Figure 2 shows the effect of photocatalyst content on surface roughness on SEM images. (The superhydrophobic composition highlighted in orange.)
  • Figure 3 shows the profiometric curve of a thin layer containing 80 % by weight photocatalyst and a pure poly(perfluorodecyl acrylate) thin layer.
  • Figure 4 shows the values of the wet edge angles measured on each thin layer as a function of the AgTi0 2 content.
  • Figure 5 shows a Zisman representation of a thin layer containing 80 % by weight of Ag Ti0 2 .
  • Figure 6 shows the UV-visible diffuse reflectance spectrum of the poly(perfluoro- decyl acrylate), the AgO Ti0 2 photocatalyst, and the r-pPFDAc thin layer, and the emission spectrum of the LED lamp used for photocatalytic tests.
  • Figure 8 shows the effect of the solvent/dispersing medium on the photocatalyst and the polymer system.
  • composition according to the present invention provides a unique opportunity to produce water-repellent and photocatalytic bifunctional thin layers active in visible light by a process that can be simply accomplished on the treated, coated surfaces.
  • the composition according to the invention can be applied to the substrate by, for example, brushing, rolling or spraying.
  • any conventional photocatalyst can be used as a semiconductor photocatalyst that can be activated by visible light.
  • a photocatalyst which can be activated by visible light.
  • visible light shall mean the wavelength range of electromagnetic radiation between 400 and 800 nm.
  • the excitability of conventional semiconductor photocatalysts (such as Ti0 2 ) is outside this range because it can only be excited by radiation with a wavelength of less than 387.5 nm.
  • the silver nanoparticle- doped photocatalyst used in the present invention is excited by photons of wavelengths greater than 400 nm, i.e. having less energy.
  • Examples are pure or doped Ti0 2 , ZnO, CdS, Sn0 2 and Ce0 2 particles.
  • Transition metal nanoparticles such as Ag, Au, Cu, and similar nanoparticles, as well as non-metallic elements such as N and P can be added to the photocatalyst. Addition can be accomplished using conventional techniques such as chemical or photodeposition, heterocoagulation.
  • the amount of the additive is generally from 0.01 % to 1.00 % by weight, in particular from 0.2 % to 0.7 % by weight, based on the weight of the photocatalyst.
  • the amount of photocatalyst is generally from 2.0 % to 9.5 % by weight, particularly from 6.0 % to 8.5 % by weight of the composition.
  • the photocatalyst is used in the form of nanoparticles, wherein the particle size is generally from 5 nm to 200 nm, in particular from 5 nm to 70 nm.
  • the photocatalyst is a Ti0 2 particle, in particular particles marketed under the trade name P25 Ti0 2 , which can be put into collective vibration in its conductive electrons by irradiation by the appropriate light, that is it is doped with transition metal nanoparticles of plasmonic properties selected from Ag, Au, Cu, and their alloys, or with a non-metallic element selected from N and P.
  • the amount of additive is 0.5 % by weight and the primary particle diameter of the additioned photocatalyst particles is approximately 50 nm.
  • ZnO particles are used as photocatalysts, which is doped with non-metallic elements selected from P and N or transition metal nanoparticles selected from Ag, Au and their alloys.
  • the amount of additive is 0.2-0.7 % by weight.
  • a polymeric support having low surface energy is used for the immobilization of photocatalysts.
  • the sign of the surface energy is g, the unit of its measurement is mJ/m .
  • Surface energy can be determined, for example, by edge angular measurements using Zisman's method. The essence of the method is that the surface energy of the surface is the same as the surface energy of the liquid that shows full wetting on the surface, i.e. the edge angle measured on the liquid will be zero.
  • the surface energy of the polymer is generally from 8 mJ / m to 35 mJ / m , especially from 10 mJ / m to 25 mJ / m .
  • the polymer is selected from the group consisting of a fluoropolymer derivative containing fluorinated - s carbon chains on the vinyl or acrylic-based main valency chain, Teflon, PDMS, polyethylene, polypropylene, PVC, polystyrene, polyacrylate derivatives, PUR, polyisoprene, especially poly(perfluorodecyl) acrylate, PDMS, PUR and polystyrene.
  • a fluoropolymer derivative containing fluorinated - s carbon chains on the vinyl or acrylic-based main valency chain Teflon
  • PDMS polyethylene, polypropylene, PVC, polystyrene, polyacrylate derivatives, PUR, polyisoprene, especially poly(perfluorodecyl) acrylate, PDMS, PUR and polystyrene.
  • the polymer is a fluoropolymer having a surface energy of l9.8 ⁇ 5.2 mJ/m .
  • the amount of polymer having low surface energy is generally from 0.5 % to 8.0 % by weight, in particular from 1.5 % to 4.0 % by weight of the composition.
  • the photocatalyst and the polymer are taken up in a solvent/dispersing medium to give a readily flowing substance.
  • a solvent/dispersing medium is used which disperses the photocatalyst only, but dissolves the polymer.
  • the solvent/dispersing medium is water or an organic solvent selected from the group consisting of toluene, acetone, xylene, benzene, ethanol, hexane, cyclohexane, propanol, methanol, dimethylformamide and butyl acetate.
