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

A surface strategy boosting the ethylene selectivity for CO2 reduction and in situ mechanistic insights

Electrochemical reduction of carbon dioxide into ethylene, as opposed to traditional industrial methods, represents a more environmentally friendly and promising technical approach. However, achieving high activity of ethylene remains a huge challenge due to the numerous possible reaction pathways. Here, we construct a hierarchical nanoelectrode composed of CuO treated with dodecanethiol to achieve elevated ethylene activity with a Faradaic efficiency reaching 79.5%. Through on in situ investigations, it is observed that dodecanethiol modification not only facilitates CO2 transfer and enhances *CO coverage on the catalyst surfaces, but also stabilizes Cu(100) facet. Density functional theory calculations of activation energy barriers of the asymmetrical C-C coupling between *CO and *CHO further support that the greatly increased selectivity of ethylene is attributed to the thiol-stabilized Cu(100). Our findings not only provide an effective strategy to design and construct Cu-based catalysts for highly selective CO2 to ethylene, but also offer deep insights into the mechanism of CO2 to ethylene.

Solar-driven CO2-to-ethanol conversion enabled by continuous CO2 transport via a superhydrophobic Cu2O nano fence

The overall photocatalytic CO2 reduction reaction presents an eco-friendly approach for generating high-value products, specifically ethanol. However, ethanol production still faces efficiency issues (typically formation rates <605 μmol g-1 h-1). One significant challenge arises from the difficulty of continuously transporting CO2 to the catalyst surface, leading to inadequate gas reactant concentration at reactive sites. Here, we develop a mesoporous superhydrophobic Cu2O hollow structure (O-CHS) for efficient gas transport. O-CHS is designed to float on an aqueous solution and act as a nano fence, effectively impeding water infiltration into its inner space and enabling CO2 accumulation within. As CO2 is consumed at reactive sites, O-CHS serves as a gas transport channel and diffuser, continuously and promptly conveying CO2 from the gas phase to the reactive sites. This ensures a stable high CO2 concentration at reactive sites. Consequently, O-CHS achieves the highest recorded ethanol formation rate (996.18 μmol g-1 h-1) to the best of our knowledge. This strategy combines surface engineering with geometric modulation, providing a promising pathway for multi-carbon production.

Tunable CO2 electroreduction to ethanol and ethylene with controllable interfacial wettability

The mechanism of how interfacial wettability impacts the CO₂ electroreduction pathways to ethylene and ethanol remains unclear. This paper describes the design and realization of controllable equilibrium of kinetic-controlled *CO and *H via modifying alkanethiols with different alkyl chain lengths to reveal its contribution to ethylene and ethanol pathways. Characterization and simulation reveal that the mass transport of CO₂ and H₂O is related with interfacial wettability, which may result in the variation of kinetic-controlled *CO and *H ratio, which affects ethylene and ethanol pathways. Through modulating the hydrophilic interface to superhydrophobic interface, the reaction limitation shifts from insufficient supply of kinetic-controlled *CO to that of *H. The ethanol to ethylene ratio can be continuously tailored in a wide range from 0.9 to 1.92, with remarkable Faradaic efficiencies toward ethanol and multi-carbon (C₂₊) products up to 53.7% and 86.1%, respectively. A C₂₊ Faradaic efficiency of 80.3% can be achieved with a high C₂₊ partial current density of 321 mA cm^-2, which is among the highest selectivity at such current densities.

Electrochemical Stability of Thiolate Self-Assembled Monolayers on Au, Pt, and Cu

