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Synthesis and Immobilization of Ag0 Nanoparticles on Diazonium Modified Electrodes: SECM and Cyclic Voltammetry Studies of the Modified Interfaces Jean-Marc No€el, Dodzi Zigah, Jacques Simonet, and Philippe Hapiot* Laboratoire Sciences Chimiques de Rennes, Equipe MaCSE, UMR CNRS 6226, Universit e de Rennes 1, Campus de Beaulieu, 35042 Rennes, France Received November 21, 2009. Revised Manuscript Received February 1, 2010 A versatile method was used to prepare modified surfaces on which metallic silver nanoparticles are immobilized on an organic layer. The preparation method takes advantage, on one hand, of the activated reactivity of some alkyl halides with Ag-Pd alloys to produce metallic silver nanoparticles and, on the other hand, of the facile production of an anchoring polyphenyl acetate layer by the electrografting of substituted diazonium salts on carbon surfaces. Transport properties inside such modified layers were investigated by cyclic voltammetry, scanning electrochemical microscopy (SECM) in feedback mode, and conducting AFM imaging for characterizing the presence and nature of the conducting pathways. The modification of the blocking properties of the surface (or its conductivity) was found to vary to a large extent on the solvents used for surface examination (H2O, CH2Cl2, and DMF).
Introduction In the field of functional surfaces, the design of interfaces bearing immobilized metallic nanoparticles is a very active subject.1 Fine control of the deposition and stability of formed interfaces is essential for their practical use. For this purpose, numerous modes of deposition and immobilization have been reported in the literature.2,3 Carbon surfaces are interesting supporting substrate because of their wide potential window, good conductivity, stability, low cost, and availability.4 In this connection, electrografting reactions, such as those based on the reduction of aryl diazonium salt,5 are attractive methods for the preparation of such stable functional surfaces.6,7 This approach has recently been used with success in immobilizing nanoparticles on carbon surfaces3a or carbon powder.3b Indeed, the electroreduction of aryl diazonium leads to the formation of polyphenyl multilayers that are characterized by robust attachment thanks to the formation of covalent bonds between electrogenerated phenyl radicals and the substrate.6 Because of the high reactivity of those radicals (they react with numerous substrates), this versatile method could be applied to many diverse materials.6 To attach functional entities with this methodology, it is generally efficient *Corresponding author. E-mail:
[email protected]. (1) (a) For some general reviews, see refs 1b and 1c. (b) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides., G. M. Chem. Rev. 2005, 105, 1103. (c) Velev, O. D.; Gupta, S. Adv. Mater. 2009, 21, 1897. (2) (a) See, for example, refs 2b-e. (b) Downard, A. J.; Tan, E. S. Q.; Yu, S. S. C. New J. Chem. 2006, 30, 1283. (c) Harnisch, J. A.; Pris, A. D.; Porter, M. D. J. Am. Chem. Soc. 2001, 123, 5829. (d) Cruickshank, A. C.; Downard, A. J. Electrochim. Acta 2009, 54, 5566. (e) Tian, R. H.; Zhi, J. F. Electrochem. Commun. 2007, 9, 1120. (3) (a) Harper, J. C.; Polsky, R.; Wheeler, D. R.; Lopez, D. M.; Arango, D. C.; Brozik, S. M. Langmuir 2009, 25, 3282. (b) Urchaga, P.; Weissmann, M.; Baranton, S.; Girardeau, T.; Coutanceau, C. Langmuir 2009, 25, 6543. (4) McCreery, R. L.; Cline, K. K. In Laboratory Techniques in Electroanalytical Chemistry; Kissinger, P. T., Heineman, W. R., Eds.; Marcel Dekker: NewYork, 1996, p 293. (5) Delamar, M.; Hitmi, R.; Pinson, J.; Saveant., J.-M. J. Am. Chem. Soc. 1992, 114, 5883. (6) (a) Downard, A. J. Electroanalysis 2000, 12, 1085. (b) Pinson, J.; Podvorica, F. I. Chem. Soc. Rev. 2005, 34, 429. (c) Gooding, J. J. Electroanalysis 2008, 20, 573. (7) (a) Kariuki, J. K.; McDermott, M. T. Langmuir 2001, 17, 5947. (b) Malmos, K.; Dong, M.; Pillai, S.; Kingshott, P.; Besenbacher, F.; Pedersen, S. U.; Daasbjerg K. J. Am. Chem. Soc. 2009, 131, 4936 and references therein.