  • the solvent/dispersing medium to be used is selected depending on the photocatalyst and the polymer. This is based on the need for the solvent/dispersing medium to dissolve the polymer while dispersing the photocatalyst particles so that the polymer does not cause aggregation of the photocatalyst particles in the particular medium.
  • the choice of solvent/dispersing medium is carried out on an empirical basis, by preliminary experiments.
  • the amount of solvent/dispersing medium is the same as that required for 100 % by weight, generally from 80 % to 95 % by weight, particularly from 85 % to 95 % by weight of the composition.
  • the photocatalyst is Ag doped Ti0 2 and the polymer is poly(perfluorodecyl acrylate), from which, using toluene as solvent/dispersing medium, a solution of 5-20 % by weight, in particular 10 % by weight is prepared.
  • the photocatalyst is ZnO
  • the polymer is PDMS
  • the solvent/dispersing medium is xylene with which a solution of 5-20 % by weight, in particular 10 % by weight is formed.
  • composition according to the invention can be prepared by simple mixing of the photocatalyst, the polymer and the solvent/dispersing medium, preferably in the first step by dissolving the polymer in the solvent/dispersing medium and then adding the photocatalyst to the resulting solution.
  • composition according to the present invention can be applied on any substrate to form a bifunctional thin layer having superhydrophobic and photocatalytic activity.
  • a preferred example of the substrate is metal, wood, glass, plastic, wall and tile surface, and a combination of these.
  • the resulting bifunctional thin layer as a coating provides a water repellent and self-cleaning property on the coated substrate.
  • the present invention also relates to a composition for use in the manufacture of a bifunctional thin layer having a superhydrophobic and photocatalytic effect on a substrate, wherein the composition comprises the following components:
  • the invention also relates to a method for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, comprising the step of applying a composition according to the invention to the substrate.
  • composition according to the invention can be applied to a substrate, for example by brushing, rolling or spraying.
  • the substrate Prior to applying the composition according to the invention, the substrate is made free of dust and grease by cleaning, and it is then dried.
  • the coating is dried to evaporate the solvent.
  • the coating thickness of the coating according to the invention is generally from 0.5 pm to 100 pm, especially from 5 pm to 70 pm.
  • the coating according to the invention comprises the following components:
  • the amount of the photocatalyst in the coating is generally from 20 % to 95 % by weight, in particular from 60 % to 85 % by weight, and the amount of the polymer is generally from 5 % to 80 % by weight, in particular from 15 % to 40 % by weight.
  • the surface of the coatings produced according to the invention is varied by micro sized, near-hemispherical structures, said structures having additional nanoscale roughness.
  • the significance of this can be demonstrated by comparing the results shown in Figures 2 and 4.
  • Figure 2 shows that at low photocatalyst content, the film does not have sufficient roughness, so that the measured angular values are also smaller ( Figure 4).
  • Figure 4 shows that if the roughness of the layers reaches an optimum value by increasing the ratio of the photocatalyst, the measured angles will also exceed the 150° value.
  • the coatings of the present invention are suitable for the photocatalytic degradation of organic pollutants: by exposure to light at 405 nm, a thin layer of 1 mg/cm specific weight on a 25 cm glass surface is capable of decreasing a quantity of EtOH present in the air at a concentration of 0.36 mM to less than its quarter.
  • the polyacrylate polymers used have antibacterial activity, and therefore the coating produced according to the invention is also suitable for killing microorganisms.
  • the present invention further relates to a super-hydrophobic and photocatalytic bifunctional thin layer-coated substrate wherein the coating is formed by applying a composition to the substrate, wherein the composition comprises the following components:
  • PFDAc ( 1 /7,17/,27/,277-pcrfluoiOdccyl acrylate)
  • pPFDAc (poly- 177, 177,277,277- -perfluorodecyl acrylate)
  • Ag-Ti0 2 titanium dioxide functionalized with silver nanoparticles (0.5m/m% silver content)
  • r-pPFDAc thin layer made of 80 % by weight of Ag-Ti0 2 and 20 % by weight of pPFDAc
  • a photoinitiator mixture of 10 ml of PFDAc monomer and 0.0164 g of 2,2-dimethoxy-2'-phenylacetophenone (Irgacure 651, Sigma- - Aldrich; 0.1 % by weight of monomer) is prepared, and nitrogen gas was bubbled through the mixture for 2 minutes.
  • a 10 % toluene solution was prepared from the bulk phase pPFDAc fluoropolymer obtained during the synthesis.
  • a coating suitable for the application is formed with a higher content of acetone (> 66 %), i.e., with less acetone than this amount, the polymer does not dissolve properly, so that the dry matter content settles.
  • the coarse dispersion system thus obtained is not suitable for the formation of suitable (micro- and nano-) roughness.
  • the observed surface roughness has proven to be able to enhance by increasing Ag-Ti0 2 content, as the surface roughness of the starting polymer increased from 3.7 ⁇ 0.9 pm to 6.8 ⁇ 0.4; 10.3 ⁇ 1.1 and 14.6 ⁇ 0.6 pm respectively, as the photocatalyst content was increased by 20 % by weight ( Figure 2).