Self-assembled monolayers (SAMs) of thiolates have increasingly been used for modification of metal surfaces in electrochemical applications including selective catalysis (e.g., CO₂ reduction, nitrogen reduction) and chemical sensing. Here, the stable electrochemical potential window of thiolate SAMs on Au, Pt, and Cu electrodes is systematically studied for a variety of thiols in aqueous electrolyte systems. For fixed tail-group functionality, the reductive stability of thiolate SAMs is found to follow the trend Au < Pt < Cu; this can be understood by considering the combined influences of the binding strength of sulfur and competitive adsorption of hydrogen. The oxidative stability of thiolate SAMs is found to follow the order: Cu < Pt < Au, consistent with each surface's propensity toward surface oxide formation. The stable reductive and oxidative potential limits are both found to vary linearly with pH, except for reduction above pH ∼10, which is independent of pH for most thiol compositions. The electrochemical stability across different functionalized thiols is then revealed to depend on many different factors including SAM defects (accessible surface metal atom sites decrease stability), intermolecular interactions (hydrophilic groups reduce the stability), and SAM thickness (stability increases with alkanethiol carbon chain length) as well as factors such as SAM-induced surface reconstruction and the ability to directly oxidize or reduce the non-sulfur part of the SAM molecule.

Effects of Ageing in Disinfectant Solution on the Corrosion Resistance and Antimicrobial Behavior of Copper Alloys

This work studies two copper-based alloys as potential antimicrobial weapons for sectors where surface hygiene is essential. Effects of different alloying elements addition at the same Cu content (92.5% by weight) on the corrosion resistance and the antibacterial performance of two copper alloys were studied in an aerated disinfectant solution (0.25% v/v Aniosurf Premium (D)) by electrochemical corrosion, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and antibacterial tests. Results showed that the nature of the alloying elements had a clear influence on the corrosion resistance and antibacterial performance. Electrochemical impedance results and surface analyses demonstrate the presence of organic compounds bound on the substrate and that a film covers part of the total active surface and may act as a protective barrier by preventing the interaction between metal and solution, decreasing the antimicrobial performance of copper-based materials. Low zinc and silicon contents in copper alloys allows for better aging behavior in D solution while maintaining good antibacterial performance. The XPS and ToF-SIMS results indicated that artificial aging in disinfectant enhanced Cu enrichment in the organic film formed, which could effectively stimulate the release of Cu ions from the surface.

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

The conversion of CO₂ into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO₂ into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C₂₊ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C₂₊ formation of ≈80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm^-2 for C₂₊ products.

Green Method for Fabrication of an Underwater Superoleophobic Phosphor-Copper Mesh and Transportation of Oily Liquids

Sea cucumber-shaped Cu₂O nanostructures are constructed on a phosphor-copper mesh by employing a one-step immersion process accomplished in distilled water without introducing any additional reagent. The phosphor-copper mesh with a Cu₂O structure thereon exhibits significant hydrophilicity and induces a large superoleophobic force at the oil/water interface. The method used for preparing the Cu₂O nanostructures represents an inexpensive, fast, and environmentally friendly approach, along with satisfying the requirements of large-scale preparation. It is found that the pickling degree of the phosphor-copper mesh during surface cleaning plays a major role in the oxidation process of the surface for the growth of Cu₂O nanostructures. Nanostructures with different morphologies can be achieved by accurately controlling the surface pickling degree. Interestingly, an underwater superoleophobic "pipe" developed using the as-prepared phosphor-copper mesh can realize gravity (buoyancy)-driven oily liquid transport in an aqueous environment, with no associated contamination by the oil. This study provides a simple method to realize surface-functionalization and demonstrates a new route for achieving liquid transportation without external energy and would help to design smart aquatic devices for diverse liquid transport thereby, enabling oil handling and oil spill cleanup.

Effect of Multilayer versus Monolayer Dodecanethiol on Selectivity and Pattern Integrity in Area-Selective Atomic Layer Deposition

Monolayer and multilayer dodecanethiols (DDT) can be assembled onto a copper surface from the vapor phase depending on the initial oxidation state of the copper. The ability of the copper-bound dodecanethiolates to block atomic layer deposition (ALD) and the resulting behavior at the interfaces of Cu/SiO₂ patterns during area-selective ALD (AS-ALD) are compared between mono- and multilayers. We show that multilayer DDT is ∼7 times more effective at blocking ZnO ALD from diethylzinc and water than is monolayer DDT. Conversely, monolayer DDT exhibits better performance than does multilayer DDT in blocking of Al₂O₃ ALD from trimethylaluminum and water. Investigation into interfacial effects at the interface between Cu and SiO₂ on Cu/SiO₂ patterns reveals both a gap at the SiO₂ edges and a pitch size-dependent nucleation delay of ZnO ALD on SiO₂ regions of multilayer DDT-coated patterns. In contrast, no impact on ZnO ALD is observed on the SiO₂ regions of monolayer DDT-coated patterns. We also show that these interfacial effects depend on the ALD chemistry. Whereas an Al₂O₃ film grows on the TaN diffusion barrier of a DDT-treated Cu/SiO₂ pattern, the ZnO film does not. These results indicate that the structure of the DDT layer and the ALD precursor chemistry both play an important role in achieving AS-ALD.

