1

Surface science & catalysis group

Cardiff Catalysis Institute

XPS, AFM & DFT studies of the

functionalization of graphite surfaces

Philip R. DaviesCardiff Catalysis Institute

School of Chemistry, Cardiff University

Cardiff

EP/I038748/1

EP/L000202

David J. Morgan

Robert J. Davies, Thomas Jones,

Jiří Kulhavý, Ryan Lewis

Vaughan Roberts, Amy Lai

Theory

David J. Willock

Carlo Buono

Neil Robinson,

Experimental

Rebecca Burgess

Thomas Legge

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Motivation

• Graphene based sensors

• Intracellular nanodiamond sensors

• Carbon catalyst supports

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1. Washing:

• HCl, HNO3,

Aqua Regia (HCl & HNO3)

2. Impregnation

• HAuCl4, H2PdCl4 etc

in H2O, HCl, HNO3,

Aqua Regia

3. Drying

• 290 oC - 200 oC

Preparation of

carbon supported metals

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Direct synthesis of H2O2

“Switching Off Hydrogen Peroxide Hydrogenation in

the Direct Synthesis Process.”

Edwards, Hutchings et al. Science 323 (2009) 1037

Table 2. Activity and selectivity of pretreated and untreated

carbon-supported catalysts

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………….oxygen surface groups affect not only the preparation, but also

influence the resistance to sintering and the catalytic activity of the catalyst.

Abstract

“The role of carbon materials in heterogeneous catalysis”Francisco Rodriguez-Reinoso, Carbon 1998, 36, 159

“Working with a vacuum, not in one!”

Bob Madix, ACS meeting

Literature

6

Strategy

1. Washing:

• HCl, HNO3,

Aqua Regia (HCl & HNO3)

2. Impregnation

• HAuCl4, H2PdCl4 etc

in H2O, HCl, HNO3,

Aqua Regia

3. Drying

• 290 oC - 200 oC

Preparation of

carbon supported metalsOur study must be:

• Relevant.

• Minimum parameters

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Strategy II

Catalyst

• Carbon powder

• Preparation in air

• Deposition from solution

HOPGHighly ordered

pyrolytic graphite

Surface Science

• Graphite crystal

• UHV

• Vapour deposition

• Surface science tools

HOPG

“Bench top” surface science

• Graphite crystal

• Preparation in air

• Deposition from solution

• Surface science tools

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AFM image of HCl treated HOPG

Clean HOPG surface

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Local delaminationBouleghlimat et al. Carbon, 2013, 61, 124–133.

HCl

• What are the oxygen states?

• How do they affect carbon-metal interactions?

• Local delamination

• Heating to 573 K removes

“bubbles”.

527 532 537 542 Binding energy /eV

O(1s) O(1s) O(1s)

(a) Clean

(b) HCl

(c) HCl/573K

531.5

O(1s)

533.3

532.7

XPS data:

• One oxygen state,

Two states heated to 573 K

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Functional Group Identification

through Chemically Specific DerivitisationD. S. Everhart and C. N. Reilley, Anal. Chem., 1981, 53, 665–676.

C. D. Batich, Appl. Surf. Sci., 1988, 32, 57–73.

OH(a) + CF3C(O)OC(O)CF3 (g) CF3C(O)O-(a) + CF3CO2H(g)

-OH groups

-CO2H groups

-CO2H(a) + CF3CH2OH(g) CF3C(OH)O-(a) + H2O(g)

-C=O groups

-CO(a) + CF3CH2NH-NH2 (g) CF3CH2NH-N=(a) + H2O(g)

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Molecule specific labeling:

Is OH(a) present?

679 684 689 694 699

Binding energy /eV

688.8

(d) HCl/573 K & TFAA

(c) HCl/TFAA

(a) Clean/TFAA

F(1s)

OH(a) + CF3C(O)OC(O)CF3 (g) CF3C(O)O-(a) + CF3CO2H(g)

OH(a)

532.7 eV

527 532 537 542 Binding energy /eV

O(1s) O(1s) O(1s)

(a) Clean

(b) HCl

(c) HCl/573K

531.5

O(1s)

533.3

HCl & HNO3

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Is –CO2H present?

