Removal Of Air Pollutants Research Articles

Atmospheric Wet Deposition of PCDD/Fs in the Ambient Air

ABSTRACT Wet deposition is an important mechanism for removing air pollutants from the atmosphere. The total PCDD/Fs-WHO2005-TEQ wet deposition from 2018–2020 was investigated for Beijing and Tianjin City in this study. In addition, the gas-particle partitioning of wet deposition, the total PCDD/Fs-WHO2005-TEQ concentrations in the rain, the PM2.5-bound total PCDD/Fs-WHO2005-TEQ content, and the PM2.5 concentration were also studied for Beijing and Tianjin City, respectively. Between 2018 to 2020, as a whole, the average seasonal variations in PCDD/F wet deposition fluxes in spring, summer, fall, and winter were 50.50, 41.47, 23.03 and 16.76 pg WHO2005-TEQ m–2 month–1, respectively, while in Tianjin, they were 35.30, 42.40, 13.37, and 14.77 pg WHO2005-TEQ m–2 month–1, respectively. Because the two cities have more rainfall in spring and summer than they do in fall and winter, rainfall has a significant influence on the wet deposition flux. In regard to PCDD/Fs-WHO2005-TEQ in the rain, in Beijing, the average total PCDD/Fs-WHO2005-TEQ concentration in the rain in spring, summer, fall, and winter were 1.70, 0.39, 1.42, and 1.52 pg WHO2005-TEQ L–1, respectively, while those in Tianjin, were 1.73, 0.42, 1.35, and 1.88 pg WHO2005-TEQ L–1, respectively. The above results show that the total PCDD/Fs-WHO2005-TEQ concentrations in the rain are significantly lower in summer, which is mainly due to the fact that in summer, the total PCDD/Fs-WHO2005-TEQ concentrations in the air are lower, and the proportion of the gas phase is increased. When the total PCDD/Fs-WHO2005-TEQ concentrations in the air are washed away by a heavy rainfall, the PCDD/F concentrations are diluted.

Modeling and Experimental Studies on Adsorption and Photocatalytic Performance of Nitrogen-Doped TiO2 Prepared via the Sol–Gel Method

Nitrogen-doped TiO2 has a great potential as a photocatalyst under visible light irradiation with applications in the removal of air and water pollutants, and the treatment of bacterial contaminations. In this study, nitrogen-doped TiO2 nanoparticles were synthesized via the sol–gel method and a post-annealing heat treatment approach. The effects of annealing treatment on the photocatalyst crystalline size and degree of crystallinity were analyzed. Methylene blue dye was used as the model water contaminant for the evaluation of the photoactivity of the synthesized nitrogen-doped TiO2 nanoparticles. The degradation of methylene blue was attributed to three mechanisms, i.e., adsorption, photocatalysis, and direct light photolysis. A kinetic model was developed to distinguish the impact of these three different mechanisms on the removal of contaminants. Adsorption and photocatalysis are heterogeneous processes for removing water organic contaminants. The characterization analysis demonstrates that they are relevant to the microstructures and surface chemical compositions of nitrogen-doped TiO2 photocatalysts. The processing–structure–performance relationship helped to determine the optimal processing parameters for nitrogen-doped TiO2 photocatalyst to achieve the best performance. While we used methylene blue as the model contaminant, the generalized quantitative model framework developed in this study can be extended to other types of contaminants after proper calibration.

Prioritizing the provision of urban ecosystem services in deprived areas, a question of environmental justice.

The distribution of urban ecosystem services (UES) is often uneven across socioeconomic groups, leading to environmental justice issues. Understanding the distribution of UES across a landscape can help managers ensure an equitable distribution of services. While many past studies have focused on the distribution of green spaces in relation to socioeconomic variables, this research analyzes the distribution of UES provided by these green spaces. This research quantified air pollution removal, atmospheric carbon reduction, and surface runoff mitigation provided by urban trees in Strasbourg city (France). The provision of these three UES was studied at the census block scale by creating an index of UES delivery, which was contrasted with a constructed social deprivation index. Our results show that there is no significant association between the delivery of UES and social deprivation. Some deprived populations benefit from high UES delivery. Results also suggest that mapping associations between UES delivery and social deprivation should be integrated with future development plans to enhance the equitable distribution of UES. This study provides insights into the French context where studies about the distribution of UES at a small-area level remain lacking.

