HK1210735A1 - Photokatalytisch aktives material zur luftreinigung - Google Patents

Description

Photocatalytic material for air purification

Technical Field

The present invention relates to a method for reducing fine dust using a photocatalyst and a photocatalyst that is active also in the absence of ultraviolet light.

Background

The photocatalyst is excited in a photo-assisted catalytic reaction. This serves, for example, to generate oxygen radicals on the photocatalyst surface, which then oxidize the harmful substances and thus render them harmless. A known photocatalytically active material is titanium dioxide (TiO)₂). Ultraviolet light is necessary to excite titanium dioxide.

Disclosure of Invention

The object of the present invention is to use the photocatalytic effect in new applications and to provide new photocatalysts for this purpose which are also active in the absence of uv light.

According to the invention, this object is achieved by a method for reducing fine dust, which is characterized in that the fine dust is removed from the gaseous medium in the absence of ultraviolet light by means of a photocatalytic material containing a photocatalyst.

The invention relates in particular to a method for reducing fine dust, characterized in that the fine dust is removed from a gaseous medium by means of a photocatalytic material containing a photocatalyst in the absence of a UV component.

It was established by the present invention that electrostatic attraction to fine dust is achieved by means of a photo-assisted catalytic reaction with a photocatalytic material, by means of which fine dust can be removed from gaseous media, in particular air. Here, the photocatalytic material is brought into an excited catalytic state by the action of light of an appropriate wavelength. Here, a continuous light action is required to maintain the reaction.

Photocatalytic materials are also referred to herein as photocatalytically active materials.

The photocatalytic material that can be used according to the present invention preferably comprises a photocatalyst and optionally further materials such as, for example, a binder. In a preferred embodiment of the invention, the photocatalytic material consists of a photocatalyst. In a more preferred embodiment, the photocatalytic material comprises a photocatalyst and a binder.

The photocatalyst, which may also be referred to as a photocatalytically active substance, preferably has semiconductor properties. In photocatalytically active semiconductors, electrons can be brought into a higher-energy state by excitation with photons. If the energy of the injected photon is sufficiently high, the electron may be converted from an energy state, such as from an energy ground state, to an energy state of a conduction band at room temperature. Electron holes or holes, i.e. positive charge carriers, are generated at the original position of the electrons (negative charge carriers). Where adjacent electrons can be exchanged. Under which electron-holes are generated again, and so on. As a result, positive and negative charge carriers are distributed relatively and can propagate on the surface of the material. A particular charge distribution results in this. This charge distribution creates an electrostatic attraction through which the fine dust can be removed from the air. This effect was confirmed by the invention of the present application for the first time. In particular, according to the invention, it is possible to deposit dust particles on the photocatalytically active surface by means of the charge distribution present.

According to the invention, the photocatalyst is preferably related to being active also under irradiation with visible light (i.e. also in particular in the absence of ultraviolet light). The charge distribution is generated here by the incidence of light in the IR or visible wavelength range, in particular by the incidence of light in the visible wavelength range (400-750nm) and without the incidence of ultraviolet light. Such materials can thus also be used for dust reduction in interior spaces, for example in living rooms or in cockpit spaces, where, in the case of conventional photocatalysts such as, for example, titanium dioxide, no light-assisted catalytic reactions occur due to the lack of uv radiation.

The method according to the invention can be carried out in daylight. Especially in sunlight without additional ultraviolet light. Such uv-free daylight is present, for example, in building rooms or in cockpit rooms, where sunlight must first pass through a glass plate. But the ultraviolet component of sunlight is blocked by the glass plate. According to the invention, it is possible to carry out the process with a gaze whose ultraviolet light fraction is attenuated, in particular the fraction of light with a wavelength <350nm, preferably <380nm and in particular <390nm is attenuated by at least 80%, more preferably by at least 90%, even more preferably by at least 95% and in particular by at least 98%, most preferably by at least 99%. An example of such a preferred embodiment is that the embodiment is carried out indoors, wherein the eye must first be penetrated by glass, for example a window pane, which has no or only a very low permeability for light in the UV range. In a preferred embodiment, the process is carried out in the absence of a UV component. This is for example when sunlight penetrates through thick glass and thus the uv light component is completely removed.

The method according to the invention can however also be carried out under artificial light, in particular with wavelengths of 380nm to 800nm, in particular 400 to 700 nm.

