1. J. W. Dickinson, C.Boxall, F. Andrieux Engineering Department, Lancaster University, Lancaster, LA1 4YW, U.K 2 nd 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

2. Contents 1. PROJECT BACKGROUND 2. FABRICATION OF THE GRAPHENE BASED-MICRO OPTICAL RING ELECTRODE (GB-MORE) 3. EXPERIMENTAL/ RESULTS 4. APPLICATIONS 5. ACKNOWLEDGEMENTS

3. 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:

4. 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 ↓

5. 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.

6. Fabrication of the Electrode Synthesis of Graphite Oxide Layer Preparation Reduction of GO Electrode construction

7. 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.

8. Formation of GO layer on a pre- treated substrate The oxidation procedure incorporates: lactol anhydrides quinone hydroxl Above: GO layer with oxygen groups

9. 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

10. 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

11. 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

12. 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

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

14. Treated 200µm fibre optic dip coated into GO solution followed by hydrazine then thermal reduction treatment

15. 15 monochrom d light light connector gold layer optical glue ball lens optical fibre optical disc electrochemical ring Connect ion of MORE to Light Source

16. Xenon Lamp with mono- chromator Earthed Faraday Cage N2N2 MOREPt wire SCE Autolab with PGSTAT 10 Personal Computer Light Coupler Light Guide Photo-Electrochemistry: Apparatus used

17. Cyclic Voltammetric Analysis of GB-MORE using K 3 Fe(CN) 6 3+ : Dark experiment E θ of K 3 Fe(CN) 6 3-/4- is 0.119V vs SCE [Bard, 2001]. Fe (II) → Fe (III) Fe (II) ← Fe (III)

18. Ru(bipy) 3 2+ h The Ruthenium/Iron, Sensitiser Scavenger System: Light experiment Ru(bipy) 3 2+ * Fe 3+ Fe 2+ Ru(bipy) 3 3+ e-e- Photo current arise due to: Photo-physical, Chemical, Electrochemical reaction

19. Measurement of a Photocurrent at the GB- MORE: the Ru (II) /Fe (III) System Photo transient change in current; E=480mV, [Ru(bipy) 3 2+ ] 10mM, [Fe 3+ ] 5mM, pH=2, white light on and off Light on Light off

20. 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) 3 2+ λmax = 453.2nm

21. Effect on the Steady State Photocurrent as a Function of the Concentration in Ru(bipy) 3 2+ Solution: [Fe(III)]=5mM, [Ru(bipy) 3 2+ ]: as x-axis, pH=2, E=480mV, Using white light

22. 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) 3 2+ ]= 10mM, [Fe(III)]= as x-axis, pH=2, E=480mV, Using white light K SV = 0.7m 3 mol -1

23. 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.

24. 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

25. UO 2 2+ + hv → * UO 2 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. *UO 2 2+ / UO 2 + = (E 0 =2.7V) λ max = 420nm-460nm *PuO 2 2+ / Pu 4+ (E 0 =4.56V) λ max = 350nm

26. Acknowledgements University of Lancaster Professor Colin Boxall Dr Fabrice Andrieux j.dickinson2@lancaster.ac.uk