Bio-inspired hydrophobicity promotes CO2 reduction on a Cu surface

The aqueous electrocatalytic reduction of CO₂ into alcohol and hydrocarbon fuels presents a sustainable route towards energy-rich chemical feedstocks. Cu is the only material able to catalyse the substantial formation of multicarbon products (C₂/C₃), but competing proton reduction to hydrogen is an ever-present drain on selectivity. Here, a superhydrophobic surface was generated by 1-octadecanethiol treatment of hierarchically structured Cu dendrites, inspired by the structure of gas-trapping cuticles on subaquatic spiders. The hydrophobic electrode attained a 56% Faradaic efficiency for ethylene and 17% for ethanol production at neutral pH, compared to 9% and 4% on a hydrophilic, wettable equivalent. These observations are assigned to trapped gases at the hydrophobic Cu surface, which increase the concentration of CO₂ at the electrode-solution interface and consequently increase CO₂ reduction selectivity. Hydrophobicity is thus proposed as a governing factor in CO₂ reduction selectivity and can help explain trends seen on previously reported electrocatalysts.

Facile Fabrication of Superhydrophobic Copper- Foam and Electrospinning Polystyrene Fiber for Combinational Oil⁻Water Separation

Membrane-based metal substrates with special surface wettability have been applied widely for oil/water separation. In this work, a series of copper foams with superhydrophobicity and superoleophilicity were chemically etched using 10 mg mL⁻¹ FeCl₃/HCl solution with consequent ultrasonication, followed by the subsequent modification of four sulfhydryl compounds. A water contact angle of 158° and a sliding angle lower than 5° were achieved for the copper foam modified using 10 mM n-octadecanethiol solution in ethanol. In addition, the interaction mechanism was initially investigated, indicating the coordination between copper atoms with vacant orbital and sulfur atoms with lone pair electrons. In addition, the polymeric fibers were electrospun through the dissolution of polystyrene in a good solvent of chlorobenzene, and a nonsolvent of dimethyl sulfoxide. Oil absorption and collection over the water surface were carried out by the miniature boat made out of copper foam, a string bag of as-spun PS fibers with high oil absorption capacity, or the porous boat embedded with the as-spun fibers, respectively. The findings might provide a simple and practical combinational method for the solution of oil spill.

Self-assembled monolayers in organic electronics

Self-assembly is possibly the most effective and versatile strategy for surface functionalization. Self-assembled monolayers (SAMs) can be formed on (semi-)conductor and dielectric surfaces, and have been used in a variety of technological applications. This work aims to review the strategy behind the design and use of self-assembled monolayers in organic electronics, discuss the mechanism of interaction of SAMs in a microscopic device, and highlight the applications emerging from the integration of SAMs in an organic device. The possibility of performing surface chemistry tailoring with SAMs constitutes a versatile approach towards the tuning of the electronic and morphological properties of the interfaces relevant to the response of an organic electronic device. Functionalisation with SAMs is important not only for imparting stability to the device or enhancing its performance, as sought at the early stages of development of this field. SAM-functionalised organic devices give rise to completely new types of behavior that open unprecedented applications, such as ultra-sensitive label-free biosensors and SAM/organic transistors that can be used as robust experimental gauges for studying charge tunneling across SAMs.

Selective Deposition of Dielectrics: Limits and Advantages of Alkanethiol Blocking Agents on Metal-Dielectric Patterns

Area selective atomic layer deposition has the potential to significantly improve current fabrication approaches by introducing a bottom-up process in which robust and conformal thin films are selectively deposited onto patterned substrates. In this paper, we demonstrate selective deposition of dielectrics on metal/dielectric patterns by protecting metal surfaces using alkanethiol blocking layers. We examine alkanethiol self-assembled monolayers (SAMs) with two different chain lengths deposited both in vapor and in solution and show that in both systems, thiols have the ability to block surfaces against dielectric deposition. We show that thiol molecules can displace Cu oxide, opening possibilities for easier sample preparation. A vapor-deposited alkanethiol SAM is shown to be more effective than a solution-deposited SAM in blocking ALD, even after only 30 s of exposure. The vapor deposition also results in a much better thiol regeneration process and may facilitate deposition of the SAMs on porous or three-dimensional structures, allowing for the fabrication of next generation electronic devices.

Thiol Adsorption on and Reduction of Copper Oxide Particles and Surfaces

The adsorption of 1-dodecanethiol at room temperature and at 75 °C on submicron cuprous and cupric oxide particles suspended in ethanol has been investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy. Thiol adsorption occurs in all cases via Cu-S bond formation, with partial dissolution of CuO at 75 °C and formation of a copper-thiolate complex replacement layer. Regardless of temperature, the surface of the CuO particles is essentially completely reduced to either Cu2O or metallic copper, as evidenced by loss of the characteristic Cu(2+) XPS features of dried powder samples. Companion ultrahigh-vacuum studies have been performed by dosing clean, oxygen-dosed, and ozone-treated single crystal Cu(111) with methanethiol (MT) gas at room temperature. In the latter case, the surface corresponds to CuO/Cu(111). XPS confirms MT adsorption in all cases, with an S 2p peak binding energy of 162.9 ± 0.1 eV, consistent with methanethiolate adsorption. Heating of MT-covered Cu(111) and oxygen-dosed Cu(111) leads to decomposition/desorption of the MT by 100 °C and formation of copper sulfide with an S 2p binding energy of 161.8 eV. Dosing CuO/Cu(111) with 50-200 L of MT leads to only partial reduction/removal of the CuO surface layers prior to methanethiolate adsorption. This is confirmed by ultraviolet photoelectron spectroscopy (UPS), which measures the occupied states near the Fermi level. For both the colloidal CuO and single crystal CuO/Cu(111) studies, the reduction of the Cu(2+) surface is believed to occur by formation and desorption of the corresponding dithiol prior to thiolate adsorption.

Wettability and permeation of ethanol/water mixture on porous mesh surface

A serial of copper meshes with different chemical composition and roughness was prepared by modifying different mixed thiols, which showed different wetting behavior and permeation behavior for different ethanol/water mixed solution.

Superhydrophobic cuprous oxide nanostructures on phosphor-copper meshes and their oil-water separation and oil spill cleanup

A simple aqueous solution-immersion process was established to fabricate highly dense ordered Cu2O nanorods on commercial phosphor-copper mesh, with which the preparation was accomplished in distilled water. The present method, with the advantages of simple operation, low cost, short reaction time, and environmental friendliness, can be well adopted to fabricate desired Cu2O nanostructures on the phosphor-copper mesh under mild conditions. After surface modification with 1-dodecanethiol, the Cu2O nanostructure obtained on the phosphor-copper mesh exhibits excellent superhydrophobicity and superoleophilicity. Besides, a "mini boat" made from the as-prepared superhydrophobic phosphor-copper mesh can float freely on water surface and in situ collect oil from water surface. This demonstrates that the present approach, being facile, inexpensive, and environmentally friendly, could find promising application in oil-water separation and off shore oil spill cleanup.

Adsorption of linear aliphatic α,ω-dithiols on plasmonic metal nanoparticles: a structural study based on surface-enhanced Raman spectra

The adsorption mechanism of linear aliphatic α,ω-dithiols with chain lengths of 6, 8 and 10 carbon atoms on silver and gold nanoparticles has been studied by surface-enhanced Raman scattering (SERS) spectroscopy.

Self-assembled monolayers of terminal acetylenes as replacements for thiols in bottom-up tunneling junctions

Why use thiols in Molecular Electronics?

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.