DOI
https://doi.org/10.25772/0ZHV-9K13
Defense Date
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Mechanical and Nuclear Engineering
First Advisor
Sheng-Chieh Chen
Abstract
Indoor air quality (IAQ) has been becoming a major concern worldwide because statistical data showed that the indoor concentrations of gas pollutants, e.g., volatile organic compounds (VOCs) and particulate matters (PMs) are often 2–5 times higher than that of outdoors. Especially, people spend 87% of their time indoors and increasing to more than 90% during COVID-19 pandemic. The high concentration of these indoor air pollutants is mainly due to the reduced air exchange rate for the design of energy-efficient building construction and the increased usage of furnishings, glues, paints, furnaces, etc., leading to VOC outgassing and particle emission. Evidence has shown that prolonged exposure to these pollutants can cause acute and chronic effects on respiratory and central nervous systems. As typical pollutants of indoor air, PMs and VOCs pose a significant threat to public health. It is urgent to simultaneously and effectively remove indoor air pollutants to improve the indoor air quality.
To simultaneously mitigate indoor PMs and VOCs, this dissertation investigated the idea of developing metal organic frameworks (MOFs) based materials coated electret filters. The idea is based on the following three facts: (1) Electret filters, with quasi-permanent electrical charges on the fibers, acquiring an additional force of electrostatic attraction, show a high initial filtration efficiency against PMs and a much lower pressure drop (ΔP) compared to mechanical filters. (2) MOFs which are made of metal clusters and organic linkers, have attracted considerable interest owing to their extraordinarily high surface areas, tunable pore size, and adjustable internal surface properties. Because of their controllable pore size and chemical functionality, MOFs outperform traditional porous materials (activated carbon, zeolite, alumina, and silica) in the adsorption of VOCs. (3) MOF-based semiconductor was demonstrated to have large surface area (> 1000 m2/g) and suppressed charge carrier (h+ and e-) recombination rate, contributing to high photocatalytic efficiency, which are advantageous for VOC photocatalytic oxidation. The selected MOFs were synthesized via a hydrothermal route and then coated in electret filter media by using a liquid filtration method for fabrication of MOF and semiconductor/MOF coated electret filter, named E-MOFilter and PE-MOFilter, respectively. Various characterizations, such as XRD, SEM, and FT-IR etc., were performed and their results demonstrated that the successful synthesis of samples. The PM filtration tests and VOC absorption and photodegradation tests were further performed. Results demonstrated that the newly developed filters were found to have high PM removal efficiency and decent VOC removal efficiency because of the negligible fiber charge degradation in filters, the highly porous structures of MOFs and the increased charge carrier densities in the photocatalytic systems.
Beyond development of advanced electret HVAC filters for simultaneous PM and VOC control, face masks and filtering facepiece respirators (FFRs), as personal protective equipment (PPE), can be used to provide indoor air pollution control and personal health protection. However, it is reported that approximately 60% of KN95s, the most widely available N95 equivalent respirators on the market that NIOSH evaluated during the COVID-19 pandemic in 2020 and 2021 did not meet the requirements. Besides, the general public has limited access to the standardized testing equipment (required by the National Institute for Occupational Safety and Health (NIOSH)) for evaluating the filtration efficiency of FFRs. Therefore, in this work, an empirical equation by using easily accessible parameters for efficiency prediction of respirator minimum efficiency at most penetrating particle size (MPPS) was provided. In the empirical equation model, the three most easily accessible parameters, pressure drop, mask area and surface potential were utilized. The predicted efficiencies showed less than 4% deviation to the experimental efficiencies, which demonstrated the acceptability of the empirical equation model. This model was further validated by extra new mask samples.
This work from this dissertation sheds light on applying the novel MOF-based materials coated electret filters in the residential and commercial HVAC systems to remove PMs and VOCs simultaneously and effectively. In addition, by providing an empirical equation for predicting filtration efficiency, this work provides an easily accessible screening method for qualifying respirators so that the general public can make informed decisions regarding the use of respirators for individual health protection and indoor air pollution control.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-10-2023