James Dickinson UNTF2010

Report
The Development of the Graphene
Based Micro-optical Ring Electrode:
Application as a Photoelectrochemical Sensor for Actinide
Detection
J . W. D i c k i n s o n , C . B o x a l l , F. A n d r i e u x
E n g i n e e r i n g D e p a r t m e n t , L a n c a s t e r U n i v e r s i t y,
L a n c a s t e r, L A 1 4 Y W, U . K
2 nd y e a r P h D
[email protected]
Contents
1 . P R O J E C T B A C KG R O U N D
2 . FA B R I C AT I O N O F T H E G R A P H E N E B A S E D - M I C R O
OPTICAL RING ELECTRODE (GB -MORE)
3 . E X P E R I M E N TA L / R E S U LT S
4 . A P P L I C AT I O N S
5. ACKNOWLEDGEMENTS
This project is aimed at:
• 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].
Microelectrode Advantages
•
Small size allows measurement in small volumes
•
Possibility of calibration less use [Szabo, 1987]
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
↓
Why Graphene?
Carbon based electrode materials include:
• Glassy carbon
• Graphite
• 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
The oxidation procedure incorporates:
• lactol
• anhydrides
• quinone
• hydroxl
Above: GO layer with oxygen groups
Reduced/conducting top side
Graphite oxide flake →
3-Aminopropyltriethoxysilane →
Quartz substrate →
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.
Recovered
product is
subsequently
washed with a
total 0f 40L of
dilute acid
solutions
The Synthesis of Graphite
Oxide (GO) via a Modified
Hummers Method.
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
•These solutions can now be:
- Evaporation cast
- Spin coated
- Dip coated
• Multiple dip coats can be used to
increase layer thickness
• Dip coating of pre-prepared quartz
substrates using GO solutions
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
Connection of MORE to Light Source
15
optical glue
gold
layer
optical
disc
light connector
monochromd
light
optical fibre
ball
lens
electrochemical
ring
Photo-Electrochemistry: Apparatus used
Light Guide
Light Coupler
Autolab with PGSTAT 10
Xenon
Lamp
with monochromator
N2
MORE
Earthed Faraday Cage
Pt wire
SCE
Personal Computer
Cyclic Voltammetric Analysis of GB-MORE using K3Fe(CN)63+:
Dark experiment
4.3a MORE pH 2 Nitric 5mM Fe(CN)6
6.00E-08
Fe (II) → Fe (III)
4.00E-08
2.00E-08
-0.6
-0.4
0.00E+00
-0.2
0
75mV/s
0.2
0.4
0.6
0.8
1
1.2
100mV/s
125mV/s
-2.00E-08
150mV/s
i/A
-4.00E-08
175mV/s
200mV/s
-6.00E-08
225mV/s
Background solution
-8.00E-08
-1.00E-07
-1.20E-07
Fe (II) ← Fe (III)
E/V
Eθ of K 3Fe(CN)63-/4- is 0.119V vs SCE [Bard, 2001].
The Ruthenium/Iron, Sensitiser Scavenger
System: Light experiment
Ru(bipy)33+
Fe2+
eh
Ru(bipy)3
2+
Fe3+
Ru(bipy)32+*
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
-4.05E-09
1130
Photo Current i/A
-4.10E-09
Time (s)
1150
1170
1190
1210
Light on
Light on
-4.15E-09
-4.20E-09
Light off
-4.25E-09
Light off
Spectral response of Ru(II)/Fe(III) at GB-MORE
Variation 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)32+
Solution: [Fe(III)]=5mM, [Ru(bipy)32+]: as x-axis,
pH=2, E=480mV, Using white light
i 
n FD s I p h  [ Ru
k2
( II )
]
a
X k2
 k 1[ Fe ( III ) ] 
b a 
( III ) 
 k o  k 1[ Fe ] 
2
2
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
( II )
1  n FD s I p h  [ Ru ]
 

i
k2

1
−
iph
/ pA-1
a
X k2

2
2
b a 


1
slope


ko
1
( III ) 
k 1[ Fe ] 

5.00E+10
4.50E+10
4.00E+10
3.50E+10
3.00E+10
2.50E+10
2.00E+10
1.50E+10
1.00E+10
5.00E+09
0.00E+00
int ercept

ko
k1

y = 1E+10x + 7E+09
R² = 0.9857
KSV= 0.7m3 mol-1
0
0.5
1
1.5
2
2.5
3
3.5
1
−
/m3 mol-1
[Fe(III)]
Literature Stern Volmer quencher constant = 0.9 m 3 mol-1 [Lin & Sutin, 1976]
1
k SV
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
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]
UO22+ + hv → * UO22+
• 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) *PuO22+/ Pu4+ (E0=4.56V)
λmax = 420nm-460nm
λmax = 350nm
Acknowledgements
University of Lancaster
Professor Colin Boxall
Dr Fabrice Andrieux
[email protected]

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