Synthesis and Thermal Degradation of MAl4(OH)12SO4·3H2O with M = Co2+, Ni2+, Cu2+, and Zn2+

Anders B.A. Andersen, Christian Henriksen, Qian Wang, Dorthe Bomholdt Ravnsbæk, Lars Pilsgaard Hansen, Ulla Gro Nielsen*


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The synthesis and thermal degradation of MAl4(OH)12SO4·3H2O layered double hydroxides with M = Co2+, Ni2+, Cu2+, and Zn2+ ("MAl4-LDH") were investigated by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, powder X-ray diffraction, Rietveld refinement, scanning electron microscopy, scanning tunnel electron microscopy, energy-dispersive X-ray spectroscopy, and solid-state 1H and 27Al NMR spectroscopy. Following extensive synthesis optimization, phase pure CoAl4- and NiAl4-LDH were obtained, whereas 10-12% unreacted bayerite (Al(OH)3) remained for the CuAl4-LDH. The optimum synthesis conditions are hydrothermal treatment at 120 °C for 14 days (NiAl4-LDH only 9 days) with MSO4(aq) concentrations of 1.4-2.8, 0.7-0.8, and 0.08 M for the CoAl4-, NiAl4-, and CuAl4-LDH, respectively. A pH ≈ 2 for the metal sulfate solutions is required to prevent the formation of byproducts, which were Ni(OH)2 and Cu3(SO4)(OH)4 for NiAl4- and CuAl4-LDH, respectively. The thermal degradation of the three MAl4-LDH and ZnAl4-LDH in a nitrogen atmosphere proceeds in three steps: (i) dehydration and dehydroxylation between 200 and 600 °C, (ii) loss of sulfate between 600 and 900 °C, and (iii) formation of the end products at 900-1200 °C. For CoAl4-LDH (ZnAl4-LDH), these are α-Al2O3 and CoAl2O4 (ZnAl2O4) spinel. For NiAl4-LDH, a spinel-like NiAl4O7 phase forms, whereas CuAl4-LDH degrades by a redox reaction yielding a diamagnetic CuAlO2 (delafossite structure) and α-Al2O3.

TidsskriftInorganic Chemistry
Udgave nummer21
Sider (fra-til)16700-16712
StatusUdgivet - nov. 2021

Bibliografisk note

Funding Information:
Dr. Dennis Wilkens Juhl, Dr. Frederik Wendelboe Lund, and Prof. Per Morgen are thanked for assistance with 950 MHz NMR data at the University of Aarhus, the X-ray diffractometers, and SEM/EDS measurements, respectively. The chalcoalumite specimen was kindly donated by Assoc. Prof. Tonci Balic-Zunic, Copenhagen University. This work was funded by the Danish Council for Independent Research (grant: DFF-7014-00198) and the access to instruments at the Danish Center for Ultrahigh-Field NMR Spectroscopy funded by the Danish Ministry of Higher Education and Science (AU-2010-612-181).

Publisher Copyright:
© 2021 American Chemical Society.


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