  • the measured roughness was 15.2 ⁇ 1.2 pm ( Figures 1 and 3).
  • the thin layer can be considered as superhydrophobic, i.e. water repellent.
  • the water droplet on the surface of the film produced from the pure photocatalyst is able to spread almost completely (0-0°), thus concluding that it is extremely wettable, i.e. superhydrophilic.
  • the superhydrophilic character can be retained by the thin layer up to 10 % by weight of pPFDAc (90 % by weight of Ag-Ti0 2 ).
  • the Shimadzu GC-14B gas chromatograph used for our measurements has a HayeSep Q loaded column and line-bound thermal conductivity (TCD) and flame ionisation (FID) detectors.
  • Figure 7 depicts the EtOH decomposition efficiency of the various Ag-Ti0 2 containing layers: increasing the ratio of photocatalyst/pPFDAc results in larger amounts of EtOH being decomposed per unit of time.
  • the breakdown efficiency is over 74 % with an hour of illumination, while for a pure photocatalyst this efficiency is close to 100 %. The differences can be explained by the different surface coverage of the catalyst particles.

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Abstract

The present invention relates to a composition for forming a bifunctional thin layer on a substrate having superhydrophobic and photocatalytic activity, said composition comprising the following components: (A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight; (B) a low surface energy polymer carrier in an amount of from 0.5 to 8.0 % by weight; and (C) to 100 % by weight of a solvent/dispersing medium. The invention further relates to a method for forming a bifunctional thin layer having a superhydrophobic and photocatalytic effect on a substrate using the composition of the present invention, and such a thin-layer coated substrate.

Description

Composition and process for the preparation of bifunctional thin layers with superhydrophobic and photocatalytic effects
Precise description of the technical field
As for its characteristics, the present invention provides a novel solution in the field of coating materials and functional coatings and layers in that the thin layer simultaneously exhibits water-repellent and, using visible light illumination, photocatalytic self-cleaning properties.
Description of the state of the art
On one hand, surfaces with water-repellent and self-cleaning properties based on lotus flower effect, on the other hand, surfaces with photocatalytic self-cleaning properties are well known in the art, and their various practical applications are becoming increasingly widespread.
Research and application of light-induced or photocatalized chemical processes to enforce the principles of green chemistry is now of particular focus. The industry prefers heterogeneous catalysis considering the aspects of cost-effectiveness and environmental considerations: it involves the use of different semiconductor solids for light induced processes. The photocatalytic activity of the semiconductors is due to the electron-hole separation caused by the absorbed photon: the separate charges, besides the possible recombination, are able to induce redox processes (photosensitization), thus numerous reaction types can be realized (weak and complete oxidations, dehydrogenation, hydrogen transfer, photoelectrochemical breakdown of water) (Fujishima, A.; Honda, K. Nature 1972, 238, 37-38). A practical application of this type of catalysts is wastewater treatment: when light-excited species are bound to the surrounding water molecules or dissolved oxygen in an aqueous solution, for example, hydroxyl or superoxide radicals are formed which, due to their oxidative effect makes able converting, the carbon content of pollutants to C02 gas in the so-called mineralization besides peroxide, aldehyde and carboxylic acid intermediates.
One of the most widely used semiconductor photocatalysts for this purpose - among others - is the type n titanium dioxide, whose popularity is, among others, due to its relatively low cost, high chemical stability and the resulting non-toxic nature. The three best-known crystalline modifications of Ti02 include rutile and anatase of the tetragonal structure, and rhombic brookite, but the latter does not deserve mention of photocatalytic applicability.
The size of the prohibited band of pure anatase Ti02 is ~ 3.2 eV, thus absorption of UV photons is needed to excite the electrons to the conducting band. Since only a fraction of the light emitted by the sun can be used to generate electron-hole pairs, a much more economical photocatalysis of visible light with Ti02 can only be achieved by reducing the size of the prohibited band practically: this may be achieved by minimizing the particle size, by reducing the oxygen content of the catalyst surface [Dette, C.; Perez-Osorio, M. A.; Kley, C. S. Nano Lett. 2014, 11, 6533-6538], or even by contamination of the catalyst with semiconductor transition metal nanoparticles (Ag, Au, Cu) or with some non-metallic elements (N, P, etc.) (doping). Contaminating transition metal nanoparticles, in addition to modifying the size of the prohibited band, reduce the charge recombination by electron trapping, and are able to concentrate the energy of entering photons due to their local plasmonic properties.
There are several possibilities for producing nanoparticulate modified semiconductor photocatalysts, but perhaps the least complicated are photodeposition methods [Chan, S.C., Barteau, M. A. Langmuir 2005, 21, 5588-5595; Wenderich, K.; Mul, G. C hem. Rev. 2016, 116, 14587-14619], and methods for deposition from solution phase using conventional chemical reducing agents (e.g. Na-citrate, NaBH4). For example, silver nanoparticles have been efficiently accumulated by on Evonik P25 Ti02 in 0.5 % by weight amount by these methods [Veres, A.; Menesi, J.; Juhasz, A. Colloid Polym. Sci. 2014, 292, 207-217].
