Alkanethiol-oxidized copper interface: The critical influence of concentration

The impact of urban rain on the changes of bare and artificially patinated bronze during 9-year exposure

Atmospheric pollutants in the air form acid rain which interacts with bronze surfaces exposed in urban outdoor environment. In this study, different types of patinas on bronze were investigated during and after 9 years of exposure to urban environment in moderately polluted continental city. Natural bronze patina and artificial brown sulphide, green chloride, and green-blue nitrate patinas were investigated. Visual assessment was carried out at defined periods. After 9 years of exposure, an electrochemical study was performed to investigate the electrochemical activity of the patinas in artificial urban rain. Additionally, the patinas were characterised using a variety of techniques, including metallographic examination, scanning electron microscopy/energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction analysis, X-ray-photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry to analyse the surface morphology, chemical composition, and stratigraphic features of the patinas. Evolution of the patinas was shown to be a result of both, the composition of the acid rain and the hydrophobicity of the patinated surfaces.

3-Mercaptopropanoic Acid-Doped Chitosan/Hybrid-Based Multilayer Sol-Gel Coatings for Cu Protection in 3.5% NaCl Solution

In this work, biopolymer based sol-gel was synthesized by doping 3-mercaptopropanoic acid (MPA) with chitosan and a hybrid of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS). Prepared MPA/hybrid-doped chitosan was applied toa copper (Cu) metal surface by the self-assembly technique to protect the Cu metal from corrosion in a 3.5% NaCl solution. The structure, mechanism and morphology of the modified electrodes were examined using Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). The decrease in surface roughness for Hy/chitosan/MPA-coated Cu indicates the formation of a dense layer on Cu metal confirmed by AFM. The corrosion protection evaluation of sol-gel coated electrodes was analyzed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies (PDS) in a 3.5% NaCl medium. The MPA/hybrid-doped chitosan sol-gel coated Cu metal showed the greatest resistance to corrosionthanother sol-gel modified electrodes. The MPA-doped-chitosan/Hy sol-gel coating protected the Cu metal by an anodic dissolution process and improved its corrosion protection to 99.9%.

Carbon-Sulfur Bond Cleavage During Adsorption of Octadecane Thiol to Copper in Ethanol

The effect of the solvent on the formation of thiol self-assembled monolayers (SAMs) on oxide-covered, reactive metals is more involved than in the well-studied gold-thiol system. In this work, copper covered with a native oxide was modified with 1-octadecanethiol (ODT) in either tetrahydrofuran or ethanol. Infrared spectroscopy indicated the formation of crystalline chain packing of alkyl chains from both solvents. Surface coverage was approximately equal in both systems, with differences in tilt angles of the chains. A detailed analysis by X-ray photoelectron spectroscopy showed the formation of Cu₂S and copper-bound carbon when the adsorption was carried out in ethanol. This observation can be explained by the cleavage of the C-S bond in ODT during adsorption. Based on the analogy of preparations, we reason that the solvation of ODT in ethanol must be such that it weakens the C-S bond in ODT, thus enabling the cleavage of this bond. Based on the evidence presented here, it is not possible to distinguish between surface solvation and bulk solvation. Electrochemical linear sweep voltammetry shows that SAMs from both solvents have an enhancing protective effect compared to the native oxide layer. The results from this work show interesting possibilities for the preparation of adsorbed monolayers with chemical interaction to reactive metals, with some similarities to carbene-based SAMs.

Analysis of the Thermal Stability of Very Thin Surface Layers of Corrosion Inhibitors by Time-of-Flight Secondary Ion Mass Spectrometry

The powerful nature of the secondary ion mass spectrometry (SIMS) technique was explored in order to analyse very thin surface layers that were self-assembled on steel material from acidic solution. These surface layers are adsorbed corrosion inhibitors. The SIMS technique proved useful to characterise the molecular structure and homogeneity of thin surface layers in the nanometre range of specific analytes on the metallic substrate. Using SIMS, the thermal stability of these layers was further investigated and the desorption energy at a certain temperature was determined, where special attention was devoted to the method's static limit. In order to compare, and for certain cases emphasise, the benefits gained by using SIMS in such surface analysis compared with the X-ray photoelectron spectroscopy (XPS) method, the same samples were also analysed by means of the latter. XPS is usually considered to be the most powerful analytical tool in surface analysis studies, but, as shown herein, it has certain limitations compared to SIMS. Finally, the surface topography was investigated by employing atomic force microscopy (AFM) in order to carry out a comprehensive surface analysis. Graphical Abstract ᅟ.

