Structural Investigation of Zn(II) Insertion in Bayerite an Aluminum Hydroxide
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review
Bayerite was treated under hydrothermal conditions (120, 130, 140, and 150 °C) in order to prepare a series of layered double hydroxides (LDHs) with an ideal composition of ZnAl4(OH)12(SO4)0.5nH2O (ZnAl4-LDHs). These products were investigated by both bulk techniques (PXRD, TEM, and elemental analysis) and atomic level techniques (1H and 27Al solid state NMR, IR and Raman spectroscopy) to gain a detailed insight into the structure of ZnAl4-LDHs and sample composition. Four structural models (one stoichiometric and three different defect models) were investigated by Rietveld refinement of the PXRD data. These were assessed using the information obtained from other characterization techniques, which favored the ideal (non-defect) structural model for ZnAl4-LDH, as e.g. 27Al MAS NMR showed that excess Al was present as amorphous bayerite (Al(OH)3) and pseudoboehmite (AlOOH). Moreover, no evidence of cation mixing, i.e., partial substitution of Zn(II) onto any of four Al sites was observed. Altogether this study highlights the challenges involved to synthesize pure ZnAl4-LDHs and the necessityary use of complementary techniques such as PXRD, elemental analysis and SSNMR for the characterization of the local and extended structure of ZnAl4-LDHs.