Preparation And Properties Of PVA/Nano-TiO₂ Hybrid Membrane Based On Diffusion Dialysis

Organic-inorganic hybrid membranes have favorable application prospect in the diffusion dialysis process because of their outstanding strength, flexibility, thermal and chemical stability as well as the other combination properties compared with the single-component membranes. In this article, poly (vinyl alcohol) (PVA) and nano-TiO2 were incorporated to prepare a series of PVA/nano-TiO2 hybrid membranes by blending the two component directly. The as-prepared membranes were used for alkali recovery from NaOH/Na2WO4 mixture by diffusion dialysis successfully and the relationship between structure of membranes and separation efficiency was detected systematically.The article was stated as follows:1.Original nano-TiO2 and pre-crosslinked PVA solution were used to prepared membrane and the optimum membrane-forming conditions were selected referring to the results of diffusion dialysis.At first, we carried out experiments and obtain the optimum thermal treatment temperature(130℃). Then PVA/nano-TiO2 hybrid membranes were prepared with the mass fraction of nano-TiO2 to PVA were 0,1%,2%,3%,4% and 5% under this membrane formation condition, respectively. XRD, SEM, TEM, TGA, mechanical test, water uptake(WR) and alkali durability tests were carried out to study the structure and properties of hybrid membranes. Separation efficiency was detected by the system of NaOH/Na2W04 through diffusion dialysis process. The results showed that addition of nano-TiO2 improved the membrane properties effectively, including thermal stability, mechanical stability and alkali durability. Dialysis coefficient of OH-(UOH) increased while the separation factors (S) were within an acceptable range. The hybrid membranes possessed optical properties while the loading content of nano-TiO2 was 2%, i.e., UOH and S was 0.0127m/h and 55.5 at room temperature, respectively.2.-SO3H was introduced to the surface of nano-TiO2 with the modification of 3-mercaptopropyltriethoxysilane(T-MPTS) and the oxidation of H2O2. Hybrid membranes were prepared by blending pre-crosslinked PVA and sulfonated nano-TiO2 suspension.The formations of Ti-O-Si on the surface of nano-TiO2 were confirmed by the results of FT-IR and TGA. XRD, SEM, TEM, TGA, element analysis, mechanical properties test and alkali durability test were carried out to character structure and properties of hybrid membranes. The separation efficiency of as-prepared membranes was studied by the system of NaOH/Na2 WO4 through diffusion dialysis process. Results indicated that the addition of sulfonated nano-TiO2 increased UOH while decreased the separation factor of hybrid membranes. Meanwhile, mechanical property and alkali resistance of membranes decreased slightly as the increasing addition of nano-TiO2. For the further study, the membrane showed highest performance with the UOH of 0.015m/h and S of 30.1 while the addition percentage of sulfonated nano-TiO2 is 3%.3.1,3-propanesultone was used to modified nano-Ti02 to introduce -SO3H into surface of nano-TiO2 directly and then hybrid membranes were prepared by blending pre-crosslinked PVA and sulfonated nano-TiO2.FT-IR, TGA and element analysis were used to confirm the successful sulfonation of nano-TiO2. XRD, SEM, TEM, TGA, element analysis, mechanical property and alkali resistance test were applied to demonstrate structure and properties of hybrid membranes. The separation efficiency of as-prepared membranes was tested by the system of NaOH/Na2WO4 mixture through diffusion dialysis process. The results showed that sulfonated nano-TiO2 dispersed better in PVA matrix compared with original nano-TiO2. Addition of sulfonated nano-TiO2 improved the UOH and S obviously while mechanical property and alkali resistance of membranes decreased slightly. For the father study, the membrane demonstrated highest performance with the UOH of 0.022m/h and S of 32.7 while the addition percentage of sulfonated nano-TiO2 is 3%.Introduction of sulfonated nano-TiO2 increased the ion flux of the hybrid membranes and the reasons were as follows:On the one hand, the exchangeable-SO3H accelerated transport of Na+ and hydroxyl of PVA provided assistant transport of OH- through hydrogen bond; On the other hand, sulfonation of nano-TiO2 increase the interfacial compatibility between PVA and nano-TiO2, which may improve the compatibility of nano-Ti02 and polymer matrix and the density of hybrid membranes. Thus, transport of WO42- become more difficult and separation property of hybrid membranes improved.