The obvious advantage of the small particle size catalysts produced by the above methods is the increased photocatalytic activity provided by the high specific surface area, however, the particle size may also impose significant limitations on applicability (greater chemical and mechanical degradation, accumulation in the product, and the like). A practical solution to this problem can be to fix the catalyst particles on a solid support.
One of the large groups of catalyst carriers is polymers whose application has the advantage that when used, they can be functionalized (influencing the catalyst-carrier interaction), they have relatively low reactivity, and that their physical parameters can be modified to fit the purpose with minor manufacturing technology changes. However, their drawbacks are their poor thermal conductivity, as well as the often inadequately controlled contamination of industrial polymers and polymeric raw materials by their manufacturers. When using the polymer in catalytic processes, its chemical degradation must also be taken into account, but this phenomenon can be utilized, for example, in waste treatment: faster decomposition of plastic products systemically contaminated by Ti02 seems to be a practical way to reduce our ecological footprint.
Polymer carriers have been successfully used, inter alia, to fix the previously mentioned Ag-Ti02 and also Ag-ZnO photocatalyst particles for producing photocatalytic and especially antibacterial thin layers [Veres, A.; Menesi, J.; Juhasz, A. Colloid Polym. Sci. 2014, 292, 207-217; Tallosy, Sz. P.; Janovak, L.; Menesi J. Environ. Sci. Pollut Res.
2014, 21, 11155-11167]
Since the polymer surfaces become rough due to the addition of catalyst particles, and it is also known that increasing the surface roughness increases the water repellent or wetting properties of the surface [Wenzel, R. Ind. Eng. Chem., 1936, 28, 988-994], their wetting properties can be tuned by the particle size and quantity of the additive. In this way, either water-repellent or so called superhydrophobic surfaces can be created by roughening thin layers of originally small surface free energy hydrophobic polymers such as perfluorinated polyacrylates such as Teflon. The literature generally regards surfaces with a surface free energy of less than 15 mJ/m2 as superhydrophobic, where the measured wet edge angle is greater than 150° [Simpson, J.T.; Hunter, R. S.; Aytug, T. Rep. Prog. Phys.,
2015, 78, 8].
Of the superhydrophobic surfaces, the best known are the leaves of certain plants, such as lotus, but we can also find artificially water-repellent layers in a number of areas of our everyday life and industrial application: the use of wall paints with so-called lotus effect for self-cleaning character, but it is also important to mention the anti-corrosion and anti-icing coatings, as well as coatings to prevent deposits of limescale and/or biofilm.
Experiments have already been carried out to combine the water repellent effect and the photocatalytic effect. Such thin layers are described, for example, by Lee J. H. et al.in Catalyst Today 2016, 260, 32-38, where they investigated the wetting and photocatalytic effect of a superhydrophobic coating consisting of Ti02 photocatalyst and a Si02 nanoparticle coated with poly(dimethyl-siloxane) (PDMS) polymer. To produce the bifunctional layer, the polymer is steamed onto the nanoparticles at 300°C for 12 hours, and then the photocatalyst is transferred in a quartz reactor in a stream of ammonia at 600°C for 5 hours. Further post-treatment is required to form the final photocatalytic and superhydrophobic film.
Kamegawa T. et ah, Adv. Mater 2012, 24, 3697-3700 investigates the superhydrophobic and photocatalytic behavior of a coating containing Ti02 photocatalyst and poly(tetrafluoroethylene) (PTFE) polymer on quartz substrates. The coating is generated by a radiofrequency magnetron spray method (RF-MS) in an appropriate RF-MS device under argon. The applied coating is washed with acetone, ethanol, then water, dried at l00°C for 1 hour, and finally the surface is structured by hydrothermal treatment with aqueous NaOH solution.
Methods known for producing superhydrophobic and photocatalytic bifunctional surfaces therefore require special large laboratory equipment and conditions that cannot be used on an industrial scale.
Since there is no data available in the literature striving to find a simple procedure for combining the water repellent and photocatalytic effect, it is an object of the present invention to provide a simple process for creating a bifunctional coating by roughening the surface of a low free energy hydrophobic polymer thin layer with a semiconductor photocatalyst that can be activated by visible light.
It has been found that when a polymeric support having low surface energy is used to immobilize the photocatalysts in the given composition, the resulting composite layer provides a rough surface at the nano- and micro-level, which gives the surface lotus-like water-repellent properties in addition to the photocatalytic properties.
General description of the invention
The present invention relates to a composition for forming a bifunctional thin layer on a substrate having superhydrophobic and photocatalytic activity, said composition comprising the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) low surface energy polymer carrier in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of a solvent/dispersing medium.
The invention further relates to a composition according to the invention for use on a substrate to form a bifunctional thin layer having superhydrophobic and photocatalytic activity.