Emission characteristics of PM, heavy metals, and dioxins in flue gases from sintering machines with wet and semi-dry flue gas desulfurization systems.

In iron and steel industry, sintering process releases large amount and different kinds of pollutants. Most sintering plants had applied the dust removal system and the flue gas desulfurization (FGD) system for exhaust treatment in China. Previous studies of FGD systems were focused on the removal of air pollutants from coal-fired boiler, rather than in the iron ore sintering process. In this study, PM, heavy metals, and dioxins were sampled at a China typical sintering plant with both wet and semi-dry FGDs. The results showed that the PM removal efficiencies of the wet and semi-dry FGDs were 29.44% and 22.28%, respectively. The size distributions of PM were at the range of 0.7~4.7 μm in the inlet flue gases of both FGDs. The overall removal efficiencies of heavy metals were above 65%. In both outlet flue gases, Pb as the most elements accounted for 93.33% of total at the wet FGD, while Pb, Cr, and Zn accounted for 76.34% at the semi-dry FGD. The proportions of gaseous heavy metals in the inlets of both FGDs were improved than those in the outlets. Furthermore, the total emission amounts of dioxins in both inlets and outlets of the flue gases were 0.0385 ng-TEQ/m3 and 0.0248 ng-TEQ/m3 at the wet FGD and 0.0078 ng-TEQ/m3 and 0.0050 ng-TEQ/m3 at the semi-dry FGD, respectively. The overall removal efficiencies of dioxins were all above 35%. The polychlorinated dibenzofurans (PCDFs) ratio in the dioxins lightly increased from 84.46 to 88.80% through wet FGD, while it decreased from 80.83 to 44.35% in semi-dry FGD.

Removal and transformation of unconventional air pollutants in flue gas in the cement kiln-end facilities

To understand the removal and transformation behaviors of unconventional air pollutants (polycyclic aromatic hydrocarbons, heavy metals and carbonyl compounds) in the flue gas in cement kiln-end facilities, including SP boiler, a slide stream SCR-DeNOx system, raw mill and baghouse filter, the gas and particle matter samples at the inlets and outlets of each kiln-end installation were collected and the contents of the unconventional air pollutants were measured. The results showed that the concentrations of the polycyclic aromatic hydrocarbons (PAHs) in particulate and gas-phase, heavy metals in the particulate matter were 17.5 μg m−3, 48.7 μg m−3 and 3113.1 μg m−3 at the inlet of the SP boiler, and decreased to 0.6 μg m−3, 17.7 μg m−3 and 39.7 μg m−3, respectively, while the concentrations of carbonyl compounds in gas-phase increased from 1988.5 μg m−3 to 2844.5 μg m−3 after flue gas successively passed through the kiln-end facilities. The cooling of flue gas and the precipitation of coarse particulate matter in the SP boiler resulted in a significant decrease of PAHs concentration in both gas-phase and particulate-phase, as well as the heavy metal concentration in the particulate-phase, while the SP boiler hardly had any influence on the removal and transformation of carbonyl compounds. Grinding and heat exchange in the raw mill accelerated the volatilization of compounds with the low boiling point in the raw meal, which increased concentrations of gas-phase PAHs and carbonyl compounds. When flue gas passed through the baghouse filter, almost all particulate-phase PAHs, heavy metals and most of the gas-phase PAHs, were removed while the carbonyl compounds concentration maintained unchanged. Furthermore, some portion of gas-phase PAHs and carbonyl compounds were removed by the SCR-DeNOx system.

