Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane
Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane
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DOI：
10.1021/es049453k
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发表时间：
2005-03-15
影响因子：
11.4
通讯作者：
Suzuki, T
中科院分区：
文献类型：
--
作者：
Kim, SH;Kwak, SY;Suzuki, T
本文用正电子湮没寿命谱(PALS)解释了以二甲基亚砜(DMSO)为界面聚合添加剂制备的TFC膜的通量增强机理。与非添加剂膜相比，TFC膜的水通量有很大提高，最高可达5倍。原子力显微镜(AFM)研究表明，当DMSO在水相溶液中通过减小不相容溶液的溶解度差来增加水和有机相间的相容时，表面粗糙度和比表面积增大。X射线光电子能谱(XPS)分析表明，通量增强型TFC膜的化学组成发生了明显的变化，膜中的交联酰胺键显著增加。通过PALS研究评估了这些结构变化对分子尺寸自由体积性质的影响。PALS结果首次实验表明，交联芳香族聚酰胺反渗透膜由两类孔组成，一类是网状孔，半径约为2.1-2.4埃；另一类是聚集孔，距离tau(4)约3.5-4.5埃。界面聚合过程中DMSO的加入增加了网络孔的大小和数量，显著提高了水通量。团聚体孔隙的大小也会增加，并可能有助于提高水分通量，尽管随着网络孔隙的增加，聚集孔隙的数量不可避免地会减少。基于Sourirajan等人建立的反渗透孔流模型，详细描述了反渗透性能与o-Ps寿命参数之间的关系。
In this study, positron annihilation lifetime spectroscopy (PALS) is applied to explain the flux-enhancement mechanism in thin-film-composite (TFC) membranes prepared by using dimethyl sulfoxide (DMSO) as an additive in the interfacial polymerization. The TFC membranes show a large increase in water flux, up to 5-fold, compared to nonadditive membrane. Atomic force microscopy (AFM) shows that surface roughness and surface area increase when DMSO in the aqueous phase solution phase works to increase miscibility of the aqueous and the organic phase by reducing the solubility difference of two immiscible solutions. X-ray photoelectron spectroscopy (XPS) reveals the variation of the chemical compositions to the extent that there is a considerable increase in the crosslinked amide linkages of the flux-enhanced TFC membranes. The effects of these structural changes on the molecular-size free volume properties are evaluated by PALS studies. The PALS results are the first to experimentally show that the thin films of cross-linked aromatic polyamide RO membranes are composed of two types of pores having radii of about 2.1-2.4 angstrom from tau(3), network pore, and 3.5-4.5 angstrom from tau(4), aggregate pore. The increase in the size and number of network pores by means of DMSO addition during interfacial polymerization enhances the water flux notably. The size of aggregate pores also increases and may contribute to enhance water flux, although their number inevitably decreases as the number of network pores becomes increased. Details on the correlations between RO performances and o-Ps lifetime parameters are clearly described based on the pore-flow model of reverse osmosis developed by Sourirajan et al.