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Surface corrosion involves a series of redox reactions that are catalyzed by the presence of ions. On infrastructure surfaces and in complex and natural environments, iron surfaces readily undergo redox reactions, impacting chemical processes. In this study, the effect of how cations influence the formation of the mineral scale on iron surfaces and its connection to surface corrosion was investigated in CaCl2(aq) and NaCl(aq) electrolytes. Polarized modulated-infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to measure the oxidation and formation of carbonates at the air/electrolyte/iron interface, which confirmed that the iron surface oxidized faster in CaCl2(aq) than in NaCl(aq). PM-IRRAS, attenuated total reflectance-Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy show that after the adsorption of atmospheric O2 and CO2, calcium carbonate (CaCO3) in the form of calcite and aragonite was produced on iron in the presence of CaCl2(aq), whereas siderite (FeCO3) was produced on the surface of iron in the presence of NaCl(aq). However, in either solution without gradual O2 and CO2 exposure, a heterogeneous mixture of lepidocrocite (γ-FeOOH) and an iron hydroxy carbonate (Fex(OH)yCO3) was grown on the iron surface. In situ liquid AFM was used to measure the surface roughness in CaCl2(aq) and NaCl(aq), as an estimation of the corrosion rate. In CaCl2(aq), Fe was found to corrode faster than Fe in NaCl(aq) due to more ions at equimolar concentrations. Surface physical changes, as measured by ex situ AFM, confirmed the presence of a heterogeneous mixture of γ-FeOOH and an Fex(OH)yCO3 in the submerged region. This indicates that the cation does not affect the type of mineral grown on the Fe surface in the region completely submerged in the electrolyte. These results suggest that the cations play a unique role in the initial stages of corrosion at the interface region, influencing the uptake of atmospheric CO2 and mineral nucleation. The knowledge gained from these interfacial reactions are important for understanding the connection between surface corrosion, mineral grown, and CO2 capture for sequestration.

Surface chemistry impacts technology, advancing the development of new heterogeneous catalysts, semiconductor devices, and materials synthesis. Carbon surfaces are ubiquitous in various fields, and the surface reactivity can be altered by surface functionalization on the molecular scale, introducing functional groups, thus shifting their macroscale properties. In this physical chemistry lab experiment, students use atomic force microscopy to investigate the surface of graphite (organic) and gold (inorganic) samples (solid phase) to compare topographical features, surface roughness, and adhesion forces of the samples. Students relate the force–displacement measurements with the Lennard-Jones potential to obtain measurable adhesion forces. Emphasis is placed on quantification of the adhesion forces between a hydrophobic highly oriented pyrolytic graphite (HOPG) surface, a hydrophilic (hydroxy) functionalized HOPG surface, and a metallic gold-coated glass slide. The surface of each sample is explored, allowing students to compare the difference between the hydrophobic and hydrophilic surfaces from surface functionalization.

Iron interfaces undergo redox and catalytic processes in various environments, on the surface of soils, dust, minerals, and materials that comprise industrial infrastructure. Measuring reactions at...

Vibrational spectroscopy techniques have evolved to measure gases, liquids, and solids at surfaces and interfaces. In the field of surface-sensitive vibrational spectroscopy, infrared spectroscopy measures the adsorption on surfaces and changes from reactions. Previous polarized modulated-infrared reflection-absorption spectroscopy (PM-IRRAS) measurements at the gas/solid interface were developed to observe catalytic reactions near reaction conditions. Other PM-IRRAS measurements use liquid cells where the sample is submerged and compressed against a prism that has traditionally been used for electrochemical reactions. This article presents a new method that is used to observe in situ adsorption of molecules using PM-IRRAS at the gas/liquid/solid interface. We demonstrate the meniscus method by measuring the adsorption of octadecanethiol on gold surfaces. Characterization of self-assembled monolayers (SAMs), the "gold standard" for PM-IRRAS calibration measurements, was measured in ethanol solutions. The condensed-phase (air/liquid) interface in addition to the liquid/solid interface was measured simultaneously in solution. These are compared with liquid attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy measurements to confirm the presence of the SAM and liquid ethanol. A model of the three-phase system is used to approximate the thickness of the liquid ethanol layer and correlate these values to signal attenuation using PM-IRRAS. This proof-of-concept study enables the measurement of reactions at the gas/liquid/solid interface that could be adapted for other reactions at the electrode and electrolyte interfaces with applications in environmental science and heterogeneous catalysis.

