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2014
This work was supported by the EU grant COST CM1005 "Supramolecular Chemistry in Water", 679/N-BELGIA/2010/0 and the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Olsztyn, Poland. We also thank the F.W.O.-Vlaanderen and the KU Leuven for financial support. T.H.N. further acknowledges the IWT (Institute for the Promotion of Innovation through Science and Technology in Flanders) and the Alexander von Humboldt Foundation for a doctoral and postdoctoral fellowship, respectively.
Self-Assembled Monolayer Formation on Copper: A Real Time Electrochemical Impedance Study
The Journal of Physical Chemistry C, 2011
Even though electrochemical impedance spectroscopy (EIS) has already been used for the in situ electrochemical study of organothiol self-assembled monolayer (SAM) formation on gold, such studies are not available on oxidizable metals. A scrupulous study of SAM formation on oxidizable metals is a challenge, even by ex situ techniques, because of their highly oxidizable nature and their high interaction with the solvent which are irrelevant with the noble metals. In this report, the self-assembling of n-dodecanethiol, n-dodecaneselenol, didodecyl disulfide, and didodecyl diselenide on copper substrate is studied in real time by in situ electrochemical impedance spectroscopy. The interfacial capacitance variation with time was used to study the adsorption process as a function of time. The selfassembling of n-dodecanethiol and n-dodecaneselenol results in the formation of a layer with coverage of around 90% within 10 s. This fast step happens with an effective removal of the surface copper oxide layer. The second stage involves a long-term additional adsorption and consolidation of the SAM. Didodecyl disulfide is incapable for the effective removal of copper oxide layer, and its adsorption is slow and ineffective. Monolayer formation with didodecyl diselenide takes longer time due to slow copper oxide removal. The in situ EIS results were supported by the polarization modulation infrared reflection absorption spectroscopic (PM-IRRAS) studies.
Self-assembled monolayers (SAMs) and electrostatically assembled multilayers of some soluble polypyrroles (including a thiol-functionalized polypyrrole) were produced on gold and platinum electrodes. Gold and platinum surfaces were used either bare or primed with an anionic monolayer of 3-mercaptopropylsulfonate or Nafion. Poly(sodium-p-styrenesulfonate) and Nafion were used as polyanions for electrostatic self-assembly (ESA). The layers were investigated by cyclic voltammetry, infrared reflection absorption spectroscopy, quartz crystal microbalance, and atomic force microscopy (AFM). ESA proceeds with a growth rate that is linear with the number of bilayers and particularly high (stored charge 30-60 µC cm -2 bilayer -1 ) with Nafion, which appears to be the primer for all the investigated polypyrroles. Gold-polymer-gold junctions, formed by contact between a polypyrrole SAM on gold and a goldcoated AFM tip, rectify current in polypyrrole sulfosuccinate, whereas they are ohmic with Simmons characteristics in poly(N-hexylcyclopenta[c]pyrrole). In the former case alternation of rectifying and ohmic characteristics is observed with progressive ESA. 3754
Electrodeposition of copper into functionalized polypyrrole films
Journal of Electroanalytical Chemistry, 1999
Copper microparticles have been dispersed in anion-exchange polymer films coated on carbon electrodes by oxidative electropolymerization of pyrrole-alkylammonium monomers. Incorporation of copper in polymeric films was effected by impregnation of copper-oxalate anionic complexes followed by an electroreductive precipitation to copper metal, or by electroreduction of polymer coated electrodes immersed in copper-oxalate aqueous solutions. The deposition process was examined by voltammetry. Scanning electron microscopy showed a dispersion of metal particles from 50-100 up to 300 nm, according to the lipophilic character of the polymer, located in a layer near the carbon polymer interface. A study of the electrocatalytic activity in the reduction of nitrobenzene to aniline at these materials was performed. The cathodes appeared much more active than bulk copper electrodes.