The method according to the invention can in particular also be carried out in an environment in which no additional ultraviolet light is incident, and in particular in an environment in which no ultraviolet light is present. The method according to the invention can therefore be carried out in particular in the absence of light having a wavelength of <400nm, in particular <380nm, more preferably <350 nm.

The absence of uv light and the absence of uv light components in the present invention means in particular that the total energy contribution of incident light with a wavelength of <400nm, in particular <380nm, is < 2%, more preferably < 1%, still more preferably < 0.1% and most preferably 0%, based on the total incident light energy.

Preference is given according to the invention to using photocatalysts which have a band gap in the visible range (i.e.in the case of < 3.2eV corresponding to > 390nm, in particular < 3.1eV corresponding to > 400 nm). Such a photocatalyst has activation energy in the visible wavelength range and can thus be excited without an ultraviolet light component.

According to the invention, the photocatalyst preferably comprises at least one of the elements Sn, Zn, Bi, Ga, Ge, In, Ta, Ti, V, W, Sb or Ti, In particular at least one of the elements Sn or Zn and more preferably Zn.

In a preferred embodiment, the photocatalyst contains Sn. In a further preferred embodiment, the photocatalyst comprises Zn. In a further preferred embodiment, the photocatalyst contains Sn and Zn.

In the photocatalyst, the element is preferably present in the form of a compound having semiconductor properties, preferably as an oxide. It is particularly preferred that the photocatalyst comprises tin oxide (SnO)₂) Or/and zinc oxide (ZnO), in particular ZnO.

It is preferable to use a photocatalyst which is doped or loaded with one or more other elements in addition to the base element so as to have a desired band gap in the range of ≦ 3.2eV, particularly ≦ 3.1 eV.

The material preferably used as photocatalyst according to the present invention is SnO₂。SnO₂Having an energy band gap corresponding to 3.5 to 3.7eV in the wavelength range 354 to 335 nm. Loaded SnO₂Having an energy band gap corresponding to about 2.9eV for a wavelength of 428 nm. Thus, this SnO₂Can be excited by blue light in the visible electromagnetic spectrum.

ZnO is further preferred as the material used for the photocatalyst. The ZnO itself has an energy band gap corresponding to about 3.37eV at a wavelength of 368 nm. The loaded ZnO has at least two active bandgaps at about 1.8eV (690nm) and at about 2.7eV (460nm) and is thus excitable with visible light.

In a particularly preferred embodiment, SnO is used₂The mixture with ZnO as photocatalyst is in particular in a weight ratio of 1: 10 to 10: 1, more preferably 1: 3 to 3: 1.

In order to further increase the usability of the photocatalyst in the process according to the invention, it is preferred to reduce the band gap.

According to the invention, therefore, preference is given to using photocatalysts doped with one or more elements, in particular selected from the group consisting of Co, C, N, P, S or H. Preferably, a photocatalyst doped with Co, C and/or N (most preferably Co) is used. In the case of doping, heteroatoms are built into the molecular structure of the photocatalyst. By said doping the band gap and thus the activation energy is reduced.

In particular in the case of doping, the molecules in the photocatalyst structure are exchanged by the doping element. This means that the molecules of the material are exchanged by a hetero molecule, in particular selected from Co, C, N, P, S or H, whereby the properties of the photocatalyst are substantially changed.

ZnO or/and SnO2 doped with Co is particularly preferably used as a photocatalyst according to the invention, in particular ZnO doped with Co. The weight ratio Zn to Co is preferably from 8: 1 to 15: 1, in particular from 9: 1 to 11: 1 and more preferably from 9.5: 1 to 10.5: 1. It was determined by the present invention that Co is built into the crystal structure of ZnO. Doped ZnO photocatalysts, in particular having particle sizes in the range from about 50nmm to 1.5 μm, in particular from about 100nm to 1.2 μm, can be produced here. The ZnO loaded with Co has energy bandgaps at about 1.8eV and 2.7eV, corresponding to wavelengths of 690nm or 460 nm. These materials can be used as photocatalysts under irradiation with light without any uv component, since the necessary activation energy is shifted into the visible wavelength range.

The doped photocatalyst may be obtained, for example, by a wet chemical or thermal process.

In the case of wet chemical doping, in particular the crystals are to be grown. It is also possible here to stimulate crystals of different materials to grow on each other, thereby producing mixed crystals. In the case of a thermal process, the different materials are mixed and pressed under high pressure. The pressed green body is then melted and the molten layers of different materials are integrated.

