| Membrane technology is one of the most attractive research areas in the 21st century, the applications of membrane technologies cover almost every fields such as environmental protection, electronics, energy and biology. Water treatment membrane technology is the subject with much concern, with the increasingly serious water problems, membrane technology used in water treatment has attracted the attention of many researchers. Flat sheet ultrafiltration membrane have better anti-fouling property, better mechanical strength, simpler maintenance and cleaning than other membranes, so that the membrane can be stable for operation in a long term. Because of its excellent characteristics, poly(vinylidene fluoride) is very suitable as a material for the preparation of flat sheet membranes.Flat sheet membrane was often used in large water treatment equipment, which needs membrane with good permeability. This study prepared the membrane via immersion precipitation phase inversion method, while used dimethylacetamide as solvent. Different additives were added into the casting solution to control the pore size and its distribution. And the effects of polymer content, solvent, additive components on membrane performance was studied in this research. The results showed that, in the casting solution, the greater water flux came with the lower polymer mass fraction, when the PVDF mass fraction was 16%, under 15kPa operation pressure, the water flux of membrane can be up to a level of 92.7 L·m2·h. PVP is a large molecular weight hydrophilic additive which enhances the pore formation, when its mass fraction was 5%, the flux reached 152.1 L·m-2·h, while the original membrane water flux was only 69.7 L·m-2·h. The mass fraction of PVP should be 2% or less, if the content of PVP is too high, it will cause the unwanted membrane pore loose structure, and reducing quality of treated water. PEG-400 is a low molecular weight additive, which can control the size and distribution of the membrane pores, while combined with PVP. This study showed that, when the PVDF mass fraction was 18%, with 2% content PVP as pore form additive and glycerol controlling membrane surface pore structure, the water flux of the membrane reached 97.4 L·m-2·h(under 15kPa operation pressure), while the quality of treated water is good.Membrane pollutant was usually deposited onto membrane surface, so it is effective to modify the membrane surface for improving the anti-fouling performance of membrane. UV-initiated graft is a simple, mild, stable method to modify the membrane surface. In the base-modification of membrane, the permeability of membrane was improved. Then the anti-fouling performance of membrane was improved by UV-initiated surface grafting. The membrane was illuminated by common ultraviolet light source. The grafting reaction was initiated by highly charged cerium ion initiator. And the modification used N’N-methylene-bis-acrylamide and N- vinyl-2-pyrrolidone as monomer. The effects of irradiation time, monomer concentration, initiator concentration on membrane anti-fouling properties was observed The results showed that irradiation time should be 3 min, for longer irradiation time it will cause the water flux of membranes reduction; MBA monomer concentration should not be too high, satisfactory membrane performance was obtained when the monomer concentration is 0.07mol·L-1.Due to the cerium ions initiator is easy to hydrolyze, the initiator concentration should not be too low, it must have at least initiator concentration of 0.04mol·L-1. Then, a good modification membrane was obtained. Under the above conditions, the membrane flux recovery rate has improved significantly, from 40% to 91.3%. And membrane surface contact angle decreased from 77.7 to 50.0 degrees. By analysis of scanning electron microscopy and surface total reflectance infrared, the membrane surface became smooth, and was introduced the hydrophilic amide groups after modification.Modified two-step method was used in this study, because its simplification and efficiency. It has a good solid performance to enhance the water flux and anti-fouling property of the membrane. This research will have an important reference value for large-scale production of high-performance PVDF membranes. |
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