The invention also relates to a process for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, comprising the step of applying a composition according to the invention to the substrate. The present invention further relates to a super-hydrophobic and photocatalytic bifunctional thin layer coated substrate wherein the coating is formed by applying the composition of the invention to the substrate.
Description of the drawings
Figure 1 shows the thin layer surface structures of (r-pPFDAc) containing 80 % by weight photocatalyst, and the pure poly(perfluorodecyl acrylate) (pPFDAc) at different magnifications.
Figure 2 shows the effect of photocatalyst content on surface roughness on SEM images. (The superhydrophobic composition highlighted in orange.)
Figure 3 shows the profiometric curve of a thin layer containing 80 % by weight photocatalyst and a pure poly(perfluorodecyl acrylate) thin layer.
Figure 4 shows the values of the wet edge angles measured on each thin layer as a function of the AgTi02 content.
Figure 5 shows a Zisman representation of a thin layer containing 80 % by weight of Ag Ti02.
Figure 6 shows the UV-visible diffuse reflectance spectrum of the poly(perfluoro- decyl acrylate), the AgO Ti02 photocatalyst, and the r-pPFDAc thin layer, and the emission spectrum of the LED lamp used for photocatalytic tests.
Figure 7 shows the relative amount of EtOH decomposed during the illumination of thin layers having a surface area of 25 cm with a specific weight of 1 mg/cm with a blue light LED (Lniax=405 nm) as a function of the Ag Ti02 content.
Figure 8 shows the effect of the solvent/dispersing medium on the photocatalyst and the polymer system.
Detailed description of the invention
The composition according to the present invention provides a unique opportunity to produce water-repellent and photocatalytic bifunctional thin layers active in visible light by a process that can be simply accomplished on the treated, coated surfaces. According to the invention, the composition according to the invention can be applied to the substrate by, for example, brushing, rolling or spraying.
Any conventional photocatalyst can be used as a semiconductor photocatalyst that can be activated by visible light. Particularly suitable is a photocatalyst which can be activated by visible light. The term “visible light” shall mean the wavelength range of electromagnetic radiation between 400 and 800 nm. The excitability of conventional semiconductor photocatalysts (such as Ti02) is outside this range because it can only be excited by radiation with a wavelength of less than 387.5 nm. In contrast, the silver nanoparticle- doped photocatalyst used in the present invention is excited by photons of wavelengths greater than 400 nm, i.e. having less energy.
Examples are pure or doped Ti02, ZnO, CdS, Sn02 and Ce02 particles. Transition metal nanoparticles such as Ag, Au, Cu, and similar nanoparticles, as well as non-metallic elements such as N and P can be added to the photocatalyst. Addition can be accomplished using conventional techniques such as chemical or photodeposition, heterocoagulation. The amount of the additive is generally from 0.01 % to 1.00 % by weight, in particular from 0.2 % to 0.7 % by weight, based on the weight of the photocatalyst.
The amount of photocatalyst is generally from 2.0 % to 9.5 % by weight, particularly from 6.0 % to 8.5 % by weight of the composition.
In one embodiment of the invention, the photocatalyst is used in the form of nanoparticles, wherein the particle size is generally from 5 nm to 200 nm, in particular from 5 nm to 70 nm.
In another embodiment of the invention, the photocatalyst is a Ti02 particle, in particular particles marketed under the trade name P25 Ti02, which can be put into collective vibration in its conductive electrons by irradiation by the appropriate light, that is it is doped with transition metal nanoparticles of plasmonic properties selected from Ag, Au, Cu, and their alloys, or with a non-metallic element selected from N and P. The amount of additive is 0.5 % by weight and the primary particle diameter of the additioned photocatalyst particles is approximately 50 nm.
In another embodiment of the invention, ZnO particles are used as photocatalysts, which is doped with non-metallic elements selected from P and N or transition metal nanoparticles selected from Ag, Au and their alloys. The amount of additive is 0.2-0.7 % by weight.
For the immobilization of photocatalysts, a polymeric support having low surface energy is used.
The sign of the surface energy is g, the unit of its measurement is mJ/m . Surface energy can be determined, for example, by edge angular measurements using Zisman's method. The essence of the method is that the surface energy of the surface is the same as the surface energy of the liquid that shows full wetting on the surface, i.e. the edge angle measured on the liquid will be zero. The surface energy of the polymer is generally from 8 mJ / m to 35 mJ / m , especially from 10 mJ / m to 25 mJ / m .
In one embodiment of the present invention, the polymer is selected from the group consisting of a fluoropolymer derivative containing fluorinated - s carbon chains on the vinyl or acrylic-based main valency chain, Teflon, PDMS, polyethylene, polypropylene, PVC, polystyrene, polyacrylate derivatives, PUR, polyisoprene, especially poly(perfluorodecyl) acrylate, PDMS, PUR and polystyrene.
In another embodiment of the invention, the polymer is a fluoropolymer having a surface energy of l9.8±5.2 mJ/m .
The amount of polymer having low surface energy is generally from 0.5 % to 8.0 % by weight, in particular from 1.5 % to 4.0 % by weight of the composition.
