Crosby Sergio, Tran Doanh, Cocke David, Duraia El-Shazly M, Beall Gary W
Department of Chemistry and Biochemistry, Texas State University, 601 University Drive, San Marcos, TX 78666, USA.
Department of Chemical Engineering, Lamar University, 4400 South MLK, Beaumont, TX 77705, USA.
Materials (Basel). 2014 Oct 17;7(10):7048-7058. doi: 10.3390/ma7107048.
Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere with the study of other anion containing systems, particularly if formed at room temperature. The dehydroxylation and decomposition of carbonate occurs simultaneously, making it difficult to distinguish the dehydroxylation mechanisms directly. To date, the majority of work on understanding the decomposition mechanism has utilized hydrotalcite precipitated at room temperature. In this study, evolved gas analysis combined with thermal analysis has been used to show that CO₂ contamination is problematic in materials being formed at RT that are poorly crystalline. This has led to some dispute as to the nature of the dehydroxylation mechanism. In this paper, data for the thermal decomposition of the chloride form of hydrotalcite are reported. In addition, carbonate-free hydrotalcites have been synthesized with different charge densities and at different growth temperatures. This combination of parameters has allowed a better understanding of the mechanism of dehydroxylation and the role that isomorphous substitution plays in these mechanisms to be delineated. In addition, the effect of anion type on thermal stability is also reported. A stepwise dehydroxylation model is proposed that is mediated by the level of aluminum substitution.
水滑石在催化、废水处理、基因传递和聚合物稳定化等方面有许多重要应用，这些应用都取决于制备历史和处理情况。在催化和聚合物稳定化中，热分解非常重要。水滑石容易与大气中的二氧化碳反应生成，并且常常干扰其他含阴离子体系的研究，特别是在室温下形成时。碳酸盐的脱羟基作用和分解同时发生，使得直接区分脱羟基机理变得困难。迄今为止，大多数关于理解分解机理的工作都使用了在室温下沉淀的水滑石。在本研究中，逸出气体分析与热分析相结合已被用于表明，在室温下形成的结晶性差的材料中，二氧化碳污染是个问题。这导致了关于脱羟基机理本质的一些争议。本文报道了水滑石氯化物形式的热分解数据。此外，还合成了具有不同电荷密度和在不同生长温度下的无碳酸盐水滑石。这些参数的组合使得能够更好地理解脱羟基机理以及同晶取代在这些机理中所起的作用。此外，还报道了阴离子类型对热稳定性的影响。提出了一种由铝取代水平介导的逐步脱羟基模型。