7638 DOI: 10.1021/la904413h
to proceed via a two-step method.8,9 The first step consists of making an anchoring layer by the electroreduction of aryl diazonium salt bearing a chosen reactive group, followed by its postfunctionalization in a subsequent chemical step.8,9 The interest lies in easier control of the properties of the first anchoring layer that could be separately optimized, for example, to adjust the blocking character of the layer versus chemical species present in a solution or the density of the functional group.10 Additionally, diazonium salts could be in situ generated from the corresponding amines with NaNO2 in aqueous HCl11 and allowing different methods of surface patterning.12 Concerning the preparation of metallic nanoparticles, an original, facile method has recently been proposed to create very small metallic particles by means of the electrochemical reduction of alkyl halides in the presence of suspensions of metalpalladium alloys.13 The feasibility of and interest in this reaction have been demonstrated in the case of the synthesis of silver nanoparticles and the preparation of metalized electrodes.13b Briefly, when doped with palladium (here, Ag-Pd alloys), silver electrode reacts rapidly with alkyl iodide (RX) or some R,ωdibromoalkanes to produce an [RAgþ, X-] intermediate at a (8) (a) Yu, S. S. C.; Tan, E. S. Q.; Jane, R. T.; Downard, A. J. Langmuir 2007, 23, 11074. (b) Nielsen, L. T.; Vase, K. H.; Dong, M.; Besenbacher, F.; Pedersen, S. U.; Daasbjerg, K. J. Am. Chem. Soc. 2007, 129, 1888. (c) Evrard, D.; Lambert, F.; Policar, C.; Balland, V.; Limoges, B. Chem.—Eur. J. 2008, 14, 9286. (d) Polsky, R.; Harper, J. C.; Wheeler, D. R.; Arango, D. C.; Brozik, S. M. Angew. Chem., Int. Ed. 2008, 47, 2631. (e) Harper, J. C.; Polsky, R.; Wheeler, D. R.; Lopez, D. M.; Arango, D. C.; Brozik, S. M. Langmuir 2009, 25, 3282. (9) (a) Pellissier, M.; Zigah, D.; Barriere, F.; Hapiot, P. Langmuir 2008, 24, 9089. (b) No€el, J.-M.; Sj€oberg, B.; Marsac, R.; Zigah, D.; Bergamini, J.-F.; Wang, A.; Rigaut, S.; Hapiot, P.; Lagrost, C. Langmuir 2009, 25, 2742. (10) (a) Anariba, F.; DuVall, S. H.; McCreery, R. L. Anal. Chem. 2003, 75, 3837. (b) Brooksby, P. A.; Downard, A. J. Langmuir 2004, 20, 5038. (11) (a) Baranton, S; Belanger, D. J. Phys. Chem. B 2005, 109, 24401. (b) Lyskawa, J.; Belanger, D. Chem. Mater. 2006, 18, 4755. (12) (a) Downard, A. J.; Garrett, D. J.; Tan, E. S. Q. Langmuir 2006, 22, 10739. (b) Slim, C.; Tran, Y.; Chehimi, M. M.; Garraud, N.; Roger, J.-P.; Combellas, C.; Kanoufi, F. Chem. Mater. 2008, 20, 6677. (c) Cougnon, C.; Grohier, F.; Belanger, D.; Mauzeroll, J. Angew. Chem., Int. Ed. 2009, 48, 4006. (d) Cougnon, C.; Mauzeroll, J.; Belanger, D. Angew. Chem., Int. Ed. 2009, 48, 7395. (13) (a) Simonet, J. J. Electroanal. Chem. 2009, 632, 30. (b) Simonet, J. J. Appl. Electrochem. 2009, 39, 1625. (c) Jouikov, V.; Poizot, P.; Simonet, J. J. Electrochem. Soc. 2009, 156, E171.
Published on Web 02/17/2010
Langmuir 2010, 26(10), 7638–7643
No€ el et al.
Article
potential that is too positive to permit the regular cleavage of the RX.13 The further reduction of this intermediate leads to the simultaneous formation of corresponding radical R 3 and Ag0 nanoparticles. In this context, the combination of this process with the electrografting of aryl diazoniums appears to be a promising route to producing functional interfaces containing both organic entities and metallic nanoparticles.13 Besides the demonstration of this method for the preparation of modified surfaces, other addressed questions concern electron transfers on such an interface with redox species in solution and the electronic communication inside the layer, which are both fundamental issues in various applications such as catalysis and the design of sensors. Investigations were performed using both classical electrochemical methods (cyclic voltammetry) when the surface is used as an electrode and scanning electrochemical microscopy (SECM)14 under conditions where the surface is not electrically connected (unbiased conditions). Steady-state SECM in feedback mode has been proven to be an efficient technique for examining the intrinsic behavior of an immobilized assembly of nanoparticles free from the influence of the substrate.15 It is noticeable that this method is complementary to cyclic voltammetry, with the difference that SECM allows investigations from the solution bulk and thus permits a different view of the same transport properties.16 The SECM principle is based on the interaction of the substrate under investigations with a redox species (the mediator) that is electrogenerated at a microelectrode. This interaction is followed through the analysis of the current flowing at the microelectrode while it is approaching the substrate. Depending on the nature of the redox couple, probing the permeation, the accessibility or the redox reactivity of the functional group is possible by varying the size of the redox couple or its standard potential. As a complement to these investigations, conducting atomic force microscopy (AFM) was used to detect the conducting pathways from the solution to the substrate without or in the presence of the nanoparticles. Finally, the electrochemical behavior and the stability of the modified surfaces were examined in different solvents (H2O, CH2Cl2, and DMF).
