Fabrication And Properties Of Multifunctional And Structural Controllable Composite Filtration Media

With the development of economy and people’s life,the humans have realized the importance of a healthy living environment.However,due to the rapid industrialization and urbanization,the air pollution has become more and more serious.More than 1.3 million premature deaths have been reported annually due to the respiratory diseases caused by air pollution in China.Poor outdoor air environment would also lead to a bad indoor air quality.To date,the predominant indoor air pollution is particulate matter（PM）and formaldehyde（HCHO）which was emitted from construction and decoration materials.Moreover,the two pollutants would exist simultaneously in the form of inorganic aerosols by nano-condensation.Air purification is one of the best options in indoor pollution abatement.However,most of the air purifiers are only effective for one pollutant and have no additional function.Therefore,developing a multifunctional and controllable composite filter media is of great importance.Among various transition metal oxides,manganese dioxides（MnO₂）have been widely used as effective catalysts in HCHO removal through which HCHO can be converted into water and carbon dioxide.In this work,several types of MnO₂ modified multifunctional composite fibrous filters have been constructed.Finally,the capabilities in removing HCHO and PM have been investigated.The detailed work mainly includes the following aspects:1.Four types of MnO₂ were synthesized via co-precipitation method or redox reaction method,and the HCHO removal performance at room temperature has been studied over these four MnO₂.It was found that the crystal structures of MnO₂ play a key role in the HCHO catalytic activity,among which the layeredδ-MnO₂ showed the best performance.In addition,a higher content of manganese vacancies could lead to a higher extent of adsorbed oxygen species and the mobility of adsorbed oxygen,thus contributing to an increased HCHO oxidation performance.Asδ-MnO₂synthesized via redox method possesses the highest content of manganese vacancies,theδ-MnO₂shows the best HCHO oxidation performance at room temperature.2.A fluffy PE/PP primary composite filtration media with uniform dispersion and anchoring of MnO₂ was prepared via through-air bonding process.The influence of MnO₂ loading fraction on morphology,pore size distribution,HCHO catalytic oxidation performance and filtration efficiency of the composite filtration media was investigated.It was found that,with the increasing of MnO₂ loading contents,the surface toughness of PE/PP fibers was increased,and the pore size of the composite filters was increased at first and decreased subsequently.The room temperature HCHO catalytic activity of the MnO₂/PE/PP composite filtration media increased with the increase of MnO₂ loading fraction,and the filters exhibited acceptable reversibility.Moreover,the MnO₂ contents showed significant influence on the filtration performance.When the loading amount reached to 8%,the filter showed the best filtration performance,which achieved the requirement of medium efficiency filter.In addition,it was found that after corona charging treatment,the electret PE/PP fibers could contribute to an enhanced filtration efficiency which increased by nearly 25%.The composite filtration media maintained satisfactory filtration efficiency after 30 days decay which only showed 1%drop.Since this MnO₂/PE/PP composite filtration media is simple in manufacture which would be produced in mass production,we expect that such appealing filtration media will provide numerous applications in air filtration field.3.By optimizing the co-precipitation approach,a MnO₂ modified activated carbon fiber（ACF）substrate was produced to construct the MnO₂/ACF composite filtration media.Results showed that after MnO₂ growth,the reduction,activation and migration of active oxygen species on the MnO₂/ACF composite filtration media was increased,which gave rise to an increased HCHO removal performance.The ACF and MnO₂ crystals acted synergistically during the HCHO removal process.In addition,the MnO₂ contents had a great influence on the morphology,surface area and pore size of the MnO₂/ACF composite filtration media,thus affecting the breakthrough time and capacity.With the increase of MnO₂ contents,the HCHO removal capacity was firstly increased and then decreased.4.Firstly,the uniform intermediate inorganic nucleation films,including Al₂O₃,TiO₂,and ZnO,formed conformally to modify PP nonwovens（MO/PP）via the atomic layer deposition（ALD）technique.Then heterogeneous nucleation and growth of MnO₂ onto metal oxide treated PP nonwovens can be achieved to produce multifunctional high-efficiency composite MnO₂/MO/PP filtration media via hydrothermal synthesis.We further investigated how different ALD thin films influence the crystallinity,morphology,surface area,and surface oxygen species of the MnO₂grown ALD-coated PP fibers.It was found that,in addition to uniformity and integrity,ZnO thin films gave rise to MnO₂ crystals with the largest fraction of available surface oxygen,enabling99.5%catalytic degradation of HCHO within 60 minutes.In addition,the MnO₂/MO/PP composite filters provided excellent PM filtration efficiencies,with PM_2.5 and PM₁₀ exceeding 87%and 98%,respectively.Moreover,after corona charging treatment,the filtration efficiency of PM_2.5 and PM₁₀ further exceeding 99.99%,making our approach feasible to produce fully multifunctional composite high-efficiency filtration media.