In fact, many professional formaldehyde removal companies are not professional. The indoor air purification industry is a rising industry promoted by the country because of its relatively low threshold and high profit. As long as you buy potions and instruments, you can use them without any theoretical knowledge. As a result, companies are uneven, and most of them use strong oxidant products to remove formaldehyde. The molecule of formaldehyde is relatively simple, HCHO, so many products can remove formaldehyde, but the release of formaldehyde is around 3 to 15 years. Short-term removal has no effect. After treatment with strong oxidants, only formaldehyde can be removed, which is not only not lasting, but also causes secondary pollution, which causes more serious harm to human body. Didn't TV news just expose a governance company posing as photocatalyst with strong oxidation? . The photocatalyst, at this time, played its huge role.
Briefly introduce photocatalyst
Photocatalyst is a generic term for photo-semiconductor materials with photocatalytic function represented by nano-scale titanium dioxide. It is coated on the surface of the substrate and produces a strong catalytic degradation function under the action of light: it can effectively degrade toxic and harmful in the air Gas; can effectively kill a variety of bacteria, and can decompose and harmless toxins released by bacteria or fungi; at the same time, it can also release a certain concentration of negative oxygen ions. With deodorization, anti-fouling, and air purification functions.
年，日本东京大学的本多建一教授和博士班学生藤岛昭发现，用光照射二氧化钛电极可进行水的电解反应。 In 1967 , Professor Kenichi Bunta and PhD student Akira Fujishima of the University of Tokyo in Japan discovered that the use of light to irradiate titanium dioxide electrodes can perform the electrolytic reaction of water. “ 本多作用的光催化反应，将空气中的水或氧气催化成氧化能力极强的羟基自由基（ ·OH ）和超氧阴离子自由基（ O2· ）、活性氧（ HO2· ， H2O2 ）等具有极强氧化能力的光生活性基团，这些光生活性基团的能量相当于 3600K 的高温，具有很强的氧化性，这些强氧化性基团可强效分解各种具有不稳定化学键的有机化合物和部分无机物，并可破坏细菌的细胞膜和凝固病毒的蛋白质载体。 This is the " multiple-action photocatalytic reaction of ***, which catalyzes water or oxygen in the air into hydroxyl radicals ( · OH ), superoxide anion radicals ( O2 · ), active oxygen ( HO2 · , H2O2 ) and other photo-living groups with extremely strong oxidizing capacity. The energy of these photo-living groups is equivalent to a high temperature of 3600K and has a strong oxidizing property. An organic compound and some inorganic compounds with unstable chemical bonds, which can damage the cell membrane of bacteria and the protein carrier of clotting virus.
TiO2 、 ZnO 、 CdS 、 WO3 、 Fe2O3 、 PbS 、 SnO2 、 ZnS 、 SrTiO3 、 SiO2 等，其中大多数易发生化学或光化学腐蚀，都不适合作为家居净化空气用光催化剂。 Materials with photocatalytic (catalyst) activity are mainly nano- TiO2 , ZnO , CdS , WO3 , Fe2O3 , PbS , SnO2 , ZnS , SrTiO3 , SiO2, etc. Most of them are prone to chemical or photochemical corrosion and are not suitable for domestic clean air With photocatalyst. TiO2 不仅具有很高的光催化活性，且具有耐酸碱腐蚀、耐化学腐蚀、无毒等优点，价格也适中，具有较高的性价比，因而作为居屋空气净化产品应该使用纳米二氧化钛作为原材料。 Among all these photocatalytically active materials, nano- TiO2 not only has high photocatalytic activity, but also has the advantages of resistance to acid and alkali corrosion, chemical corrosion, non-toxicity, etc., the price is also moderate, and it has a high cost performance. HOS air purification products should use nano titanium dioxide as a raw material.
TiO2 ）是一种半导体，主要有锐钛型（ Anatase ），金红石型（ Rutile ）及板钛型（ Brookite ）三种晶体结构，其中：板钛型晶体稳定性差，一般认为不具备光催化活性。 Nano-titanium dioxide ( TiO2 ) is a semiconductor, which mainly has three crystal structures: anatase, rutile , and Brookite . Among them: the stability of plate-titanium crystals is generally not considered to have light. Catalytic activity. Anatase type crystals have stronger photocatalytic performance than rutile type crystals. The anatase nano-titanium dioxide has powder morphology and colloidal morphology. The former has a certain degree of soft and hard agglomeration; the latter has excellent monodispersity and is more suitable as a raw material for photocatalysts. Therefore, the photocatalyst raw material should be an anatase nano-titanium dioxide crystal colloid solution, which is usually called a nano-titanium dioxide colloid.
