Siebecker Matthew G, Sparks Donald L
University of Delaware , Delaware Environmental Institute (DENIN), Interdisciplinary Science and Engineering (ISE) Laboratory, 221 Academy Street, Newark, Delaware 19716, United States.
J Phys Chem A. 2017 Sep 21;121(37):6992-6999. doi: 10.1021/acs.jpca.7b07940. Epub 2017 Sep 7.
Layered double hydroxides (LDHs) are anionic clays important in disciplines such as environmental chemistry, geochemistry, and materials science. Developments in signal processing of extended X-ray absorption fine structure (EXAFS) data, such as wavelet transformation (WT), have been used to identify transition metals and Al present in the hydroxide sheets of LDHs. The WT plots of LDHs should be distinct from those of isostructural single metal hydroxides. However, no direct comparison of these minerals appears in the literature using WT. This work systematically analyzes a suite of Ni-rich mineral standards, including Ni-Al LDHs, single metal Ni hydroxides, and Ni-rich silicates using WT. The results illustrate that the WT plots for α-Ni(OH) and Ni-Al LDHs are often indistinguishable from each other, with similar two-component plots for the different mineral types. This demonstrates that the WT of the first metal shell often cannot be used to differentiate an LDH from a single metal hydroxide. Interlayer anions adsorbed to the hydroxide sheet of α-Ni(OH) affect the EXAFS spectra and are not visible in the FT but are clearly resolved and discrete in the WT.
层状双氢氧化物（LDHs）是一类阴离子型黏土，在环境化学、地球化学和材料科学等学科中具有重要意义。扩展X射线吸收精细结构（EXAFS）数据的信号处理技术，如小波变换（WT），已被用于识别LDHs氢氧化物层中存在的过渡金属和铝。LDHs的WT图应与同构单金属氢氧化物的WT图不同。然而，文献中尚未使用WT对这些矿物进行直接比较。这项工作使用WT系统地分析了一系列富镍矿物标准样品，包括镍铝LDHs、单金属氢氧化镍和富镍硅酸盐。结果表明，α-Ni(OH)和镍铝LDHs的WT图通常难以区分，不同矿物类型的WT图具有相似的双组分特征。这表明，第一金属壳层的WT通常无法用于区分LDH和单金属氢氧化物。吸附在α-Ni(OH)氢氧化物层上的层间阴离子会影响EXAFS光谱，在傅里叶变换（FT）中不可见，但在WT中能清晰分辨且呈离散状态。
