Electrostatic Air Filtration by Multifunctional Dielectric Heterocaking Filters with Ultralow Pressure Drop

Advances in Electrostatic Plasma Methods for Purification of Airborne Pathogenic Microbial Aerosols: Mechanism, Modeling and Application

The transmission of pathogenic airborne microorganisms significantly impacts public health and societal functioning. Ensuring healthy indoor air quality in public spaces is critical. Among various air purification technologies, electrostatic precipitation and atmospheric pressure nonthermal plasma are notable for their broad-spectrum effectiveness, high efficiency, cost-effectiveness, and safety. This review investigates the primary mechanisms by which these electrostatic methods collect and disinfect pathogenic aerosols. It also delves into recent advancements in enhancing their physical and chemical mechanisms for improve efficiency. Simultaneously, a thorough summary of mathematical models related to the migration and deactivation of pathogenic aerosols in electrostatic purifiers is provided. It will help us to understand the behavior of aerosols in purification systems. Additionally, the review discusses the current research on creating a comprehensive health protection system and addresses the challenges of balancing byproduct control with efficiency. The aim is to establish a foundation for future research and development in electrostatic aerosol purification and develop integrated air purification technologies that are both efficient and safe.

Field-Assisted Efficient Capturing and Analysis of Airborne Nanoparticulate Matter Using a Multifunctional Nanoporous Membrane

As the potential adverse health and environmental effects of nanoscale pollutants have garnered significant attention, the demand for monitoring and capturing ultrafine particulate matter has been growing. With the rise in ultrafine dust emissions, this issue has become increasingly important. However, submicron particles require advanced strategies to be captured because of their limited inertial effect. For example, electrostatic air filters have been investigated for their improved performance in the fine particle regime. On the other hand, Raman spectroscopy was proposed as a promising analytical strategy for aerosol particles because it can be used to conveniently detect analytes in a label-free manner. Thus, the synergistic integration of these strategies can open new applications for addressing environment-related challenges. This study presents a multifunctional approach for achieving both air filtration and surface-enhanced Raman scattering (SERS) for analyte identification. We propose a nanoporous membrane composed of a thin gold layer, copper, and copper oxide to provide the desired functions. The structures are produced by performing scalable electrodeposition and subsequent electron-beam evaporation, attaining an excellent filtration efficiency of 95.9% with an applied voltage of 5 kV for 300 nm KCl particles and a pressure drop of 121 Pa. Raman intensity measurements confirm that the nanodendritic surface of the membrane intensifies the Raman signals and allows for the detection of 10 μL of nanoplastic particle dispersion with a concentration of 50 μg/mL. Rhodamine 6G aerosol stream with an approximate particle deposition rate of 0.040 × 106 mm-2·min-1 is also identified in a minimum detectable time of 50 s. The membrane is shown to be recyclable owing to its structural robustness in organic solvents. In addition, the fatigue resistance of the structure is evaluated through 22,000 iterative loading cycles at a pressure of 177 kPa. No performance degradation is observed after the fatigue loading.

Evaluation of the adsorption performance and thermal treatment-associated regeneration of adsorbents for formaldehyde removal

Indoor air pollution remains a major concern, with formaldehyde (HCHO) a primary contributor due to its long emission period and associated health risks, including skin allergies, coughing, and bronchitis. This study evaluated the adsorption performance and economic efficiency of various adsorbents (biochar, activated carbon, zeolites A, X, and Y) selected for HCHO removal. The impact of thermal treatment on adsorbent regeneration was also assessed. The experimental apparatus featured an adsorption column and HCHO concentration meter with an electrochemical sensor designed for adsorption analysis. Zeolite X exhibited the highest adsorption performance, followed by zeolite A, zeolite Y, activated carbon, and biochar. All adsorbents displayed increased HCHO removal rates with an extended length/diameter (L/D) ratio of the adsorption column. Zeolite A demonstrated the highest economic efficiency, followed by zeolite X, activated carbon, zeolite Y, and biochar. Higher L/D ratios improved economic efficiency and prolonged the replacement cycle (the optimal timing for adsorbent replacement to maintain high adsorption performance). Sensitivity analysis of adsorbent regeneration under varying thermal treatment conditions (150, 120, and 80°C) and durations (60, 45, and 30 min) revealed minimal changes in adsorption efficiency (±3%). The results indicated the potential of adsorbent regeneration under energy-efficient thermal treatment conditions (80°C, 30 min). In conclusion, this study underscores the importance of a comprehensive assessment, considering factors such as adsorption performance, replacement cycle, economic efficiency, and regeneration performance for the selection of optimal adsorbents for HCHO adsorption and removal.Implications: This study underscores the importance of adsorption technology for the removal of formaldehyde and similar volatile organic compounds (VOCs), highlighting the potential of alternative adsorbents, such as environmentally friendly biochar, in addition to traditional strategies, such as activated carbon and zeolites. Our findings demonstrate the feasibility of adsorbent regeneration under energy-efficient thermal treatment conditions. These results hold promise for improving indoor air quality, reducing environmental pollutants, and enhancing responses to air contaminants like fine dust and VOCs.