Third, the role of photocatalyst
Photocatalyst, as an emerging air purification product, is more and more applied to indoor and indoor air purification. It mainly has the following functions:
空气净化：对甲醛、苯、氨气、 TVOC 、二氧化硫、一氧化碳、氮氧化物等影响人类身体健康的有害有机物起到净化作用。 1. Air purification: Purify harmful organic substances that affect human health, such as formaldehyde, benzene, ammonia, TVOC , sulfur dioxide, carbon monoxide, nitrogen oxides.
负氧离子：使用合格的可见光光触媒处理过的居屋会长期释放负氧离子（ O3- ），有利于人体健康。 2. Negative oxygen ion: HOS treated with qualified visible light photocatalyst will release negative oxygen ion ( O3- ) for a long time , which is good for human health. “ 空气中负氧离子 ” 介绍。 The effect of negative oxygen ions on human health is described in " Negative Oxygen Ions in Air " .
杀菌防霉：对大肠杆菌、黄色葡萄球菌等具有杀菌功效。 3. Bactericidal and mildew-proof: It has bactericidal effect on E. coli and Staphylococcus aureus. While sterilizing, it can also break down the harmful compounds released from the dead body of bacteria.
Fourth, photocatalyst characteristics
全面性光触媒是目前国际上最安全和最洁净的环境净化材料，在欧美和日本、韩国等区域广泛运用，美国宇航空间站净化工程、海上油污降解工程和日本公交公司消毒工程均使用光触媒进行处理。 1. Comprehensive photocatalyst is currently the safest and cleanest environmental purification material in the world. It is widely used in Europe, America, Japan, South Korea and other regions. Photocatalysts are used for purification projects of American space stations, degradation of oil pollution at sea and disinfection projects of Japanese public transportation companies deal with. TVOC 等污染物，并具有高效广泛的消毒性能，能将细菌或真菌释放出的毒素分解及无害化处理。 Photocatalyst can effectively degrade pollutants such as formaldehyde, benzene, toluene, xylene, ammonia, TVOC, etc., and has high efficient and extensive disinfection performance, can decompose and harmless toxins released by bacteria or fungi.
持续性在环境污染不严重的条件下，只要不磨损、不剥落，光触媒本身不会发生变化和损耗，在光的照射下可以持续不断的净化污染物，具有时间持久、持续作用的优点。 2. Sustainability Under the condition of not serious environmental pollution, as long as it is not worn or peeled off, the photocatalyst itself will not change and lose, and it can continuously purify pollutants under the irradiation of light. It has the advantages of long-lasting and continuous effect. .
安全性无毒、无害，对人体安全可靠；不会产生二次污染。 3. Safety is non-toxic, harmless, safe and reliable for human body; no secondary pollution will occur.
V. Relevant properties of photocatalyst products
Wavelength range of photocatalyst absorption light
387.5nm 以下的紫外光，在自然环境下，紫外光占有比例较低，不足自然光的 3% ，因而纯净的纳米二氧化钛基本没有实际空气净化使用价值。 Pure nano-titanium dioxide can only absorb ultraviolet light below 387.5nm . Under natural environment, the proportion of ultraviolet light is relatively low, less than 3% of natural light , so pure nano-titanium dioxide has almost no practical value for air purification. Therefore, in order for the photocatalyst to absorb visible light, it is necessary to use a special material preparation doping technology. - 有机络合物、表面敏化、半导体复合等多种方法，对纳米二氧化钛进行可见光活化。 For example , multiple methods such as transition metal ions and non-metal ions doping, metal - organic complexes, surface sensitization, and semiconductor compounding are used to activate nano-titanium dioxide under visible light.
