Metal–organic framework (MOF), an emerging class of porous hybrid inorganic–organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO2 gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO2 capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.
This study explores a novel approach of multiscale modeling and simulation to characterize the filtration behavior of a facepiece in varied particulate conditions. Sequential multiscale modeling was performed for filter media, filtering facepiece, and testing setup. The developed virtual models were validated for their morphological characteristics and filtration performance by comparing with the data from the physical experiments. Then, a virtual test was conducted in consideration of a time scale, simulating diverse particulate environments with different levels of particle size distribution, particle concentration, and face velocity. An environment with small particles and high mass concentration resulted in a rapid buildup of resistance, reducing the service life. Large particles were accumulated mostly at the entrance of the filter layer, resulting in a lower penetration and slower buildup of resistance. This study is significant in that the adopted virtual approach enables the prediction of filtration behavior and service life, applying diverse environmental conditions without involving the costs of extra setups for the physical experiments. This study demonstrates a novel and economic research method that can be effectively applied to the research and development of filters.
With the increasing demand for filtering face pieces as daily personal protection, inevitable problems associated with filter wastes have been addressed. To mitigate this concern, an eco-friendly alternative filter material is developed using plant-sourced biomaterials, poly(lactic acid) (PLA) and fungal chitin. Heterogeneous electrospun fibers with distinctive chitin-rich and PLA-rich regions are formed by inducing phase separation between hydrophilic chitin and hydrophobic PLA polymers. The PLA and chitin-incorporated PLA (ChPLA) webs are evaluated for filtration performance against NaCl nanoparticles, examining the contribution of mechanical and electrostatic particle capture mechanisms, with and without aging under two different environmental conditions of 40 °C and a 3% relative humidity and 25 °C and a 90% RH. The adverse effect of humid treatment on filtration efficiency is apparent for the ChPLA web, and the loss of overall filtration efficiency is mostly attributed to the reduced electrostatic filtration mechanism, as is evidenced by the decreased surface potential measurement. The ChPLA web displays lower tensile stress than the PLA web, and the mechanical strength is further reduced when ChPLA is exposed to moisture. In the soil burial test, ChPLA shows higher degradability than PLA during 56 days of burial. This research provides practical information to design environmentally sustainable filter media, primarily with biobased polymers, especially shedding light on accelerated biodegradation via induced phase separation.
Worldwide attention has been paid to effective protection strategies against the COVID-19 pandemic. Filtering masks are generally kept for a certain period of shelf-life before being used, and frequently, they are used repeatedly with recurrent storages. This study investigates the effect of storage temperature and humidity on the structural characteristics and charges of an electret filter, associating with the filtration performance in terms of efficiency and pressure drop based on a practical use-storage scenario. For the repeated use conditions with recurrent storage, humid storage conditions significantly deteriorated the filtration efficiency as hygroscopic particles quickly wetted the surface and masked the surface charges. The high temperature rapidly deteriorated the filter charges and caused a lowered electrostatic filtration efficiency. In a heated condition, the web became fluffier, yet it did not directly affect the pressure drop or mechanical filtration efficiency. The approach of this study is progressive in that rigorous analysis was performed on examining the particle morphology and internal structure of filter media with varied storage conditions to link with the filtration performance and the effective lifetime. This study intends to provide a scientific reference guiding a desirable storage condition and replacement cycle of filtering masks considering the actual use habits and storage environment.
Mushroom chitin membranes with controllable pore structures were fabricated through a simple process with naturally abundant Agaricus bisporus mushrooms. A freeze-thaw method was applied to alter the pore structures of the membranes, which consist of chitin fibril clusters within the glucan matrix. With tunable pore size and distribution, mushroom chitin membranes could effectively separate stable oil/water emulsions (dodecane, toluene, isooctane, and chili oil) with various chemical properties and concentrations and particle contaminants (carbon black and microfibers) from water. Chitin fibrils tightly pack with each other to form a dense membrane, leading to no permeation of contaminants or water. An increasing number of applied freezethaw cycles confers more tortuous pore structures throughout the mushroom chitin membranes, leading to higher flux while maintaining rejection performance. The 3D simulation constructed by the X-ray computed tomography and GeoDict software also demonstrated capturing a considerable amount of contaminants within the membranes' pores, which can be easily removed by water rinsing for further successive filtration. Furthermore, mushroom chitin membranes were almost completely biodegraded after approximately a month of being buried in the soil or kept in a lysozyme solution while possessing mechanical durability demonstrated by consistent filtration performance for repeated usage up to 15 cycles under ambient and external pressure. This research is a proof of concept that mushroom-derived chitin develops functional and biodegradable materials for environmental applications with scalability.
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