Intercalation, Exfoliation, and Assembly of 2D MaterialsThomas E. Mallouk

Departments of Chemistry, Physics, and Biochemistry and Molecular BiologyPennsylvania State University

H3PO4

h-BN

h-BN

2D solids have a broad range of interesting properties

Transition metal dichalcogenides

TiS2, NbSe2, WS2,…

Semi-metals (TiS2)

Semiconductors, catalysts, fluorescent &

topological materials (MoS2, WS2, WTe2)

CDW materials (NbxTa1-xS2)

Intergrowth structures

Semiconductors

Superconductors

Ferroics

Energy storage materials

Lamellar π-bonded nets

Graphite, h-BN,

Cx(BN)1-x, C3N4

Two-dimensional conductors

Metallic, magnetic, and semiconducting ribbons

Atomic membranes

Exfoliated GO

Exfoliation of van der Waals solids, e.g., graphite

K

Kovtyukhova and Mallouk Chem. Mater. 1999

electrochemical oxidation

Li+O3SC8F17-/

CH3NO2

1. S2O82-

H2SO4/P2O5

2. H2SO4/ KMnO4

R.Ruoff et al. J. Mater. Chem. 2006

hydrazinePSS

Bulk graphene materials, but redox cycles induce defects

Graphene suspension

Carbon nanoscrolls

R.B. Kaner et al. Science 2003

M.M. Lerner et al., Chem. Mater. 1996

Exfoliated sheets

K+C8-

Intercalation chemistry: a very long history of redox reactions

0

2

4

6

8

C E g~

5.5

eV h-BN

C

Vacuum level

Elec

tron

ener

gy, e

V c.b.

v.b.

0

1.5

-1.5

3.5

4.5

vs SHE

~ 2 V

Although h-BN is isoelectronic withgraphite, its electronic structure isquite different. Graphite is asemimetal whereas h-BN is a wide gap(~5.5 eV) insulator.

Thus the BN oxidation potential is~ 2V more positive than graphite andits intercalation requires strongeroxidants.

The only example of successful oxidative intercalation of h-BN was reported using the very powerful oxidant S2O6F2 [J. Solid state Chem.1999,147, 74].

Oxidative intercalation of layered boron nitride

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

7.4 A

002 BN

001

002003

004 005004 BN100 BN

Non-redox interalation of h-BN and graphite

* **

* New in-plane reflections

XRD: h-BN/H3PO4

11 11.5 12 12.5 13

7.4 A7.3 A

001

100 nm

1.71.0

0.64

N. I. Kovtyukhova et al., JACS 2013, 135, 8372; Nature Chem. 2014, 6, 957.

2 τηετα

Layers consist of Brønsted- (h-BN), Lewis- (MX2) or π-basic (graphite) sheets.

Anhydrous Brønsted acids (H2SO4, H3PO4, HClO4, alkylsulfonic acids) intercalateto form stage-1 compounds of h-BN & graphite.

XPS, IR, and Raman spectra indicate minimal oxidation and an acid-basemechanism for h-BN and graphite intercalation.

h-BN and graphite intercalation by H3PO4

h-BN/H3PO4

DFT calculations of H3PO4intercalation compounds support the model of host-guest H-bonding in h-BN and strong dipolar interactions in graphite.

H3PO4

h-BN

h-BN

Nina Kovtyukhova Yuanxi Wang Vin Crespi

Delamination by solvent “dissolution”

Versatile method, minimal damage to sheets (like physical delamination)

However, yield of single/few layer sheets is typically very low

Match Hansen solubility parameters (γDispersive, γPolar, γH-bonding) of solvent to solid

Sonication or shear delaminates solid to few-layer and single-layer sheets

J. N. Coleman et al., Science 2011, 331, 568.

H.-L. Zhang et al., Angew. Chem. Int. Ed. 2011, 50,10839.

MoS2, WS2, h-BN, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2,Bi2Te3

Exfoliation of acid-intercalated h-BN and graphite

Once the galleries of h-BN and graphite are opened by intercalation, simple stirring in polar solvents leads to exfoliation to single and few-layer sheets.

Single sheets dominate the distribution.

The yield is markedly higher than that obtained by high power/high shear sonication of the parent solids in polar liquids.

500 nm

500 nm

50 nm

G/H3PO4 + DMF

G/H3PO4 + DMF

500 nm

h-BN/H3PO4 + H2O

3-layer graphene sheet

DM

F

i-PrO

H

C5O

H

3-C

8OH

C8O

OH 20

30405060708090100

0.10.20.30.40.50.60.70.80.9

11.11.21.3

Frac

tion

of

mon

olay

ers,

%

RE

D n

umbe

r

Graphene

Graphene

h-BN

h-BN

HSP= [4(sδD-lδD)2 + (sδP-lδP)2 +(sδH-lδH)2] /Ro

AFM of a monolayer graphene sheet shows solvent occluded at the G/Si interface that is not removed by drying in vacuum.

