Study On The Preparation And Properties Of Functional Cellulose-Based Composite Air Filters

Air pollution,especially fine particulate matters,toxic gases and pathogenic bacteria,has intimate and severe impacts on human health and the environment.Additionally,statistics have showed that PM_2.5?Aerodynamic equivalent diameter?2.5?m?concentration increments of 10?g.m^-3 on average can lead to a 6-8%increased risk in lung cancer and cardiopulmonary diseases.Nowadays,porous membrane filters and fibrous filters are common and popular in the market.However,the disposal of synthetic polymer-based filters results in secondary pollution because of their nonrenewable and non-degradable properties.In contrast with synthetic fibers,cellulose fibers may be a suitable candidate to fabricate renewable and sustainable filters due to the abundance in nature,biodegradable sources and low cost.Nevertheless,traditional cellulose filters can not reach a satisfactory filtration performance because of their loose lamellar structure.Some limitations of traditional cellulose-based filters still exist,such as lacking toxic gases adsorption ability and vulnerability to bacterial infection.Therefore,there are urgent needs and great challenges to design and fabricate multifunctional air filters.In this study,we chose green and biodegradable cellulose fibers as raw materials to prepare cellulose-based filters using an in-situ growth method and freeze casting technique.Firstly,in order to fabricate biodegradable cellulose filters with controllable designer pore structures,different organic solvents were employed as freeze media to explore the mechanism on the growth of ice crystals and the pore size of cellulose-based air filters.Secondly,for preparing functional cellulose-based air filters applied in adsorbing toxic gases and antibacterial fields,different metal-organic frameworks?MOFs?including ZIF-8,MOF-199 and Ag-MOFs were synthetized and further employed to prepare functional MOFs@CF air filters.The adsorption property,antibacterial activity and filtration ability of MOFs@CF air filters were further studied.Thirdly,in order to improve the mechanical property of cellulose-based air filters,double-component MOFs?ZIF-8 and Ag-MOFs?and cellulose nanofiber?CNF?as a green bridge substance endow the air filter with versatility and reinforce its compressive strength.The conclusions are as follows.Green and biodegradable cellulose filters with controllable designer pore structures were prepared using organic solvent-based freeze casting.In this paper,the relationship between the different freeze media,including ethanol,isopropanol,and tertiary-butyl alcohol,and the microstructure of the porous filters was investigated.And the effect mechanism was also studied.The results of the pore size distribution indicated that the pore channel size decreased remarkably when organic solvents were used as the freezing media.Furtheremore,the effects of different contents of TBA on the pore structure and size were investigated.The pore size of air filter based on 90%TBA concentred on 60.5?m,40.3?m,27.8?m and 4.5?m.Moreover,the filters showed high filtration efficiency,up to 99.70%and 99.66%for 0.5?m and 0.3?m particles,respectively.Biodegradable composite filters were fabricated by an in-situ deposition method to isolate pollutants and inactivate bacteria.The zeolitic imidazolate framework-8@cellulose fibers?ZIF-8@CF?filters had filtration efficiency as high as 98.36%and 99.94%against 0.3?m and 0.5?m particles,respectively,under a pressure drop of 134 Pa.Moreover,the nitrogen adsorption capacities of the composites were about 20 times higher than that of pure cellulose filters.In addition,theAg-basedmetal-organicframeworks@cellulosefibers?Ag-MOFs@CF?exhibited excellent antimicrobial activity against Escherichia coli?E.coli?with an inhibition zone diameter of 20.8 mm.A biodegradable cellulose-based air filter?Ag-MOFs@CNF@ZIF-8?with multi-layer structure was fabricated by in-situ generation of double-component metal-organic frameworks and reinforcement of cellulose nanofiber.It exhibits good filtration performance,gas adsorption,antibacterial activity and mechanical property.The presence of MOFs could enhance the interaction between the filter and particulate matter and significantly improve the specific surface area of the composite filter.Thus,the Ag-MOFs@CNF@ZIF-8 composite air filters exhibited high filtration efficiency for PM_2.5.And the nitrogen adsorption capacity increased to 109 cm³·g^-1.Furthermore,the Ag-MOFs@CNF@ZIF-8filter exhibited excellent antibacterial activity against E.coli with an inhibition zone diameter of 18.1 mm.The compressive strength of the composite filter could be up to 501 kPa.Herein,this composite filter has a great application potential in PM_2.5 removal,toxic gas adsorption and healthcare fields.