Experimental Section Substrate Preparation before Modification. The substrate surface consists of a 3-mm-diameter disk glassy carbon electrode (CH Instruments, Austin, TX). Between each series of experiments, the electrode surface was successively polished using 5 μm SiC paper (Struers) and 1 μm DP-Nap paper (Struers) with a 0.3 μm Al2 O 3 slurry (Struers). After each polishing step, the electrode was thoroughly washed with ultrapure water (18.2 MΩ cm). Before proceeding to the electrografting of the aryl diazonium salts, the surface state was checked by recording a cyclic voltammogram of aqueous potassium ferrocyanide to ensure good electron transfer at the surface.
(14) (a) Bard, A. J.; Mirkin, M. V.; Unwin, P. R.; Wipf, D. O. J. Phys. Chem. 1992, 96, 1861. (b) Bard, A. J., Mirkin, M. V., Eds. Scanning Electrochemical Microscopy; Marcel Dekker: New York, 2001. (c) Wei, C.; Bard, A. J.; Mirkin, M. V. J. Phys. Chem. 1995, 99, 16033. (d) Wittstock, G.; Burchardt, M.; Pust, S. E.; Shen, Y.; Zhao, C. Angew. Chem., Int. Ed. 2007, 46, 1584. (e) Amemiya, S.; Bard, A. J.; Fan, F. R. F.; Mirkin, M. V.; Unwin, P. R. Annu. Rev. Anal. Chem. 2008, 1, 95. (15) (a) Zhang, J.; Lahtinen, R. M.; Kontturi, K.; Unwin, P. R.; Schiffrin, D. J. Chem. Commun. 2001, 1818. (b) Liljeroth, P.; Vanmaekelbergh, D.; Ruiz, V.; Jiang, H.; Kauppinen, E.; Quinn, B. M. J. Am. Chem. Soc. 2004, 126, 7126. (c) Liljeroth, P.; Quinn, B. M.; Ruiz, V.; Kontturi, K. Chem. Commun. 2003, 1570. (d) Nicholson, P. G.; Ruiz, V.; Macpherson, J. V.; Unwin, P. R. Phys. Chem. Chem. Phys. 2006, 8, 5096. (e) Li, F.; Ciani, I.; Bertoncello, P.; Unwin, P. R.; Zhao, J.; Bradbury, C. R.; Fermin, D. J. J. Phys. Chem. C 2008, 112, 9686. (16) (a) Liu, B.; Bard, A. J.; Mirkin, M. V.; Creager, S. E. J. Am. Chem. Soc. 2004, 126, 1485. (b) Ghilane, J.; Hauquier, F.; Fabre, B.; Hapiot, P. Anal. Chem. 2006, 78, 6019. (c) Wittstock, G.; Burchardt, M.; Pust, S. E.; Shen, Y.; Zhao, C. Angew. Chem., Int. Ed. 2007, 46, 1584.
Langmuir 2010, 26(10), 7638–7643
Scheme 1. Cell Used for Nanoparticle Adsorption
Substrate Modification. The modification of the glassy carbon surface by the electrochemical reduction of in situ generated diazonium was carried out following the general procedure presented by Belanger et al. at room temperature.11 For that, NaNO2 (final concentration 38 mmol L-1) was added to the aqueous electrolytic solution containing 20 mmol L-1 4-aminophenylacetic acid and 0.5 mol L-1 HCl under stirring. The electrografting procedure was potentiostatically achieved over 300 s by applying a potential of -1.0 V at the electrode. After glassy carbon modification, electrodes were rinsed with ultrapure water and dipped into an aqueous solution of 0.1 mol L-1 KOH for 5 min to neutralize the -CH2COOH groups. Nanoparticle Synthesis. Silver nanoparticles were generated according to the following procedure: a solution of 25 mg of 1,3dibromopropane in 20 mL of DMF is placed in contact with an Ag sheet (
