xDLVO理论解析微滤膜海藻酸钠污染中pH值影响机制

用extended Derjaguin-Laudau-Verwey-Overbeek(xDLVO)理论定量解析不同pH值下海藻酸钠微滤膜污染过程中的界面相互作用,评价范德华力(LW)、双电层作用力(EL)、极性力(AB)对海藻酸钠微滤膜污染的相对贡献.结果表明,在pH5~9范围内,AB相互作用能起着关键作用,决定了总界面相互作用能的性质与强度.不同pH值下海藻酸钠微滤膜污染趋势(K)为pH 5 > pH 7 > pH 8 > pH 9. 由于与海藻酸钠之间的界面作用为引力,疏水性膜在过滤初期膜污染更为严重;污染后期亲、疏水性膜污染行为差异不明显,因为此时海藻酸钠之间的排斥性界面作用为主导.初始、后期阶段K值分别与膜-海藻酸钠界面自由能、海藻酸钠-海藻酸钠界面自由能有较强的线性相关性,说明xDLVO理论可以有效预测不同pH值下海藻酸钠微滤膜污染行为.

The impact of pH on microfiltration membrane fouling by sodium alginate: mechanism analysis using xDLVO theory.

Extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory was used to quantitatively evaluate the role of interfacial interactions, i.e. Lifshitz van der Waals (LW), acid-base (AB) and electrostatic (EL) interactions, involved in microfiltration (MF) membrane fouling by sodium alginate (SA) at various pH. In the pH range of 5~9, the AB interaction energy played a dominant role and determined the nature and magnitude of the total interaction energy. As pH increased from 5to 9, fouling potential (K) for SA fouling of MF membrane decreased in the order of pH 5 > pH 7 > pH 8 > pH 9. During initial filtration stage, the hydrophobic membrane was subject to more severe fouling due to its attractive total interfacial interaction with SA. During subsequent fouling stage, no significant difference was found between fouling behaviors of hydrophobic and hydrophilic membranes because of the identical repulsive interfacial interaction between SA themselves for both membranes. Fouling potentials of initial and subsequent fouling stages correlated well with the interfacial free energies of membrane-SA and SA-SA combinations, respectively. This indicated that the xDLVO theory could effectively predict SA fouling behavior of MF membrane at different solution pH.