Electroactive, Antibacterial, and Biodegradable Poly(lactic acid) Nanofibrous Air Filters for Healthcare

Poly(lactic acid) (PLA)-based nanofibrous membranes (NFMs) hold great potential in the field of biodegradable filters for air purification but are largely limited by the relatively low electret properties and high susceptibility to bacteria. Herein, we disclosed a facile approach to the fabrication of electroactive and antibacterial PLA NFMs impregnated with a highly dielectric photocatalyst. In particular, the microwave-assisted doping (MAD) protocol was employed to yield Zn-doped titanium dioxide (Zn-TIO), featuring the well-defined anatase phase, a uniform size of ∼65 nm, and decreased band gap (3.0 eV). The incorporation of Zn-TIO (2, 6, and 10 wt %) into PLA gave rise to a significant refinement of the electrospun nanofibers, decreasing from the highest diameter of 581 nm for pure PLA to the lowest value of 264 nm. More importantly, dramatical improvements in the dielectric constants, surface potential, and electret properties were simultaneously achieved for the composite NFMs, as exemplified by a nearly 94% increase in surface potential for 3-day-aged PLA/Zn-TIO (90/10) compared with that of pure PLA. The well regulation of morphological features and promotion of electroactivity contributed to a distinct increase in the air filtration performance, as demonstrated by 98.7% filtration of PM_0.3 with the highest quality factor of 0.032 Pa^-1 at the airflow velocity of 32 L/min for PLA/Zn-TIO (94/6), largely surpassing pure PLA (89.4%, 0.011 Pa^-1). Benefiting from the effective generation of reactive radicals and gradual release of Zn²⁺ by Zn-TIO, the electroactive PLA NFMs were ready to profoundly inactivate Escherichia coli and Staphylococcus epidermidis. The exceptional combination of remarkable electret properties and excellent antibacterial performance makes the PLA membrane filters promising for healthcare.

Modifying the Fiber Structure and Filtration Performance of Polyester Materials Based on Two Different Preparation Methods

How to build a satisfactory indoor environment has become increasingly important. In this paper, the synthesis and improvement of the most widely used polyester materials in China were carried out based on two different preparation methods, and the structures and filtration performances were tested and analyzed. The results showed that a carbon black coating was wrapped on the surfaces of the new synthetic polyester filter fibers. Compared with the original materials, the filtration efficiencies of PM₁₀, PM_2.5, and PM₁ were increased by 0.88-6.26, 1.68-8.78, and 0.42-4.84%, respectively. The best filtration velocity was 1.1 m/s, and the new synthetic polyester materials with direct impregnation demonstrated superior filtration performance. The filtration efficiency of the new synthetic polyester materials was improved on the particulates with sizes of 1.0-5.0 μm. The filtration performance of G4 was better than that of G3. The filtration efficiencies of PM₁₀, PM_2.5, and PM₁ were improved by 4.89, 4.20, and 11.69%, respectively. The quality factor value can be used to assess the comprehensive filtration performance of air filters in practical applications. It could provide reference values for the selection of synthetic methods of new filter materials.

Development and Performance Evaluation of Polytetrafluoroethylene-Membrane-Based Automotive Cabin Air Filter

A high-efficiency, long-life cabin filter unit is required for the effective purification of the air inside a vehicle. However, conventional cabin air filters that utilize electrostatic effects are less efficient and less effective owing to environmental factors. Polytetrafluoroethylene (PTFE) membranes exhibit a high porosity and surface-to-surface dust-removal performance, and maintain a stable pressure drop, indicating their good potential as filter materials. Therefore, in this study, the use of PTFE membranes for the fabrication of automobile filters and the filtration performance of the filters were examined. To this end, first, the properties of PTFE membranes mainly used in HEPA air conditioning filters and those of membranes used as vehicle cabin filters were compared. Next, the thickness, weight, stiffness, pore size, and filtration performance characteristics of filter media fabricated by blending melt-blown (MB) nonwoven, PTFE membranes, and supporting nonwoven into a total filtration layer were compared and analyzed. Lastly, the environmental change durability performance of the automobile cabin filter based on PTFE membrane and the results of the test after the installation of the filter in a vehicle were demonstrated.

Optimization Study of Sampling Device for Semi-Volatile Oil Mist in the Industrial Workshop

A large number of metalworking fluids in industrial manufacturing processes generate high-concentrations of oil mist pollution, which is a typical semi-volatile aerosol and is generally composed of liquid particles and volatile gas components. Long-term exposure to oil mist pollution brings a series of occupational diseases to workers. For the semi-volatile aerosol, the traditional filter sampling method will lead to particle volatilization, which underestimates the concentration of particles and overestimates the concentration of gas. Therefore, this study combined the advantages of the electrostatic method and the Tenax tube adsorption method, to develop a more accurate measurement technology. First, a dichotomous sampler that could efficiently separate the gas and liquid phases of aerosols was optimized through a numerical model, which was validated by literature results. Next, a test table for oil mist sampling was built with a sampler which was fabricated by 3D printing, and the performance of the sampler was evaluated. The results show that the sampling technique can separate the gas and particulate phases of the oil mist efficiently and accurately. Compared with the traditional single sampling methods, the new sampler can better determine the true concentration of oil mist.