Co-benefits of reducing CO2 and air pollutant emissions in the urban transport sector: A case of Guangzhou

The transport sector has become an important source of urban greenhouse gas (GHG) and air pollutant emissions, with the continuous growth of transportation demand. The co-benefits of reducing GHG and air pollutant emissions in the transport sector are receiving more and more attention. Taking Guangzhou as the case study city, this study quantitatively analyzed the co-benefits of reducing CO2 and air pollutant emissions under the sustainable scenario in the transport sector by developing a quantitative analysis model based on the Long-range Energy Alternatives Planning (LEAP) framework. The co-benefits quantitative parameter and the co-benefits radar chart analysis method are used to identify and evaluate the generated co-benefits, and then the co-benefits generated by implementing the sustainable measures are discussed. The results show that adjusting transport modes and increasing the application of electricity are the two most effective measures for achieving the co-benefits of reducing CO2 and air pollutant emissions in the Guangzhou transport sector. Thus, these two measures are highly preferential for mitigating CO2 and air pollutant emissions. In addition, increasing the application of biofuel and hydrogen energy also has good co-benefits. However, increasing the application of Liquefied Natural Gas (LNG) has poor co-benefits. Promoting the utilization of LNG intercity buses, trucks, and cargo ships will lead to emission increases of CO and HC compared to the current policy scenario, and small emission reductions of CO2 and other air pollutants. Therefore, to promote the utilization of LNG vehicles and ships, it is necessary to cooperate with the use of air pollutant end removal devices and high-pressure direct injection (HPDI) gas engines.

A highly efficient triboelectric negative air ion generator

Negative air ions (NAIs) have been widely harnessed in recent technologies for air pollutant removal and their beneficial effects on human health, including allergy relief and neurotransmitter modulation. Herein, we report a corona-type, mechanically stimulated triboelectric NAI generator. Using the high output voltage from a triboelectric nanogenerator, air molecules can be locally ionized from carbon fibre electrodes through various movements, with the electron–ion transformation efficiency reaching up to 97%. Using a palm-sized device, 1 × 1013 NAIs (theoretically 1 × 105 ions cm−3 in 100 m3 space) are produced in one sliding motion, and particulate matter (PM 2.5) can be rapidly reduced from 999 to 0 µg m−3 in 80 s (in a 5,086 cm3 glass chamber) under an operation frequency of 0.25 Hz. This triboelectric NAI generator is simple, safe and effective, providing an appealing alternative, sustainable avenue to improving health and contributing to a cleaner environment. Negative air ions (NAIs) have been widely harnessed for air purification and environmental therapeutics. Herein, the authors construct a triboelectric NAI generator that produces NAIs with high efficiency, stimulated by mechanical motions.

Efficiencies Evaluation of Photocatalytic Paints Under Indoor and Outdoor Air Conditions.

The removal of indoor and outdoor air pollutants is crucial to prevent environmental and health issues. Photocatalytic building materials are an energy-sustainable technology that can completely oxidize pollutants, improving in situ the air quality of contaminated sites. In this work, different photoactive TiO2 catalysts (anatase or modified anatase) and amounts were used to formulate photocatalytic paints in replacement of the normally used TiO2 (rutile) pigment. These paints were tested in two different experimental systems simulating indoor and outdoor environments. In one, indoor illumination conditions were used in the photoreactor for the oxidation of acetaldehyde achieving conversions between 37 and 55%. The other sets of experiments were performed under simulated outdoor radiation for the degradation of nitric oxide, resulting in conversions between 13 and 35%. This wide range of conversions made it difficult to directly compare the paints. Thus, absorption, photonic, and quantum efficiencies were calculated to account for the paints photocatalytic performance. It was found that the formulations containing carbon-doped TiO2 presented the best efficiencies. The paint with the maximum amount of this photocatalyst showed the highest absorption and photonic efficiencies. On the other hand, the paint with the lowest amount of carbon-doped TiO2 presented the highest value of quantum efficiency, thus becoming the optimal formulation in terms of energy use.