Effective concentration of photocatalyst
The photocatalyst itself is a catalyst that does not directly participate in the degradation reaction. It absorbs light energy to convert water or oxygen into strong oxidation active groups, and the strong oxidation active groups produce a photocatalyst function. The photocatalytic function process is a photocatalytic reaction at the gas-solid interface, which is related to the structure of the film. A dense nano-titanium dioxide film with a certain thickness is favorable for the photocatalytic process. 1% 浓度值是光触媒允许的***浓度。 Therefore, within a certain range, the higher the effective concentration of the photocatalyst, the better, but too high a concentration is not conducive to construction. Studies have shown that the 1% concentration value is the *** concentration allowed by the photocatalyst.
Photocatalyst Nanoparticle Size
50 纳米以下的纳米二氧化钛就可以显现出好的光催化活性。 The photocatalytic activity of nanophotocatalysts is related to many factors, and particle size is just one of the factors. Generally, nanometer titanium dioxide below 50nm can show good photocatalytic activity. Within a certain range, the smaller the particle size, the better the photocatalytic activity, but not the smaller the better. Photons generated on the surface of particles that are too small are easy to recombine, which is not conducive to photocatalytic efficiency. Particle size is not the *** standard for judging the quality of photocatalysts.
pH 值 PH value of photocatalyst products
pH 应该在 5-9 的范围。 Photocatalyst products are used in homes, people's living environment or the surface of objects in the car, so it must be guaranteed not to be corrosive. From this point of view, the pH should be in the range of 5-9 . 6.25 ，当体系的 pH 接近这个数值时体系会失稳，因此，光触媒的 pH 值应该是 5-6 。 On the other hand, high-quality photocatalyst products should be prepared from nano titanium dioxide colloids. The isoelectric point of nano titanium dioxide particles is 6.25 . When the pH of the system is close to this value, the system will be unstable. Therefore, the pH of the photocatalyst should be 5-6. .
Photocatalyst product adhesion
50 纳米，常常会是数纳米，这些粒子的表面有许多不饱键，表面能很高，这也是纳米材料的一个最基本性质，这些不饱键或者说高的表面能使得光触媒纳米粒子非常容易在物体表面附着。 Nanoparticles in photocatalyst products should be at least less than 50 nanometers, often several nanometers. The surface of these particles has many unsaturated bonds, and the surface energy is very high. This is also a basic property of nanomaterials. The surface energy of photocatalyst makes the photocatalyst nanoparticles very easy to adhere to the surface of the object. On the other hand, high-quality photocatalysts often have rich hydroxyl groups and positive charges on the surface, and the surfaces of objects around us are often negatively charged and have many hydroxyl groups. The photocatalyst nanoparticles and the surface of the objects will form hydrogen bonds and electrostatic adsorption. Therefore, the high-quality photocatalyst itself will have very good adhesion on the surface of the object.
Limitations of Photocatalysts
Photocatalysts, as air purification products for homes and cars, are safe, durable and versatile. However, the concentration of pollutants is too high, and it is difficult to solve the problem with photocatalysts at the moment. Therefore, it is necessary to combine treatment with other methods when doing treatment construction. And the place where the light cannot reach should be treated with relevant special products.
The photocatalyst project should be constructed with a special sprayer. If it is a bottled product, the container should have excellent atomization effect. During construction, pay attention to uniformity, spray everywhere, and do not spray excessively. The standard is not to produce large droplets, and not to cause liquid sagging. If you accidentally drip or form large droplets on the treated surface, wipe it off with a soft cloth or paper money. After the large droplets of photocatalyst are dried, a film with a thickness of several micrometers will be formed, resulting in traces. Due to the good adhesion of the nanomaterial, the photocatalyst traces can be difficult to remove (gentle wipe with toothpaste). 5 亿亿个光触媒粒子时时刻刻在发挥光触媒功能。 The photocatalyst nanofilm formed by the correct construction is invisible, but don't worry, the dense nanofilm will have 500 billion photocatalyst particles per square centimeter at all times.
At present, photocatalyst is a long-term effective product for indoor treatment of formaldehyde removal. However, domestic products are not complete, and many of them are directly made of titanium dioxide powder, which causes the visible light activity of photocatalysts to be inadequate and cannot function under indoor lighting. The average consumer cannot distinguish between the pros and cons of photocatalysts without experimental instruments. Can only listen to the side of the salesman who governs the company