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Journal of Applied Electrochemistry

, Volume 44, Issue 2, pp 279–292 | Cite as

Comparative EIS study of the adsorption and electro-oxidation of thiourea and tetramethylthiourea on gold electrodes

  • A. E. BolzánEmail author
  • L. M. Gassa
Research Article

Abstract

A comparative study of the electrochemical behaviour of thiourea (TU) and tetramethylthiourea (TMTU) on gold in sulphuric acid was performed using a gold rotating disc electrode. The electrochemical impedance spectra are interpreted through an equivalent circuit involving the electrolyte resistance, a constant phase element for the capacity double layer, a charge transfer resistance and, depending on the electrode potential, a second parallel impedance element whose interpretation depends on the potential region considered. Thus, for both thioureas, the Nyquist plots for E < −0.6 V (vs. MSE) exhibit a single capacitive time constant related to the adsorption of the molecule on the electrode surface. As E increases, the Nyquist plots exhibit a new time constant assigned to the formation of a soluble complex species. This time constant appears in the potential region also related to the electro-oxidation of the thioureas to the corresponding formamidinium disulphide. This means that these processes are coupled and, therefore, only one time constant can be observed. An inductive loop at low frequencies is associated with the pitting of the gold electrode for E ≥ −0.20 V, in agreement with SEM micrographs. The value of the corresponding charge transfer resistance decreases markedly with the electrode potential, indicating the increase in the rate of the electrochemical processes. Electrodissolution of gold results more importantly in the presence of TMTU. At potential values associated with the formation of the anodic oxide layer on gold, a negative resistance is recorded, indicating the passivation of the electrode surface. Eventually, at E > 0.6 V, the electrode surface passivation disappears and the Nyquist plots exhibit two strongly overlapped capacitive constants assigned to the oxide film growth at the monolayer level and the second electro-oxidation process of thioureas, the latter resulting in the formation of carbon dioxide and sulphate ions according to FTIRRAS data.

Keywords

Gold Thiourea Tetramethylthiourea EIS Electro-oxidation Electrodissolution 

Notes

Acknowledgments

This work was financially supported by the Agencia Nacional de Promoción Científica y Tecnológica of Argentina (ANPCYT, PICT 2008-1902), the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CICPBA). AEB is member of CICPBA

References

  1. 1.
    Lawrence RW, Marchant P (1987) In: Salter RS, Wyslouzil DM, McDonald GW (eds) Gold metallurgy. Pergamon Press, New YorkGoogle Scholar
  2. 2.
    Chandra I, Jeffrey MI (2004) Hydrometallurgy 73:305CrossRefGoogle Scholar
  3. 3.
    Yang X, Moats MS, Miller JD (2010) Electrochim Acta 55:3643CrossRefGoogle Scholar
  4. 4.
    Li J, Miller JD (2002) Hydrometallurgy 63:215CrossRefGoogle Scholar
  5. 5.
    Zhang H, Ritchie IM, Brooy SRL (2001) J Electrochem Soc 148:D146CrossRefGoogle Scholar
  6. 6.
    Pesic B, Seal T (1990) Metall Trans 21B:419CrossRefGoogle Scholar
  7. 7.
    Gaspar V, Mejerovich AS, Meretukov MA, Schmiedl J (1994) Hydrometallurgy 34:369CrossRefGoogle Scholar
  8. 8.
    Tremblay L, Deschênes G, Ghali E, McMullen J, Lanouette M (1996) Int J Miner Process 48:225CrossRefGoogle Scholar
  9. 9.
    Kai T, Hagiwara T, Haseba H, Takahashi T (1997) Ind Eng Chem Res 36:2757CrossRefGoogle Scholar
  10. 10.
    Aguayo Salinas S, Encinas Romero MA, González I (1998) J Appl Electrochem 28:417CrossRefGoogle Scholar
  11. 11.
    Chai L, Okido M, Wei W (1999) Hydrometallurgy 53:255CrossRefGoogle Scholar
  12. 12.
    Porter LC R Acad Sci, Fackler JP, Costamagna J, Schmidt R (1992) Acta Cryst C48:1751Google Scholar
  13. 13.
    Piro OE, Castellano EE, Piatti RCV, Bolzán AE, Arvia AJ (2002) Acta Cryst C58:252Google Scholar
  14. 14.
    Bunge E, Port SN, Roelfs B, Meyer H, Baumgärtel H, Schiffrin DJ, Nichols RJ (1997) Langmuir 13:85CrossRefGoogle Scholar
  15. 15.
    Bolzán AE, Iwasita T, Arvia AJ (2005) Electrochim Acta 51:1044CrossRefGoogle Scholar
  16. 16.
    Groenewald T (1976) Hydrometallurgy 1:277CrossRefGoogle Scholar
  17. 17.
    Schulze RG (1984) J Metals 36:62–66Google Scholar
  18. 18.
    Parker GK, Hope GA (2008) Miner Eng 21:489CrossRefGoogle Scholar
  19. 19.
    Groenewald T (1975) J Appl Electrochem 5:71CrossRefGoogle Scholar
  20. 20.
    Iwasita T (2002) Electrochim Acta 47:3663CrossRefGoogle Scholar
  21. 21.
    Garcia G, Rodriguez JL, Lacconi GI, Pastor E (2004) Langmuir 20:8773CrossRefGoogle Scholar
  22. 22.
    Hoffmann M, Edwards JO (1977) Inorg Chem 16:3333CrossRefGoogle Scholar
  23. 23.
    Bierbach U, Barklage W, Saak W, Pohl S (1992) Z Naturforsch 47b:1593Google Scholar
  24. 24.
    Bolzán AE, Güida J, Piatti RCV, Arvia AJ, Piro OE, Sabino JR, Castellano EE (2007) J Mol Struct 271:131CrossRefGoogle Scholar
  25. 25.
    Bunge E, Nichols RJ, Baumgärtel H, Meyer H (1995) Ber Bunsenges Phys Chem 99(10):1243Google Scholar
  26. 26.
    Bunge E, Nichols RJ, Roelfs B, Meyer H, Baumgärtel H (1996) Langmuir 12:3060CrossRefGoogle Scholar
  27. 27.
    Port SN, Horswell SL, Raval R, Schiffrin DJ (1996) Langmuir 12:5934CrossRefGoogle Scholar
  28. 28.
    Tian M, Conway BE (2004) J Appl Electrochem 34:533CrossRefGoogle Scholar
  29. 29.
    Bolzán AE, Piatti RCV, Arvia AJ (2003) J Electroanal Chem 552:19CrossRefGoogle Scholar
  30. 30.
    Iwasita T, Nart F (1995) In: Gerischer H, Tobias CW (eds) Advances in electrochemical science and engineering, vol 4. Wiley-VCH, Weinheim, p 123CrossRefGoogle Scholar
  31. 31.
    Shevtsova O, Bek R, Zelinskii A, Vais A (2006) Russ J Electrochem 42:239CrossRefGoogle Scholar
  32. 32.
    Bolzán AE, Iwasita T, Arvia AJ (2003) J Electroanal Chem 554(555):49CrossRefGoogle Scholar
  33. 33.
    Reddy SJJ, Krishnan VN (1970) J Electroanal Chem 27:473CrossRefGoogle Scholar
  34. 34.
    Larsen AG, Johannsen K, Gothelf KV (2004) J Colloid Interface Sci 279:158CrossRefGoogle Scholar
  35. 35.
    Woods R (1976) In: Bard AJ (ed) Electroanalytical chemistry, vol 9, chap 1. Marcel Decker, New York, p 98Google Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas - INIFTAUNLP, CONICETLa PlataArgentina

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