Surface analysis of 2-mercapto-1-methylimidazole adsorbed on copper by X-ray photoelectron spectroscopy

A detailed analysis using X-ray photoelectron spectroscopy (XPS) is presented for the system of 2-mercapto-1-methylimidazole (MMeI) adsorbed on Cu in 3wt% NaCl solution. High-resolution and survey XPS spectra and XPS-excited Auger L₃M_4,5M_4,5 spectra were analysed in detail. Surface analysis revealed that the MMeI molecules do not lie flat on the surface via π-d interactions, but adsorb on the surface through an N-S-bridge configuration. Moreover, the characteristic Cu(I)-MMeI connection fingerprint, which is usually observed for these kinds of molecules, was not observed. Tougaard thickness analysis showed that a relatively thin MMeI surface layer (0.3-0.6nm) is formed on the Cu substrate after 1h of immersion. Herein, MMeI is considered as a Cu corrosion inhibitor for chloride solution for short-term immersion periods. Based on the XPS analysis, an explanation of why MMeI is not effective for longer-term immersion periods, compared with similar compounds, is given.

Superhydrophobic surface on copper via a one-step solvent-free process and its application in oil spill collection

An environment-friendly process was developed to fabricate a superhydrophobic surface on copper, which could be applied in oil spill collection.

Superoleophobic textured copper surfaces fabricated by chemical etching/oxidation and surface fluorination

We report a convenient route to fabricate superoleophobic surfaces (abridged as SOS) on copper substrate by combining a two-step surface texturing process (first, the substrate is immersed in an aqueous solution of HNO3 and cetyltrimethyl ammonium bromide, and then in an aqueous solution of NaOH and (NH4)2S2O8) and succeeding surface fluorination with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) or 1-decanethiol. The surface morphologies and compositions were characterized by field emission scanning electron microscopy and X-ray diffraction, respectively. The results showed that spherical micro-pits (SMP) with diameter of 50-100 μm were formed in the first step of surface texturing; in the second step, Cu(OH)2 or/and CuO with structures of nanorods/microflowers/microballs were formed thereon. The surface wettability was further assessed by optical contact angle meter by using water (surface tension of 72.1 mN m(-1) at 20°C), rapeseed oil (35.7 mN m(-1) at 20°C), and hexadecane (25.7 mN m(-1) at 20°C) as probe liquids. The results showed that, as the surface tension decreasing, stricter choosing of surface structures and surface chemistry are required to obtain SOS. Specifically, for hexadecane, which records the lowest surface tension, the ideal surface structures are a combination of densely distributed SMP and nanorods, and the surface chemistry should be tuned by grafted with low-surface-energy molecules of PFDT. Moreover, the stability of the so-fabricated sample was tested and the results showed that, under the testing conditions, superhydrophobicity and superoleophobicity may be deteriorated after wear/humidity resistance test. Such deterioration may be due to the loss of outermost PFDT layer or/and the destruction of the above-mentioned ideal surface structures. For UV and oxidation resistance, the sample remained stable for a period of 10 days.