In a further preferred embodiment, the photocatalyst is loaded with one or more elements, in particular from the group of Pb, Au, Ag, Pt, Al, Cu, Sb, Mo or Cd, preferably from the group of Au, Pt, Ag, Sb, Fe, Al, Cd, Cu or Pb. Most preferred is loading with Au or/and Pt.

In the case of loading, the loading element, i.e. in particular Pb, Au, Ag, Pt, a1, Cu, Sb, Mo or Cd, is attached to the molecule of the photocatalyst. There is no molecular exchange, but rather an additional insertion of the loading element into the structure of the photocatalyst.

Particular preference is given to loading with nanoparticles, in particular with nanoparticles having a median particle size of <10nm, in particular <5 nm. In a particularly preferred embodiment, the loading is carried out with Au nanoparticles and/or Pt nanoparticles having a median particle size of 10nm or less, in particular 5nm or less. During loading, the smaller particles are in stable contact with the larger particles through surface effects. The band gap of the active material is also reduced by the loading and thus the activation energy is reduced.

In a further preferred embodiment of the photocatalyst, different particles and/or different particle sizes are mixed. Preferred examples are ZnO and SnO₂And (3) mixing. It is further preferred that the same or different materials are used in different particle sizes, e.g. in particle size<50nm of a mixture, in a particle size of 50 to<150nm and mixtures with particle sizes of 150 to 300 nm. It was confirmed that the particle size also has an influence on the band gap. Therefore, small particles are particularly preferred. On the other hand, larger particles provide more potential deposition surface for the mote. From this, rootMixtures of different particle sizes are preferably used according to the invention.

In a particularly preferred embodiment, the photocatalyst material used according to the invention comprises

(i) Photocatalyst and

(ii) and (3) a binder.

The photocatalyst is preferably used in the form of small particles. Preferably the photocatalytic material has a particle size of 1000nm or less, more preferably 500nm or less, still more preferably 300nm or less, most preferably 150nm or less and especially 50nm or less. The particle size in this context means the median value of the particle diameter, respectively, unless otherwise stated.

The binder is preferably selected such that it does not change or decompose during the photocatalytic process. During the photocatalytic process, the chemical species may be partially dissolved or converted. The binder used for the photocatalytic coating and thus also the photocatalytic coating itself must therefore withstand photochemical reactions.

Particularly suitable binders here are silanes. Particularly suitable are tetraalkoxysilanes and in particular Tetraethylorthosilicate (TEOS). Particular preference is given to using colloidal SiO₂The particles additionally embed a prehydrolyzed silicate-hybrid binder. The silanes preferably have 5 to 70 mol%, preferably 10 to 50 mol% and in particular 15 to 30 mol% of SiO₂Most preferably, the binder further comprises a solvent and/or a catalyst (particularly sulphuric acid).

As solvents, for example for applying the photocatalytic material to a substrate, preference is given to using alcohols, in particular primary, secondary and tertiary alcohols, and also water and mixtures thereof. It is particularly preferred to use primary alcohols, in particular methanol, ethanol or propanol, in particular ethanol.

The composition for applying the photocatalytic material to the substrate also preferably comprises a surfactant. Such surfactants hinder the aggregation of the active particles so that the composition can be applied, for example, by spraying.

Preferably, the process according to the invention is carried out under light having a wavelength of from 400nm to 800 nm.

In a particularly preferred embodiment, the method according to the invention for reducing mote is carried out in an open system. The open system is characterized in particular by normal air circulation. The photocatalytically active coating functions here with little to no uv component. Other requirements that must be met by open systems are the health care and abrasion resistance of the coating.

In particular, open systems must be free of input of extraneous energy and of forced air flows as in the case of closed systems, such as air conditioning. In a closed system, the photocatalytically active surface is located inside the machine. Air laden with hazardous substances, such as gas or bioaerosols, is forced through such surfaces. The placement of the surface inside the machine has the advantage there that, in a closed system, it can be irradiated with strong, unhealthy uv light. Such irradiation is precisely not required according to the invention. In conclusion, it is possible to ascertain that the preferred open coating systems according to the invention have no forced air guidance and do not require irradiation with wavelengths and/or electromagnetic radiation intensities that are harmful to human health, compared to conventional closed systems.

