Background
TiO was discovered by Fujishima and Honda in 1972
2Since the semiconductor electrode photolyzes water, research on semiconductor photocatalytic reaction is deeply and widely carried out. Carey et al first proposed TiO in 1976
2The method for degrading polychlorinated biphenyl by photocatalysis opens up a new field of application of semiconductor photocatalysts in the aspect of environmental protection, and plays a great role in promoting the rapid development of photocatalysis. Researches prove that a plurality of semiconductor materials have photocatalysis, hundreds of main organic or inorganic pollutants can be decomposed by a photocatalysis oxidation method, and the semiconductor materials have bright application prospects in the aspects of pollution control of soil, water quality and atmosphere, antibiosis and the like. Corresponding water purifiers, air purifiers, indoor cleaning materials, food and flower preservative films, self-cleaning and anti-fog glass, antibacterial ceramics and other photocatalysis products with excellent performance have been developed internationally, and huge social and economic benefits are shown. Commonly used semiconductor photocatalytic materials include TiO
2ZnO, ZnS, CdS, etc., among which anatase type TiO
2The catalyst is most important and widely applied due to the characteristics of stable chemical property, no toxicity, high catalytic activity, low cost and the like. When the photon energy of the semiconductor photocatalytic material exceeds the bandwidth under illumination, electrons e on the valence band of the semiconductor
-Transition to conduction band, leaving hole h in valence band
+. Most of the holes recombine with electrons in the semiconductor, only a small portion diffuses to the surface, and with H in air
2Reaction of O to generate hydroxyl radical:
the hydroxyl free radical has strong oxidizing property and can react with nitrogen oxide, sulfur dioxide, hydrogen sulfide, ammonia gas and most of organic matters, thereby achieving the aim of purifying air and water.
In the theoretical research aspect of the photocatalytic technology, Japan, Europe and America and other countries invest huge investment to develop research and development work, and the industrialization of the photocatalysis technology is greatly promoted. The application research of the photocatalysis technology in the aspect of life begins from the 90 s of the 20 th century, and gradually results appear in the last 6 and 7 years. The world is advanced in the civil product field in Japan, the most patents are related to the photocatalysis technology, and the emphasis is placed on the aspects of sterilization, air purification, self-cleaning and the like, for example, the TiO plating is applied to the surface of ceramics by the company such as Towa in Japan2The method of the film is used for preparing the ceramic and the glass with the functions of purifying air, resisting bacteria and self-cleaning; in Europe and America, the emphasis is on removing carcinogens from polluted groundwater, treating sewage waste water, treating harbour waste oil, treating atmospheric pollution and the like; in China, research is mainly focused on air purification, deep treatment of low-concentration and high-toxicity polluted water and the like. The nano photocatalytic coating is also researched by various countries, products are applied to hospitals, tunnels, sound insulation walls, houses and the like, and other products applying the photocatalytic technology are dozens of products. There are over 1000 patents in question worldwide and there is still an increase.
The existing photocatalytic technology has two key problems, so that the photocatalytic activity is not high, and the wide industrial application of the photocatalytic technology is greatly restricted. These two problems are: (1) the quantum efficiency is low, and the waste gas and the waste water with large capacity and high concentration are difficult to process; (2) the solar energy utilization rate is low, and only the ultraviolet part in sunlight can be absorbed and utilized. The method improves the quantum efficiency of the existing photocatalytic system, enables the absorption spectrum of the photocatalyst to red shift to a visible light region, improves the utilization rate of sunlight, and is one of the research focuses in the current international photocatalytic field.
Summary of the invention
The invention aims to provide an air purification powder material with better photocatalysis effect under the conditions of ultraviolet light, visible light and micro radiation.
The high-activity photocatalytic air purification powder material provided by the invention is a nano-micron composite powder material formed by coating micron polar mineral tourmaline particles with nano titanium oxide with doping elements, wherein the doping elements are rare earth elements or/and transition elements.
In the high-activity photocatalytic air purification powder material, the rare earth element is one or more of oxides or nitrates of elements Ce, Pr, La, Sm, Eu and Nd.
In the high-activity photocatalytic air purification powder material, the transition element is one or more elements selected from Fe, Ag, Co, Cu and Zn.
In the high-activity photocatalytic air purification powder material, the doping amount of the doping element in the nano titanium oxide with the doping element is 0.005-0.09 in molar ratio to Ti atoms.
In the high-activity photocatalytic air purification powder material, the content of the tourmaline in the composite powder material is 5-98% by weight.
The invention also aims to provide a preparation method of the air purification powder material.