Carboranedithiols: building blocks for self-assembled monolayers on copper surfaces

Two different positional isomers of 1,2-dicarba-closo-dodecaboranedithiols, 1,2-(HS)(2)-1,2-C(2)B(10)H(10) (1) and 9,12-(HS)(2)-1,2-C(2)B(10)H(10) (2), have been investigated as cluster building blocks for self-assembled monolayers (SAMs) on copper surfaces. These two isomers represent a convenient system in which the attachment of SH groups at different positions on the skeleton affects their acidic character and thus also determines their reactivity with a copper surface. Isomer 1 exhibited etching of polycrystalline Cu films, and a detailed investigation of the experimental conditions showed that both the acidic character of SH groups and the presence of oxygen at the copper surface play crucial roles in how the surface reaction proceeds: whether toward a self-assembled monolayer or toward copper film etching. We found that each positional isomer requires completely different conditions for the preparation of a SAM on copper surfaces. Optimized conditions for the former isomer required the exposure of a freshly prepared Cu surface to vapor of 1 in vacuum, which avoided the presence of oxygen and moisture. Adsorption from a dichloromethane solution afforded a sparsely covered Cu(0) surface; isomer 1 effectively removes the surface copper(I) oxide, forming a soluble product, but apparently binds only weakly to the clean Cu(0) surface. In contrast, adsorption of the latter, less volatile isomer proceeded better from a dichloromethane solution than from the vapor phase. Isomer 2 was even able to densely cover the copper surface cleaned up by the dichloromethane solution of 1. Both isomers exhibited high capacity to remove oxygen atoms from the surface copper(I) oxide that forms immediately after the exposure of freshly prepared copper films to ambient atmosphere. Isomer 2 showed suppression of Cu film oxidation. A number of methods including X-ray photoelectron spectroscopy (XPS), X-ray Rutherford back scattering (RBS), proton-induced X-ray emission (PIXE) analysis, atomic force microscopy (AFM), cyclic voltammetry, and contact angle measurements were used to investigate the experimental conditions for the preparation of SAMs of both positional isomers on copper surfaces and to shed light on the interaction between these molecules and a polycrystalline copper surface.

Electrochemical and spectroscopic study of the self-assembling mechanism of normal and chelating alkanethiols on copper

The self-assembly of aliphatic thiol (RSH), dithiol (R(SH)(2)), and dithiocarboxylic acid (RS(2)H) onto mildly oxidized and highly oxidized copper was studied in real time by in situ electrochemical impedance spectroscopy (EIS). Ex situ characterization of the films was carried out using linear sweep voltammetry (LSV), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). In situ EIS studies found a very fast adsorption of RSH, R(SH)(2), and RS(2)H (within 10-15 s). This fast adsorption step is followed by the long-term additional adsorption and consolidation of SAM. However, the self-assembly of RS(2)H passes through an intermediate step of molecule rearrangement for around 10 to 30 min after around 2 to 7 min of self-assembly. The binding of both sulfur moieties of R(SH)(2) with Cu happens simultaneous. The oxide reduction capacity of RSH, R(SH)(2), and RS(2)H was good. However, the XPS studies showed the decomposition of RS(2)H-based SAMs to Cu(2)S. Monolayers prepared on both mildly oxidized and heavily oxidized Cu with R(SH)(2) had the highest stability. Monolayers of RS(2)H showed the least stability on both mildly oxidized and heavily oxidized Cu. Although RSH-based SAMs had good organization on both mildly oxidized and highly oxidized Cu, R(SH)(2)-based SAMs did not show good organization in either case. The RS(2)H monolayer had good organization only on mildly oxidized Cu.

1-Dodecanethiol self-assembled monolayers on cobalt

Cobalt and its alloys are used in a broad range of application fields. However, the use of this metal is especially limited by its strongly oxidizable nature. The use of alkanethiol self-assembled monolayers (SAMs) is a very efficient way to protect against such oxidation and/or to inhibit corrosion. This surface modification method has been particularly applied to oxidizable metals such as copper or nickel, yet the modification of cobalt surfaces by alkanethiol SAMs received limited attention up to now. In this work, we study the influence of parameters by which to control the self-assembly process of 1-dodecanethiol monolayers on cobalt: nature of the surface pretreatment, solvent, immersion time, and concentration. Each of these parameters has been optimized to obtain a densely packed and stable monolayer able to efficiently prevent the reoxidation of the modified cobalt substrates. The obtained monolayers were characterized by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection-absorption spectroscopy, and contact angle measurements. The stability of the optimized 1-dodecanethiol monolayer upon air exposure for 28 days has been confirmed by XPS.