The removal of fine dust from gaseous media, in particular air, is possible by the effect determined according to the invention. The fine dust here relates to particles which are present in a floating state, in particular in a gaseous medium, for example air (free-floating particles), in particular particles having a median particle diameter of < 50 μm. Preferably, the mote particles have a particle size of 40 μm or less. In the sense of the present invention, mote means in particular all particles having a median particle diameter of <10 μm. However, according to the invention, dust particles having a particle size of 2 μm or less or 350nmm or less and dust particles having a particle size of 100nm or less are also separated off. In the sense of the present invention, motes also include ultrafme dust having a particle size of 100nmm or less. Outstanding results are obtained precisely in the case of fine dust having a median particle diameter of ≦ 100 nmm. It is further preferred that the fine dust has a particle size of 1nm or more, particularly 5nm or more.

According to the invention, motes are also understood to mean pollen particles which likewise need to be removed from the air. Pollen particles typically have a median particle diameter of 10 μm to 30 μm.

Since the physical properties of a dust particle are highly dependent on its shape, the particle diameters given herein relate to the aerodynamic (equivalent) diameter. Under this determination, the aerodynamic behavior of the particles is equivalent to that of a spherical object.

The fine dust can be released into the atmosphere by many natural processes, such as smoke, weathering, or by mechanical abrasion. Bioaerosols also fall into the concept of motes, such as pollen or fungal spores. In the case of ultrafine dust, for example, there are exhaust gases of internal combustion engines, and wear through machinery such as brake devices.

Preferably for use in the method according to the invention for applying the above-mentioned photocatalytic material to a substrate which is then in contact with a gaseous medium. Suitable substrates are, for example, glass, plastics, textile structures, walls, cement, metals, ceramics, wood or/and composite materials. Glass is particularly preferably used as the substrate. By using a coating of photocatalytic material on the inside glazing of a building or driving tool which is also activated in the absence of ultraviolet light, the removal of fine dust can be carried out continuously and without other measures. The photocatalytically active coating is preferably used here indoors, such as in private homes, open buildings, hospitals, schools, etc., or in driving tools, such as the cabins of buses, passenger cars and trucks, boats or airplanes.

The coating is preferably applied to walls and/or ceilings (Decken), most preferably to window panes.

The photocatalytic material can be applied to the substrate by conventional methods, for example Spraying (spra hen), calendering, painting, Spraying (Spraying), dip coating or vapor-through coating.

The invention also includes photocatalysts described herein that are activated in the absence of ultraviolet light.

In a particularly advantageous embodiment of the method according to the invention for reducing dust particles, the dust particles in the air are removed in the absence of uv light by means of a photocatalytic material applied to the glazing. For this application form, the photocatalyst preferably has a particle size of less than 300nm and is thus invisible or transparent to the human eye.

The invention will be further elucidated by means of the appended drawings and the following examples.

Drawings

FIG. 1 shows SnO₂XRD analysis of the sample.

Figure 2 shows XRD analysis of ZnO samples.

Figure 3 shows XRD measurements of ZnO doped with Co. It is clearly seen that Co is built into the crystal structure of ZnO.

Figure 4 shows ZnO particles doped with Co photographed by a grating electron microscope.

Detailed Description

Example 1

ZnO doped with Co

The ZnO was doped with Co using two different methods, wet chemical and thermal processes. The weight ratio Zn to Co is in each case 10: 1. The weight ratio of the elements in the doped photocatalyst largely corresponds to the weight ratio of the starting materials, as determined by energy dispersive X-ray analysis (EDX), i.e. the ratio Zn: Co = 10: 1. It was confirmed by UV/Vi s/NIR analysis that the ZnO doped with Co has at least two active band gaps at about 1.8eV (690nm) and 2.7eV (460 nm). The particle size of the obtained photocatalyst was in the range of about 100nm to 1.2 μm (median particle diameter) as can be determined according to a Raster Electron Microscope (REM) (see fig. 4). Depending on the cathodoluminescence measurements carried out, it can be confirmed that almost all ZnO was converted.

The two photocatalytic materials doped with ZnO (one doped with wet chemistry and one doped with a thermal process) are applied as a coating to a substrate. After 30 minutes, the result of the dust reduction measurement was a dust reduction to 8% or 6.35%. Without comparative measurements of the photocatalytically active material according to the invention, the corresponding end value was significantly higher, namely 15.84%. This shows that the air purification process can be accelerated significantly with the photocatalytically active coating according to the invention.