In another embodiment of the invention, a low surface free energy (g=21 mJ/m ), hydrophobic (0=105.0°) poly(perfluorodecyl acrylate) fluoropolymer is used, the water repellency of which becomes significant by increasing the photocatalyst content of the coating, thereby making the surface of the thin layers rough. Optimal superhydrophobicity is achieved with 8.0 % by weight catalyst content (1.0-2.0 % by weight fluoropolymer content) (g=9,2 mJ/m2, hydrophobic (0=150. 9°).
According to the invention, the photocatalyst and the polymer are taken up in a solvent/dispersing medium to give a readily flowing substance. This ensures easy application of the composition to the substrate. For this, a solvent/dispersing medium is used which disperses the photocatalyst only, but dissolves the polymer.
In one embodiment of the invention, the solvent/dispersing medium is water or an organic solvent selected from the group consisting of toluene, acetone, xylene, benzene, ethanol, hexane, cyclohexane, propanol, methanol, dimethylformamide and butyl acetate.
The solvent/dispersing medium to be used is selected depending on the photocatalyst and the polymer. This is based on the need for the solvent/dispersing medium to dissolve the polymer while dispersing the photocatalyst particles so that the polymer does not cause aggregation of the photocatalyst particles in the particular medium. The choice of solvent/dispersing medium is carried out on an empirical basis, by preliminary experiments.
The amount of solvent/dispersing medium is the same as that required for 100 % by weight, generally from 80 % to 95 % by weight, particularly from 85 % to 95 % by weight of the composition. In one embodiment of the invention, the photocatalyst is Ag doped Ti02 and the polymer is poly(perfluorodecyl acrylate), from which, using toluene as solvent/dispersing medium, a solution of 5-20 % by weight, in particular 10 % by weight is prepared.
In another embodiment of the invention, the photocatalyst is ZnO, the polymer is PDMS, and the solvent/dispersing medium is xylene with which a solution of 5-20 % by weight, in particular 10 % by weight is formed.
The composition according to the invention can be prepared by simple mixing of the photocatalyst, the polymer and the solvent/dispersing medium, preferably in the first step by dissolving the polymer in the solvent/dispersing medium and then adding the photocatalyst to the resulting solution.
The composition according to the present invention can be applied on any substrate to form a bifunctional thin layer having superhydrophobic and photocatalytic activity. A preferred example of the substrate is metal, wood, glass, plastic, wall and tile surface, and a combination of these. The resulting bifunctional thin layer as a coating provides a water repellent and self-cleaning property on the coated substrate.
The present invention also relates to a composition for use in the manufacture of a bifunctional thin layer having a superhydrophobic and photocatalytic effect on a substrate, wherein the composition comprises the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) a polymer carrier with low surface energy in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of solvent/dispersing medium.
The invention also relates to a method for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, comprising the step of applying a composition according to the invention to the substrate.
In one embodiment of the invention, the composition according to the invention can be applied to a substrate, for example by brushing, rolling or spraying.
Prior to applying the composition according to the invention, the substrate is made free of dust and grease by cleaning, and it is then dried.
After application of the composition according to the invention, the coating is dried to evaporate the solvent.
The coating thickness of the coating according to the invention is generally from 0.5 pm to 100 pm, especially from 5 pm to 70 pm. The coating according to the invention comprises the following components:
(A) semiconductor photocatalyst particles which can be activated in visible light;
(B) polymeric support having low surface energy.
The amount of the photocatalyst in the coating is generally from 20 % to 95 % by weight, in particular from 60 % to 85 % by weight, and the amount of the polymer is generally from 5 % to 80 % by weight, in particular from 15 % to 40 % by weight.
The surface of the coatings produced according to the invention is varied by micro sized, near-hemispherical structures, said structures having additional nanoscale roughness. The significance of this can be demonstrated by comparing the results shown in Figures 2 and 4. Figure 2 shows that at low photocatalyst content, the film does not have sufficient roughness, so that the measured angular values are also smaller (Figure 4). However, if the roughness of the layers reaches an optimum value by increasing the ratio of the photocatalyst, the measured angles will also exceed the 150° value.
The coatings of the present invention are suitable for the photocatalytic degradation of organic pollutants: by exposure to light at 405 nm, a thin layer of 1 mg/cm specific weight on a 25 cm glass surface is capable of decreasing a quantity of EtOH present in the air at a concentration of 0.36 mM to less than its quarter.
In one embodiment of the present invention, the polyacrylate polymers used have antibacterial activity, and therefore the coating produced according to the invention is also suitable for killing microorganisms.
The present invention further relates to a super-hydrophobic and photocatalytic bifunctional thin layer-coated substrate wherein the coating is formed by applying a composition to the substrate, wherein the composition comprises the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) a polymer carrier with low surface energy in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of solvent/dispersing medium.
