Growth Processes and Reductive Desorption Behaviors of 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111)

Growth processes and electrochemical behaviors of 4-fluorobenzenethiol (4-FBT) self-assembled monolayers (SAMs) on Au(111) prepared by vapor deposition at 323 K were examined using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging revealed that 4-FBT SAMs at the initial growth stage (deposition for 1 min) were mainly composed of bright molecular aggregates and liquid-like disordered phase. After longer deposition for 3 min, 4-FBT SAMs had three distinct surface features: a few molecular aggregates, small ordered domains, and disordered phase. These small ordered domains with sizes ranging from 5 to 10 nm had a (4× √3)R30° packing structure. As deposition time increased to 24 h, long-range ordered domains larger than 40 nm were formed on Au(111) surfaces. From this STM study, we demonstrate that phase transitions of 4-FBT SAMs on Au(111) occur from molecular aggregates to large ordered domains via formation of small ordered domains as deposition time increases. CV measurements showed reductive desorption peaks for 4-FBT SAMs in the range of −638~−648 mV regardless of SAM morphology, suggesting that S–Au binding strength of 4-FBT SAMs on Au electrodes is a dominant factor for electrochemical stability.

Origin of the overpotentials for HCOO− and CO formation in the electroreduction of CO2 on Cu(211): the reductive desorption processes decide

Potential-related free energy profiles of CO and HCOO− pathways in CO2RR on Cu(211) are computed with implicit solvent model.

Effects of Introducing 2-aminoethanethiol into 4-pyridineethanethiol Self-assembled Monolayer Applicable to Enhance Sensitivity of Hg(II) Electrochemical Analysis

In our work, enhancement of sensitivity of Hg(II) determination by introducing 2-aminoethanethiol (AET) from solutions into the self-assembled monolayers (SAMs) of 4-pyridineethanethiol (PET) on gold nanoparticles (Au-NPs) capped on glassy carbon electrode was studied. The formation of binary SAMs was indicated by the shift of reductive desorption peak to negative potentials in voltammograms recorded in 0.5 M KOH solution. Effects of introduction AET were monitored by FTIR that there was a rapid increase of intensities at bands of 1296 and 1189 cm-1 ascribed to (C-H) ring deformation and (C-N) ring stretching, respectively, with increasing immersion time. However, these bands became lower with prolonging more time as well as increasing the concentration of AET in solution. These effects were interpreted due to the conformation of pyridine ring and formation of intermolecular hydrogen bonding between PET and AET. The differential pulse voltammetry for reoxidation of Hg(0) showed the increase of peak current induced by the first effect, whereas the later caused the decrease. Since the optimized conditions, the detection limit for the binary SAMs could approach to 3.85 × 10-12 M Hg(II), approximately three times lower than that of PET SAM.

Self-assembly of a Ru(II)-deuteroporphyrin lipoic acid derivative on Au(111) surfaces

The synthesis of a new carbonyl ruthenium(II) deuteroporphyrin-IX lipoic acid derivative (Ru(PLip)(CO)) (4) and its self-assembly on Au(111) surfaces were accomplished. Ru(PLip)(CO) 4 was prepared by reduction of the ester groups of carbonyl-ruthenium(II) deuteroporphyrindimethylester 1 and further esterification with D,L-α-lipoic acid 3. The self-assembly of Ru(PLip)(CO) 4 was confirmed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The S2p XP spectrum of SAM formed by Ru(PLip)(CO) showed the S2p3/2 peak at 162.4 eV which corresponds to thiolated species bounded to gold. The influence of the interaction of porphyrin moieties on SAM stability was studied. The reductive desorption voltammogram of Ru(PLip)(CO) 4 self-assembled on gold showed an intense reduction peak at -1.02 V while when pyridine was coordinated to the central ruthenium(II) the reductive desorption peak was shifted to -0.85 V. The capacity of the modified Ru(PLip)(CO) gold electrode to detect nitric oxide (NO) was investigated by cyclic voltammetry. An irreversible reduction peak which increased with time on NO exposure was registered at -0.69 V indicating NO coordination to ruthenium(II).