679 684 689 694 699 Binding energy /eV

F(1s)

(a) Clean/TFE

(b) HCl/TFE

(c) HCl/573 K & TFE

688.4

-CO2H

Not significant

-CO2H(a) + CF3CH2OH(g)

CF3C(OH)O-(a) + H2O(g)

527 532 537 542 Binding energy /eV

O(1s) O(1s) O(1s)

(a) Clean

(b) HCl

(c) HCl/573K

531.5

O(1s)

533.3

13527 532 537 542

Binding energy /eV

O(1s) O(1s) O(1s)

(a) Clean

(b) HCl

(c) HCl/573K

531.5

O(1s)

533.3

680 685 690

688.4

F(1s)

(a)

(d)

(c)

Binding energy /eV

Clean

HCl /TFH

HCl /573 K /TFH

-CO(a) + CF3CH2NH-NH2 (g)

CF3CH2NH-N=(a) + H2O(g)

C=O(a)

531.5 eV

OH(a)

532.6 eV

-C-O-C-(a)

533.3 eV

Is C=O present?

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Conclusions: 1

• Acid treatment of HOPG surfaces leads to local

delamination through functionalisation at

defects.

• HCl & HNO3 treatment of HOPG gives

exclusively OH(a) covered surfaces

• Heating to 573 K converts OH(a) to C=O

& C-O-C groups

E. Bouleghlimat et al., Carbon, 2013, 61, 124–133

C. Buono et al, Faraday Discuss., 2014, 173 257–272

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Gold deposition

78 83 88 93 Binding energy /eV

Au(4f)

84.086.5

(a) Clean

(b) HCl /Au

(c) HCl /573 K & Au

84.9

HOPG

OH(a)

195 200 205 Binding energy /eV

Cl(2p)

(a)

(b)

(c)

198.0

199.7

Au0

Au3+

C. Buono et al, Faraday Discuss., 2014, 173 257–272

R. Burgess et al. J. Catalysis, 2015, DOI: 10.1016/j.jcat.2014.12.021

C=O

C-O-C

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AFM images of nanoparticles

deposited on HOPG from HAuCl4(aq)

HOPG

Untreated

HNO3

treated

HNO3

treated and heated

to 573 K

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The stabilisation of gold by different

functional groups: DFT

Adsorption of Au atom in vicinity of:

OH functionalised edge = ~ -1.27 eV

C=O functionalised edge = ~ -0.77 eV

OH functionalised step

CO functionalised step

Flexibility of OH groups allows

additional bonding.

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Increasing HCl concentration:

effect on Gold deposition

• Acid treatment increases HOPG

hydrophobicity!

• Drying time decreased Gold

deposition decreased.

• OH increases nucleation rate

• OH increases extent of Au3+

reduction

80.00 84.00 88.00 92.00

Binding Energy /eV

Au4f

Auo

Au3+

Au+

0.25 M

0.5 M

5.0 M

1.0 M

Clean

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Conclusions

• Acid treatment of HOPG surfaces leads to local delamination

through functionalisation at defects.

• HCl & HNO3 treatment of HOPG gives exclusively OH(a)

• Heating to 573 K converts OH(a) to C=O & C-O-C groups

• Gold nucleation is more rapid on OH(a) covered surfaces.

• Stabilisation of Au on OH(a) is stronger

than on C=O covered surfaces because of

multiple interactions

E. Bouleghlimat et al., Carbon, 2013, 61, 124–133

C. Buono et al, Faraday Discuss., 2014, 173 257–272

R. Burgess et al. J. Catalysis, 2015, DOI: 10.1016/j.jcat.2014.12.021

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Surface science & catalysis group

Cardiff Catalysis InstituteGold 2015

7th International Gold Conference

26th – 29th July 2015 in Cardiff, UK

www.cardiff.ac.uk/gold2015

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Comparison of HCl and HNO3:

Effect of acid concentration II

0.5 M HCl

10 M HCl

10 M

0.5 M

x10

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Clean HOPG surface

Deionised water

Control experiments

Ultra pure water

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Models to account for the features

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XPS

HNO3

HCl

Clean

HNO3

HCl

Clean

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HNO3

HCl

HNO3

HCl

XPS

• No Ca, K, Na

• Maximum O(a) ~ 4% monolayer

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Models to account for the features