Removal Of Indoor Air Pollutants Research Articles

Photocatalytic Self-cleaning Eco-Friendly Paint: A Unique Approach for Efficient Indoor Air Pollutant Removal and Surface Disinfection

Improving of air quality, particularly the removal of indoor-air pollutants with direct environmental and health implications, remains a significant challenge in modern society. We, herein, present a novel approach using photocatalytic eco-friendly paint to effectively eliminate indoor air pollutants and disinfect surfaces. Ultra Small Porous Nitrogen-doped Titanium dioxide (USPNT), which has been successfully incorporated into the paint by different coating techniques. The UPSNT photocatalyst was synthesized via probe sonication coupled sol-gel technique, resulting in anatase phase with a high surface area of 83m²/g. The efficiency of the UPSNT-coated paint in removing air pollutant like p-xylene under simulated indoor illumination is considered. In additional, it showed the capability to disinfect pathogens like E. coli, remove surface dirt, such as organic dyes, confirming its self-cleaning properties. This will lead to develop a direct eco-friendly paint by formulating USPNT directly with suitable binders promotes the durability of indoor and outdoor air quality as well as reducing “sick building syndrome’’.

Indoor Air Pollutant (Toluene) Reduction Based on Ultraviolet-A Irradiance and Changes in the Reactor Volume in a TiO2 Photocatalyst Reactor.

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.

Decahedral BiVO4/tubular g-C3N4 S-scheme heterojunction photocatalyst for formaldehyde removal: Charge transfer pathway and deactivation mechanism

Designing a durable and efficient heterojunction photocatalyst for the removal of indoor air pollutants has attracted significant attentions. However, the interfacial charge transfer pathway and deactivation mechanism of photocatalysts are still challenges. In this study, the decahedral BiVO4/tubular g-C3N4 (BiVO4/TCN) S-scheme heterojunction photocatalyst was synthesized, which exhibited excellent photocatalytic activity and stability for the removal of formaldehyde (HCHO) in a continuous-flow reactor. The formation of the S-scheme heterojunction promoted spatial separation of charges, enhanced the redox capability, and maintained favorable charge carrier potentials. Based on Central Composite Design, a semi-empirical equation was successfully established to predict the removal efficiency of HCHO, and photocatalyst load and initial concentration played important roles in the removal of HCHO. The interfacial charge transfer pathway in the S-scheme heterojunction was clearly confirmed through photo-irradiated Kelvin probe and in situ irradiated X-ray photoelectron spectroscopy analysis. The superficial state changes of BiVO4/TCN before and after the reaction indicated that the formation of coke could inhibit separation and transfer of electron-hole pairs, resulting in a slight decrease in photocatalytic activity. In summary, this study not only presents an effective technology for constructing S-scheme heterojunction photocatalyst, but also offers a new insight on the deactivation mechanism of photocatalyst during removal of volatile organic compounds.

The effectiveness of potted plants in improving indoor air quality: A comparison between chamber and field studies

People spend up to 90% of their time inside buildings, making indoor air quality an extremely important factor affecting public health and building design. Due to the inherent ability to absorb/filter pollutants, plants present a promising method for improving indoor air quality. In recent decades, many studies have quantified plants’ effectiveness in removing indoor air pollutants using both chamber and field methods. This paper presents a review working covering these studies and discusses the differences between chamber and field studies, in terms of study methods and results. Through a meta-analysis of 41 chamber studies and 16 field studies, the effectiveness of 182 species in removing 25 pollutants has been estimated. From this work, a larger proportion of significant results were observed in chamber studies (88%), comparing to field studies (65%). Additionally, comparable studies revealed greater removal effectiveness of plants in chamber studies. These discrepancies could be attributed to many factors, such as the size and the airtightness of experimental setup, ventilation, gas exposure scheme, and environmental conditions. It is envisaged that these findings will help reduce the gap between chamber studies and field studies, and provide guidance for the future use of plants in buildings to improve indoor air quality.

