A critical assessment of the methods for intercalating anionic surfactants in layered double hydroxides
A critical assessment of the methods for intercalating anionic surfactants in layered double hydroxides
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DOI：
10.1007/s10853-008-2935-0
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发表时间：
2008-08
影响因子：
4.5
通讯作者：
Lumbidzani Moyo;N. Nhlapo;W. Focke
中科院分区：
文献类型：
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作者：
Lumbidzani Moyo;N. Nhlapo;W. Focke
高纯度的阴离子表面活性剂插层的层状双氢氧化物（LDH）容易通过直接共沉淀法和离子交换法制备，条件是前体含有单价阴离子，LDH-Cl或LDH-NO3。然而，LDH-CO 3是一种有吸引力的起始材料，因为由于其作为聚烯烃中的PVC稳定剂和酸清除剂的大规模应用，其可以散装形式商购获得。因此，探索了十二烷基硫酸盐和十二烷基苯磺酸盐插入具有近似组成[Mg0.654Al0.346（OH）2]（CO 3）0.173· 0.5H2O]的商业（LDH）中。直接离子交换是困难的，因为碳酸盐被牢固地保持。在再生方法中，通过热处理除去它，并通过与在水性介质中形成的层状双氢氧化物反应获得表面活性剂形式。不幸的是，所得产物不纯，结晶不良，并且仅实现部分插层。使用水溶性有机酸，例如，乙酸、丁酸或己酸，以帮助LDH-CO 3的脱碳。嵌入在环境温度下进行，其中前体粉末悬浮在阴离子表面活性剂的水性分散体中。据信羧酸通过促进消除阴离子粘土层中存在的碳酸根离子来辅助插层。
Anionic surfactant intercalated layered double hydroxides (LDH) of high purity are easily prepared via direct coprecipitation and also by the ion exchange method provided that the precursor contains a monovalent anion, e.g., LDH–Cl or LDH–NO3. However, LDH–CO3is an attractive starting material as it is commercially available in bulk form owing to large-scale applications as a PVC stabilizer and acid scavenger in polyolefins. Thus, intercalation of dodecyl sulfate and dodecylbenzenesulfonate into a commercial (LDH) with approximate composition [Mg0.654Al0.346(OH)2](CO3)0.173· 0.5H2O] was explored. Direct ion exchange is difficult as the carbonate is held tenaciously. In the regeneration method it is removed by thermal treatment and the surfactant form obtained by reaction with the layered double hydroxide that forms in aqueous medium. Unfortunately the resulting products are impure, poorly crystallized and only partial intercalation is achieved. Better results were obtained using water-soluble organic acids, e.g., acetic, butyric, or hexanoic acid, to aid decarbonation of LDH–CO3. Intercalation proceeded at ambient temperatures with the precursor powder suspended in an aqueous dispersion of the anionic surfactant. The carboxylic acids are believed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries.