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Controlling Nitrogen Oxide and Ultraviolet-A irradiance in ventilation duct system using TiO2 photocatalyst
Abstract
In this study, we verified the application of TiO2 photocatalysts on ventilation ducts used in buildings and their effects on reducing nitrogen oxide (NOx), which is a typical particulate matter precursor. The TiO2 photocatalyst produces a radical dioxide with a strong acid oxidation power through photochemical reactions with ultraviolet-A (UV-A) rays and removes NOx through oxidation. The removal experiment was conducted by applying TiO2 photocatalyst coatings inside the duct to comply with the conditions of the ISO 22197-1: 2007. In addition, changes in the NOx removal were confirmed through changes in the concentration of NOx and UV-A irradiance inside the duct. At approximately 100 min after switching on the UV-A lamp during the experiment conduced according to ISO 22197-1: 2007, the NOx concentration decreased to 0.053 ppm (by 94.87%). Moreover, it has been confirmed that the trend of reduction is proportional to the changes in UV-A irradiance and NOx concentration, that is, an increase in UV-A irradiance has a significant impact on the reduction of NOx concentration; NOx reduction increases as a secondary function due to an increase in the UV-A irradiance. Through this study, it is believed that NOx, a representative precursor material that generates particulate matter, can be removed through a building ventilation system using a TiO2 photocatalyst.
... First, when a photocatalyst is applied inside the device and an artificial light source is added, the efficiency of the photocatalyst may vary depending on the intensity of the light source. Song et al. [45] demonstrated that applying UV rays in confined spaces such as ventilation ducts, as well as preventing the rays from leaking indoors (to avoid UV damage to all life forms), can safely remove indoor air particulate matter. However, only a few studies have investigated changes in UV-A irradiance according to the lifespan of artificial light sources. ...
This study experimentally confirmed the effect of TiO2 photocatalysts on the removal of indoor air pollutants. In the experiment, toluene, a representative indoor air pollutant, was removed using a coating agent containing TiO2 photocatalysts. Conditions proposed by the International Organization for Standardization (ISO) were applied mutatis mutandis, and a photoreactor for an experiment was manufactured. The experiment was divided into two categories. The first experiment was conducted under ISO conditions using the TiO2 photocatalyst coating agent. In the second experiment, the amount of ultraviolet-A (UV-A) light was varied depending on the lamp’s service life, and the volume of the reactor was varied depending on the number of contaminants. The results showed that the TiO2 photocatalytic coating agent reduced the effect of toluene. This reduction effect can be increased as a primary function depending on the changes in the amount of UV-A light and reactor volume. However, because toluene is decomposed in this study, additional organic pollutants such as benzene and butadiene can be produced. Because these pollutants are decomposed by the TiO2 photocatalysts, the overall reduction performance may change. Nonetheless, TiO2 photocatalysts can be used to examine the effect of indoor pollutant reduction in indoor ventilation systems and building materials.
... As a result, TiO 2 is known to have photocatalytic characteristics in ultraviolet (UV) light irradiation, whereas doping compounds alter the TiO 2 structure to give photocatalytic activity in visible light. Bulk TiO 2 has low photocatalytic potential, regardless of the kind of TiO 2 (anatase and rutile TiO 2 are the most commonly reported photocatalysts) [6]. Due to their high surface-to-volume ratio, improved charge transport, increased number of delocalized carriers on the surface, improved lifetime obtained by their dimensional anisotropy, and the effective distribution for the separation of electrons and holes as shown by photo magnification, TiO 2 nanocrystals have several advantages over their bulk counterparts in terms of potential applications [1,7]. ...