Characterization of exfoliated graphene

1000

1500

2000

500 1000 1500 2000 2500 3000 3500

G

D 2D1 µm

Exfoliated sheets agglomerate

Raman shift, cm-1

https://commons.wikimedia.org/wiki/File:Molybdenite.GIFhttps://www.webelements.com/compounds/gallium/gallium_sulphide.html

MoS2 MnPS3 GaSehttp://sites.psu.edu/robinsonresearch/

Intercalation/exfoliation of MoS2

BuLi + MoS2 ½ C8H18 + LiMoS2 exfoliated MoS2 + LiOH (aq)semiconducting 2H phase metallic 1T phase

Joensen, P., Frindt, R. F. & Morrison, Mater. Res. Bull. 21, 457–461 (1986).

H2O

But what happens when we use sub-stoichiometric BuLi?

236 234 232 230 228 226 224

Mo 3d5/2

Mo6+

x=0Mo 3d3/2

S 2s

1Tx=0.6

x=0.41T

Binding Energy (eV)

x=0.1

x=0.2

5 10 15 20 25 30 35 40

2θIn

tens

ity Nor

mal

ized

Inte

nsity

**

**

*x=0.6x=0.4x=0.2

x=0.1

2θ

(002)

x=0

*

pure 2H

phase

XPS XRD

Exfoliation of Li0.1MoS2 into trilayer nanosheets

Intercalation-exfoliation at low Li/Mo ratio yields suspensions of trilayer sheets in the 2H structure.

This suggests staging or selective edge intercalation by Li

Xiaobin Fan

X. Fan et al., JACS 138, 5143-5149 (2016).

Intergrowth Structures – CaSi2 to Silicene

H. Nakano et al., J. Am. Chem. Soc., 2012, 134 (12), pp 5452–5455

Intergrowth Structures - MXenes

M. Naguib et al., Adv. Mater. 2011, 23, 4248–4253

Ti3AlC2

Alkali – Transition Metal Oxide Intergrowths

Dion-Jacobson[KCa2Nb3O10]

Ruddlesden-Popper[K 2La2Ti3O10]

Aurivillius[Bi 2O2(W2O7)]

Perovskite[SrTiO3]

• Intergrowths of perovskite and “salt” structures• Interlayers are exchangeable

Layer perovskites

Aurivillius Ruddlesden-Popper(Proton Form)

Ruddlesden-Popper(Alkali Form)

Dion-Jacobson(Alkaline Earth Form)

AII(NO3)2

Perovskite(Non-Defective)

Perovskite(A-Site Defective)

H2, ∆

H2, ∆∆ - H2O

BiOCl, ∆

HCl

Ruddlesden-Popper(Mixed Acid/Alkali)

x AOH

AOH

H+

Gopalakrishnan, et al., JACS 2000, 122, 6237

Sugimoto et al., JACS1999, 121, 11601

Schaak and Mallouk., Chem. Mater., 2002, 14, 1455-1471.

Topochemical reactions of layer perovskites

Rb+ Rb+ Rb+

Rb+ Rb+ Rb+

H+ H+ H+

H+ H+ H+

(Bu)4N+ OH-

Rb2SrTa2O7H2SrTa2O7

SrTa2O6

H2O

H+A-

• Oxide sheets are typically anionic• Intercalation = cation exchange• Exfoliation => layer-by-layer films,

nanoscrolls, composites• Topochemical dehydration/redox rxns

2D => 3D oxide structures

(layer perovskite)

Review: R.E. Schaak & T. E. Mallouk, Chem. Mater. 2002, 14, 1455.

Exfoliation of layered oxides by acid-base reactions

Quantitative yield of crystalline single sheets

Exfoliation of H0.8[Ti1.2Fe0.8]O4·H2O by TBP+OH-

Osmotic swelling drives layer expansionMost effective at low salt concentration (small excess of base)

F. Geng et al., Chem. Comm. 2014, 50, 9977 and Nature Comm. 2013, 4, 1632

Polyelectrolyte layer-by-layer assembly

G. Decher, J. D. Hong, and J. Schmitt, Thin Solid Films 1992, 210, 831-835.

Self-limiting adsorption of polyanions and polycations

Very simple and user-friendly

Fuzzy nanostructures with interpenetration of successively grown "spaghetti" layers

Lasagna noodles from layered phosphates and oxides

Layer-by-layer assembly works by charge inversion

TEM of exfoliated HCa2Nb3O10

AFM of HCa2Nb3O10monolayer

Ellipsometric data for nanosheetlayer-by-layer assembly

S. W. Keller et al., J. Am. Chem. Soc. 1994, 116, 8817.R. E. Schaak et al., Chem. Mater. 2000, 12, 2513.

X-

- - -

- - -+

++

++

+

+

++

+

X-

X- X-

Y-

Y-

- - -

- - -+

+

+

+

+

+

+

+

+

+

Y- Y-

Y-

X-

- - -Na+ Na+ Na+ Na+

- - - - - -++

++

++

Charge-mismatchedpolycation

Lamellar cation exchanger(clay, layer perovskite,…)

polycation

Polymer nanocomposite(charge matched unreactive)

