Sustainability from intercalation compounds

Intercalation chemistry has been known for a long time. In fact, the first acknowledged intercalation process is the insertion of sulfate ions in graphite by Schauffautl in 1841.¹ Who could have foreseen that this was going to be the basis of a very important energy storage device in the 20^th and 21^st centuries and, about 180 years later, lead to the Nobel Prize for research in the area? Professors John B. Goodenough, Stanley Whittingham and Akira Yoshino were the 2019 Nobel Prize awardees in Chemistry for their pioneering work on a lithium battery concept associating electrode materials with host structures and intercalation processes.

Over time, intercalation into several types of compounds comprising 2D-layered structures and, recently, 3D-framework materials has flourished. As a matter of fact, IUPAC's Gold Book defines the intercalation reaction as a reversible process, in general described as the insertion of a guest into a host without major modification of the host,² and presents two important characteristics of the process: (i) it can refer to the insertion of a guest species into a one-, two- or three-dimensional host structure; and (ii) contrary to occupying random positions in the host, the intercalation process provides predetermined positions for the guest in the host structure.

Readers will observe that these two characteristics appear across all the articles in this themed issue. The vast majority of contributions deal with layered double hydroxides (LDH), recognized since the commencement of the field as very interesting and versatile matrices to develop intercalation processes. Some deal with the capacity of these materials to be used as carriers of drugs (DOI: 10.1039/D0NJ00045K), simple bioactive organic molecules (DOI: 10.1039/D0NJ00238K) or borate for agronomic usage (DOI: 10.1039/C9NJ06042A and DOI: 10.1039/C9NJ04952E), and how to use them in chemical separation devices (DOI: 10.1039/C9NJ05771D). Others highlight the use of LDH in composite preparation with polymers (DOI: 10.1039/C9NJ06444C and DOI: 10.1039/C9NJ06322F) or the preparation of core@shell hybrid materials (DOI: 10.1039/C9NJ06341B). The application of ternary LDH as electrocatalysts for oxygen evolution is reviewed in the context of sustainability (DOI: 10.1039/D0NJ00021C).

Original synthesis methods are also discussed here. The influence of molecular anions on the thermal properties of LDH is also under examination (DOI: 10.1039/C9NJ06441A), besides evidence for the formation of radical anions in Co-based LDH (DOI: 10.1039/D0NJ00380H).

Theoretical calculations appear in this issue in the area of gibbsite-based LDH solid structure analysis (DOI: 10.1039/C9NJ06454K), as well as in the investigation of the electronic structure of zirconium amino-phosphonates (DOI: 10.1039/C9NJ06278E).

Natural clays are also good matrices for intercalation. In fact, the synthesis of saponite is the subject of one contribution (DOI: 10.1039/D0NJ00253D) to show how an already known synthesis method can be modified to render objects full of details and particularities. The same type of solid is used to recover lanthanide ions (DOI: 10.1039/C9NJ05983K), while clay intercalation compounds are shown to be useful for drug-delivery systems (DOI: 10.1039/C9NJ06433H).

Hydrated layered silicates were reviewed (DOI: 10.1039/C9NJ06222J) in this issue, showing how they are interesting and still full of different aspects to discover. Their porosity was also carefully examined by vapor adsorption (DOI: 10.1039/D0NJ00389A) without the influence of thermal pre-treatment. Carbon dioxide adsorption is presented here with the use of composites constituted by a mesoporous silica (KIT-6) and a Metal Organic Framework (CPO-27-Mg, DOI: 10.1039/C9NJ06358G).

Graphite intercalation compounds (GIC) are represented by the superconducting GIC's of Sr, Ba and Yb (DOI: 10.1039/C9NJ06423K), while a reversible chemical transformation in a luminescent two-dimensional Eu(III) coordination polymer is shown in the aqueous phase (DOI: 10.1039/C9NJ06075H). Upconversion from near-infrared (NIR) to green is shown for Nb-layered perovskites co-doped with Yb and Er ions (DOI: 10.1039/D0NJ00261E).

Finally, the lithiation mechanism of iron trifluoride was revealed by operando X-ray absorption spectroscopy and the combination of Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) chemometric tools (DOI: 10.1039/C9NJ06321H).

This issue is a very concentrated selection of interesting studies of intercalation compounds showing that, from the first discoveries, the breadth of studies and materials has increased considerably, encompassing several fields from biology/health studies to new materials for energy conversion, superconductivity, mechanisms of intercalation and so forth. It is an expanding area, as it has been since ca. a century ago, which finds applications in very different fields, as well as in efforts concerning environmental issues.

It has been a pleasure to put together this themed issue; we hope that the NJC readership enjoys reading it as much as we have enjoyed compiling it. Finally, we would like to acknowledge Mike Andrews and Paige Boxhall for their invaluable efforts and support in producing this themed issue.

 

Prof. Fabrice Leroux, Prof. Heloise de Oliveira Pastore and Prof. Vera Regina L. Constantino

Co-Guest Editors of NJC Themed Issue

References

1. Intercalation Chemistry, ed. M. S. Whittingham and A. J. Jacobson, Academic Press, New York, 1982, Preface.
2. IUPAC, Compendium of Chemical Terminology, The Gold Book, Compiled by A. D. McNaught and A. Wilkinson, Blackwell Scientific Pub., Oxford, 2nd edn, 1997.

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