Electrostatic Precipitators as an Indoor Air Cleaner—A Literature Review

Many people spend most of their time in an indoor environment. A positive relationship exists between indoor environmental quality and the health, wellbeing, and productivity of occupants in buildings. The indoor environment is affected by pollutants, such as gases and particles. Pollutants can be removed from the indoor environment in various ways. Air-cleaning devices are commonly marketed as benefiting the removal of air pollutants and, consequently, improving indoor air quality. Depending on the type of cleaning technology, air cleaners may generate undesired and toxic byproducts. Different air filtration technologies, such as electrostatic precipitators (ESPs) have been introduced to the market. The ESP has been used in buildings because it can remove particles while only causing low pressure drops. Moreover, ESPs can be either in-duct or standalone units. This review aims to provide an overview of ESP use, methods for testing this product, the performance of existing ESPs concerning removing pollutants and their byproducts, and the existing market for ESPs.

A single tree model to consistently simulate cooling, shading, and pollution uptake of urban trees

Extremely high temperatures, which negatively affect the human health and plant performances, are becoming more frequent in cities. Urban green infrastructure, particularly trees, can mitigate this issue through cooling due to transpiration, and shading. Temperature regulation by trees depends on feedbacks among the climate, water supply, and plant physiology. However, in contrast to forest or general ecosystem models, most current urban tree models still lack basic processes, such as the consideration of soil water limitation, or have not been evaluated sufficiently. In this study, we present a new model that couples the soil water balance with energy calculations to assess the physiological responses and microclimate effects of a common urban street-tree species (Tilia cordata Mill.) on temperature regulation. We contrast two urban sites in Munich, Germany, with different degree of surface sealing at which microclimate and transpiration had been measured. Simulations indicate that differences in wind speed and soil water supply can be made responsible for the differences in transpiration. Nevertheless, the calculation of the overall energy balance showed that the shading effect, which depends on the leaf area index and canopy cover, contributes the most to the temperature reduction at midday. Finally, we demonstrate that the consideration of soil water availability for stomatal conductance has realistic impacts on the calculation of gaseous pollutant uptake (e.g., ozone). In conclusion, the presented model has demonstrated its ability to quantify two major ecosystem services (temperature mitigation and air pollution removal) consistently in dependence on meteorological and site conditions.

The botanical biofiltration of elevated air pollution concentrations associated the Black Summer wildfire natural disaster

The ‘Black Summer’ wildfires that affected Australia over the 2019–2020 summer have led to concern over the health effects of exposure to wildfire emissions, and generated a need for means to reduce exposure. Recently, active green infrastructure has been implemented in cities to assist in the removal of urban air pollution, however the filtration of wildfire emissions has not been previously tested. Here, we field trial botanical biofiltration for the reduction of elevated air pollutant concentrations associated with Black Summer. Two active green walls were installed in outdoor environments in Sydney over Black Summer, with the concentrations of NO2, O3 and PM2.5 in ambient and filtered air streams monitored over 14 days with elevated air pollution concentrations due to wildfire emissions. Average pollutant single pass removal efficiencies of 63.17%, 38.79% and 24.84% for NO2, O3 and PM2.5 respectively were recorded, with clean air delivery rates of 558.90 m3/h, 343.19 m3/h and 219.77 m3/h for NO2, O3 and PM2.5 respectively for each 5 m2 biofilter wall. Weak negative associations were observed between the removal efficiency of NO2 and PM2.5 and their corresponding ambient concentrations. Strategic employment of botanical biofiltration may thus be of value in reducing wildfire emissions in sensitive populations.

Radical-Induced Oxidation Removal of Mercury by Ozone Coupled with Bromine

Ozone oxidation and absorption is an effective technique for air pollutant removal from industrial flue gas. However, it is hard to remove Hg0 because of the competition reaction between O3 and NOx...