Lamellar anion exchanger

Converting layered oxides to anion exchangers

- Na+

- Na+

20 nm

Intercalating anionic nanoparticles and dyes

Hata, et al., J. Am. Chem. Soc. 2007, 129, 3064, and Chem. Mater. 2007, 19, 79

Blue dye-intercalated

fluoromica/PDDA

Au nanoparticle-intercalated

fluoromica/PAH

Hideo Hata

TBAOH

But something unexpected happened with anionic Rh(OH)3 particles…

1 μm250 nm

50 nm5 nm

10 nm

5 nm

20 nm

RhCl3 in base: 1 min RhCl3 in base: 10 min5% Rh(OH)3 on KCa2Nb3O10 5% Rh(OH)3 on KCa2Nb3O10

“Reverse” ripening of Rh(OH)3 on KCa2Nb3O10

Hata, H.; Kobayashi, Y.; Bojan, V.; Youngblood, W. J.; Mallouk, T. E. Nano Letters 2008, 8, 794-799.

Strayer. M.E., Binz, J.M. Tanase, M., Kamali Shahri, S.M., Sharma, R., Rioux, R.M., Mallouk, T.E., J. Am. Chem. Soc. 2014, 136, 5687-5696.

Anomalously strong binding of Rh(OH)3 and Rh to niobate sheets

“Grind & Bake” Acid Exchange Deposition Flocculation

cKOH

ExfoliateKCa2Nb3O10 HCa2Nb3O10

Rh(OH)3

Measuring interfacial bonding energy by using isothermal titration calorimetry (ITC)

Metal oxidenanosheet

Sample Cell

Metal oxidenanosheet & metal oxide

nanoparticlesᐃH

Periodic trends in interfacial bonding energies

Degree of nanoparticle dispersion and thermal stability correlate with interfacial bonding energy (⊗H)

Metal oxide ΔH (kJ mol-1)

Co(OH)3 -13 ± 4Rh(OH)3 -35 ± 9

[Ir(OH)5(H2O)]2- -83 ± 17

Ni(OH)2 -14 ± 2

CuO -17 ± 3

Ag2O 6 ± 7

Thermal stability of nanoparticles on HCa2Nb3O10

Iridium-83 ± 17 kJ/mol

Silver6 ± 7 kJ/mol

Degree of nanoparticle dispersion and thermal stability correlate with interfacial energy (⊗H3)

DFT calculations correlate with experimental ITC data

• Both theory (gas phase atoms) and experiment (solution phase ions) show strong correlation between interfacial bonding energy and M-O bond strength (ΔHsub-ΔHf).

• With silicate supports, this trend is much weaker. Why?

M. E. Strayer et al., J. Am. Chem. Soc. 2015, 137, 16216–16224.

Experiment Theory

d-acid/base chemistry of transition metals

Leo Brewer

Wayne Goodman

d-electron transfer from late to early transition metals was used by Brewer to explain the extra stability of ZrPt3and related alloys.

L. Brewer, Science 1968, 161,115-122.

Data for monolayer films of metals on TM supports. Large shifts in XPS core-level binding energies and CO TPD maxima can be explained by d-electron transfer from late to early transition metals.

Rodriguez & Goodman, J. Phys. Chem. 1991, 95,4196-4206.

d-acid/base chemistry in metal-support bonding

Late TM clusters donate d-electron density to d-electron poor Nb atoms in the nanosheets (a Brewer-type d-acid/base

interaction)

There is little mixing of Ag and Nb orbitals because of d-orbital energy mismatch

This d-acid/base interaction is not possiblewith main group supports (silicates,

phosphates, alumina…)

M. E. Strayer et al., J. Am. Chem. Soc. 2015, 137, 16216–16224.

Conclusions

Different intercalation/exfoliation strategies are needed for van der Waals and intergrowth 2D materials.

Simple ion-exchange and acid-base interactions lead to quantitative exfoliation of transition metal oxide nanosheets.

Combining physical (sonication, shear) and chemical (acid-base, redox) methods can be effective for van der Waals solids.

Anionic nanosheets act as lasagna noodles in layer-by-layer assembly, which works by charge inversion.

Anomalously strong binding and stabilization of late TM & metal oxide nanoparticles is a result of d-acid/base interactions with early transition metal oxide nanosheets.

Acknowledgments

Hideo Hata Megan Strayer Nina Kovtyukhova Yuanxi Wang Xiaobin Fan Tom Senftle

Renu Sharma (CNST - NIST)Mihaela Tanase (CNST – NIST)Jonathan Winterstein (CNST – NIST)Jeff Miller (Argonne National Lab)

Jason Binz Alyssa Rosas Ritesh Uppuluri Mike Janik Rob Rioux Vin Crespi Maurcio Terrones