Analytical Chemistry, 2006
Fabrication and electrochemical characterization of a novel nanosensor for determination of Cu 2+ in subnanomolar concentrations is described. The sensor is based on gold cysteamine self-assembled monolayer functionalized with salicylaldehyde by means of Schiff's base formation. Cyclic voltammetry, Electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal microbalance were used to probe the fabrication and characterization of the modified electrode. The sensor was used for quantitative determination of Cu 2+ by the EIS in the presence of parabenzoquinone in comparison with stripping Osteryoung square wave voltammetry (OSWV). The attractive ability of the sensor to efficiently preconcentrate trace amounts of Cu 2+ allowed a simple and reproducible method for copper determination. A wide range linear calibration curve was observed, 5.0 × 10-11-5.0 × 10-6 and 5.0 × 10-10-5.0 × 10-6 M Cu 2+ , by using the EIS and OSWV, respectively. Moreover, the sensor presented excellent stability with lower than 10% change in the response, as tested for more than three months daily experiments, and a high repeatability with relative standard deviations of 6.1 and 4.6% obtained for a series of eight successive measurements in 5.0 × 10-7 M Cu 2+ solution, by the EIS and OSWV, respectively. Monomolecular-level modification of the electrode surface through the self-assembly approach is, of late, gaining importance in view of its many functional applications in different areas of science and technology such as the following: modification of the surface electronic properties, charge-transfer kinetic studies at the controlled distances, and recognition of biological and inorganic species in electroanalysis. Application of chemisorbed organosulfur self-assembled monolayer (SAM) films on gold surface has received much attention in recent years. The benefits of SAM films for sensor applications include chemical specificity, rapid response, high sensitivity, and possibility for in situ immobilization of biological recognition agents (e.g., enzymes) or functionalization of the film terminals by chemical reagents. 1-4
ChemPhysChem, 2013
The wire-like properties of four S,-[4-[2-[4-(2-phenylethynyl)phenyl]ethynyl]phenyl]thioacetate derivatives, PhCCC6H4CCC6H4SAc 1, H2NC6H4CCC6H4CCC6H4SAc 2, PhCCC6H2(OMe)2CCC6H4SAc 3 and AcSC6H4CCC6H4CCC6H4SAc 4 (Figure 1), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self-assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)6] 4was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate-protected precursor molecules 1 and 2 form well-ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of self-assembled monolayers (SAMs) of all four compounds were examined using electron tunnelling theory. The analysis of the results revealed that the well-ordered SAMs of 1 and 2 exhibit higher charge transfer resistance in comparison to the defect-ridden SAMs of 3 and 4. The addition steric bulk offered by the methoxy groups in 3 likely prevent efficient packing within the SAM, leading to microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers and height images gave root-mean-square (RMS) roughness's which are in agreement with the proposed SAM structures.
Pure 1,10-decanedithiol (C 10 -SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free -SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN) 6 3-, in KNO 3 solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C 10 -SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free -SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C 10 -SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C 10 -SH SAM upon layer-by-layer modification was performed ex situ in air.
Sensors and Actuators B: Chemical, 2011
A 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate (AHMP)-based self-assembled monolayer (SAM) was formed on the gold electrode surface. Ellipsometric measurements evidenced the SAM formation on the gold electrode surface. The structural integrity of the modified gold electrode was also characterized by insulating properties of the SAM that were detected by cyclic voltammetry. The results of cyclic voltammetry showed that the SAM, which was formed by assembly of AHMP, was stable but did not completely block the redox-activity of ferrocene and K 3 [Fe(CN) 6 ]/K 4 [Fe(CN) 6 ]. In contrast completely blocked redox-activity was observed after the treatment of AHMP-based SAM with saturated solution of 4-formylphenylboronic acid in 1,4-dioxan. The modified electrodes exhibited a selective response towards Cu(II) ions in the presence of some interfering ions such as Cd(II), Co(II), Fe(II), Ni(II) and Pb(II). This study is the first scientific report on the application of AHMP-modified electrode as a selective Cu(II) sensor in the presence of some interfering cations.
Journal of the American Chemical Society, 1997
This paper describes the use of gold films that contain underpotentially deposited (upd) metal layers of copper or silver as substrates in the generation of self-assembled monolayers (SAMs). The assembly of alkanethiols to form SAMs is compatible with the presence of the upd layer and forms a system that contains an interlayer of the upd metal that is between the gold substrate and the adsorbed organic monolayer. The assembly on these substrates can accommodate both polar and nonpolar tail groups, and the resulting SAMs span the range of wettabilities (θ a-(H 2 O)) <15°to 113°). The SAMs on the upd substrates have highly organized structures that are distinct from those that form on the parent bulk metal surfaces. In addition, the upd metal has a more noble redox potential than the corresponding bulk metal and allows an expanded potential window in cyclic voltammetry. For example, ferroceneterminated alkanethiolssdespite having redox potentials that are positive of bulk silverscan be assembled onto silver upd substrates and form stable electroactive SAMs. The presence of the upd layer improves the stability of alkanethiolate monolayers against both desorption at elevated temperatures and molecular exchange within thiolcontaining solutions.