Example 2

Reduction of the load of fine dust in the interior of a truck

The measurements were made in a passenger car model Mini. The cabin has a volume of 7.58m 3. The vehicle has six side glass sheets in addition to a front glass sheet and a rear glass sheet, and the roof side is additionally provided with two panoramic glasses. The ratio of glass surface to other surfaces (plastic inner panel and base) was 1: 3.8.

To achieve an average illumination intensity of 3500LuX, the test carriage was illuminated from the outside by means of 6 HQ illuminators. Thus, there is no light source inside the vehicle, and activation of the ultraviolet component of the lighting fixture used can be eliminated.

The fine dust particles generated by means of a standby generator (4-stroke engine) are introduced into the vehicle interior. Aerosol was loaded at the front right door and sample air was vented at the rear left door. For measuring the mote loading, aerosol particles having a diameter of between 5nm and 2 μm were counted using a Condensation Particle Counter (CPC) from Grimm. The particle size distribution was determined by means of a Differential Mobility Analyzer (DMA), also from the company Grimm.

During the experiment, a control measurement without the inventive indoor coating was first carried out, which obtained a value for the natural drop in the concentration of the mote. Introducing into the vehicle for 2 secondsExhaust gas from standby generator, whereby particle concentration reaches per cm³Over 150000 particles. Thereafter, the mote concentration was recorded for 36 minutes.

All glazing insides were then coated with Co-doped ZnO (see example 1). The retest is then performed as described above.

The values thus obtained with respect to particle reduction were compared with the control measurements. The effectiveness of the photocatalytically active coating was converted from the difference. It was confirmed to be 4.27% after 6 minutes; 12.10% after 12 minutes; 15.94% after 18 minutes; 20.08% after 24 minutes; improvement in particle reduction 23.02% after 30 minutes and 25.18% after 36 minutes.

The method according to the invention thus leads to a significant reduction in the dust load in the passenger compartment of the truck.

Example 3

Reduction of indoor dust load by photocatalytically active coating

For the measurement, two adjacent identical spatial chambers are used. One chamber was used as a reference chamber and the other chamber was coated with Co-doped ZnO (see example 1). The motes are loaded through the standby generators, respectively. For measuring motes, use was made of CPCs with DMA (see example 2). The 4-stroke engine with the aid of a backup generator spreads the gas long enough to ensure an initial concentration per cm³Over 150000 particles.

Particle concentration was then measured over 120 minutes. The result of this measurement is a 27.6% improvement in the particle reduction efficacy of the spatial cell coated with cobalt-doped zinc oxide.

Claims (12)

1. Method for reducing motes, characterized in that motes are removed from a gaseous medium by means of a photocatalytic material comprising a photocatalyst in the absence of ultraviolet light.

2. Method for reducing fine dust, characterized in that fine dust is removed from a gaseous medium by means of a photocatalytic material comprising a photocatalyst in the absence of a uv light component.

3. Method according to one of the preceding claims, characterized in that the photocatalytic material comprises a photocatalyst and a binder.

4. A method according to claim 3, characterized in that the binder comprises a silane.

5. Method according to one of the preceding claims, characterized In that the photocatalyst comprises at least one of the elements Sn, Zn, Bi, Ga, Ge, In, Ta, V, W, Sb or TI, and In particular comprises Sn or/and Zn.

6. Method according to one of the preceding claims, characterized in that the photocatalyst is doped with one or more elements selected from the group consisting of Co, C, N, P, S or H, or/and the photocatalyst is loaded with one or more elements selected from the group consisting of Pb, Au, Ag, Pt, a1, Cu, Sb, Mo, Fe or Cd.

7. Method according to one of the preceding claims, characterized in that the photocatalytic material is applied to a substrate, in particular to glass, metal, building material or/and ceramic.

8. Method according to one of the preceding claims, characterized in that the method for reducing mote is carried out in an open system.

9. Method according to one of the preceding claims, characterized in that it is carried out in the absence of light with a wavelength <350 nm.

10. Method according to one of the preceding claims, characterized in that the motes are particles having a median particle diameter of < 50 μm, in particular < 100 nm.

11. Method for reducing motes according to one of the preceding claims, characterized in that motes are removed from the gaseous medium without ultraviolet light by means of a photocatalytic material containing a photocatalyst applied to the glazing.

12. The method of claim 11, wherein the photocatalyst has a particle size of <300 nm.