Preparation And Properties Of Sulfonated Poly (2,6-dimethyl-1,4-phenyleneoxide)/Mesoporous Silica Hybrid Membranes

Compared with the single component of organic membrane and inorganic membrane, organic-inorganic hybrid membrane which prepared by mixing mesoporous silica and organic polymer,combined the advantages of inorganic materials and organic polymer, and possessed good flexibility, thermal stability, chemical stability and mechanical strength. In this paper, the mesoporous silica (MS) with a certain morphology was synthesized successfully, and mixed with sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide) (SPPO) for preparing organic-inorganic hybrid membranes via solution blending method. Diffusion dialysis experiment of NaOH/Na2WO4 system has been carried out for alkali recovery to detect the separation property of as-prepared membranes. Effects of loading content of mesoporous silica on mechanical and thermal stability, micro-morphology and separation properties of hybrid membranes have been studied. The research will be spread from the following two aspects:Content of the first section was preparation and properties of sodium type sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide)/amino-modified mesoporous silica (Na-SPPO/AMMS) hybrid membranes. Firstly, amino-modified mesoporous silica (AMMS) was synthesized via template method and sol-gel process, transmission electron microscopy images (TEM) and N2 adsorption-desorption curve-results showed that the synthetic AMMS has a uniform pore size and highly ordered pores, pore size at about 5.5nm. Na-SPPO/AMMS hybrid membranes were prepared by solution blending method and the loading content AMMS was 0,2%,4%,6%,8% (mass ratio to Na-SPPO).The water uptake (WR), ion exchange capacity, alkali resistance, mechanical strength, thermal stability and microstructure of as-prepared membranes were tested. The results indicated that the membrane water content between 136.4% -193.6%, ion exchange capacity between 2.13-2.32mmol, swelling degree between 114.9%-186.2%, mass loss rate between 17.1%-25.8%, tensile strength (TS) between 17.7MPa-21.9MPa, elongation at break between 7.5%-12%, initial decomposition temperature (IDT) between 271.3℃-275.8℃. NaOH/Na2WO4 system was involved to simulate alkali recovery properties of membranes via diffusion dialysis process.The results showed that the introduction of AMMS might solve the "trade-off’ effect between flux and selectivity to some extent:UOH and S reached 0.0115 m/h and 37.4 at 25℃ while loading content of AMMS was 2%, which was increased by 13.9% and 34.1% compared with the pure SPPO membrane; UOH and S reached 0.02 m/h and 31.7 at 55℃ while the loading content of AMMS is 6%, but the S values of the pure SPPO membrane is only 11.6 at the same temperature. There was two reasons for this:1) Incorporation of AMMS restricted the mobility of SPPO chain and reduced the void structure of the membranes which limited the penetration of WO42-; 2) The mesoporous structure and -NH2 of the AMMS increased the transport channel of OH-, and promoted the transmission of OH- while blocking the transmission of WO42-.The second part is preparation and properties of hydrogen type sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide)/amino-modified mesoporous silica (H-SPPO/AMMS) hybrid membranes. A series of H-SPPO/AMMS hybrid membranes were prepared by solution blending method, the loading content of AMMS was 0,2%,4%,6%,8%(mass ratio to H-SPPO).The water uptake (WR), alkali resistance, mechanical strength, thermal stability and microstructure of as-prepared membranes were tested. The results indicated that the membrane water uptake between 36%-42%, the swelling degree between 49.7%-60.5%, mass loss rate between 8%-16.6%, tensile strength between 26MPa-31MPa, breaking elongation rate between 10%-24%, initial decomposition temperature between 255℃-262℃. NaOH/Na2WO4 system was involved to simulate alkali recovery properties of membranes via diffusion dialysis process. The results showed that when the loading content of AMMS was 2%, the hybrid membrane exhibit excellent selectivity:at 35 ℃, the separation factor reached to 51.9, which was increased by 17.7% compared with pure SPPO membrane; at 55℃, UOH and S reached to 0.0115 m/h and 39.8, which was increased by 5.5% and 11.8% compared with the pure SPPO membrane. There might be two aspects for this:1) The mesoporous structure can facilitate the transfer of water molecules; 2)The acid-base pairs formed between the amino group on the surface of AMMS and the sulfonic acid group in H-SPPO provides an auxiliary channel for the transfer of OH-, which promoted the transportation of OH’ions and hindered transport of WO42- ions.