Predicting the emissions of VOCs/SVOCs in source and sink materials: Development of analytical model and determination of the key parameters

The emissions of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) from indoor materials pose an adverse effect on people's health. In this study, a new analytical model was developed to simulate the emission behaviors for both VOCs and SVOCs under ventilated conditions. Based on this model, we further introduced a hybrid optimization method to accurately determine the key parameters in the model: the initial emittable concentration, the diffusion coefficient, the material/air partition coefficient, and the chamber surface/air partition coefficient (for SVOCs). Experiments for VOC emissions from solid wood furniture were performed to determine the key parameters. We also evaluated the hybrid optimization method with the data of flame retardant emissions from polyisocyanurate rigid foam and VOC emissions from a panel furniture in the literature. The correlation coefficients are high during the fitting process (R² = 0.92-0.99), demonstrating effectiveness of this method. In addition, we observed that chemical properties could transfer from SVOC-type to VOC-type with the increase of temperature. The transition temperatures from SVOC-type to VOC-type for the emissions of tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCIPP) were determined to be about 45 ℃ and 35 ℃, respectively. The present study provides a unified modelling and methodology analysis for both VOCs and SVOCs, which should be very useful for source/sink characterization and control.

A Simple Preparation Method of Graphene and TiO2 Loaded Activated Carbon Fiber and Its Application for Indoor Formaldehyde Degradation

Formaldehyde has a significant impact on human health. This study used a simple dipping method to load graphene-titanium dioxide (GR-TiO2) on activated carbon fibers (ACFs). The microstructure of GR-TiO2/ACF hybrid material was observed by SEM, combined with XRD and BET analysis. The result showed that the GR-TiO2/ACF hybrid material had a specific surface area of 893.08 m2/g and average pore size of 2.35 nm. The formaldehyde degradation efficiency of the prepared material was tested under different conditions, such as ultraviolet (UV) radiation, air supply volume, relative humidity, initial mass concentration. The results showed that the UV radiation intensity, airflow and the initial mass concentration were positively correlated with the formaldehyde removal rate, and the relative humidity was negatively correlated with the formaldehyde removal rate. The GR-TiO2/ACF hybrid material had a maximum formaldehyde removal rate of 85.54% within 120 min.

Indoor air quality improvement and purification by atmospheric pressure Non-Thermal Plasma (NTP)

Non-thermal plasma (NTP) is a promising technology for the improvement of indoor air quality (IAQ) by removing volatile organic compounds (VOCs) through advanced oxidation process (AOP). In this paper, authors developed a laboratory scale dielectric barrier discharge (DBD) reactor which generates atmospheric NTP to study the removal of low-concentration formaldehyde (HCHO), a typical indoor air VOC in the built environment associated with cancer and leukemia, under different processing conditions. Strong ionization NTP was generated between the DBD electrodes by a pulse power zero-voltage switching flyback transformer (ZVS-FBT), which caused ionization of air molecules leading to active species formation to convert HCHO into carbon dioxide (CO₂) and water vapor (H₂O). The impact of key electrical and physical processing parameters i.e. discharge power (P), initial concentration (C_in), flow rate (F), and relative humidity (RH) which affect the formaldehyde removal efficiency (ɳ) were studied to determine optimum conditions. Results show that, the correlation coefficient (R²) of removal efficiency dependence on the processing parameters follow the order R² (F) = 0.99 > R² (RH) = 0.96, > R² (C_in) = 0.94 > R² (P) = 0.93. The removal efficiency reached 99% under the optimum conditions of P = 0.6 W, C_in = 0.1 ppm, F = 0.2 m³/h, and RH = 65% with no secondary pollution. The study provided a theoretical and experimental basis for the application of DBD plasma for air purification in the built environment.

Physical-Chemical Coupling Model for Characterizing the Reaction of Ozone with Squalene in Realistic Indoor Environments

Squalene can react with indoor ozone to generate a series of volatile and semi-volatile organic compounds, some of which may be skin or respiratory irritants, causing adverse health effects. Better understanding of the ozone/squalene reaction and product transport characteristics is thus important. In this study, we developed a physical-chemical coupling model to describe the behavior of ozone/squalene reaction products, that is, 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA) in the gas phase and skin, by considering the chemical reaction and physical transport processes (external convection, internal diffusion, and surface uptake). Experiments without intervention were performed in a single-family house in California utilizing time- and space-resolved measurements. The key parameters in the model were extracted from 5 day data and then used to predict the behaviors in some other days. Predictions from the present model can reproduce the concentration profiles of the three compounds (ozone, 6-MHO, and 4-OPA) well (R² = 0.82-0.89), indicating high accuracy of the model. Exposure analysis shows that the total amount of 6-MHO and 4-OPA entering the blood capillaries in 4 days can reach 14.6 and 30.1 μg, respectively. The contribution of different sinks to ozone removal in the tested realistic indoor environment was also analyzed.

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.