Fabrication Of Branched Polyethyleneimine Modified Hydrous Zirconium Oxide/polyacrylonitrile Nano Fibers For Efficient Removal Of Fluoride

Defluoridation from groundwater has become a worldwide problem.Adsorption is the most wide used method to remove fluoride from the water.It is significant to develop high performance adsorbent.Hydrous zirconium oxide(HZO)is a potential adsorbent for defluoridation because of its high defluoridation capacities,low cost and satisfactory stability in water.However,it is faced with such technical challenges as poor p H adaptability,easy agglomeration and difficult separation in the actual application of defluoridation from the groundwater.In this paper,branched polyethyleneimine modified hydrous zirconium oxide/polyacrylonitrile nanofibers(b PEI-HZO/PAN NFs)is prepared for defluoridation from groundwater.The b PEI-HZO is prepared by modifying the surface of HZO with b PEI.Then the one-dimensional b PEI-HZO/PAN NFs are synthesized by electrospinning with polyacrylonitrile as organic substrate.The physical properties,chemical composition and surface electrical properties of the adsorbent were characterized by scanning electron microscopy,fourier transform infrared spectroscopy,zeta potential analysis and nitrogen adsorption-desorption isotherm.In addition,the dynamic adsorption and re-usability were accomplished by the fixed-bed column experiment.The fluoride adsorption mechanism of the adsorbent was also investigated.The main conclusions are as follows:(1)Uniform porous HZO with diameter of about 200 nm are successfully prepared by using Zirconium n-butoxide as precursor.The surface of HZO is modified by b PEI.The modification of b PEI has no obvious effect on the appearance of HZO.The point of zero charge(p H_pzc)of b PEI-HZO is p H=10.8,which is much higher than that of HZO(p H_pzc=6.8).Profited from the modification of b PEI,the working p H range of b PEI-HZO is strengthened.The maximum fluoride adsorption capacity of b PEI-HZO is 69.24 mg/g at p H=7 and T=298K,which is 34%higher than that of HZO(51.71 mg/g).The adsorption of b PEI-HZO on fluoride conforms to the pseudo-second-order kinetic equation.In addition,b PEI-HZO has excellent selective adsorption capacity for fluoride,satisfactory recycling performance and high stability in water.(2)Porous one-dimensional b PEI-HZO/PAN NFs were synthesized by immobilizing b PEI-HZO on PAN via electrospinning.The adsorbent can be directly used in fixed bed column and can be easily separated from water.The diameter of b PEI-HZO/PAN NFs is about 900-1200 nm.The adsorption of fluoride by b PEI-HZO/PAN NFs is studied.The maximum fluoride adsorption capacity of b PEI-HZO/PAN NFs was 67.51 mg/g.The adsorption process of b PEI-HZO/PAN NFs is according with pseudo-second-order adsorption kinetics.The actual groundwater is taken from Nanjing province,China and the fluoride solution is added to make the fluoride concentration reach 4 mg/L,so as to explore the practical application of b PEI-HZO/PAN NFs in defluoridation from the groundwater.The practical application experiment is carried out in a small fixed bed column reactor.When the adsorption penetration point is set as 1.5 mg/L,the water treatment capacity of b PEI-HZO/PAN NFs can reach 4300 kg of water/kg of b PEI-HZO/PAN NFs.After four adsorption-desorption cycles,the water treatment capacity of b PEI-HZO/PAN NFs can still maintain 4100 kg of water/kg of b PEI-HZO/PAN NFs.(3)The adsorption mechanism of b PEI-HZO/PAN NFs was explored and summarized as follows:1.ligand exchange or metal-ligand interaction between fluoride and hydroxyl radicals on zirconium atom;2.electrostatic interaction between fluoride ion and amino group;3.hydrogen bond adsorption between fluoride and amino group.This paper successfully solved two major problems in the application of HZO in the actual groundwater fluoride removal,and strengthened the application ability of zirconia-based nanomaterials in the process of groundwater fluoride removal.