Study On Preparation And Performance Of The Hybrid Nanofiltration Membrane With Titanium Dioxide And Polyelectrolyte

Nowadays low permeate flux and unavioding membrane fouling are the mainly drawbacks of nanofiltration. The choice of materials and research of methods for improving the flux and anti-fouling property of membrane had been the improtant researchs. Rencent years, combine of inorganic nanomaterials with special property and organic solvent or high-molecular polymer to prepare organic/inorganic hybrid membrane materials can improve the hydrophily and flux of membrane,which is one of the most effective method to solve the flux and antifouling problem of membrane.In this paper, the TiO2 nanoparticles were modified by the anion and cation polyelectrolyte. The chraged anatase titanium dioxide nanoparticles were prepared by the low temperature precipitation-peptization process(LTPP). The prepared chraged anatase titanium dioxide nanoparticles were mixed with polyelectrolyte to prepared TiO2/polyelectrolyte hybrid nanofiltration membrane, through the layer by layer self-assembly(LbL) method. The nanofiltration separating and self-cleaning property of the hybrid membrane were investigated.First, the anatase TiO2 nanoparticles were synthesized via a low temperature precipitation-peptization process(LTPP) at 50 ℃ precipitation temperature. The chraged and tunable PEI-TiO2 and PSS-TiO2 nanopraticles were obtained by the modification of poly(ethyleneimine)(PEI) and poly(sodium4- styrenesulfonate)(PSS), respectively.X-ray diffraction(XRD) pattern and high-resolution transmission electron microscope(HRTEM) confirmed the anatase crystalline phase. The results showed that the phase of TiO2, PEI-TiO2 and PSS-TiO2 were all anatase. The charges of the prepared TiO2, PEI-TiO2 and PSS-TiO2 nanoparticles were investigated by zeta potentials. The results showed:the zeta potentials of PEI-TiO2 nanoparticles can reach the highest positive charge +69.85 mV at pH 5; with the concentration of PEI solution increased from 1.0wt% to 15wt%, the charge of PEI-TiO2 can be tuned from +39.47 mV to +95.46 mV; the zeta potentials of PSS-TiO2 nanoparticles can reach the highest negative charge-89.48 mV at pH 5; with the concentration of PSS solution increased from 1.0wt% to 15wt%, the charge of PSS-TiO2 can be tuned from-56.63 mV to-119.32 mV. Investigating the adsorption and degradation for dye molecules to compare the photocatalytic activity of the three nanoparticles and the resluts showed that PSS-TiO2>TiO2>PEI-TiO2. The photocatalytic performances of these charged nanoparticles were elucidated by the results of UV-vis diffuse reflectance spectra(DRS) and the photoluminescence(PL) spectra, which indicated that the PSS-TiO2 nanoparticles showed a lower recombination rate of electron-hole pairs than TiO2 and PEI-TiO2.Secondly, highly positive charged PEI-TiO2/PSS hybrid nanofiltration membrane was prepared by PEI-TiO2 nanoparticles and polyanion electrolyte PSS via Lb L method; highly negtively charged PEI/PSS-TiO2 hybrid nanofiltration membrane was prepared by PSS-TiO2 nanoparticles and polycation electrolyte PSS via Lb L method. Which were aimed to improved the dispersibility and stability of the nanoparticles in solution. The variation of Zeta potential values, SEM, AFM, ATR-FTIR were investigated, which proved the successful preparation of TiO2/polyelectrolyte hybrid nanofiltration membrane. The contact wetting angle of the PEI-TiO2/PSS membrane and PEI /PSS-TiO2 can reached to 1.5° and 3.1°, which is characteristic of a superhydrophilic membrane surface.At last, It was found that the positively PEI-TiO2/PSS membranes had excellent metal iron removal capacity. The rejection of Ni2+ and Cd2+ were 91.2% and 85.8%, the flux of Ni2+ and Cd2+ were 147.3 and 167.9 L·m-2·MPa-1·h-1, respectively. In the case of the separation of dye molecule, the negatively PEI/PSS-TiO2 membranes had show well rejection and high flux of xylenol orange(97.8%, 133.9 L?m-2?MPa-1?h-1) and eriochrome black T(96.7%, 140.4 L?m-2?MPa-1?h-1). During the nanofiltration of xylenol orange run, the PEI/PSS-TiO2 membrane showed slowly flux declined with time, which is mainly because of the membrane fouling. After being radiated certain time by UV light, the performance of fouled membranes flux can be recovered to about 70.6%~80.5% of its initial value by simple. This fact indicates that the self-cleaning property have been created on the surface of PEI/PSS-TiO2 membrane which enhanced its stability and life.