Underpotential Deposition of Thallium, Lead, and Cadmium at Silver Electrodes Modified with Self-Assembled Monolayers of (3-Mercaptopropyl)trimethoxysilane

Abstract

Investigation of the underpotential deposition (UPD) of three metals-Tl, Pb, and Cd-on Ag surfaces modified with self-assembled monolayers (SAMs) of (3-mercaptopropyl)trimethoxysilane (3MPT) is reported. On the basis of the observation of negative potential shifts for their UPD processes, Tl and Pb undergo UPD directly on the underlying Ag surface by insertion between the Ag-S bond. This process is proposed to occur by penetration of the 3MPT monolayer by hydrated metal ions through spaces in six-membered siloxane rings that form at the terminus of the 3MPT layer after hydrolysis and condensation. In contrast, Cd does not undergo similarly facile UPD at 3MPT-modified Ag electrodes due to a hydrated ion size too large to fit through these openings. The voltammetric evidence that suggests that the hydrated metal cation size, as described by the Stokes diameter, is the primary determinant of Ag electrode accessibility for UPD through the cross-linked 3MPT layer is further supported by molecular mechanics energy minimization computations of six-membered siloxane rings on each of the three low-index faces of Ag. Finally, the 3MPT monolayer is shown to be exceptionally stable to repeated UPD/stripping cycles of Tl and Pb in contrast to SAMs of similar thickness formed from normal alkanethiols.

Electrochemically Assisted Deposition of Nanoporous Silica Membranes on Gold Electrodes: Effect of 3‐Mercaptopropyl(trimethoxysilane) “Molecular Glue” on Film Formation, Permeability and Metal Underpotential Deposition

“…The MPTMS layer is probably not sufficiently dense to prevent the diffusion of Cu 2+ species although it is enough to anchor the silica film onto the gold electrode as no delamination was observed after Cu UPD. This is consistent with the existing literature that showed that defects in a MPTMS layer resulted in the formation of Pb and Tl UPD monolayers by insertion between the S atom of the MPTMS and the underlying silver electrode [65] . Cu 2+ diffusion through the silica walls and deposition under the silica film is unlikely as proven by the control experiments showing the cyclic voltammetry of Cu 2+ UPD at a silica modified electrode before removal of the surfactant (see Figure S7 in Supporting Information) and by the absence of any stripping peak when performing potentiometric deposition at 0.00 V (as in Figure 6).…”

“…This is consistent with the existing literature that showed that defects in a MPTMS layer resulted in the formation of Pb and Tl UPD monolayers by insertion between the S atom of the MPTMS and the underlying silver electrode. [65] Cu 2 + diffusion through the silica walls and deposition under the silica film is unlikely as proven by the control experiments showing the cyclic voltammetry of Cu 2 + UPD at a silica modified electrode before removal of the surfactant (see Figure S7 in Supporting Information) and by the absence of any stripping peak when performing potentiometric deposition at 0.00 V (as in Figure 6). No Cu UPD is observed at a silica modified electrode before extraction of the surfactant confirming that the silica does not allow diffusion of Cu 2 + and also that the film is defect-free.…”

Rapid screening of silver nanoparticles for the catalytic degradation of chlorinated pollutants in water

“…In order to achieve these goals, the lead underpotential deposition (Pb UPD) represents the most convenient and adopted method used for calibrating Ag-based electrodes [54,55].…”

“…For this process, we adopted the calibration charge density value reported in the literature for a polyoriented silver electrode, which is 280 µC cm −2 [54,55]. Thus, the initial surface area of all 3 Ag NPs samples determined by Pb UPD was 0.0025 cm 2 µL -1 for sample S1, 0.0056 cm 2 µL -1 for C1 and 0.0090 cm 2 µL -1 for C2.…”

Siloxane-based thin films for corrosion protection of stainless steel in chloride media

“…Siloxane-anchored self-assembled monolayer (SAM) films have attracted enormous interest [9][10][11][12][13] as surface modifiers since the study on them by Sagiv in 1980 [14]. They are composed of molecules that organize spontaneously by chemisorption from solution onto an appropriate substrate.…”