Multifunctional Z-scheme CuxO/Ag/SrTiO3 heterojunction for photothermocatalytic VOCs degradation and antibiosis

Development of multifunctional material for efficient removal of indoor air pollutants, such as volatile organic compounds (VOCs) and bacteria, is an urgent need. Herein, Z-scheme CuxO/Ag/SrTiO3 (or STO) heterojunction photothermal catalyst is constructed and evaluated for the removal of chemical containment toluene and bacteria E. coli. The surface plasmon resonance effect of Ag nanoparticles and unique Z-scheme photogenerated charges transfer and separation route in CuxO/Ag/STO promotes the production of reactive oxygen species (OH and O2−). The photothermocatalytic synergistic function of CuxO/Ag/STO leads to an efficient toluene degradation performance. The coupling of photocatalytic disinfection by reactive oxygen species with chemical disinfection by Ag and CuxO with a high Cu+ content endows CuxO/Ag/STO with well antibacterial performance against E. coli. Such a coupling and strengthening concept and the corresponding multifunctional Z-scheme heterojunction show great application potential in indoor air purification field.

Fe(III)-Pt(II) oxide-co-sensitized brookite TiO2 nanorods for photocatalytic degradation of acetaldehyde under visible light

Platinum is widely investigated as co-catalysts for photocatalytic degradation of volatile organic compounds but studies seldom focus on their visible light sensitizing properties. Herein, Pt sensitizers of different oxidation states (0, II, IV) were modified on brookite TiO2 nanorods and investigated for acetaldehyde degradation under visible light. Pt(II) oxide/TiO2 showed the best photocatalytic activity but its stability was compromised by its self-oxidation to Pt(IV) during photo-oxidation reaction. Surface modification of an Fe(III) oxide thin film sensitizer layer around the Pt(II) oxide sensitizer was found to enhance both the stability and activity of Pt(II) oxide/TiO2. In situ double beam photoacoustic spectroscopy (DB-PAS) supported by DFT modeling showed the rapid injection of photoexcited electrons from Fe(III) oxide to Pt(II) oxide promote the stability of Pt(II) oxide, leading to enhanced performance. The findings provide guidance for the rational design of visible light-active metal oxide sensitizers for oxidative removal of indoor air pollutants.

Study on the kinetic characteristics of indoor air pollutants removal by ventilation

Ventilation is an efficient and convenient method to remove indoor air pollutants, such as particulate matter and VOCs. The computational fluid dynamics (CFD) method is an economical and efficient method to study the removal efficiency of indoor air pollutants by ventilation. However, CFD method is usually restricted by the extensive computational time. In this study, the kinetic characteristic of removing indoor air pollutants by ventilation was investigated to reduce the CFD computational time. The impact of ventilation rate and ventilation model on the removal efficiency of indoor air pollutants was studied. The results show that the removal of particulate matter and VOCs is consistent with the Langmuir–Hinshelwood (L-H) kinetic model when there are no barriers. The fit coefficients (R2) are larger than 0.984 and 0.978 under different ventilation rates and ventilation models, respectively. The fit coefficients of VOCs removal are larger than those of particulate matter. The removal of VOCs in a benchmark full-scale indoor model was successfully predicted by the L-H kinetic model with a mean prediction error of 0.8%. Meanwhile, 99% CFD computational times were reduced. The removal of particulate matter cannot be predicted accurately by the L-H kinetic model when the barriers present (prediction error reached 18.0%). Therefore, the L-H kinetic model is a high-efficient tool to design the ventilation rate and ventilation model when the main air pollutants are airflow-determined (gaseous pollutants or no barriers condition).

