J. W. Dickinson, C.Boxall, F. AndrieuxEngineering Department, Lancaster University, Lancaster, LA1 4YW, U.K

2nd year PhD

The Development of the Graphene Based Micro-optical Ring Electrode:

Application as a Photo-electrochemical Sensor for Actinide

Detection

j.dickinson2@lancaster.ac.uk

Contents

1. PROJECT BACKGROUND

2. FABRICATION OF THE GRAPHENE BASED-MICRO OPTICAL RING ELECTRODE (GB-MORE)

3. EXPERIMENTAL/ RESULTS

4. APPLICATIONS

5. ACKNOWLEDGEMENTS

• The development of the Graphene Based Micro-Optical Ring Electrode (GB-MORE) as a photo-electrochemical sensor for:

• Selective

• Quantitative

measurements of actinide species in a range of nuclear processed waste streams.

• Actinides show good electrochemistry on carbon based electrodes which show

durability when being operated in highly corrosive conditions [Kwon, 2009;

Wang, 1995].

This project is aimed at:

• Small size allows measurement in small volumes

• Possibility of calibration less use [Szabo, 1987]

Microelectrode Advantages

Convergent analyte diffusion field associated with micro-ring electrodes results in:

• Enhanced material flux

• Rapid attainment of the steady state • Short response time

Easy to construct and low costs

↓

Carbon based electrode materials include:

• Glassy carbon

• Graphite

• Graphene

Why Graphene?

A single graphene layer has a thickness of ~0.355nm [Ni, 2007]

Graphene exhibits ballistic electron mobility resulting in super conducting electrical properities.

A high density of defect states on graphene flakes provide a loci for promoting electron transfer.

Fabrication of the Electrode

• Synthesis of Graphite Oxide

• Layer Preparation

• Reduction of GO

• Electrode construction

Top-Down formation of single layer graphite oxide from bulk graphite powder.

1. Bulk graphite

2. The oxidative procedure incorporates oxygen functionalities between the carbon layers forcing them apart

3. Heavy sonication in solution separates these layers forming single layers of GO

1.2. 3.

Formation of GO layer on a pre- treated substrate

OH

O

O

O

OC

OH

CC

OOO

OO

OO

OH

O

CO

HO O

OHOH

OHOH

OH

O

O

O

OO

O OO

O

O

The oxidation procedure incorporates:

• lactol

• anhydrides

• quinone

• hydroxl

Above: GO layer with oxygen groups

Graphite oxide flake →

Chemical and Thermal Reduction:

•Reduction By chemical treatment using hydrazine vapour and thermal

annealing

• Removes a majority of the oxygen functionalities and produce a conducting

layer.

3-Aminopropyltriethoxysilane →

Quartz substrate →

Reduced/conducting top side

The Synthesis of Graphite Oxide (GO) via a Modified

Hummers Method.Recovered product is subsequently washed with a total 0f 40L of dilute acid solutions

Collected Filter Cake of Washed Graphite Oxide

• Solutions of GO are made from the

dried material and heavily sonicated to

delaminate the layers of graphite oxide.

• 0.1- 10wt% solution loadings

• TGA analysis

Bottom-up formation of homogenous GO layers

• Dip coating of pre-prepared quartz

substrates using GO solutions

•These solutions can now be:

- Evaporation cast

- Spin coated

- Dip coated

• Multiple dip coats can be used to increase

layer thickness

Above: Dip coated GO on quartz

Left/ Above: Tapping mode AFM image of the reduced GO surface topography

Treated 200µm fibre optic dip coated into GO solution followed by hydrazine

then thermal reduction treatment

15

monochromd

light

light connector

gold layer

optical glue

ball lens

optical fibre

optical disc

electrochemical ring

Connection of MORE to Light Source

Xenon Lampwith

mono-chromator

Earthed Faraday Cage

N2

MORE

Pt wire

SCE

Autolab with PGSTAT 10

Personal Computer

Light Coupler

Light Guide

Photo-Electrochemistry: Apparatus used

Cyclic Voltammetric Analysis of GB-MORE using K3Fe(CN)63+:

Dark experiment

Eθ of K 3Fe(CN)63-/4- is 0.119V vs SCE [Bard, 2001].

Fe (II) → Fe (III)

Fe (II) ← Fe (III)

Ru(bipy)32

+

h

The Ruthenium/Iron, Sensitiser Scavenger System: Light experiment

Ru(bipy)32+

*

Fe3+

Fe2+Ru(bipy)3

3+

e-

Photo current arise due to: Photo-physical, Chemical, Electrochemical reaction

Measurement of a Photocurrent at the GB- MORE: the Ru(II)/Fe(III) System

Photo transient change in current; E=480mV, [Ru(bipy)32+] 10mM, [Fe3+]

5mM, pH=2, white light on and off

Light onLight on

Light offLight off

Spectral response of Ru(II)/Fe(III) at GB-MOREVariation of steady state photocurrent as a function of irradiation wavelength

at the MORE. pH=2

Ru(bipy)32+

λmax = 453.2nm

Effect on the Steady State Photocurrent as a Function of the Concentration in Ru(bipy)3

2+

Solution: [Fe(III)]=5mM, [Ru(bipy)32+]: as x-axis,

pH=2, E=480mV, Using white light

2

( ) ( )2 2 1

( )2 1

[ ] [ ][ ]

II IIIs ph

IIIk o

nFD I Ru a k Fei b a

k X k k Fe

SV

o

kkk

erceptintslope 1

1

2

1( )

2 2( )

2 1

[ ]11

[ ]

IIs ph o

IIIk

nFD I Ru a kb a

i k X k Fe

Literature Stern Volmer quencher constant = 0.9 m 3 mol-1 [Lin & Sutin, 1976]

Effect on the Photocurrent as a Function of the Concentration in Iron(III)

Solution: [Ru(bipy)32+]= 10mM, [Fe(III)]= as x-axis,

pH=2, E=480mV, Using white light

KSV= 0.7m3 mol-1

Conclusion

Graphene Based Micro- Optical Ring Electrodes have been

successfully fabricated with inner/ outer ring ratios >0.99.

Highly reversible electrochemistry has been observed in the

absence of any illuminating wavelength.

Very promising results have been obtained towards meeting the

aim of this project during photo-electrochemical experiments.

Applications of the GB-MORE

• As a sensor for monitoring photo active species

• As a calibration less sensor

• selective

• quantitative

• actinide species in a range of nuclear processed waste streams

• Ability to differentiate between two or more actinide species

UO22+ + hv → * UO2

2+

Further Work:

• To investigate dark electrochemistry of the uranyl ion on GB-MOREs

• To investigate the photo-electrochemistry of the uranyl ion using ethanol as

quencher in acidified aqueous media using the GB-MORE [Nagaishi, 2002]

• Study the results obtained using theoretical architecture [Andrieux, 2006]

• Look at further selectivity of GB-MORE in other species.

• Provided that the λmax of given actinide species is sufficiently separated

differentiation between two or more species in solution should be possible.

*UO22+/ UO2

+ = (E0=2.7V)

λmax = 420nm-460nm

*PuO22+/ Pu4+ (E0=4.56V)

λmax = 350nm

Acknowledgements

University of Lancaster

Professor Colin Boxall

Dr Fabrice Andrieux

j.dickinson2@lancaster.ac.uk