Preparation And Characterization Of PAN-based Membrane Immobilized Zero-valent Iron Nanoparticles

In recent years,zero-valent iron technique has been widely applied in water purification and remediation due to its degradation and transformation power to organic pollutants.Because of the strong reducibility,the toxicity of pollutants is reduced and the completeness of follow-process such as biological treatment is improved.With the development of nanotechnology,zero-valent iron nanoparticles(ZVI NPs),which exhibit more excellent capacity,become the most widely studied nanomaterial for water treatment,because of their cheap cost,environmental compatibility,large specific surface area,high reactivity and easy migration.However,ZVI NPs tend to agglomerate in the routine preparation and application process via Van der Waals and magnetic attraction forces due to their small size effect and surface effect,which leads to the benefit loss.In order to improve the dispersity and stability of ZVI NPs,some promising methods,i.e.surface treatment and immobilization of ZVI NPs have been developed.And immobilizing ZVI NPs onto a continuous medium with good stability is anticipated to meet the requirements for environmental applications.We used polyacrylonitrile(PAN)as raw material,which presents good thermal and chemical stabilities,and prepared high strength PAN membrane by plasticized melt method.For the first time,PAN membrane,PAN-based oxidized membrane and PAN-based carbon membrane,which are in the form of flat and hollow fiber membrane,are developed as novel carrier of ZVI NPs.The influences of modified conditions on membrane properties are discussed and the morphology and loading percentage of ZVI NPs are tested.The pollutant removal capability of ZVI NPs immobilized PAN-based composite membranes are evaluated by model wastewater containing anionic dye methyl blue,cationic dye methylene blue,chlorinated organics trichloroethylene and nitro aromatics nitrobenzene,respectively.The specific research results of this paper are described as follows:(1)The high strength PAN membrane was prepared by plasticized melt method and the porous PAN membrane was prepared after the addition of porogen.FTIR results showed that membrane surface modification allowed C=N to hydrolyze to COOH for the chelation of Fe(III)and ZVI NPs were immobilized on PAN membrane through in situ synthesis method.SEM and TGA results showed that,on the surface of PAN flat membrane,the size of small spherical ZVI NPs was 15-40nm and the loading percentage was 14%.On the surface of PAN hollow fiber membrane,the size of needle-like ZVI NPs was 30-100nm and the loading percentage was 10%.The decolorization efficiency was tested by UV-vis and decreased visibly after regeneration.(2)In order to further improve the stability of membrane carrier,PAN membrane was oxidized.FTIR and XPS results showed that membrane surface modification converted partial C≡N to C=O and COOH for the chelation of Fe(III)and ZVI NPs were immobilized on PAN-based oxidized membrane through in situ synthesis method.SEM and TGA results showed that,on the surface of PAN-based flat oxidized membrane,the size of small hemispherical ZVI NPs was 20-200nm and the loading percentage was 20%.On the surface of PAN-based hollow fiber oxidized membrane,the loading percentage of chain-like ZVI NPs was 10%.The removal efficiency to dyes and chlorinated organics were tested by UV-vis and GC-MS and decreased slightly after regeneration and half a year storage.(3)After the carbonization of PAN-based oxidized membrane,PAN-based carbon membrane was obtained with adsorption,which could enrich pollutants and accelerate their contact with ZVI NPs and increase the removal efficiency.Meanwhile,micro-electrolysis of iron-carbon primary cell was conducive to the removal of pollutants.FTIR results showed that membrane surface modification allowed unsaturated carbon atom to be acid oxidized to COOH for the chelation of Fe(Ⅲ)and ZVI NPs were immobilized on PAN-based carbon membrane through in situ synthesis method.SEM and TGA results showed that,on the surface of PAN-based flat carbon membrane,the size of small spherical ZVI NPs was 20-50nm and the loading percentage was 4%.On the surface of PAN-based activated carbon hollow fiber membrane,the size of granular ZVI NPs was 100-500nm and the loading percentage was 5%.The decolorization efficiency was tested by UV-vis and decreased a little after regeneration.