Firstly, preparing nano TiO by sol-gel method2Sol, and then nano Ti02Adding rare earth elements and tourmaline powder into the sol, uniformly stirring, standing to obtain gel, and calcining at 400-750 ℃ for 1-4 hours to obtain the air purification powder material.
Or in the presence of TiCl4Method for preparing nano TiO by hydrolysis method2And simultaneously, the powder is compounded with rare earth elements and tourmaline, and the obtained powder is washed, dried and calcined to obtain the air purification powder material.
The method specifically comprises the following steps:
the first step is as follows: preparing TiCl under ice water cooling4An aqueous solution;
the second step is that: mixing TiCl4Increasing the temperature of the aqueous solution, gradually increasing the temperature under heating until the system is boiled, and making TiCl by adopting a mode of boiling reflux of the system4Hydrolyzing the aqueous solution, and adding doping elements in the temperature rising process; then, micron-sized tourmaline is added; after full reaction, stopping heating, and cooling to obtain powder precipitate;
the third step: and precipitating and filtering the obtained powder, washing to be neutral, drying, and calcining at a high temperature of 400-700 ℃ for a certain time of 1-4 hours to obtain the air purification powder material.
The invention also aims to provide the application of the high-activity photocatalytic air purification powder material as a functional component added into a building material decoration and finishing material. In the application, the air purification powder material is added into the interior wall latex paint in an amount of 1-5 wt%.
According to the technical scheme, the material is prepared by coating micron polar mineral tourmaline particles with rare earth element and transition element doped nano titanium oxide to form a nano-micron composite structure, and experiments prove that the material has a good photocatalytic effect under ultraviolet, visible light and micro radiation conditions, so that the material has a good air purification function and solves the problem that the nano particles are not easy to disperse. The material is a novel high-efficiency air purification material, and can be applied to building material decoration and finishing materials, such as paint, wallpaper and ceramic.
Detailed Description
The present invention is described in detail below in several aspects.
(1) Principle of operation
The air purification material is prepared by adding polar mineral tourmaline powder while preparing nanometer titanium dioxide doped with rare earth and transition elements, so that nanometer titanium dioxide particles are coated on tourmaline particles to form a nanometer-micrometer structure, as shown in figure 1. In fig. 1, the large black part is tourmaline particles, and the small black part is nano titanium dioxide particles doped with rare earth and transition elements. On one hand, rare earth elements and transition elements are added and introduced into crystal lattices of titanium dioxide to generate active centers and new energy levels, so that the optical activity is increased; on the other hand, the surface electric field of the tourmaline acts on titanium oxide particles to increase the diffusion speed of electrons and holes and improve the light quantization efficiency, so that the air purification material has better photocatalysis effect under the conditions of ultraviolet light, visible light and microwave, OH free radicals generated by photocatalysis are strong oxidants and can react with polluted gases such as formaldehyde, nitric oxide, sulfur dioxide, hydrogen sulfide, ammonia gas, VOC and the like, and the aim of purifying air is fulfilled.
In the present invention, rare earth elements are used as activators. Due to the unique characteristics of the rare earth elements, the rare earth elements have 4f orbital electrons, and the 4f electrons are easy to excite, so that the coordination of the rare earth elements generates variability, and the electrons of the 4f orbital can play a role of a 'backup chemical bond' or 'residual atomic valence'. The invention utilizes the electron transferred in the process of the valence state change of the rare earth element to activate and participate in the photocatalytic reaction, thereby promoting the generation of hydroxyl free radicals. Therefore, when designing the chemical composition of the catalyst, rare earth elements are selected as the activators. In consideration of photochemical quantum yield and realization of a photocatalytic function in a visible light range, the rare earth activator is one or more of oxides or nitrates of elements such as Ce, Pr, La, Sm, Eu, Nd and the like.
Second, in nano TiO2The rare earth element can be introduced into TiO2Introducing lattice defects or changing crystallinity in the crystal, in TiO2Additional energy levels are created in the forbidden band. TiO 22If the electrons in the valence band firstly jump to the additional energy levels and then jump to the conduction band, the required energy is much smaller than that of the electrons which directly jump from the valence band to the conduction band, so that the rare earth element doped nano TiO can be excited by visible light2So that it can produce photocatalysis and expand TiO2Spectral response range of (c). In addition, the competition of rare earth elements for electrons reduces TiO2Surface photo-generated electrons e-And h for generating holes+Thereby making TiO compound2More OH is generated on the surface, and the activity of the catalyst is improved.
