Fabrication Of Inorganic Separation Membrane Using TiO₂ Nanowires

Membrane separation technology has important applications in many fields such as chemical industry,petroleum industry,food processing,metallurgy,biotechnology,environment and water treatment.High selectivity and high permeability are two important properties that an ideal separation membrane should possess.However,the separation membrane fabricated by traditional methods has trade-off relationship between the selectivity and permeability.Compared to polymer membranes,inorganic ceramic membrane has the advantages of high temperature and pressure resistance,acid and alkali corrosion resistance,organic solvent resistance,long life,anti-fouling and other advantages.Traditional inorganic ceramic membranes are made by sintering oxide nanoparticles,but the porosity of nano-ceramic membranes is very low,causes the low permeation flux of the traditional inorganic ceramic membrane.How to build a separation membrane with both high selectivity and high rejection is an important challenge.In this paper,we use TiO₂ nanowires with high porosity as raw materials to fabricate TiO₂ nanowires microfiltration and ultrafiltration membranes with both high selectivity and high permeability.A polymer-modified TiO₂ nanowires oil-water separation membrane with under-liquid dual superlyophobicity was prepared.The main results obtained in the paper are as follows:1.The hydrogen titanate nanowires with a diameter of 100 nm were coated on a stainless steel mesh by a simple gravity deposition method,and the stainless steel mesh supported TiO₂ nanowires membrane was prepared by sintering.The pore diameter of the prepared TiO₂ nanowire membrane is 180 nm,indicates the prepared TiO₂ nanowire membrane is microfiltration membrane.Due to the high porosity?91.7%?of the TiO₂nanowires,the thin separation layer,and the almost zero penetration resistance of the stainless steel mesh,the prepared TiO₂ nanowire membrane exhibits ultra-high pure water permeability(2.74×10⁶ L?m^-2?h^-1).The stainless steel mesh supported TiO₂nanowires membrane shows superhydrophilic and underwater superoleophobic properties,and can efficiently and quickly separate not only surfactant-free but also surfactant-stabilized oil-in-water emulsions.The separation efficiency is 99.1%,and the permeation flux of emulsion is more than 6000 L?m^-2?h^-1.Also,the stainless steel mesh supported TiO₂ nanowires membrane has photocatalytic performance,and the surface pollutants can also be cleaned by high temperature heat treatment.2.The hydrogen titanate nanofibers with a diameter of 10 nm were coated on a porous metal titanium substrate by means of suction filtration deposition,and porous titanium-supported TiO₂ nanofibers ultrafiltration membrane is prepared by sintering.The average pore diameter of the prepared TiO₂ nanofibers ultrafiltration membrane was 14 nm,and the pure water flux was 940 L?m^-2?h^-1.The thickness of the TiO₂nanofibers coated layer is 5?m,the porosity is 74.8%,and it has superhydrophilic property.Porous titanium supported TiO₂ nanofibers ultrafiltration membrane can efficiently reject bovine serum albumin,the rejection efficiency can reach 98.4%,and the permeate flux is 80 L?m^-2?h^-1.The prepared TiO₂ nanofibers ultrafiltration membrane has excellent anti-fouling performance,and the flux recovery rate?FRR?is97%.In addition,high-temperature heat treatment can eliminate organic pollutants adsorbed inside the TiO₂ nanofibers layer,thereby regenerating the membrane.3.A layer of polyvinylidene fluoride?PVDF?polymer was modified on the surface of TiO₂ nanowire by simple immersion and adsorption methods.The PVDF-modified TiO₂ nanowires membrane is prepared by suction filtration and drying.After modification,PVDF is coated on a TiO₂ nanowire with a thickness of 6 nm.The modification of PVDF makes the surface wettability of the TiO₂ nanowires membrane change,from the original underwater superoleophobicity/underoil superhydrophilicity to the under-liquid dual superlyophobicity.The wettability of PVDF-modified TiO₂nanowires membrane can be reversibly switched between the underwater superoleophobicity and underoil superhydrophobicity.Moreover,the modification of PVDF improves the mechanical strength of the TiO₂ nanowires membrane,and the TiO₂ nanowires membrane changes from the original brittleness to the flexibility.PVDF-modified TiO₂ nanowires membrane can separate not only oil-in-water but also water-in-oil emulsions.The separation efficiency is more than 99.3%.The binary cooperative effect between PVDF and TiO₂ nanowires results in the under-liquid dual superlyophobicity of PVDF-modified TiO₂ nanowires membrane.TiO₂ nanowires provide high roughness surface,PVDF coated layer provides under-liquid dual lyophobicity and collaboratively forms under-liquid dual superlyophobic membrane.The synergistic effect of the TiO₂ nanowires and PVDF layer makes the wetting model of PVDF modified TiO₂ nanowire membrane changes to the Cassie state.