TiO2 has become the most well-known photocatalysts for solving environmental problems as a wide-band n-type semiconductor. This research aimed to coat a carbon steel substrate with Zn-Co-TiO2 nanocomposite via the electrodeposition method. Scanning electron microscopy (SEM) was used to examine the microstructure, (energy-dispersive X-ray spectroscopy) EDS analysis was used to examine the composition of the coating, and a pull-off test was used to determine the adhesion of the coating. In this regard, the electrodeposition of the coatings was carried out at the optimum conditions of 0.1 A, the concentration of TiO2 equal to 15 g/L, deposition time of 20 min, the temperature of 25.5 °C, and pH of 5-5.5 in different electrolyte compositions. Also, the photocatalytic properties of TiO2 were determined by the fungal growth on the sample surface. According to the results, the fungal growth was reduced with the increase in the TiO2 content in the coating.
High-efficiency particulate air (HEPA) and charcoal filters have been applied to ventilation systems to save energy and reduce pollutants. However, such filters only work for specific types of pollutants, and their performance is not always sustainable. This study compares the pollutant reduction performance of TiO2 photocatalytic filters with HEPA and charcoal filters in mock-up experiments with toluene as the pollutant, changing air volume, and varying ventilation frequencies. The results show that the HEPA filter was ineffective at reducing toluene, and the charcoal filter was found to have the fastest reduction rate until 180 min after the start of the experiment. However, after 180 min when the charcoal filter was saturated, its pollutant reduction performance rapidly declined, resulting in low persistence. Conversely, the TiO2 photocatalytic filter had a lower reduction rate than that of the charcoal filter but had a continuous pollutant reduction performance during 720 min. Comparing the pollutant reduction effect of the TiO2 photocatalyst filter and the charcoal filter with a reduced amount based on the experimental time, the TiO2 photocatalyst filter has a maximum pollutant reduction effect of about seven times and at least about two times. This study confirms that HEPA and charcoal filters reduce gas pollutants, and it was found that combining TiO2 photocatalysts with ventilation devices can improve indoor air quality in apartment buildings.
In this study, the nitrogen oxide (NOX) removal performances and micropore structures of foam composites with activated carbon (AC) and titanium dioxide (TiO2) powder were investigated. AC was used to increase the NOX removal efficiency through TiO2 powder by increasing the specific surface areas of the foam composites. The foam composites were fabricated with the replacement ratios of TiO2 powder and AC, as well as the specimen thickness and density, as variables. The NOX removal performance was evaluated according to the test method presented in ISO-22197. The specific surface area of the foam composite tended to increase with increasing AC content but decreased by AC content more than 15 %. The NOX removal efficiency was the highest when the AC replacement ratio was 15 %. The NOX removal efficiency improved as the replacement ratio of TiO2 powder increased but decreased as the density of the foam composite increased. The NOX removal efficiency was the highest when the thickness of the specimen was 20 mm and was greatly affected by the ultraviolet light intensity.
In South Korea, the gradual increase in particulate matter generation has received significant attention from central and local governments. Exhaust gas, which contains nitrogen oxides (NOx), is one of the main sources of particulate matter. In this study, the reduction of NOx using a coating material mixed with a titanium dioxide (TiO2) photocatalyst was demonstrated. The NOx reduction performance of the TiO2 photocatalyst-infused coating was evaluated by applying the ISO 22197-1: 2007 standard. Subsequently, the performance was evaluated by changing the NO gas concentration and ultraviolet (UV)-A irradiance under standard experimental conditions. It was determined that NOx reduction can be achieved even if the NO gas concentration and UV-A irradiance are lower than those under the standard conditions when the TiO2 photocatalyst-infused coating was used. This study revealed that NOx reduction can be realized through TiO2 photocatalyst-infused coating in winter or cloudy days with a low solar altitude. It was also confirmed that compared with the UV-A irradiance, the NO gas concentration has a greater effect on the NOx reduction performance of the TiO2 photocatalyst-infused coating. These findings can be used to evaluate a variety of construction materials with TiO2 photocatalysts in the future.