The Potential for Urban Vegetation to Mitigate Ambient Air Pollution Threats to Public Health


 
 
 This paper assesses the threat that ambient air pollution poses to urban public health and the potential role of urban vegetation to mitigate those threats. Air pollution is a major global risk to health, especially in urban areas. In this paper, four major air pollutants were assessed: particulate matter, tropospheric ozone, nitrogen dioxide, and sulfur dioxide. These pollutants were found to have several adverse effects, including increasing mortality and respiratory morbidity. These pollutants come from a variety of sources, but a major contributor in urban areas is the burning of fossil fuels in automobiles. The adverse health effects of pollution are expected to grow as climate change worsens air quality. Research and case studies find that urban vegetation can filter air and remove pollutants through deposition and stomatal uptake. The effectiveness of air pollution removal is dependent upon specific variables, including leaf characteristics, type of vegetation, and seasons. Urban vegetation may worsen air quality in some cases due to slowing ventilation and producing biological volatile organic compounds. While urban vegetation has potential to mitigate ambient air pollution, conducting site specific research is needed when implementing greenspace policies.
 
 

Improving Air Quality by Nitric Oxide Consumption of Climate-Resilient Trees Suitable for Urban Greening.

Nitrogen oxides (NOx), mainly a mixture of nitric oxide (NO) and nitrogen dioxide (NO2), are formed by the reaction of nitrogen and oxygen compounds in the air as a result of combustion processes and traffic. Both deposit into leaves via stomata, which on the one hand benefits air quality and on the other hand provides an additional source of nitrogen for plants. In this study, we first determined the NO and NO2 specific deposition velocities based on projected leaf area (sV d) using a branch enclosure system. We studied four tree species that are regarded as suitable to be planted under predicted future urban climate conditions: Carpinus betulus, Fraxinus ornus, Fraxinus pennsylvanica and Ostrya carpinifolia. The NO and NO2 sVd were found similar in all tree species. Second, in order to confirm NO metabolization, we fumigated plants with 15NO and quantified the incorporation of 15N in leaf materials of these trees and four additional urban tree species (Celtis australis, Alnus spaethii, Alnus glutinosa, and Tilia henryana) under controlled environmental conditions. Based on these 15N-labeling experiments, A. glutinosa showed the most effective incorporation of 15NO. Third, we tried to elucidate the mechanism of metabolization. Therefore, we generated transgenic poplars overexpressing Arabidopsis thaliana phytoglobin 1 or 2. Phytoglobins are known to metabolize NO to nitrate in the presence of oxygen. The 15N uptake in phytoglobin-overexpressing poplars was significantly increased compared to wild-type trees, demonstrating that the NO uptake is enzymatically controlled besides stomatal dependence. In order to upscale the results and to investigate if a trade-off exists between air pollution removal and survival probability under future climate conditions, we have additionally carried out a modeling exercise of NO and NO2 deposition for the area of central Berlin. If the actually dominant deciduous tree species (Acer platanoides, Tilia cordata, Fagus sylvatica, Quercus robur) would be replaced by the species suggested for future conditions, the total annual NO and NO2 deposition in the modeled urban area would hardly change, indicating that the service of air pollution removal would not be degraded. These results may help selecting urban tree species in future greening programs.

New Holistic Conceptual Framework for the Assessment of the Performance of Photocatalytic Pavement.