Preparing visible photocatalytic paper with improved catalytic activity by adding N-TiO2/diatomite@regenerated cellulose composite filler

N-doped TiO2 (N-TiO2) photocatalyst was prepared by the sol-gel method, using butyl titanate and urea as raw materials, and then loaded onto diatomite to prepare a composite photocatalyst. Bleached sulfate softwood pulp fiber was dissolved and mixed with the composite photocatalyst and then regenerated to prepare composite fillers for the manufacture of visible light-responsive photocatalytic paper suitable for the removal of toxic formaldehyde gas. Photocatalytic paper containing 20% composite filler with a ratio of 4/6 N-TiO2 (60% N-doping)/diatomite had good photocatalytic activity, with 50.1% formaldehyde degraded after 10 h under visible light irradiation. This photocatalytic paper also had good physical properties, with a paper density of 0.36 g cm−3, a burst index of 3.0 kPa·m2 g−1 and a tensile index of 43.33 Nm g−1, indicating that it has good prospects for removal of indoor air pollutants.

Plant and Plant Associated Microflora: Potential Bioremediation Option of Indoor Air Pollutants

Indoor air pollution is a significant problem today because the release of various contaminants into the indoor air has created a major health threat for humans occupying indoors. Volatile Organic Compounds (VOCs) are pollutants released into the environment and persist in the atmosphere due to its low boiling point values. Various types of indoor activities, sources, and exposure to outdoor environments enhance indoor VOCs. This poor indoor air quality leads to adverse negative impacts on the people in the indoor environment. Many physical and chemical methods have been developed to remove or decompose these compounds from indoors. However, those methods are interrupted by many environmental and other factors in the indoor atmosphere, thus limit the applications. Therefore, there is a global need to develop an effective, promising, economical, and environmentally friendly alternatives to the problem. The use of the plant and associated microflora significantly impact reducing the environmental VOC gases, inorganic gases, particulate matter, and other pollutants contained in the air. Placing potted plants in indoor environments not only helps to remove indoor air pollutants but also to boost the mood, productivity, concentration, and creativity of the occupants and reduces stress, fatigue, sore throat, and cold. Plants normally uptake air pollutants through the roots and leaves, then metabolize, sequestrate, and excrete them. Plant-associated microorganisms help to degrade, detoxify, or sequestrate the pollutants, the air remediation, and promote plant growth. Further studies on the plant varieties and microorganisms help develop eco-friendly and environmentally friendly indoor air purifying sources.

Experimental and simulated evaluations of airborne contaminant exposure in a room with a modified localized laminar airflow system.

The traditional mixing ventilation is not an energy effective approach to remove indoor air pollutants, maintain breath zone air quality, and control the airborne transmission. This study investigated the potential of a localized laminar airflow ventilation system to alleviate human exposure to pollutants. Breathing thermal manikins with sitting posture and supine posture were used to simulate the human. N2O was used as the tracer gas to simulate the indoor pollutant emission. The contaminant exposure index (εexp) and intake fraction index (IF) were used to assess the risk of human pollutant exposure for various supply air velocities given different emission source positions. Enhanced pollutant removal efficiency (Eff) (from the result) showed the qualification and desirability of the localized laminar airflow ventilation system in improving the breath zone air quality. The results showed that the CFD results could fit well with the experimental data and found out the interaction between thermal plume and supply air. The results also indicated a low εexp and IF, with over 90%, all of which were highly correlated with the supply velocity. Human's different breathing methods have little influence on the pollutant exposure so as to the location of the pollution source. This study found that localized laminar airflow ventilation system could efficiently provide fresh air to the breathing zone without sacrificing the thermal environment around human. It can be used for small region air quality control such as that in the bedroom and living room where desired air quality is favored.