In the invention, the transition elements are Fe, Ag, Co, Cu and Zn and one or more of the elements. The transition element has valence-changing effect, and proper transition metal ion doping can introduce lattice defect or change crystallinity in semiconductor crystal to form more photocatalytic active sites, and the competition for electrons reduces TiO because the metal ion is electron acceptor2Surface photo-generated electrons e-And photogenerated holes h+Thereby making TiO compound2More OH is generated on the surface, and the activity of the catalyst is improved.
In the invention, the tourmaline particles are also coated by the nano titanium dioxide particles doped with rare earth and transition elements. The tourmaline has strong surface electric field and can ionize water molecules to form H+And OH-Ions; OH group-Ions and rare earth elements attached to the surface of tourmaline are doped with nano TiO2H produced by photocatalysis+Combines to generate OH free radical, thereby improving the photocatalytic activity. In addition, the surface electric field provided by the tourmaline is beneficial to TiO2The electron-hole pairs generated by photocatalysis are separated, and the quantum efficiency is improved.
(2) Preparation scheme
The first technical scheme is as follows: the invention firstly prepares nano TiO by sol-gel method2Sol and then nanometer TiO2Adding rare earth elements and tourmaline powder into the sol, uniformly stirring, standing to obtain gel, and calcining at 400-750 ℃ to obtain the air purification material.
The second technical scheme is as follows: in the presence of TiCl4Method for preparing nano TiO by hydrolysis method2And simultaneously is compounded with rare earth elements and tourmaline. In the first step, an aqueous TiCl4 solution (concentration about 1.84mol/L) is prepared: with TiCl4Method for preparing nano TiO2Firstly, the liquid pure TiCl is mixed4Preparing aqueous solution with certain concentration. TiCl (titanium dioxide)4The aqueous solution can stably exist at normal temperature at a certain pH value (below 4). Step two, preparing an air purification material: TiCl (titanium dioxide)4The temperature of the aqueous solution increases and thepH changes such that TiCl is produced4And (4) hydrolyzing. The scheme adopts the mode of heating to gradually raise the temperature until the system boils (the temperature is higher than 100 ℃), and making the TiCl boil and reflux4Hydrolyzing with water solution, adding diluent during hydrolysisEarth oxide or rare earth salt, and micron-level or even nano-level tourmaline derivative is added in the hydrolysis process. And after full reaction, stopping heating, cooling, filtering the obtained powder, fully washing the powder by using deionized water, washing the powder to be neutral, drying the powder, and calcining the powder for 1 to 4 hours at the high temperature of 500 ℃ to obtain a final product. The scheme adopts the steps of raising the temperature and boiling and refluxing the system to prepare the nano TiO2Compounding with rare earth elements and tourmalineThe novel air purification material.
The tourmaline is micron-sized powder, and the generated nanometer TiO2Continuously collide with the rare earth composite powder and the tourmaline and are attached to the surface of the tourmaline to form novel powder.
The doping element is one or more of rare earth elements and transition elements. The rare earth elements are rare earth salts, including: ce. One or more of oxides or nitrates of Pr, La, Sm, Eu, Nd and other elements, and transition elements including salts or oxides of Fe, Ag, Co, Cu, Zn and other elements with valence-changing effect. The doping amount is 0.005-0.05 mol ratio of total doping elements and Ti atoms. The content of the tourmaline in the composite powder is 5-98% by weight.
(3) Examples and effects
Example 1
1) The preparation method comprises the following steps: scheme one is adopted. Hydrolyzing with tetrabutyl titanate to obtain nano-grade TiO2La is doped in the tourmaline and the tourmaline (with the average grain diameter of 2.5 microns) is coated.
2) Material composition:
component (g)
Nano TiO 2278
La(NO3)32
Tourmaline 20
Total 100
3) And (4) testing results: the electron micrograph and the analytical micrograph of the material of this example are shown in FIGS. 1 and 2, respectively. Structural X-ray analysis of the material is shown inFig. 3. By performing the spectrum analysis, the phase composition of the material is as follows: t (tourmaline), Q (silicon dioxide) and A (anatase TiO)2). With anatase type TiO2Standard comparison of spectra, A (anatase TiO)2) The diffraction peak of (a) is remarkably broadened. The XRD analysis found a silica phase, probably due to the higher content of silica in tourmaline.
4) The air purification effect: the powder material produced by the method is added into the interior wall latex paint of the three-flag brand in an adding amount of 3 wt%, is fully dispersed, does not influence the apparent quality of the paint, and is coated with 0.5m2Glass plate, put into a known formaldehyde gas concentration of 3.50mg/m31m of3In a sealed cabin, measuring the concentration of formaldehyde in the sealed cabin by a chemical sampling analysis method after 24 hours, and measuring that the concentration of the formaldehyde is reduced to 0.20mg/m3The purification rate of the material to formaldehyde in 24 hours is calculated to be 94.3%.