Despite serious health and environmental burdens associated with air pollution by NOx, the emission ceilings have been systematically exceeded in big European cities for several years. Photocatalytic technology can be an efficient solution for the removal of chemical air pollutants. Because diesel engine exhaust is the main source of NOx emissions, the application of a photocatalyst onto road pavement appears to be an effective NOx abatement method due to the large surface area, proximity to the emission source, and relatively good solar irradiance. Several laboratory-scale studies provided evidence demonstrating that most harmful contaminants can be readily mineralized. Furthermore, several projects were aiming to scale up this technology to pilot and real scales. Although the photocatalytic performances of selected materials in real urban environments were determined in some of these studies, the data are not conclusive for evaluating the overall performance because other material characteristics relevant to their functionality were not assessed. The lack of conformity criteria suitable for the evaluation of the overall performance of photocatalytic pavement under real operational conditions has generated skepticism and mistrust among public authorities and relevant stakeholders, which constrains the widespread implementation of this promising technology. In this context, the project LIFE–Photoscaling was focused on developing a new holistic conceptual framework to assess the photocatalytic pavement performance using the decision tool “Photoscaling Decision Maker” based on a set of quantitative indicators. For this purpose, a large volume of data obtained for 10 types of photocatalytic pavement materials was systemized on both the laboratory and pilot plant scales and three main indicators were defined: (1) photocatalytic performance effectiveness, (2) intrinsic performance, and (3) undesired secondary effects. Each top-level indicator includes several low-level subindicators associated with specific material characteristics. Finally, the ranges of the main indicators and subindicators and methods for their assessment were determined. These methods include standard, adopted, and original characterization techniques, which were selected based on the criteria such as simplicity, cost- and time-effectiveness, and relevance regarding the operational conditions.

Characterization of Urban Greening in a District of Lecce (Southern Italy) for the Analysis of CO2 Storage and Air Pollutant Dispersion

This paper is devoted to the assessment of urban greening effects on two important ecosystem services, i.e., air quality and CO2 storage, including the corresponding economic impacts in a real urban area, i.e., a district located in the Mediterranean city of Lecce (southern Italy). Two tools were employed, i-Tree Canopy and the computational fluid dynamics (CFD) microclimate model ENVI-met. i-Tree Canopy allowed fully determining the land-cover percentage on the basis of different ground cover classes and obtaining an estimate of annual values of CO2 storage, air pollutant removal, and economic benefits in the presence of urban greening. The estimate in i-Tree Canopy considered only the amount of greening; therefore, air pollutant removal estimates were only potential. As the vegetation was located in street canyons, its interaction with local meteorology and urban geometry strictly affected the dispersion of nitrogen oxides (NOx) (taken here as an example) as obtained from ENVI-met simulations. In ENVI-met, both deposition/absorption and aerodynamic effects were considered, and local increases in concentration were found in the district. The analysis of results obtained from different tools (one complex (CFD model) and the other simple (i-Tree model)) showed the error associated with the simple model in the computation of impacts if the interaction among the vegetation characteristics, the meteorological conditions, and the urban geometry was neglected; however, it also uncovers a novel approach for comprehensively characterizing a given area in terms of its vegetation cover, CO2 storage, and economic benefits, as well as local effects on air quality. This study is set in a broader context aimed at assessing the air quality in urban canopies of Mediterranean areas characterized by the presence of narrow street canyons where pollutants can accumulate due to ineffective air exchange with the above atmosphere.

Improving the adsorption performance and surface roughening of rayon fibers via enzymatic treatment with cellulase

In recent years, expectations have increased for the development of filters for removing air pollutants. Rayon fibers have rough surfaces and excellent adsorption characteristics. Therefore, rayon is a promising material for such filters. By further roughening its surface, its adsorptivity to substances such as volatile organic compounds can likely be improved. The surface of rayon fibers was roughened via wet spinning carried out by adding oleic acid to a raw viscose. As a result, porous fibers containing several pores with a diameter of about 0.5–1.0 µm were obtained. A weight reduction treatment of the porous rayon fibers with cellulase, a cellulose-degrading enzyme, resulted in the appearance of several streaks and asperities on their surfaces. To investigate the adsorption behavior of the rayon fibers after cellulase treatment, dye adsorption was examined using an aqueous methylene blue solution. The porous rayon fibers adsorbed much more dye than the regular fibers. In addition, the fibers absorbed more dye after treatment with cellulase than without treatment in both fibers. The deodorizing function of the rayon fibers was also investigated using ammonia gas. The porous rayon fibers treated with cellulase had a very high deodorizing effect. In the proposed study, rayon fibers (which are porous inside) were treated with cellulase, and their surface was found to be considerably rough.

