Layered Materials, Preparation of Nanocomposites and Catalysts Utilizing Nanostructured Materials Flashcards
What do you understand with the term “layered material”?
2D-materials (atomic scale sheets) held together by weak forces in the z-direction. Anisotropy in chemical bonding in xy-direction relative to z-direction.
What is delamination, exfoliation and reconstruction? Explain in brief, aspects connected to chemical bonding in the 3D layered materials relative to their ability to delaminate/exfoliate. Give examples of layered materials where layers are held together by van der Waals forces, H-bonding, electrostatic forces and polar covalent bonding.
- Delamination/exfoliation: Separating the layers of a layered material
- Reconstruction: Put layers together again in a certain manner to produce (new) properties
(Handbook in clay science definition:
- Exfoliation: Total separation of layers from each other
- Delamination: Still some interaction between layers)
1) vdW - graphite - easily exfoliated
2) H-bonding, electrostatic forces - LDHs - stronger, but still exfoliatable (from formamide and sonication)
3) polar covalent bonding - RP-oxides - stronger bonds in z-direction, harder to separate layers from each other
Chemically and mechanically, how can you facilitate exfoliation?
Chemical
- Intercalation: Introducing particles between layers
- Exchange: Switch out already present particles in the intergallery layer with other particles
Mechanical
- Sonication: Disperse sheets in a solution by applying sound energy to agitate the layers
- Scotch-tape: Remove a layer of graphene from graphite with tape :)
Explain in brief the atomic arrangement in graphite, h_BN and h_MoS2.
- What do you think about these materials ability to delaminate/exfoliate?
- Suggest specific applications of the delaminated/exfoliated constituents of these three compound.
Graphite, h_BN and h_MoS2 forms interconnected 6-rings –> forms 2D layers connected by weak vdW-forces.
- Easy to separate with exfoliation, used widely as lubricants
- They have insulation properties, often used to increase heat resistance
What is layered double hydroxide, and how will you describe its crystal structure? Why is this class of compounds often found very interesting for applications? What do you think is "the driving force" of the delamination process of the layered double hydroxide MG(masse) in formamide.
LDH: Ionic solid materials with layers of metals (cations) with OH-group under and above. Between these 2D-layers, there are neutral molecules (eg water) or anions
Easy to exchange anions between layers. Used in batteries and as catalysts.
Delamination process driving force: H attached to formamide will interact strongly with NO3-anions between layers.
Suggest why 2D nanosheets may be an excellent starting point to create nanostructures giving rise to materials with enhanced properties.
Starting from 2D materials gives good control over the material, and maintain the atomic arrangement and chemical composition as the mother material.
Suggest an approach what would allow you to form metallic Ni NPs anchored on an oxide composed of an Al-, Mg-mixed oxide, Ni/Mg(Al)O. Discuss key factors that would allow you to manipulate the chemical structuring in the LDH or the catalyst Ni/Mg(Al)O.
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Which type of Bragg-reflections would you expect NOT to observe for the corresponding 2D nanoflakes of a LDH material? Why?
What species do you believe is attached to the surface of the 2D-nanosheets?
As there is no long range order in the z-direction, these reflections will not show.
Layers must be charge neutral.
Outline the principles behind preparing the RGO/NiFe-LDH nanocomposite. What is the main objective of forming the nanocomposite rather than mixing RGO and NiFe-LDH mechanically?
At which length scale can you at best assume the mixing of the two constituents to be at, and which type of chemical analysis would you perform to document the nanostructuring? Justify answer.
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In the work of Leng et al., 2D hybrid perovskites are formed via delamination of Ruddlesden-Popper type phases. The optic properties of the compounds change when going from bulk to monolayers. Suggest an explanation to this. Additionally, would you expect a more “classic” RP-phase as La4Ni3O10 to delaminate? Justify
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What do we mean with the terms “homogeneous catalysis” and “heterogeneous catalysis”?
- Homogeneous: Catalyst and reactants are in same phase (e.g. liq-liq)
- Heterogeneous: Catalyst has different phase than the reactants (e.g. solid catalyst with gaseous reactants)
Supported catalyst can be formed by classic impregnation routes or by depositing colloidal free-standing nanoparticles directly onto the support. Outline the latter approach, and explain briefly potential benefits and issues in the preparation route. Suggest ways to document successful characterization of the as-synthesized catalyst.
- NP coated with org.surf. with hydrophobic and -philic end (e.g. oleic acid). Immersed in beaker with support (e.g. Al2O3) dispersed in solvent (e.g. hexane). Solvent evaporated, left with surf-coated NPs. NP oxidized at HT to remove organic ligands, then reduced in H2 –> well-dispersed NP on support.
- Beneficial: Better control of size/shape.
- Issue: Complicated and time consuming, requires organic precursor that must be removed.
- TEM images. EDX for elemental analysis. FT-IR to check for organic residue.
What do you understand with the term “metal-on-support interaction”? Elaborate on how this interface can affect catalytic performance and the stabilization of a metal particle on the support material. Suggest also why particles with different faceting may act differently as catalyst for a specific chemical reaction.
The interface between the metal and the support brings interesting properties (particle and surface)
With reference to the lecture notes “Catalysis utilizing nanostructured materials” suggest explanations to why there is an optimal Pt-cluster size for the water-splitting active nanocomposite Pt/CdSe.
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