Titanium implants have been widely used in bone tissue engineering for decades. However, orthopedic implant-associated infections increase the risk of implant failure and even lead to amputation in severe cases. Although TiO2 has photocatalytic activity to produce reactive oxygen species (ROS), the recombination of generated electrons and holes limits its antibacterial ability. Here, we describe a graphdiyne (GDY) composite TiO2 nanofiber that combats implant infections through enhanced photocatalysis and prolonged antibacterial ability. In addition, GDY-modified TiO2 nanofibers exert superior biocompatibility and osteoinductive abilities for cell adhesion and differentiation, thus contributing to the bone tissue regeneration process in drug-resistant bacteria-induced implant infection.
According to the characteristics of asphalt pavement, a kind of nano-TiO2 photocatalytic coating was prepared by using the emulsified asphalt as the carrier. All of its properties met the technical requirements. An exhaust gas degradation test device and its test steps were developed. The evaluation indexes, cumulative degradation rate, and degradation efficiency, were put forward. From the two aspects of the nano-TiO2 content in photocatalytic coatings and the spraying amount of photocatalytic coatings in the surface of slabs (300 mm × 300 mm), the exhaust gas degradation effects, the performances of skid resistance, and the water permeability of asphalt mixture were analyzed. The test results showed that the cumulative degradation rate of exhaust gas was better when nano-TiO2 content was increased in the range of 0–8% and the spraying amount was changed in the range of 0–333.3 g/m2. In practical engineering applications, the anti-skid performance of asphalt pavement can be satisfied when the spraying amount of photocatalytic coating was limited to under 550 g/m2. The spraying amount of nano-TiO2 photocatalytic coating had little effect on the water permeability of the asphalt mixture. Therefore, 8% nano-TiO2 content in the coating and a 400 g/m2 spraying amount were finally recommended based on the photocatalytic properties, as well as for economic reasons.
Airborne particulate matter (PM) is a heterogeneous mixture of particles with a variety of chemical components and physical features acting as a potential risk to human health. The ability to pose health risk depends upon the size, concentration and chemical composition of the suspended particles. PTEs associated with PM have multiple sources of origin and each sources have the ability to generate multiple particulate PTEs. In urban areas, automobile, industrial emissions, construction and demolition activities are the major anthropogenic sources of pollution. Fine particles associated with PTEs have the ability to penetrate deep into respiratory system resulting in an increasing range of adverse health effects, at ever-lower concentrations. In depth investigation of potential toxic elements (PTEs) content and mode of occurrence in PM is important from both environmental and pathological point of view. Considering this air pollution risk, several studies had addressed the issues related to these pollutants in road and street dust, indicating high pollution level than the air quality guide lines. Observed from literature particulate PTEs pollution can lead to respiratory symptoms, cardiovascular problems, lungs cancer, reduced lungs function, asthma and in sever case mortality. Due the important role of PM and associated PTEs, detailed knowledge of their impacts on human health is of key importance.
X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed that TiO2 particles synthesized by a sol─gel procedure exhibited uniform size about 16─20 nm. This nanopowder was deposited on a porous quartz tube (D = 74 mm, L = 418 mm, deposit density ̃16.4 mg cm−2) through an intermediate adhesive polymethylmethacrylate layer to manufacture a photocatalytic filter tube. A polypropylene pre-filter was coated with a nanosilver layer (particle size ̃20 nm) prepared by aqueous molecular solution method. An air cleaner of 250 m3 h−1 capacity equipped with this pre-filter, an electrostatic air filter, 4 photocatalytic filter tubes and 4 UV-A lamps (36 W) presented the high degradation ability for certain volatile organic compounds (VOCs), bacteria and fungi. The VOCs degradation performances of the equipment with respect to divers compounds are different: in a 10 m3 box, 91.6% of butanol was removed within 55 min, 80% of acetone within 100 min, 70.1% of diethyl ether within 120 min and only 43% of benzene was oxidized within 150 min. Over 99% of bacteria and fungi were killed after the air passage through the equipment. For application, it was placed in the intensive care room (volume of 125 m3) of E hospital in Hanoi; 69% of bacteria and 63% of fungi were killed within 6 h.