Effectiveness and Eco-Costs of Air Cleaners in Terms of Improving Fungal Air Pollution in Dwellings Located in Southern Poland—A Preliminary Study

Epidemiological evidence shows that air pollution is responsible for several million premature deaths per year. By virtue of being responsible for these deaths, economic evidence shows that air pollution also imposes a so-called economic cost to society of several trillion dollars per year. The diseases caused by biological air pollutants are of primary global concern for both social and economic reasons, and given that people may spend more than 90% of their time in enclosed spaces, the investigation into methods to remove indoor air pollutants is of paramount importance. One of the methods to improve indoor air quality (IAQ) is to use air cleaners (ACLs) with high-efficiency particulate air filters (HEPA) that remove biological indoor air pollutants from indoor environments. This work presents the results of a study of fungal aerosol samples collected during the summer season from inside two dwellings (DG1 and DG2) before and after starting the use of ACLs. The fungal aerosol samples collected from each of the six stages of the sampler were incubated on agar plates at 26 °C, and the colony forming units (CFU) were manually counted and statistically corrected. The concentration of living airborne fungi was expressed as the CFU in the volume of air (CFU·m−3). The average concentration of fungal aerosol decreased the most when the ACLs were active for 24 min. The reduction was from 474 CFU·m−3 to 306 CFU·m−3, and from 582 CFU·m−3 to 338 CFU·m−3 in DG1 and DG2, respectively. The use of ACLs was assessed by the life cycle assessment (LCA) methodology. This study highlights the benefits of controlling biological air pollutants in order to keep occupants of buildings happy and healthy.

A comparative study of the effects of ventilation-purification strategies on air quality and energy consumption in Beijing, China

In countries suffering from heavy ambient air pollution, ventilation is a problem, as ventilation intakes outdoor air pollutants, such as particulate matter with an aerodynamic diameter less than 2.5 um (PM2.5), while removing indoor air pollutants. Thus, it is important to identify appropriate ventilation-purification strategies to build healthy indoor environments with low energy consumption. This study reports the comparison of two sets of strategies, i.e., mechanical ventilation with filters and natural ventilation with indoor air cleaners, in respect to energy consumption and the PM2.5 and carbon dioxide (CO2) exposure of occupants in a typical apartment in Beijing, China. A dynamic mass balance model was employed to calculate the PM2.5 and CO2 exposure concentrations, while the energy consumption of heating and cooling was simulated with the Designer’s Simulation Toolkit. It was found that natural ventilation with air cleaners provided lower PM2.5 exposure compared with that of mechanical ventilation with filters; however, mechanical ventilation achieved a lower CO2 exposure concentration. The annual cooling, heating, and fan energy consumption of natural ventilation strategies are lower than those of mechanical ventilation strategies. With respect to natural ventilation, an infiltration rate of 0.3–0.4 h−1 was the preferred setting, which led to low PM2.5 and CO2 exposure with lower energy consumption. The basic requirements for controlling indoor PM2.5 could be met if the threshold is set at 25 µg/m3. The results provide guidelines on how to combine multiple ventilation purification strategies to improve indoor air quality with lower energy usage.

Recent progress on removal of indoor air pollutants by catalytic oxidation.

Indoor air pollutant is a serious problem due to its wide diversity and variability. The harmful substances from construction materials and decorative materials may make the indoor air pollution become more and more serious and cause serious health problems. In this paper, the review summarizes the advanced technologies for the removal of indoor air pollutants and the development in the treatment of indoor air pollution by catalytic oxidation technologies. Meanwhile, some catalytic oxidation mechanisms of indoor air pollutants are proposed in detail, and suggestions for the indoor air pollution treatment are also presented, in order to provide some reference for subsequent research.

Characterisation of fungal and bacterial dynamics in an active green wall used for indoor air pollutant removal

Indoor air quality (IAQ) is of growing public health concern which has prompted the use of plants to phytoremediate air pollution in interior spaces. Active green walls are emerging as a means of reducing indoor contaminants and have demonstrated efficacy comparable to conventional air filtering technologies. However, the use of active airflow through organic substrates has the potential to emit bioaerosols into the surrounding environment, where the potential risk to human health is largely unknown. In this study, we demonstrate that two indoor green walls (with and without active airflow) contribute significantly to the ambient fungal load, however concentrations remained well below WHO safety guidelines. Bacterial dynamics within the rhizosphere/substrate of the operational botanical biofilters displayed variability across plant species. Phyla-wide distribution generally aligned with previous literature; however, differences from those previously reported were observed at the genus level, possibly due to geographic location, substrate composition, or plant species selection. Targeted assessment of Legionella aerosol contamination, an under-addressed potential pathogen for these active systems, yielded no positive identification during the sampling period. We conclude that active green walls host a unique bacterial profile and do not emit harmful levels of fungal propagules or pose significant risk of aerosolised Legionella species, provided systems are well monitored and maintained.

