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首页> 外文期刊>Separation and Purification Technology >Relation between salt rejection and electrokinetic properties on Shirasu porous glass (SPG) membranes with nano-order uniform pores
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Relation between salt rejection and electrokinetic properties on Shirasu porous glass (SPG) membranes with nano-order uniform pores

机译：具有纳米级均匀孔的Shirasu多孔玻璃（SPG）膜的排盐率与电动特性之间的关系

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The salt rejection by Shirasu porous glass (SPG) membranes having nano-order uniform pores was investigated for understanding the electrokinetic mechanism resulting from the surface charge developed on the membrane when in contact with salt solutions. Due to the dissociation of the hydroxyl groups such as silanol groups on the membrane surface, the membrane was negatively charged over a pH range of 3-10 from electrophoretic measurements. Cross-flow filtration experiments showed that up to 63% of NaCl was rejected by an SPG membrane having a mean pore diameters of 33 nm in a 1 mol m~(-3) NaCl solution at pH 7 under a transmembrane pressure of 74 kPa, even though the pore diameter is much larger than the ion diameter. This is a consequence of the electrostatic repulsive interaction between the co-ions (Cl~- ions) and the membrane surface. At the same pH, the rejection factor of NaCl decreased with increasing salt concentration due to an increase in the ionic strength. More negative charge on the membrane surface at higher pH resulted in higher rejection factors of NaCl for a fixed salt concentration. Higher rejection factors of NaCl by SPG membranes with smaller pore sizes for a fixed concentration are due to the higher ratio of the thickness of the electric double layer (Debye length) to the pore radius. The SPG membrane showed a salt rejection sequence: Na2SO4, NaCl and CaCl2 at the same pH. This is because divalent anions (SO_4~(2+)) are more strongly repelled by the negatively charged membrane, while divalent cations (Ca~(2+)) adsorb specifically onto the membrane surface than monovalent cations (Na~+). The salt rejection factor increased with increasing permeate volume flux. Due to the stronger acidity of the membrane materials, SPG membranes had a higher rejection factor and a lower isoelectric point (IEP<3) than ceramic membranes.
机译：研究了具有纳米级均匀孔的Shirasu多孔玻璃（SPG）膜对盐的排阻作用，以了解与盐溶液接触时在膜上形成的表面电荷导致的电动机理。由于在膜表面上羟基如硅烷醇基的解离，根据电泳测量，膜在3-10的pH范围内带负电荷。错流过滤实验表明，在74 kPa的跨膜压力下，在pH值为7的1 mol m〜（-3）NaCl溶液中，平均孔径为33 nm的SPG膜最多可以去除63％的NaCl，即使孔径远大于离子直径。这是共离子（Cl-离子）与膜表面之间静电排斥相互作用的结果。在相同的pH值下，由于离子强度的增加，NaCl的截留率随盐浓度的增加而降低。在较高的pH值下，膜表面更多的负电荷会导致在固定盐浓度下NaCl的排斥系数更高。对于固定浓度的孔径较小的SPG膜，NaCl的截留系数较高，这是由于双电层厚度（德拜长度）与孔径的比率较高。 SPG膜在相同的pH值下显示了脱盐顺序：Na2SO4，NaCl和CaCl2。这是因为二价阴离子（SO_4〜（2+））被带负电荷的膜所排斥，而二价阳离子（Ca〜（2+））则比一价阳离子（Na〜+）更特异性地吸附在膜表面。脱盐率随渗透液通量的增加而增加。由于膜材料的酸性更高，因此SPG膜比陶瓷膜具有更高的排斥因子和更低的等电点（IEP <3）。

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