White cement is a key ingredient in architectural and decorative concrete. By using it, in particular, the resulting concrete not only becomes an expressive material that having an infinite range of colour tones, intensifies one of its aesthetic qualities, but could also gain remarkable validity in terms of structural qualities due to its high mechanical strength. This paper is intended to provide technical information to both designers, architects and contractors, in order to obtain a high performance concrete, similar to the natural materials like marble, possessing relevant properties in terms of durability, performances and added environmental properties. Indeed, a new type of white cement is here proposed, containing TiO 2 , possessing photocatalytic properties which allow to maintain the aesthetic characteristics of concrete over time and contribute to eliminate dangerous pollutants from the urban environment. A remarkable application is also described, concerning the innovative construction of a church in Rome, named "Dives in Misericordia" whose sails were built using white High Performance Concrete, based on this new cement. Main physical and mechanical properties of this HPC are described.
This work presents promising results for air purification by heterogeneous photocatalysis on new titanium dioxide loaded cementitious materials. A set of eight concretes and plasters is enriched with TiO2 photocatalyst by dip-coating and/or sol–gel methods.First, the macro-structural features of the cementitious materials have been studied in terms of porosity and roughness. The first parameter has been determined using mercury intrusion porosimetry or by vacuum saturation, and ranged between 9 and 75%, with the highest values obtained for autoclaved aerated white concrete. Surface roughness, determined by laser profilometry, has been characterized by the Ra factor. This expresses the mean deviation of the profile from the centre line and ranged between 0.7 and 252 μm, with the highest value obtained for conventional grey concrete finished with surface brush.Secondly, the weathering resistance of the TiO2 coatings has been determined by exposing them to different abrasive conditions and by performing SEM-Edax analyses to measure quantitatively the coating's titanium content. Hereby, it is shown that high porosity and roughness are favourable for TiO2 particles retention.Finally, the preliminary air purification potential of both dip-coated and sol–gel coated TiO2 enriched concrete samples has been investigated on lab-scale using toluene as a model pollutant. High removal efficiencies (up to 86%) were obtained with the dip-coated samples, indicating their attractive photocatalytic properties for future application as air purifying building materials.
Nowadays, the heating, ventilation, and air conditioning (HVAC) system has been an important facility for maintaining indoor air quality. However, the primary function of typical HVAC systems is to control the temperature and humidity of the supply air. Most indoor air pollutants, such as volatile organic compounds (VOCs), cannot be removed by typical HVAC systems. Thus, some air handling units for removing VOCs should be added in typical HVAC systems. Among all of the air cleaning techniques used to remove indoor VOCs, photocatalytic oxidation is an attractive alternative technique for indoor air purification and deodorization. The objective of this research is to investigate the VOC removal efficiency of the photocatalytic filter in a HVAC system. Toluene and formaldehyde were chosen as the target pollutants. The experiments were conducted in a stainless steel chamber equipped with a simplified HVAC system. A mechanical filter coated with Degussa P25 titania photocatalyst and two commercial photocatalytic filters were used as the photocatalytic filters in this simplified HVAC system. The total air change rates were controlled at 0.5, 0.75, 1, 1.25, and 1.5 hr(-1), and the relative humidity (RH) was controlled at 30%, 50%, and 70%. The ultraviolet lamp used was a 4-W, ultraviolet-C (central wavelength at 254 nm) strip light bulb. The first-order decay constant of toluene and formaldehyde found in this study ranged from 0.381 to 1.01 hr(-1) under different total air change rates, from 0.34 to 0.433 hr(-1) under different RH, and from 0.381 to 0.433 hr(-1) for different photocatalytic filters.
