| Under the situation of aggravating water contamination and higher demand of water quality and security, membrane technology is drawing the world's attention by its advantages of wide range of application, high effluent quality and no byproducts. Water flux and rejection capacity of membranes are largely influenced by the pore structures of the membranes. Reduction of mass transfer resistance and accurate separation of particles based on the size-diference could be realized by membranes with uniform pore size. However, the traditional immersion-precipitation method can prepare membranes with uniform pore size hardly, while some other methods such as track-etch and block copolymer self-assembly, are difficult to accomplish in large-scale application because of complicated process and high cost. So, a simple, general and tunable method that can produce membranes with uniform pore structure is very meaningful for water treatment.Selecting highly volatile dichloromethane, dioxane or acetone as an organic solvent and nonvolatile liquid such as propylene glycol, diethylene glycol or glycerol as additive. By changing the composition of the casting solution, two kinds of uniform pore morpholoyg were obtained, one is honeycomb on polysulfone, polystyrene, polyvinylidene fluoride and cellulose acetate membrane surface, the other is nanoporous on cellulose acetate membrane. Both the strutures could be explained by the diffuse-in/condense-out behavior of liquid additive. With the fast evaporation of solvent from the top surface of the layer in the spin-casting or vaccum pumping process, both polymer and the nonvolatile additive were immediately concentrated on the surface layer, the additive molecules collide more frequently and finally flock together to form many very small droplets that act as the polymer-lean nucleuses in the polymer solution layer, which is just undergoing phase-inversion, and thus gradually develop into the uniform membrane pores in the membrane solidification process.Compared with those smooth membrane surfaces, the honeycomb pattern can markedly increase the water contact angle and thus the hydrophobicity of the membrane surface. The increment of contact angle can reach to32°,13°, and28°for the PSF, PVDF, and PS membrane with honeycomb pattern, respectively. Nanoscale membrane pore size can be regulated by varying the polymer concentration, to achieve more sophisticated separation of particals with different sizes.Nanoporous CA membranes with mass fraction of5%,7%and9%presented significant effectiveness on removal nano-Au particals with sizes of20nm,13.5nm and5nm.The dense homopore membranes have relative low water flux, but two types of homopore membrane have certain intercept effect of bovine serum albumin, up to97.6% and84.8%. Nanoporous CA membrane has a certain anti-pollution capacity compared with blank dense membrane. In comparison to the dense polysulfone membrane prepared by traditional immersion precipitation method, the homopore membranes have good purifying effects of colliform, suspended particles and organic matter in the Songhua River. The lowest turbidity is0.15NTU, the TOC is1.59mg/L and the UV254is0.011cm-1. The removal rate of Fe, Mn, Al in raw water by the homopore membrane are almost100%, for Ca and Mg,which can not be remove by ordinary ultrafiltration membrane, could be rejected by homopore membranes to certain extents. |
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