An experimental work to investigate the capabilities of plants to remove particulate matters in an enclosed greenhouse

Many studies, especially those conducted in laboratory chambers, have shown that plants are effective in removing indoor air pollutants. However, some researchers claim that laboratory results are not adequate evidence of validating the effectiveness of plants. Thus, an experimental work was designed and conducted by this research to investigate the capabilities of plants to remove particulate matters (PMs), given PM2.5 and PM10 are the primary air pollutants in both indoor and outdoor environment in China. The experimental results have indicated that an enclosed space had a lower PM concentration than the outdoor environment. In addition, plants can further reduce the indoor PM concentrations because they increased the surface area of the space. Airflow speed has adverse effects on the efficiency of plants’ PM removal. A relative slow airflow speed is beneficial to creating a stable indoor environment and to increase plants’ efficiency in removing PMs. The experiment recorded removal efficiencies of plants were approximately 0.2–0.36 for PM2.5 and 0.24–0.39 for PM10, respectively. Moreover, measures, such as reducing infiltration rate, can further increase the removal efficiencies.

Adsorption of acetic acid and hydrogen sulfide using NaOH impregnated activated carbon for indoor air purification

Excessive exposure to hydrogen sulfide (H2S) and acetic acid (CH3COOH) gases is extremely dangerous in a confined space. An effective indoor air pollutant removal porous carbon filter was developed using NaOH impregnated on activated carbon (NaOH/AC) for the adsorption of H2S and CH3COOH. Activated carbon (NaOH/AC) filter was characterized using various methods, indicating good physical and chemical properties (especially ‐OH functional groups) for the adsorption of air pollutants. The prepared NaOH/AC filter was cured at different curing temperatures and residence times to understand the effect of the curing conditions on the adsorption performance. The best results were obtained with NaOH/AC filter cured at 100°C for 20 minutes as it eliminated the initial concentration of 400 ppm of CH3COOH in 15 minutes and H2S in 30 minutes at 20°C and 60% relative humidity. Isotherm and kinetic models were used to analyze the adsorption process. Langmuir isotherm and pseudo‐second order kinetic models provided the best fit to the adsorption of CH3COOH and H2S on NaOH/AC filter. The adsorption mechanism was controlled by the intraparticle diffusion combined with film diffusion. The maximum adsorption capacity of NaOH/AC filter was 473 mg/g for H2S adsorption, and 550 mg/g for CH3COOH adsorption. In addition, the spent NaOH/AC filter was regenerated for reuse. This study is expected to develop low‐cost and effective porous carbon filter using NaOH‐modified activated carbon for indoor air purification.

Bimetallic nickel molybdate supported Pt catalyst for efficient removal of formaldehyde at low temperature

Efficient removal of formaldehyde from indoor environments is of significance for human health. In this work, a typical binary transition metal oxide that could provide various oxidation states, β-NiMoO4, was employed as a support to immobilize the active Pt component (Pt/NiMoO4) for catalytic formaldehyde elimination at low ambient temperature (15°C). The results showed that the hydrothermal preparation temperature and time had a noticeable impact on the morphology and catalytic activity of the samples. The catalyst prepared with hydrothermal temperature of 150°C for 4 hr (Pt-150-4) exhibited superior catalytic activity and stability mainly due to its distinctly porous structure, relative abundance of adsorbed surface hydroxyls/water, and high oxidation ability, which resulted from the interaction of Pt with Ni and Mo of the bimetallic NiMoO4 support. Our results might shed light on the rational design of multifunctional catalysts for removal of indoor air pollutants at low ambient temperature.