The following examples illustrate the invention without limiting the scope to the Examples. Examples
Abbreviations:
PFDAc: ( 1 /7,17/,27/,277-pcrfluoiOdccyl acrylate), pPFDAc: (poly- 177, 177,277,277- -perfluorodecyl acrylate), Ag-Ti02: titanium dioxide functionalized with silver nanoparticles (0.5m/m% silver content), r-pPFDAc: thin layer made of 80 % by weight of Ag-Ti02 and 20 % by weight of pPFDAc
Example 1
Synthesis of nanoscale Ag-Ti02 photocatalyst particles
10 g of P25 Ti02 was dispersed in 100 ml of doubly distilled water and 40 ml of
50*10 mM AgN03 solution was added to the suspension under vigorous stirring. The pH of the resulting dispersion was adjusted to 7.2 by the addition of 1 M NaOH solution and 60 ml of 40 mM NaBH4 solution was added dropwise with stirring for 60 minutes. The solid phase is then decanted with doubly distilled water, then centrifuged, filtered and dried at 60°C.
Example 2
Bulky photoinitiated synthesis of pPFDAc polymer
In a 30 ml bottle- stoppered glass vial, a photoinitiator mixture of 10 ml of PFDAc monomer and 0.0164 g of 2,2-dimethoxy-2'-phenylacetophenone (Irgacure 651, Sigma- - Aldrich; 0.1 % by weight of monomer) is prepared, and nitrogen gas was bubbled through the mixture for 2 minutes. The vial was then placed in front of a UV-lamp (Q81, Heraeus GmbH, P=70 W, lIIIί1c= 265 nm) at a distance of 5 cm and illuminated for half an hour. A 10 % toluene solution was prepared from the bulk phase pPFDAc fluoropolymer obtained during the synthesis.
Example 3
Preparation of Ag-TiC pPFDAc and Ag-Ti02 thin layer by spray technique
To prepare Ag-Ti02/pPFDAc fluoropolymer thin layers with a surface area of 5x5 cm the appropriate weight of Ag-Ti02 photocatalyst was added to the pPFDAc polymer solution described in Example 2, then the suspension was sonicated in an ultrasonic bath for 2 minutes than the dry matter content of the suspension was applied by spray gunning at a distance of 15 cm on a 25 cm glass surface (type Rl80-spray gun, 3 bar N2 propellant). The layers are constructed under gravimetric control until a specific mass of 0.1 to 5 (preferably 2) mg/cm is reached.
The same experimental conditions may be used to form layers of a pure photocatalyst without polymer, but in this case Ag-Ti02 was suspended in distilled water at a concentration of 10-20 % by weight instead of the dispersion of pPFDAc. This version is illustrated by films containing the pure (100 %) Ag-Ti02 photocatalyst shown in Figures 6 and 7.
Example 4
The effect of solvent/dispersing medium on the photocatalyst and polymer system
The appropriate choice of solvent/dispersing medium used in the application which contains the polymer in the dissolved state and the photocatalyst in the dispersed state is important for forming the layers. This is represented by Figure 8, where fluoro- polymer/photocatalyst systems dispersed in water/acetone mixtures of variable compositions are shown. The acetone content is 10, 33, 66, and 90 v/v%, respectively. The Ag-Ti02 is present in the photocatalyst in an amount of 8 % by weight, while the polymer pPFDAc is in an amount of 2 % by weight.
It can be stated that a coating suitable for the application is formed with a higher content of acetone (> 66 %), i.e., with less acetone than this amount, the polymer does not dissolve properly, so that the dry matter content settles. The coarse dispersion system thus obtained is not suitable for the formation of suitable (micro- and nano-) roughness.
Test methods for qualifying thin layers according to the invention
Characterization of the surface structure and morphological structure of thin layers
It is known from the literature that knowing of the surface morphology of the thin layers formed by spraying from the coating according to the invention is of primary importance for the understanding and explanation of the wetting properties, since the roughening of a surface can enhance its hydrophilic or hydrophobic nature. (Wenzel, R. Ind. Eng. Chem., 1936, 28, 988-994). By scanning electron microscopy (Hitachi S-4700, resolution of 1.2- 1.5 nm, applied acceleration voltage: 5 kV) and profilometry (Form Talysurf Series 2 mechanical profilometer, TaylorHobson Ltd., Leicester, GB); resolution in x, y, and z directions: 0.25 pm, 1 pm, and 3 nm) methods, it has been shown that the layers formed using the coating containing also the Ag-Ti02 photocatalyst according to the invention as compared to the pure pPFDAc fluoropolymer thin layer formed by the analog spray technique, have increased surface roughness on both the micrometer and on the surface of these microstructures in the nanometer range (Figure 1). The observed surface roughness has proven to be able to enhance by increasing Ag-Ti02 content, as the surface roughness of the starting polymer increased from 3.7 ± 0.9 pm to 6.8 ± 0.4; 10.3 ± 1.1 and 14.6 ± 0.6 pm respectively, as the photocatalyst content was increased by 20 % by weight (Figure 2). Optimally, i.e. when the thin layer exhibits both superhydrophobic and photocatalytic properties, the measured roughness was 15.2 ± 1.2 pm (Figures 1 and 3).
