Preparation And Properties Of Poly (Aryl Ether Sulfone) Composite Ultrafiltration Membranes

With the increase of population and the rapid development of industrialization,the massive discharge of domestic sewage and industrial wastewater not only causes the serious waste of water resources but also poses a threat to human health and safety.Therefore,the purification of wastewater is responsible for the national economy and people’s livelihood.Compared with traditional separation methods,membrane separation technology has the advantages of energy saving,environmental protection and simple operation in wastewater treatment.However,in the practical application,there are some problems such as low permeation flux,low selectivity,poor anti-fouling performance and serious trade-off effect.The problems are closely related to the morphology structures and chemical properties of membranes itself.Therefore,in this paper,poly(aryl ether sulfone)materials with excellent comprehensive performance are used as the ultrafiltration(UF)membrane materials.Starting from the membrane itself,the morphology structure and chemical properties of poly(aryl ether sulfone)UF membrane are modified by different methods to obtain the membranes with high permeability flux,high selectivity and excellent anti-fouling performance.First,the simple and general modification method?blending modification,will be chosen.Specifically,a kind of hydrophilic but insoluble sulfonated hyperbranched polyether sulfone(SHBPES)was successfully synthesized via a series of chemical reactions.SHBPES acted as the filler was blended with polyethersulfone(PES)to prepare a series of PES composite UF membranes.It can be found that the addition of SHBPES enhanced the hydrophilicity and porosity of the membranes,and then the permeability and anti-fouling performance of the membranes were improved.When the addition of SHBPES was 30%,the corresponding membrane M3 exhibited the best performance.Its pure water flux reached 265.4 L/m2 h,which was 1.8 times higher than that of pure PES membrane.The BSA rejection rate and flux recovery rate reached 98.2% and 82.7%,respectively.However,the magnitude of the flux increase was not satisfactory.Therefore,in order to greatly improve the water flux of the membrane,halloysite nanotubes(HNTs)with medium hollow tubular structure was introduced.This porous structure can be used as a water transport channel and improve the porosity of the membrane to a greater extent.Meanwhile,in order to enhance the hydrophilicity and compatibility with the matrix materials of HNTs,the SHBPES in the previous chapter was used to decorate the HNTs to obtain HNT-SHBPES.Then,HNT-SHBPES as the filler was blended with PES to prepare a series of hybrid membranes.The addition of HNT-SHBPES significantly improved the hydrophilicity and porosity of the membranes.Compared with pure PES membrane,the permeability and anti-fouling performance of the hybrid membranes were significantly enhanced.When the addition of HNT-SHBPES was 8%,the corresponding membrane exhibited the best performance.Its pure water flux reached 351.6 L/m2 h,which was 2.2 times higher than that of pure PES membrane.This was mainly the result of the synergistic effect of hydrophilic-SO3 H of SHBPES and porous HNTs.Meanwhile,the hybrid membranes owned high permeability with a high level of rejection and then the trade-off effect was weakened,which was attributed to the good compatibility between HNT-SHBPES and PES matrix.However,from the point of view of large-scale industrial production and application,the compatibility between filler and matrix always exists in blending modification,especially inorganic nano-materials.It is difficult to guarantee the defectfree properties of the membranes in preparation and the durable stability of their properties in application.Therefore,by mean of bulk modification,phenolphthalein(PPL)containing hydrophilic carboxy were introduced into the molecular framework of polysulfone(PSF)via nucleophilic condensation polymerization,and then a series of carboxylated polysulfone copolymers(PSF-COOH)were synthesized successfully and were used as membrane materials to prepare UF membranes via phase separation method.With the increase of the content of carboxyl group in the molecular framework of copolymer,the hydrophilicity and porosity of the corresponding UF membranes gradually increased,the thickness of skin layers became thinner and the upper surface changed from dense to porous,which resulted in significant improvement of the permeability and anti-fouling performance of the membranes.When the molar ratio of PPL was 1,the membrane exhibited the best performance,mainly reflected in the pure water flux as high as 329.6 L/m2?h that was 2.65 times that of PSF,the maximum flux recovery rate of 92.5%,and the BSA rejection rate of 94.6%.Finally,in order to further develop new properties and applications of UF membranes,tight ultrafiltration membranes that can effectively separate dyes with the smaller size were prepared via simple phase separation method.Specifically,carboxyl potassium salt polysulfone PSF-COOK60% was selected as the filler and carboxylated polysulfone PSF-COOH60% as the membrane matrix material to prepare the composite membranes.With the increased addition of PSF-COOK60%,the viscosity of the casting solutions,the electronegativity,hydrophilicity and the thickness of skin layer of the mixed matrix membranes greatly enhanced,while the morphology of the upper surface changed from porous to dense.When the mass ratio of PSF-COOK60% and PSF-COOH60% was 3:7,the membrane M3 exhibited the maximum electronegativity,the minimum aperture as small as 1.825 nm.It belonged to the tight ultrafiltration membrane(TUF)and showed outstanding separation efficiency of dye/salt mixtures,mainly reflected in the rejection rate of dyes over 95.5%,the rejection rates of Na Cl and Na2SO4 as low as 5.6%,and a higher pure water flux of 153.8 L/m2?h?bar that far exceeded the water flux of the traditional nanofiltration membranes.Additionally,M3 possessed excellent anti-dyefouling performance and showed wide application conditions including solution p H,temperature,pressure.