To develop an air purifier for a smoking room, an ozone (O3) decomposition manganese catalyst, capable of the oxidative decomposition of the volatile organic compounds (VOCs) in tobacco smoke, was applied in this study. The actual concentration of the total VOCs (TVOCs) that was measured in a smoking room was ~2,000 μg m⁻³, toluene, benzene, and acetaldehyde were also obtained in high concentrations.
An O3 oxidative decomposition catalyst, MnOx/TiO2, synthesized by chemical vapor condensation (CVC) (MnOx/CVC-TiO2) was subjected to decomposition experiments, at room temperature (25 °C), utilizing acetaldehyde as the target material. The catalyst-coated filter was installed as a fixed bed, and after supplying O3, at a concentration of 25 ppm, it was confirmed that the catalyst had facilitated the complete decomposition of 10 ppm of acetaldehyde. Next, a decomposition experiment was conducted for TVOCs with a prototype smoke purifier, which employed the catalyst-coated filter, in a 1-m³ bench-scale chamber. The initial concentration of TVOC, 4,300 μg m⁻³, was reduced to 171 μg m⁻³ after 30 min (treatment efficiency, 96%). Finally, the treatment performance of the practical smoke purifier was tested in a real smoking room (61.9 m³). The initial TVOC concentration was reduced from 2,229 to 493 μg m⁻³ after 30 min with a removal efficiency of 80%. Moreover, ~70% of the acetaldehyde concentration was also decomposed.
Over the last few years, photocatalytic titanium dioxide coatings have been explored in laboratory conditions to create building materials with self-cleaning and depolluting abilities. Assessing the performances of the photocatalytic surfaces under real conditions may provide basic knowledge to evaluate the potential of real applications of TiO2 coatings in buildings.
In this study, the performance of photocatalytic limestone surfaces obtained through coating with water-dispersed TiO2 nanoparticles were investigated in an urban environment. Coated and uncoated samples were exposed to an urban site for one year. Before the exposure and periodically afterwards, optical microscopy observations, colour and contact angle measurements were performed on the sample surface. At the end of the exposure period, samples underwent a capillary water absorption test and self-cleaning efficiency was evaluated by a Rhodamine B photodegradation test. Ti and soluble fraction amounts on the sample surfaces were determined by X-ray Fluorescence (XRF) and ion chromatography, respectively. The overall results showed the TiO2 coating was better able to preserve the surface colour properties early after exposure. After eight months, this effect was lost and the self-cleaning efficiency was reduced to negligible final rates. No clear wettability results and no meaningful capillary behaviour were recorded. A decrease of the photocatalytic activity was due to both partial titania loss and deactivation phenomena. The role of soluble salt ions either adsorbed from the environment or produced by the photocatalytic abatement of pollutants was recognized in the deactivation of the photocatalysts and their accumulation deserves attention for possible stone damage risk implications.
The mass concentration and the elemental composition of PM2.5 and polycyclic aromatic hydrocarbons were measured in 30 residential apartments during spring in the city of Xian and Chongqing, China. A total of 45 major, minor and trace elements were determined by X-Ray Fluorescence analysis. The carbonaceous species were determined with the thermal–optical transmittance technique. The daily PM2.5 mass concentration ranged from 25 to 140 µg/m³. The following compounds had higher concentrations outdoors than indoors and had higher concentrations in Xi'an than in Chongqing: Na, Al, Si, K, Mn, Fe, Cu, Zn, Br. Sulfur had higher concentrations in Chongqing than in Xi'an and had higher concentrations outdoors than indoors. For the strongly enriched elements (enrichment factor > 100) like S, Cl, Zn, Br, an anthropogenic origin can be suggested. In this study, the average ratio of organic carbon to elemental carbon was 4.9, indicating the possible presence of secondary organic carbon.