By the same method, the addition amount of the powder material is changed, the powder material is added into the interior wall latex paint of the three-flag brand in the amount of 1 wt%, the powder material is fully dispersed, the apparent quality of the paint is not influenced, and the powder material is brushed for 0.5m2Glass plate, put into a known formaldehyde gas concentration of 3.50mg/m31m of3In a sealed cabin, measuring the concentration of formaldehyde in the sealed cabin by a chemical sampling analysis method after 24 hours, and measuring that the concentration of the formaldehyde is reduced to 0.40mg/m3The purification rate of the material to formaldehyde in 24 hours is 88.6 percent; adding 5 wt% of the emulsion into the interior wall latex paint of the three-flag brand, fully dispersing without influencing the apparent quality of the paint, and brushing 0.5m2Glass plate, put into a known formaldehyde gas concentration of 3.50mg/m31m of3Sealing in a sealed chamber, and using chemical after 24 hoursMeasuring the concentration of formaldehyde in the sealed bin by a sampling analysis method, and measuring that the concentration of formaldehyde is reduced to 0.10mg/m3The purification rate of the material to formaldehyde in 24 hours is calculated to be 97.1%.
Example 2
1) The preparation method comprises the following steps: scheme two is adopted. With TiCl4Hydrolyzing to prepare titanium dioxide, wherein Ce is doped, and the coated tourmaline is micron-sized.
2) And (2) assembling:
component (g)
Nano TiO 2269.5
Ce(NO3)30.5
Tourmaline 30
Total 100
3) And (4) testing results: the measurement results of hydroxyl radicals of the powder of this example under ultraviolet, visible and no-light conditions are shown in FIG. 4. As can be seen from FIG. 4, the material has strong free radical generating capability not only under the condition of ultraviolet light, but also under the conditions of visible light and no light irradiation.
4) The air purification effect: when the amount of the added powder was 3 wt%, the formaldehyde purification rate of the powder in this example was 90% and the acetaldehyde purification rate was 92% for 24 hours, as measured by the same method as in example 1.
Example 3
1) The preparation method comprises the following steps: scheme two is adopted. TiCl (titanium dioxide)4Hydrolyzing to prepare titanium dioxide, wherein Fe and Zn are doped, and the coated tourmaline is in a micron order.
2) And (2) assembling:
component (g)
Nano TiO 2250
Fe2O30.4
Zn(NO3)20.4
Tourmaline 49.2
Total 100
3) The air purification effect: when the amount of the catalyst added was 3 wt% as measured in the same manner as in example 1, the gas was toluene, and the powder in this example had a toluene purification rate of 82.6% for 24 hours.
Example 4
1) The preparation method comprises the following steps: scheme two is adopted. With TiCl4Hydrolyzing to prepare titanium dioxide, wherein Ce and Zn are doped, and the coated tourmaline is in a micron order.
2) And (2) assembling:
component (g)
Nano TiO 2249.2
Ce(NO3)30.4
Zn(NO3)20.4
Tourmaline 50
Total 100
3) The air purification effect: when the amount of the added powder was 3 wt%, the formaldehyde purification rate in 24 hours was 96.6% and the toluene purification rate was 91.2% as measured in the same manner as in example 1.
Example 5
1) The preparation method comprises the following steps: scheme two is adopted. With TiCl4Hydrolyzing to prepare titanium dioxide, wherein Ce, La and Cu are doped, and the coated tourmaline is in a micron order.
2) And (2) assembling:
component (g)
Nano TiO 2290
Ce(NO3)30.4
La2O33.2
Cu(NO3)21.4
Tourmaline 5
Total 100
3) The air purification effect: when the amount of the added powder was 3 wt%, the formaldehyde removal rate for 24 hours was 86.6% and the nitrogen oxide removal rate was 92.2% as measured in the same manner as in example 1.
Example 6
1) The preparation method comprises the following steps: scheme two is adopted. With TiCl4Hydrolyzing to prepare titanium dioxide, wherein Pr, Zn and Co are doped, and the coated tourmaline is in a micron order.
2) And (2) assembling:
component (g)
Nano TiO 224.6
Pr(NO3)30.1
Co(NO3)20.2
Zn(NO3)20.1
Tourmaline 95
Total 100
3) The air purification effect: when the amount of the added powder was 3 wt%, the formaldehyde removal rate for 24 hours was 56.8% and the ammonia removal rate was 87.5% as measured in the same manner as in example 1.