The knowledge of chemical functionalization for area selective deposition (ASD) is crucial for designing the next generation heterogeneous catalysis. Surface functionalization by oxidation was studied on the surface of highly oriented pyrolytic graphite (HOPG). The HOPG surface was exposed to with various concentrations of two different acids (HCl and HNO3). We show that exposure of the HOPG surface to the acid solutions produce primarily the same -OH functional group and also significant differences the surface topography. Mechanisms are suggested to explain these strikingly different surface morphologies after surface oxidation. This knowledge can be used to for ASD synthesis methods for future graphene-based technologies.

Vibrational spectroscopy techniques have evolved to measure gases, liquids, and solids at surfaces and interfaces. In the field of surface-sensitive vibrational spectroscopy, infrared spectroscopy measures the adsorption on surfaces and changes from reactions. Previous polarized modulated-infrared reflection-absorption spectroscopy (PM-IRRAS) measurements at the gas/solid interface were developed to observe catalytic reactions near reaction conditions. Other PM-IRRAS measurements use liquid cells where the sample is submerged and compressed against a prism that has traditionally been used for electrochemical reactions. This article presents a new method that is used to observe

Reactions on iron oxide surfaces are prevalent in various chemical processes from heterogeneous catalysts to minerals. Nitrogen (N

It is now well established by numerous experimental and computational studies that the adsorption propensities of inorganic anions conform to the Hofmeister series. The adsorption propensities of inorganic cations, such as the alkali metal cations, have received relatively little attention. Here we use a combination of liquid-jet X-ray photoelectron experiments and molecular dynamics simulations to investigate the behavior of K+ and Li+ ions near the interfaces of their aqueous solutions with halide ions. Both the experiments and the simulations show that Li+ adsorbs to the aqueous solution−vapor interface, while K+ does not. Thus, we provide experimental validation of the “surfactant-like” behavior of Li+ predicted by previous simulation studies. Furthermore, we use our simulations to trace the difference in the adsorption of K+ and Li+ ions to a difference in the resilience of their hydration shells.

Direct recycling of Li-ion batteries (LIBs) reclaims electrode materials using physical separation followed by materials' rejuvenation processes. The cathode composites in LIBs contain both carbon black and PVDF binders in its chemistry. For the rejuvenation process to work, an ability to remove these impurities is desirable. In the present work, de-agglomeration of individual components from the cathode composites has been carried out using a mechanical process that is developed for preserving functional integrity of the cathode active materials. It has been shown that the size of the cathode composites is effectively reduced upon a de-agglomeration process due to a liberation of PVDF binders from the cathode composites. The de-agglomeration performance has been evaluated by separating mixed materials by the degree in surface hydrophobicity using the froth flotation method. The performance improves with end-of-life (EOL) LIBs compared to new LIBs, benefiting from a degradation of PVDF binders after charging-discharging cycles. X-ray photoelectron spectra suggests that the de-agglomeration is done by breaking intermolecular bond between PVDF and cathode active materials as well as covalent bond within PVDF binders. The present work demonstrates a non-chemical method for liberating individual components from cathode composites for the direct recycling of LIBs.