Titanium dioxide (TiO2) is a photocatalyst which can accelerate the oxidation of nitrogen oxides (NOx) and other pollutants under ultraviolet (UV) radiation. In this study, a new method to coat TiO2 onto asphalt pavements was developed with the aim to enhance the NOx decomposition efficiency and durability of the coating material for asphalt pavements. In this method, pulverized TiO2-cement mortar is used as the spreading material, which is bonded to asphalt pavement surface by epoxy resin. The composition of the TiO2-cement mortar was optimized in terms of its mechanical properties. The long-term NOx degradation efficiency, abrasion resistance, and skid resistance of the spreading material were measured after it was subjected to 300 min polishing by the advanced Aachen Polishing Machine (APM). It was concluded that durable NOx degradation efficiency can be achieved by the developed method and the method is feasible for practical implementation.
Urban residents spend about 80% of their life indoors for the various activities: hence the quality of indoor environment is becoming an important issue. However, most modern buildings adopt a close Heating Ventilation and Air Conditioning (HVAC) with poor air exchange frequency. Indoor
pollution or crowding condition will lead to proliferation of indoor air-borne pathogens that cause respiratory allergic reactions or even asthma in more serious cases. In this research, a nanoscale silver-doped titanium dioxide-HVAC (nanoscale Ag/TiO2 enhanced HVAC) system that
combines Ag/TiO2 photocatalyst net, ultraviolet light and cross-flow fan is proposed to disinfect air-borne bacteria and to improve indoor air quality. A full-scale of the proposed system is evaluated onsite at a medical-nursing institution to evaluate its disinfecting efficiency.
After operating the nanoscale Ag/TiO2-HVAC, the total bacterial count in a room (11.6 m by 3.4 m by 3.0 m) is reduced from 248.47 to 81.27 CFU/0.5 m3 with 67.29% disinfection efficiency. The proposed equipment can disinfect air to restrain bacteria effectively as demonstrated
on-site in medical-nursing institutions; the results will also be for designing an integrated commercialized for large-scale applications in the future.
The United States is facing the problem of controlling air pollution from vehicle emissions, especially in growing urban areas. This study investigates the photocatalytic effect of titanium dioxide (TiO2) applied onto pervious concrete pavement to remove some of these pollutants from the air, so that pervious concrete pavement can be installed for two sustainable applications: storm water management and air pollutant removal. The photocatalyst, TiO2, activates with UV radiation to oxidize air pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). This study compared different methods to apply TiO2 onto the surface of pervious concrete and measured the photocatalytic activity of the concrete, the infiltrating characteristics of the pervious concrete, and its ability to withstand environmental impact. High pollutant reductions were seen with a driveway protector mix, a commercial water-based TiO2 preparation, TiO2 in water, a cement-water slurry with low cement concentration, and the commercial PURETI coating. It was found that nitrogen oxide (NO) was efficiently removed with each of these treatments, while VOCs displayed more variability in removal efficiency. Different coating methods can cause different degree of infiltration rate reduction depending on the specific design of coating materials while none of the application methods decreased the infiltration rates below levels applicable for standard hydrological design. When pervious concrete was compared to traditional concrete, pervious concrete showed higher NO reductions. Published by Elsevier Ltd.
De-pollution activity of cement paste samples, added with 0.0%, 0.5%, 1.0%, 3.0% and 5.0% (based on the dry weight of the cement used) of titanium dioxide nanoparticles, TiO2, was evaluated through the deg- radation of nitrogen oxides, NOx, pollutants. Different blend of titania phases were considered as well, for each addition 100:0, 85:15 and 50:50 anatasa:rutile ratios were used. Measurements were carried out at two aging times, 65 h and 28 days, finding that at early ages the samples with the best photocatalytic activity, in terms of moles per square meter eliminated and percentage of conversion of NO and NOx, were the ones with a ratio of 85:15 and 5.0% of TiO2, while at late ages the samples with a ratio of 100:0 and 5.0% of TiO2.
