Fabrication And Separation Performance Of Novel Microporous Silica Hybrid Membranes

Due to many advantages with good acid/alkali resistance,thermal stability,designed and controlled pore-size,microporous silica membranes had increasing application prospects in gas separation,pervaporation,desalination,catalytic membrane reactors and other fields in recent years.However,with rich hydroxyl groups on the surface of amorphous inorganic silica membranes,it was easy to cause the collapse of Si-O-Si membrane framework thus showing poor hydrothermal stability under a high-temperature water vapor conditions.Therefore,amorphous inorganic silica membranes are limited to their large-scale application due to such these disadvantages.Generally,the silica hybrid membranes were prepared by modification with organic groups and doped with metal in silica framework to improve hydrothermal stability.In this thesis,the aluminum-doped SiO₂ hybrid membranes and naphthyl group modified SiO₂ hybrid membranes were designed and prepared by the sol-gel method for enhanced hydrothermal stability.The preparation conditions and separation performance of the two novel SiO₂ hybrid membranes were systematically investigated.The details results were as follows:（1）The Al-1BTESE-2TEOS-SiO₂ hybrid membranes were successfully prepared by sol-gel method with 1,2-bis（triethoxysilyl）ethane（BTESE）and tetraethyl orthosilicate（TEOS）as silane precursors and Al（NO3）3?9H2O as aluminum source.The synthesized sols and hybrid membranes were characterized by TG,FTIR,XPS,BET,SEM and so on.Moreover,the influence of preparation conditions such as Al doped amount,the mole ratio of BTESE/TEOS,and calcination temperature on the silica hybrid membrane microstructure and separation performance were also investigated.The results showed that,compared with SiO₂ hybrid membranes undoped aluminum,the Al-doped silica hybrid membranes prepared under the optimized conditions（Si/Al=9.5/0.5,BTESE/TEOS=1/2,calination temperature of 250 oC）exhibited an excellent desalination performance in the pervaporation desalination test.For 3.5 wt% NaCl feed solution,the permeation flux of 3.2 kg?m-2?h-1 and rejection ratio over 99.9% were obtained at 25 oC,meanwhile the flux of 6.1 kg?m-2?h-1 and rejection ratio of 97.8% were also achieved at 75 oC.It is significantly higher than those of most silica-based membranes reported in current literature for desalination performance.In addition,such these Al-doped silica hybrid membranes showed good hydrothermal stability in a continuous test under different temperature and different concentrations of NaCl solution.（2）The organic-inorganic silica hybrid membranes containing naphthyl functional groups in the framework were successfully prepared by sol-gel method with 1-naphthyltriethoxysilane（NTEOS）as the precursor and γ-glycidoxypropyltrimethoxysilane（KH560）as silane coupling agent.Combined with the characterization results of TG,FTIR,BET and SEM,the influence of prepared conditions such as the amount of KH560,H2 O and HCl,and calcination temperature on the silica hybrid membrane microstructure and separation performance were investigated in details.The optimized preparation conditions were as follows: NTEOS/KH560/H2O/HCl/EtOH=1/0.2/30/0.2/9,and calcination temperature of 500 oC.Compared with amorphous inorganic SiO₂ membranes,it could easily control the membrane pore size,beneficially enhance hydrothermal stability and acid resistance thus improve separation performance of silica hybrid membrane by introducing naphthyl groups into the SiO₂ framework.The naphthyl group modified SiO₂ hybrid membranes exhibited high permeation flux of 76.1 L?m-2?h-1 and rejection ratio over 99.0%,respectively,during the filtration separation process for 7.5 mg·L-1 methylene blue solution.Moreover,there were maybe synergistic effect of molecular sieving and electrostatic adsorption during the sepration process for dyes wasterwater treatment.Due to effects of concentration polarization and membrane fouling,the tested membranes were calcined at 400 oC for recycle treatment.It showed that such these silica hybrid membranes after 5 cycles still remained the good separation performance and corresponding good cycling stability.