Layered materials
{{Short description|Solids with high anisotropic bonding; layers are strongly bonded but weakly bonded to other layers}}
File:Kristallstruktur Cadmiumiodid.png is an example of a layered material. The individual sheets are interconnected by van der Waals forces between the sulfide centers.]]
In material science, layered materials are solids with highly anisotropic bonding, in which two-dimensional sheets are internally strongly bonded, but only weakly bonded to adjacent layers.{{cite book|year=1979|title=Intercalated Layered Materials|editor=Lévy, Francis|isbn=978-94-009-9415-7}} Owing to their distinctive structures, layered materials are often suitable for intercalation reactions.{{cite book |doi=10.1002/9780470132616.ch35|chapter=Layered Intercalation Compounds|series=Inorganic Syntheses|year=1995|last1=Kikkawa|first1=S.|last2=Kanamaru|first2=F.|last3=Koizumi|first3=M.|title=Inorganic Syntheses |pages=181–184|isbn=9780470132616 }}{{cite book |doi=10.1002/9780470132616.ch36|chapter=Lithium Insertion Compounds|series=Inorganic Syntheses|year=1995|last1=Murphy|first1=D. W.|last2=Zahurak|first2=S. M.|title=Inorganic Syntheses |pages=185–191|isbn=9780470132616 }}
One large family of layered materials are metal dichalcogenides. In such materials, the M-chalcogen bonding is strong and covalent. These materials exhibit anisotropic electronic properties such as thermal and electrical conductivity.
Exfoliation
Because the layers bond to each other by relatively weak van der Waals forces, some layered materials are amenable to exfoliation, the complete separation of the layers of the material. Exfoliation can be done using sonication, mechanical, hydrothermal, electrochemical, laser-assisted, and microwave-assisted methods.{{Cite journal |last1=Zheng |first1=Weiran |last2=Lee |first2=Lawrence Yoon Suk |title=Beyond sonication: Advanced exfoliation methods for scalable production of 2D materials |url=https://linkinghub.elsevier.com/retrieve/pii/S2590238521006354 |journal=Matter |year=2022 |language=en |volume=5 |issue=2 |pages=515–545 |doi=10.1016/j.matt.2021.12.010|s2cid=245902407 }}
Typically aggressive conditions are required involving highly polar solvents and reagents.{{cite journal |first1=V. |last1=Nicolosi |first2=M. |last2=Chhowalla |first3=M. G. |last3=Kanatzidis |first4=M. S. |last4=Strano |first5=J. N. |last5=Coleman |display-authors=1 |title=Liquid Exfoliation of Layered Materials |journal=Science |year=2013 |volume=340 |issue=6139 |doi=10.1126/science.1226419 |hdl=2262/69769 |s2cid=177513486 |hdl-access=free }} In the ideal case, exfoliation affords single-layer materials, such as graphene.
Examples
- metal dichalcogenides such as tantalum disulfide,{{cite book|doi=10.1002/9780470132616.ch32|title=Tantalum Disulfide (TaS2) and Its Intercalation Compounds|volume=30|pages=155–169|series=Inorganic Syntheses|year=1995|last1=Revelli|first1=J. F.|last2=Disalvo|first2=F. J.|chapter=Tantalum Disulfide (TaS2 ) and Its Intercalation Compounds |isbn=9780470132616 }} titanium disulfide,{{cite book | last1 = Mckelvy | first1 = M. J. | last2 = Claunsinger | first2 = W. S. | title = Inorganic Syntheses | series = Inorganic Syntheses | year = 1995 | chapter = Titanium Disulfide | volume = 30 | pages = 28–32 | doi = 10.1002/9780470132616.ch7 | isbn = 9780470132616 }} and vanadium disulfide.
- graphite
- iron oxychloride
- layered double hydroxides, ionic solids where intercalated anions are exchangeable.Khan, Aamir I.; O'Hare, Dermot "Intercalation chemistry of layered double hydroxides: recent developments and applications" Journal of Materials Chemistry (2002), 12(11), 3191-3198. {{doi| 10.1039/b204076j}}
- Transition metal dichalcogenide monolayers