In the present work the degradation of nitrogen oxides (NOx) by concrete paving stones containing TiO2 to be applied in road construction is studied. A kinetic model is proposed to describe the photocatalytic reaction of NOx (combining the degradation of NO and the appearance and disappearance of NO2) in a standard laminar flow photoreactor irradiated with UV lamps employing only NO as the contaminant source. In addition, the influences of several parameters that can affect the performance of these stones are investigated, such as NO inlet concentration, reactor height and flow rate. The kinetic parameters present in the NO and NO2 reaction rate are estimated employing experimental data obtained in the photoreactor. The obtained model predictions employing the determined kinetic constants are in good agreement with the experimental results of NO and NO2 concentration at the reactor outlet.
The field of photocatalysis can be traced back more than 80 years to early observations of the chalking of titania-based paints and to studies of the darkening of metal oxides in contact with organic compounds in sunlight. During the past 20 years, it has become an extremely well researched field due to practical interest in air and water remediation, self-cleaning surfaces, and self-sterilizing surfaces. During the same period, there has also been a strong effort to use photocatalysis for light-assisted production of hydrogen. The fundamental aspects of photocatalysis on the most studied photocatalyst, titania, are still being actively researched and have recently become quite well understood. The mechanisms by which certain types of organic compounds are decomposed completely to carbon dioxide and water, for example, have been delineated. However, certain aspects, such as the photo-induced wetting phenomenon, remain controversial, with some groups maintaining that the effect is a simple one in which organic contaminants are decomposed, while other groups maintain that there are additional effects in which the intrinsic surface properties are modified by light. During the past several years, powerful tools such as surface spectroscopic techniques and scanning probe techniques performed on single crystals in ultra-high vacuum, and ultrafast pulsed laser spectroscopic techniques have been brought to bear on these problems, and new insights have become possible. Quantum chemical calculations have also provided new insights. New materials have recently been developed based on titania, and the sensitivity to visible light has improved. The new information available is staggering, but we hope to Offer an overview of some of the recent highlights, as well as to review some of the origins and indicate some possible new directions. (C) 2008 Elsevier B.V. All rights reserved
The enhancement effect of using TiO2 immobilized on activated carbon (TiO2/AC) filter for removing indoor air pollutant at parts-per-billion (ppb) levels has been previously reported. To further evaluate the TiO2/AC filter for practical application, it was installed in an air cleaner available in the commercial market and tested inside an environmental chamber. Nitrogen oxide (NO) and toluene were selected as target pollutant. Results showed that a higher removal efficiency of NO was achieved using shorter wavelength ultraviolet lamp than longer wavelength ultraviolet lamp. A higher NO removal was achieved using TiO2/AC filter compared to TiO2 filter only. The intermediate, NO2, generated from the photodegradation of NO was also successfully suppressed from exiting the system using TiO2/AC filter. A 25% higher of nitrogen oxides (NOx) was achieved using TiO2/AC filter compared to the TiO2/AC only. The higher removal efficiency of using TiO2/AC is owing to the large adsorption capacity provided by the activated carbon. The adsorbed NO is then transferred to the TiO2 for photodegradation. The difference in toluene removal efficiency using TiO2/AC filter compared to the TiO2 filter is even more significant.
Airborne microorganisms present a challenge to engineering control of indoor air quality (IAQ) in hospital, commercial, and residential buildings. This paper analyses the generation, transmission and control mechanism of airborne microbes, and presents one engineering control method that is ventilation commonly used in indoor air microbial contamination control. A mathematical calculous model of building ventilation system is developed to study on microbial contamination control. Discusses the relationship between different ventilation parameters and microbial concentration due to ventilation model, and gives the connection between ventilation rate and infection rate based on the Wells-Riley equation. Theoretical calculation results show that natural ventilation is ineffective if microbial pollution control is the main purpose of indoor air contamination control, mechanical ventilation should be taken. When indoor microbial pollution density is high, only ventilation cannot reduce the infection rate effectively, then other methods, such as air filtration, ultraviolet germicidal irradiation etc, should be combined for better control.