People are inseparable from oxygen every moment, and obtain oxygen by inhaling air. An adult needs to inhale 6,500 liters of air every day to obtain enough oxygen. Therefore, polluted air has a direct impact on human health. People spend more than 90% of their lives indoors, and the impact of indoor air quality on people is even more crucial.

 

With the continuous development of market economy and science and technology, the development of the construction field is also changing with each passing day. People's requirements for the quality of life are getting higher and higher, and the standards of building decoration are also increasing, so the phenomenon of indoor air pollution is also accompanied.

 

Sources of major indoor pollutants

 

There are five main sources of indoor air pollutants:

 

Outdoor air pollution, dust in the atmosphere, NOx, CO, SO2 and inhalable particulate matter in automobile and industrial exhaust.

 

Building decoration materials and indoor equipment, related pollutants such as formaldehyde in phenolic resin and urea-formaldehyde resin compounds, various bacteria, fungi and spores brought by humidifying agents, various volatile organic compounds in adhesives, etc.; toxic substances, Exhaled breath contains 16 volatile toxic substances.

 

Radioactive pollution: that is, ionizing radiation pollution, radon, thorium, radium and other radionuclides. Radon and its daughters permeated by the building foundation itself and radioactive substances in various building materials. Among them, C-rays come from building materials such as marble and granite, or building decoration materials mixed with industrial waste, ceramic tiles, etc. Radon and its daughters come from building materials such as granite, brick sand, cement, gypsum, and gas and water polluted by radon sources.

 

Biological pollution: bacteria such as Legionella and actinomycetes, fungi such as Aspergillus and botrytis, germs, pollen, insects and mites, etc. Under natural circumstances, the vast majority of human respiratory infectious diseases are pathogenic bacteria that spread infection indoors. There are as many as 200 kinds of viruses that only cause respiratory tract infections, and most of these infections are transmitted indoors through the air.

 

Indoor Pollutant Control Technology

 

With people's emphasis on indoor air quality and the development of technology, indoor pollution prevention and control measures are increasing day by day. Mainly include adsorption purification, ultraviolet disinfection, chemical disinfection, photocatalytic oxidation, negative air ion technology, biological purification, plant purification, etc. In recent years, photocatalytic oxidation and its combination with other technologies have developed rapidly.

 

photocatalytic oxidation

 

The principle of photocatalytic oxidation technology is to use titanium dioxide (TiO2) for photocatalysis, directly use ultraviolet light from various sources including solar energy, to decompose or oxidize various organic and inorganic pollutants at room temperature, and decompose them into H2O and CO2, to achieve the purpose of purifying the air [4]. According to reports, under ultraviolet light with a wavelength of 254 nm, the photocatalyst TiO2 activated carbon fiber was used as a carrier to adsorb and photocatalytically oxidize formaldehyde, and 96% of formaldehyde was removed [5]. The advantages of photocatalytic oxidation are low energy consumption, simple operation, and no secondary pollution; the disadvantages are low efficiency of using sunlight and slow reaction speed. It has been pointed out in the literature that when photocatalytic oxidation is combined with other technologies, the synergistic effect between different technologies can be used to improve the removal effect of harmful gases.

 

1. Combination of photocatalytic oxidation and catalytic oxidation technology

 

Platinum plating on TiO2, when the temperature is 333K or higher, the oxidation conversion effect of volatile organic compounds such as toluene, ethylene and other low activity VOCS is improved. Under the joint action of thermocatalysis and photocatalysis, the complete oxidation of all VOCS can be achieved.

 

2. Combination of photocatalytic oxidation and adsorption technology

 

The harmful gas is adsorbed on the catalyst by the adsorbent, and then the catalytic reaction is carried out on its surface, which can make the harmful gas diffuse to the surface of the catalyst in a short period of time, and increase the surface gas concentration, speed up the reaction rate, and strengthen the removal process. Effect. Activated carbon with a high specific surface area is used as an adsorbent, and TiO2 is loaded on a HZSM-5 molecular sieve as a catalyst. Under ultraviolet light irradiation, the formaldehyde concentration decreases from 1. 0 mg/m3 to 0. 1 mg/m3 within 10 minutes; after 90 minutes, almost No formaldehyde was detected.

 

3. Combination of photocatalytic oxidation and plasma technology

 

This technology uses active particles such as O- (or O2-) and OH- produced by the bombardment of a large number of high-energy electrons to decompose organic molecules into CO2 and H2O. With the radiation of ultraviolet light, it can also play a role in sterilization and disinfection. By using plasma and photocatalysis to remove trichlorethylene, it was found that when the two were used alone, the degradation rates of trichlorethylene were 32.0% and 141%, respectively, and when the plasma and photocatalysis were combined, the degradation rate reached 75.4%[8]. It can be seen that there is an obvious synergistic effect between plasmonics and photocatalysis, which can significantly enhance the reactivity of the catalyst.

 

Ozone Purification Technology

 

Because ozone is a slight ion complex, the combined state is extremely unstable, and it will slowly decompose into oxygen at room temperature, and the single oxygen will be separated, and ozone will be reduced to oxygen after participating in the decomposition of substances. The decomposition mechanism of formaldehyde and carbon monoxide is as follows:

 

Formaldehyde: 3HCHO+2O3y3H2O+3CO2, carbon monoxide: CO+O3yCO2+O2 Studies have shown that low concentration ozone (0. 050~0. 075mg/m3) can purify formaldehyde pollution in indoor air, and the purification rate is 42%.

 

The disadvantage is that ozone is a harmful gas with irritating and strong oxidizing properties, which will pollute the indoor air.

 

Negative air ion technology

 

On the one hand, air negative ion technology can adsorb tiny particles in the indoor air and become charged large ions to settle down. On the other hand, it can reverse the electrical poles of the surface layer of bacterial proteins and promote the death of bacteria, which is very beneficial to human health. The emission technologies of negative air ions mainly include: corona discharge, water generation and radiation generation. Experiments show that the HE series negative air ion generator can significantly reduce the radon daughter concentration by about 50%. The advantage is that the main machine is cheap, the noise is small, and the volume is small; the disadvantage is that the particles are not collected or the filtering effect is poor, and ozone is generated, causing secondary pollution.

 

Biological purification technology

 

Biological treatment of air pollutants is an emerging technology, mainly because the surface of the porous filler in the filter is covered with biofilm, and the pollutants contact with the microorganisms in the film to undergo biochemical reactions, making them completely degraded into CO2 and H2O. [11] The basic methods of biological purification technology include biological filtration, biological washing, biological absorption and so on. When NO passes through the filter tower filled with biological soil, when the NO inlet concentration is 211mg/m3 and the residence time is 2min, the NO removal rate is about 60% [12]. Qiang Ning et al. studied the purification of toluene waste gas with a biological trickling filter. The results showed that: under the conditions of toluene load less than 280g/ms per hour and residence time of 15.73s, when the superficial gas velocity was 230m/h, more than 90% of the purification could be maintained. Rate.


Find out more air quality detector @ RenhotecICcom