A stochastic epidemic model coupled with seasonal air pollution: analysis and data fitting

Air pollution increases the risk of getting respiratory diseases. Both the removal of air pollutants and the transmission of diseases can be influenced by random perturbations. In this work, we develop a stochastic differential equation (SDE) model, coupled with seasonal air pollution, to study the dynamics of infectious respiratory disease spread. The periodicity of disease outbreaks is assumed to be caused by seasonal air pollution. The SDE of the air quality index (AQI) is proved to be ultimately bounded. The complexity of the SDE of infected individuals lies in the transmission rate that depends on air pollution. We prove that the system driven by the periodic clearance rate has at least one stochastic periodic solution under certain conditions. By computing the closed form of the Hermite expansion of transformation density, we construct an approximate likelihood function to fit the data of AQI and influenza-like illness cases, as a case study. Data fitting shows that the stochastic periodic model can well capture the dynamical behavior of air pollution and outbreaks of the infectious respiratory disease. We also study the impact of parameters on the reduction of air pollution and disease spread. This work shows the correlation between air pollution and infectious respiratory disease outbreaks and illustrates that the intensity of the environmental disturbance is a factor that cannot be ignored.

Coal bottom ash use in traditional ceramic production: evaluation of engineering properties and indoor air pollution removal ability

Coal bottom ash (CBA) disposed to landfills causes environmental issues. Thus, we used CBA in traditional clay ceramics that had the triple advantage of consuming troublesome waste, adsorbing volatile organics and being decorative indoors, replacing up to 40% by weight of clay with CBA and firing from 700 to 1300 °C. Clay and CBA mixtures were cast, cured at room temperature for 24 h and fired at several temperatures. Firing temperature impacted linear shrinkage, water absorption and fracture toughness, more strongly than CBA mixing proportion. Above 1000 °C, fracture toughness and water absorption resistance was enhanced but shrinkage increased. However, adding CBA lessened the contraction. SEM confirmed complete sintering as clay particles fused as a rigid solid above 1000 °C. X-ray diffraction patterns of ceramics containing CBA showed crystobalite and labradorite, in addition to quartz, due to flux materials in CBA. Leachability tests showed that the CBA ceramics were not ‘toxic’ on the USEPA TCLP regulatory list. Adsorption of gaseous toluene, a representative indoor pollutant, followed a Freundlich model: CBA made the adsorption sites more homogeneous, reduced the interaction mechanisms on the surfaces and thus the Freundlich exponent. Increased CBA increased toluene adsorption by 2–7 times.

Photocatalytic property of cement mortars coated with graphene/TiO2 nanocomposites synthesized via sol–gel assisted electrospray method

Titanium dioxide (TiO2) photocatalyst coatings on cement material surfaces of buildings or structures that require high mechanical integrity, such as tunnel walls and pedestrian roads, can directly utilize solar energy for self-cleaning surfaces and removing air pollutants in the environment. However, TiO2 can utilize only ultraviolet (UV) light, which accounts for only 5% of sunlight. To improve photocatalytic efficiency, graphene/TiO2 nanocomposites are prepared by a sol-gel assisted electrospray method and characterized by various instrumental analysis methods. Photocatalytic cement mortars are prepared by incorporating the as-prepared nanocomposites and commercial TiO2 into cement mortar. The self-cleaning and air purifying properties of the cement mortars are evaluated by the discoloration of rhodamine B (RhB) and the removal of nitric oxide (NO). As desired, cement mortar coated with graphene/TiO2 nanocomposites expresses high photocatalytic effectiveness on both RhB and NO. In addition, the regeneration of graphene/TiO2 nanocomposite photocatalysts has also been studied. The results show that the photocatalytic activity can be effectively regenerated by UV irradiation, with good repeatability and stability. Therefore, graphene/TiO2-coated cement mortar is a potential candidate for effective building self-cleaning and air purification through the use of solar irradiation.