Investigation of wetting properties of thin layers
The wettability of the resulting thin layers with distilled water was investigated by edge angle measurements with an EasyDrop (Kriiss GmbH, Hamburg, Germany) edge angle measuring device at 25±0.5 °C. Figure 4 shows the value of the water edge angles (Q) measured for the different layers of Ag-Ti02 containing thin layers: it can be seen that with a photocatalyst content of 80 % there is a surface roughness at which the edge angle measured on the fluoropolymer being water-repellent alone (0=105,0°) already exceeds the 150° value (0=150.9°). Thus, the thin layer can be considered as superhydrophobic, i.e. water repellent. As expected, the water droplet on the surface of the film produced from the pure photocatalyst is able to spread almost completely (0-0°), thus concluding that it is extremely wettable, i.e. superhydrophilic. The superhydrophilic character can be retained by the thin layer up to 10 % by weight of pPFDAc (90 % by weight of Ag-Ti02).
In case of r-pPFDAc layers using the Zisman-method [Zisman, W.A. Adv. Chem.
Ser., 1964, 43, 1-51] the surface free energy has a value of 9.2 mJ/m , which is about half
2
the value measured on low energy Teflon-like surfaces (20-22 mJ/m ).
Optical characterization of the photocatalysts used and the pPFDAc carrier polymer
Absorption parameters of plasmonic photocatalysts and their hybrid thin layers formed from coatings according to the invention are described on the basis of UV-visible diffuse reflectance spectra recorded with a CHEM2000 (Ocean Optics Inc.) device. Figure 6 shows on an example of the Ag-Ti02 photocatalyst that, while the starting P25 Ti02 does not exhibit light absorption in the visible range, the absorption maximum is shifted to the visible range ( g=500 nm) due to the 0.5 % by weight of plasmonic additive. It can also be said that the pPFDAc carrier modifies the optical properties of the catalyst only to a minimal extent.
Photocatalytic classification of thin Sims
The photocatalytic efficacy of the thin layers formed from the coatings of the present invention against organic contaminants was investigated by decomposing the ethanol model compound at the solid gas interface, following by gas chromatography of the quantitative change of EtOH. Films containing each photocatalyst were placed in a FV 0165 reactor followed by an injection of 5 mΐ abs. EtOH into the gas space and after a 30- minute adsorption period, it was illuminated by a blue LED light (lIIIί1c=405 nm) at a distance of 5 cm for 60 minutes. The Shimadzu GC-14B gas chromatograph used for our measurements has a HayeSep Q loaded column and line-bound thermal conductivity (TCD) and flame ionisation (FID) detectors. Figure 7 depicts the EtOH decomposition efficiency of the various Ag-Ti02 containing layers: increasing the ratio of photocatalyst/pPFDAc results in larger amounts of EtOH being decomposed per unit of time. For superhydrophobic compositions, the breakdown efficiency is over 74 % with an hour of illumination, while for a pure photocatalyst this efficiency is close to 100 %. The differences can be explained by the different surface coverage of the catalyst particles.

Claims

Claims
1. A composition for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, said composition comprising the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) a low surface energy polymer carrier in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of a solvent/dispersing medium.
2. The composition according to Claim 1, wherein the photocatalyst particle is selected from the group consisting of pure or doped Ti02, ZnO, CdS, Sn02 and Ce02 particles.
3. The composition according to Claim 2, wherein the photocatalyst particle is a particle doped with transition metal nanoparticles selected from the group consisting of Ag, Au, and Cu, or non-metallic elements selected from the group consisting of N and P.
4. The composition according to any one of Claims 1 to 3, wherein the polymeric carrier is a polymer having a surface energy of from 8 mJ/m 2 to 35 mJ/m 2.
5. The composition according to Claim 4, wherein the polymer is selected from the group consisting of a fluoropolymer derivative containing fluorinated - s carbon chains on the vinyl or acrylic -based main valency chain, Teflon, PDMS, polyethylene, polypropylene, PVC, polystyrene, polyacrylate derivatives, PUR, polyisoprene, especially poly(perfluorodecyl) acrylate, PDMS, PUR and polystyrene.
6. The composition according to any one of Claims 1 to 5, wherein the solvent/dispersing medium is water or an organic solvent selected from the group consisting of toluene, acetone, xylene, benzene, ethanol, hexane, cyclohexane, propanol, methanol, dimethylformamide and butyl acetate.
7. A composition according to any one of Claims 1 to 6 for use in the preparation of a bifunctional thin layer having a superhydrophobic and photocatalytic effect on a substrate.
8. A process for forming a bifunctional thin layer having superhydrophobic and photocatalytic activity on a substrate, comprising the step of applying a composition to the substrate, wherein the composition comprises the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) a low surface energy polymer carrier in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of a solvent/dispersing medium.
9. A substrate coated by a super-hydrophobic and photocatalytic bifunctional thin layer, wherein the coating is formed by applying a composition to the substrate, wherein the composition comprises the following components:
(A) semiconductor photocatalyst particles which can be activated by visible light in an amount of from 2.0 % to 9.5 % by weight;
(B) a low surface energy polymer carrier in an amount of from 0.5 to 8.0 % by weight; and
(C) to 100 % by weight of a solvent/dispersing medium.
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