Fabrication And Properties Of Novel Organic-inorganic Negatively Charged Hybrid Nanofiltration Membranes

In a wide range of biochemical, pharmaceutical, food, textile printing and othermodern industries, it is a common problem to separate and remove electrolyte fromorganic matter. Nanofiltration (NF) membrane technology, as a kind of high efficiency,energy saving and environmental sepreating technology, is widely used in the field ofremoving salts from organics. Conventional NF membrane, make it possible toremove monovalent salt from organics; but it is impossible to romove divalent ions.Then, in this paper, a series negatively charged NF membrane with loose skin layerwere prepared by means of blending-phase inversion, expecting the membranes couldachieve a higher permeation performance for tha salts, especially for the divalent ionsand highly-charged metal ions, as well as a higher retention for the organics. Themain contents are as follows:(1) HNTs-SO3H nanoparticles containing sulfonic acid group and HNTs wereprepared and blended into PES casting solutions as nanofillers. HNTs-SO3Hnanoparticles were synthesized by chemical modification of HNTs with3-Methacryloxypropyltrimethoxysilane, then anchoring phenyl group onto the surfaceof the HNTs by distillation-precipitation, lastly introducing the sulfonic acid grouponto the HNTs by sulfonation of the modified HNTs in concentrated sulfuric acid. Themorphology and performance of the membranes were characterized by SEM, contactangle, and permeation test. The hybrid membranes were shown to be morehydrophilic, with a smooth surface at the same time. Besides, when the content ofHNTs-SO3H was3%, the IEC of the hybrid membrane was0.05mmol/g, which was59.4%higher than that of pure membrane; and at0.4MPa, the retention for the dyesmaintained above85%; but for the MgSO4and MgCl2, the retention were13.63%and7.5%, respectively.(2) HNTs were modified successfully by polymerization of sodiumstyrenesulfonate monomer onto surfaces of HNTs via ATRP, and then negativelycharged hybrid nanofiltration membranes were fabricated by adding various contentsof HNTs-poly(NASS) composites using phase inversion method. The SEM resultsdemonstrated that the adding of the HNTs-poly(NASS) did not change the structure ofthe membrane. Besides, the water flux of the hybrid membranes increased with theincrease of HNTs-poly(NASS) contents. The molecular weight cut-off (MWCO) was estimated through permeation tests using different PEG solutions, and the MWCOwas about700g/mol, and the pore size was about0.7nm. What is more, at0.4MPa,the retention for the dyes reached85%; for the MgSO4and MgCl2, the retentions were13.63%and7.5%, respectively; and the retention order was Na2SO4> MgSO4>MgCl2> NaCl.(3) SiO2sol was prepared through sol-gel method, and then the2-Bromoisobutyryl Bromide was anchored on the surface of the SiO2. Finally,SiO2-poly(NASS) was synthesized by ATRP, followed by developingSiO2-poly(NASS)/PES hybrid membrane via phase inversion method. When thecontent of SiO2-poly(NASS) was3%, the contact angle of the hybrid membrane was57.3o, which was31.4%lower than that of the pure membrane.The pore size wasabout0.7nm, which was in the range of NF membrane. The retention for the dyesreached85%, but for the salts, the retention was lower than15%, making it possibleto separate salts from dyes.Given the fact that the apparent difference of the retention for the dyes and thesalts, it was expected to use in the sepreate salts from dyes, especially for the divalentions and highly-charged metal ions, establishing the foundation for the purification ofthe dyes.