A simple two-step, shaking-assisted polydopamine (PDA) coating technique was used to impart polypropylene (PP) mesh with antimicrobial properties. In this modified method, a relatively large concentration of dopamine (20 mg ml−1) was first used to create a stable PDA primer layer, while the second step utilized a significantly lower concentration of dopamine (2 mg ml−1) to promote the formation and deposition of large aggregates of PDA nanoparticles. Gentle shaking (70 rpm) was employed to increase the deposition of PDA nanoparticle aggregates and the formation of a thicker PDA coating with nano-scaled surface roughness (RMS = 110 nm and Ra = 82 nm). Cyclic voltammetry experiment confirmed that the PDA coating remained redox active, despite extensive oxidative cross-linking. When the PDA-coated mesh was hydrated in phosphate saline buffer (pH 7.4), it was activated to generate 200 μM hydrogen peroxide (H2O2) for over 48 h. The sustained release of low doses of H2O2 was antibacterial against both gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria. PDA coating achieved 100% reduction (LRV ~3.15) when incubated against E. coli and 98.9% reduction (LRV ~1.97) against S. epi in 24 h.

Iron oxide nanomaterials participate in redox processes that give them ideal properties for their use as earth-abundant catalysts. Fabricating nanocatalysts for such applications requires detailed knowledge of the deposition and growth. We report the spontaneous deposition of iron oxide nanoparticles on HOPG in defect areas and on step edges from a metal precursor solution. To study the nucleation and growth of iron oxide nanoparticles, tailored defects were created on the surface of HOPG using various ion sources that serve as the target sites for iron oxide nucleation. After solution deposition and annealing, the iron oxide nanoparticles were found to nucleate and coalesce at 400 °C. AFM revealed that the particles on the sp3 carbon sites enabled the nanoparticles to aggregate into larger particles. The iron oxide nanoparticles were characterized as having an Fe3+ oxidation state and two different oxygen species, Fe–O and Fe–OH/Fe–OOH, as determined by XPS. STEM imaging and EDS mapping confirmed that the majority of the nanoparticles grown were converted to hematite after annealing at 400 °C. A mechanism of spontaneous and selective deposition on the HOPG surface and transformation of the iron oxide nanoparticles is proposed. These results suggest a simple method for growing nanoparticles as a model catalyst.

Reactions on iron oxide surfaces are prevalent in various chemical processes from heterogeneous catalysts to minerals. Nitrogen (N2) is known to dissociate on iron surfaces, a precursor for ammonia production in the Haber–Bosch process, where the dissociation of N2 is the limiting step in the reaction under equilibrium conditions. However, little is known about N2 adsorption on other iron-based materials, such as iron oxide surfaces that are ubiquitous in soils, steel pipelines, and other industrial materials. An atomistic description is reported for the binding of N2 on the Fe3O4(001) surface using first principles calculations with ambient pressure X-ray photoelectron spectroscopy. Two primary adsorption sites are experimentally identified from N2 dissociation on Fe3O4(001). The electronic signatures associated with the valence band region unambiguously show how the electronic structure of magnetite transforms near ambient pressures due to the binding of atomic nitrogen to different surface sites. Overall, the experimental and theoretical results of our study bridge the gap between ultra-high vacuum studies and reaction conditions to provide insight into other nitrogen-based chemistry on iron oxide surfaces that impact the agriculture and energy industries.

Ion adsorption to the interfaces of aqueous salt solutions plays a key role in a wide variety of chemical and biochemical processes. For example, the adsorption of ions to the surface of aqueous aerosol particles in the atmosphere influences their reactivity to gas-phase oxidants. While the so-called chaotropic anions (e.g., I−, SCN−, and ClO4−) are known to have strong adsorption propensities, inorganic cations are generally regarded as being repelled from aqueous solution−air interfaces. Here we report a concerted experimental and computational study that reveals that Li+ adsorbs to the interfaces of aqueous lithium halide solutions and, hence, is an exceptional cation.

We report photoelectron spectroscopy measurements from binary acetonitrile–water solutions, for a wide range of acetonitrile mole fractions (xCH3CN = 0.011–0.90) using a liquid microjet. By detecting the nitrogen and carbon 1s photoelectron signal of CH3CN from aqueous surface and bulk solution, we quantify CH3CN’s larger propensity for the solution surface as compared to bulk solution. Quantification of the strong surface adsorption is through determination of the surface mole fraction as a function of bulk solution, xCH3CN, from which we estimate the adsorption free energy using the Langmuir adsorption isotherm model. We also discuss alternative approaches to determine the CH3CN surface concentration, based on analysis of the relative amount of gas- versus liquid-phase CH3CN, obtained from the respective photoelectron signal intensities. Another approach is based on the core-level binding energy shifts between liquid- and gas-phase CH3CN, which is sensitive to the change in solution surface potential an...

