The Role of Covalent Functionalization in the Thermal Stability and Decomposition of Hybrid Layered Hydroxides

Abstract

Hybrid organic-inorganic materials represent one of the hottest research topics in materials science. The close structureproperty relationship exhibited in these materials gives rise to a wide variety of applications in fields ranging from biomedicine, catalysis or magnetism to energy storage and conversion. [1-4] Layered and 2D systems, especially those based on earthabundant metals, are playing a key role in the hybrid materials family. The possibility of combining their physical, chemical, and mechanical properties, and the precise control over their structures, placed them in a privileged position. [5-12] Among others, layered hydroxides (LHs) offer a broad range of possibilities due to their tunable chemistry, which allows to modify at will both the inorganic layers and (in)organic intercalated anions. [13] Layered double hydroxides (LDHs) constitute the most famous member of the LHs family exhibiting purely electrostatic sheet/anion interactions. These lamellar systems display hydrotalcite-like structures composed of positive charged sheets where both M II and M III octahedral cations can be tuned. [14] In line with that, hybrid LDHs have been proposed, among others, used for stimuli-responsive materials, or as a precursor for the synthesis of carbon-based nanocomposites of interest in energy storage and conversion. [15-17] In all cases, the main properties are governed by the chemical nature of both components (inorganic host and organic guest) and the interaction between them, which is always electrostatic. In the search of new levels of functionality and complexity, different functionalization strategies have been explored, mainly based in the covalent functionalization (e.g., sylilation) of the interface, resulting in improved absorption properties but slight modifications of the magnetic or electrochemical properties. [18] Along this front, α-Co II hydroxides (or simonkolleite-like structures) are positioned as key members in the LHs family, because they can be considered as naturally occurring covalently functionalized LHs. They present two coordination environments, octahedral centers-Co II (O h)-within the layers, as in the case of LDHs and tetrahedral ones-Co II (T d)-attached to both sides by 3OH bridges. The fourth position can be used to graft different inorganic to organic ligands (Scheme 1). [19] The electronic and magnetic properties can be tuned by changing ligand and/or Co II (T d) ratio, resulting in more conductive systems (mainly by ligand to metal charge transfer) with higher magnetization temperatures (T M) as to the related LDHs. [20-22] Moreover, as recently reported by our group, in hybrid α-Co II hydroxydicarboxylates, Co 5 (OH) 8 [(CH 2) n (COO) 2 ] with n ranging from 1 to 8, the magnetic behavior can be dramatically modified by changing the parity of the organic linker: whereas odd members present T M < 20 K the even ones have T M > 55 K. [23] These results demonstrate that the nature of the interaction between the inorganic layers and the organic guest is crucial for determinin...

Crystallographic and Geometrical Dependence of Water Oxidation Activity in Co-Based Layered Hydroxides

“…The estimation of the intralayer ( a ) parameters can be extracted from the 110 reflections at higher 2θ values, corresponding to ca 3.18, 3.06, and 3.14 for β-LH, LDH, and α-LH phases, respectively. As expected, the lower a value for the LDH is based on the incorporation of a smaller cation such as Al III ( O h ) within the layers (Co O h II = 0.745 Å; Al O h III = 0.535 Å). , Table S1 compiles the cell parameters as a function of LH phases, which are in good agreement with previous reports. ,, …”

Crystallographic and geometrical dependence of water oxidation activity in Co-based layered hydroxides

“…The sharper and more defined band observed in the case of the ɑ-LH phase is attributed to a higher water confinement degree. 38 In the particular case of the LDH structure, the bands at 1345 and 800 cm -1 confirm the incorporation of carbonate molecules, which was to be expected considering that the synthetic method uses urea as an alkalinization agent. 39 Finally, signals below 1000 cm -1 are associated with Co-O stretching and Co-OH bending vibrations.…”

“…As expected, the lower a value for the LDH is based on the incorporation of a smaller cation such as Al III (O h ) within the layers ( Å; Å). 37,38 26,32,39 Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR) also provides valuable structural information about each LH phase, as depicted in Figure 1B. The β-LH phase can be distinguished by the presence of an intense and sharp band at around 3630 cm -1 attributed to the O-H stretching mode, characteristic of free-OH groups in brucite-like structures.…”

Influence of Fe-clustering on the water oxidation performance of two-dimensional layered double hydroxides

“…This technique arises as a powerful way to analyse the presence of ligands, impurities, and track the thermal evolution of LDH samples. 48,49 Fig. 2A shows the thermogravimetric analysis of both samples.…”