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J. W. D ickinson, C.Boxall , F. Andrieux

The Development of the Graphene Based Micro-optical Ring Electrode: Application as a Photo-electrochemical Sensor for Actinide Detection. J. W. D ickinson, C.Boxall , F. Andrieux Engineering Department, Lancaster University, Lancaster, LA1 4YW, U.K 2 nd year PhD.

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J. W. D ickinson, C.Boxall , F. Andrieux

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  1. The Development of the Graphene Based Micro-optical Ring Electrode: Application as a Photo-electrochemical Sensor for Actinide Detection J. W. Dickinson, C.Boxall, F. Andrieux Engineering Department, Lancaster University, Lancaster, LA1 4YW, U.K 2nd year PhD 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. 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].

  4. 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 ↓

  5. 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.

  6. Fabricationof 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. • 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 3. 2. 1.

  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. 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.

  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 • 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

  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. optical glue optical disc light connector monochromd light optical fibre ball lens electrochemical ring Connection of MORE to Light Source gold layer

  16. Light Guide Light Coupler Autolab with PGSTAT 10 Xenon Lamp with mono-chromator N2 Personal Computer MORE Pt wire SCE Earthed Faraday Cage Photo-Electrochemistry: Apparatus used

  17. Cyclic Voltammetric Analysis of GB-MORE using K3Fe(CN)63+: Dark experiment Fe (II) → Fe (III) Fe (II) ← Fe (III) Eθ of K 3Fe(CN)63-/4- is 0.119V vs SCE [Bard, 2001].

  18. Ru(bipy)33+ Fe2+ e- h Fe3+ Ru(bipy)32+ Ru(bipy)32+* The Ruthenium/Iron, Sensitiser Scavenger System: Light experiment 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)32+] 10mM, [Fe3+] 5mM, pH=2, white light on and off Light on Light on Light off 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)32+ λmax = 453.2nm

  21. 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

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

  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. 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+ + hv → * UO22+ *UO22+/ UO2+ = (E0=2.7V) λmax = 420nm-460nm *PuO22+/ Pu4+ (E0=4.56V) λmax = 350nm

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

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