Screening Foliage Plants for Indoor Air Pollution Abatement

Indoor air pollution is a major environmental health problem affecting people in both developed and developing countries. The use of houseplants is one of the emerging methods for abatement of indoor air pollution. Plants can remove indoor air pollutants by stomatal uptake, absorption and adsorption to plant surfaces. Indoor air characteristically contains a large consortium of volatile organic compounds (VOCs), such as formaldehyde, benzene and toluene. The volatile tested in this study toluene, is commonly found in buildings. The main objective of this project was to find the removal efficiency of toluene by four plant species, Aglaonema spp., Dracaena deremensis, Hedera helix and Chlorophytum comosum. This main goal was achieved by constructing a sealed closed chamber resembling the indoor environment in order to find the activity of selected indoor plants to the indoor air pollutant toluene. The concentration of introduced toluene was measured through gas-chromatography mass spectrometry (GC/MS). The possible causes for the differences in removal of toluene among selected plant species were determined by studying leaf morphology, stomatal numbers, plant physiology and growth related parameters. The removal efficiency, expressed on percentage level using toluene peak areas of the GCMS analyses varied among plant species. H. helix had the highest toluene removal percentage per plant over 24 hours (91.1%) followed by D. deremensis (75.0%), A. spp. (60.5%) and C. comosum (47.9%). The study found that stomatal index and stomatal pore length play a key role in VOC removal and that there was a positive relationship between stomatal conductance with toluene removal potential. Based on the results it can be further concluded that thickness of the cuticle is a hindrance to VOC penetration. In addition VOC removal is higher in plants having high photosynthetic rates and there was no relationship of leaf area with the VOC removal capacity. Further studies focusing on screening additional plant species for superior VOC removal efficiencies are warranted. Keywords: Indoor air pollution, Volatile organic compounds, Gas-chromatography Mass spectrometry, Stomatal conductance

Plants for Sustainable Improvement of Indoor Air Quality.

Indoor pollution poses a serious threat to human health. Plants represent a sustainable but underexploited solution to enhance indoor air quality. However, the current selection of plants suitable for indoors fails to consider the physiological processes and mechanisms involved in phytoremediation. Therefore, the capacity of plants to remove indoor air pollutants through stomatal uptake (absorption) and non-stomatal deposition (adsorption) remains largely unknown. Moreover, the effects of the indoor plant-associated microbiome still need to be fully analyzed. Here, we discuss how a combination of the enhanced phytoremediation capacity of plants together with cutting-edge air-cleaning and smart sensor technologies can improve indoor life while reducing energy consumption.

Energy saving potential of an air treatment system for improved building indoor air quality in Singapore

The design of air conditioning mechanical ventilation (ACMV) system affects the building energy performance and the indoor pollutant removal process. The present study aims to reduce energy consumption on ACMV systems by employing a renewable air treatment system (ATS). The ATS is able to purify the recirculated air through the ozone-based oxidation process and air scrubbing devices. The air purification performance of primary equipment in the ATS has been studied in order to demonstrate the capability to remove indoor air pollutants. Due to the air purification process, the ATS allows a reduced supply of outdoor-air translating to a lower cooling load. In addition, the reduced outdoor-air fraction results in an improved chiller efficiency. Therefore, the ATS is capable of achieving marked energy savings because of the reduced cooling load for conditioning outdoor airflow. The proposed ATS is particular adept during a period when Singapore faces periodic bad haze situations. Activating the ATS while decreasing the outdoor-air fraction can be an attractive solution. Based on Singapore climatic condition, an energy consumption analysis has been carried out to estimate the energy saving potential of the proposed ATS with varying outdoor-air intake. The “plug-and-play” ATS can be easily integrated into any new or existing ACMV systems to realize immediate improvement in indoor air quality and building energy efficiency.