Selective deposition using atomic layer deposition has potential as a viable method for growing patterned nanostructured materials, thus advancing the design of next-generation electronics and catalysts. This study investigated how etching HOPG produces different densities of functional groups and different morphologies that were found to influence the growth of Al2O3 structures. Hydrochloric acid produced a high density of –OH and –COOH functional sites on terrace regions on HOPG in comparison to nitric acid that produced –OH functional sites at defects. After exposure to ALD cycles of trimethylaluminum and water, different structures of Al2O3 were found to grow on the functional sites compared to defect sites. Field emission scanning electron microscopy, atomic force microscopy and Raman spectral imaging were used to characterize the changes in surface topography after etching and ALD. Vibrational spectroscopy and X-ray photoelectron spectroscopy were used to measure surface functionalization and quantify Al2O3 growth. Results suggest that the Al2O3 nucleation and growth at submonolayer coverage is affected by the surface functionalization as well as the topography and density of functional sites. This study finds that selective deposition on active areas are determined by the morphology and the functional groups that depend on the etching mechanism with the surface. These results suggest that understanding both the topography and type of functional site are necessary for designing the next-generation electronic devices and catalysts.

In the work described here, the electronic structure of sulfuric acid in water is explored by liquid-jet photoelectron spectroscopy. From the S2p photoelectron spectra of H2SO4 (aq), measured over a large concentration range and aided by previously reported HSO4–/SO42- and HSO4–/H2SO4 concentration ratios in the bulk solution, we obtain detailed electronic structure information of each species. Comparing our results with previous studies on the dissociation of nitric acid, we argue that the solvation structure of H2SO4 (aq) changes around 5–7 M concentration, at which point a dramatic change in both the HSO4– photoelectron peak width and binding energy occurs.

With scaling down the size of the features in modern electronic devices, it becomes vital to control surface reactions at the interface for clean deposition on semiconductor substrates. Chemical functionalization of silicon surfaces provides a new approach for tuning the structure and properties of the interfaces formed with this semiconductor. The functionalized surfaces, such as H–Si(100), NH–Si(100), and NH2–Si(100) can be used to prevent surface oxidation at the silicon interface, and OH–Si(100) can be utilized to limit surface diffusion in a reaction with a metal–organic precursor. A model copper metal–organic precursor, copper (hexafluoroacetylacetonato)vinyltrimethylsilane or Cu(hfac)VTMS, was used to grow copper nanostructures by chemical vapor deposition (CVD), as verified by atomic force microscopy (AFM), infrared spectroscopy (MIR-FTIR), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD) supported with density functional theory calculations (DFT). These methods ...

Ultrathin film deposition schemes often result in the growth of disordered structures whose surface chemistry is complex and can make predicting its reactivity difficult. Here, the surface reactivity of a disordered TiCN film is described using density functional theory calculations with simple cluster models of a general formula Ti4CxN4–x (0 < x < 4). These models allow for the simulation of adsorption on a Ti atom or along Ti–C and Ti–N surface sites. For the TiCN material, localized surface–adsorbate interactions are accurately predicted with the Ti4CxN4–x models and compared with experiments. The energetics of adsorption on TiCN was simulated on our cluster models, using small probe molecules, and compared with the results of temperature programmed desorption studies. The robustness of the cluster model is validated by varying its atomic composition and utilizing different cluster terminations. This convenient approach can be used to design models of other disordered surfaces if localized interactions...

Constant miniaturization of electronic devices and interfaces needed to make them functional requires an understanding of the initial stages of metal growth at the molecular level. The use of metal-organic precursors for metal deposition allows for some control of the deposition process, but the ligands of these precursor molecules often pose substantial contamination problems. One of the ways to alleviate the contamination problem with common copper deposition precursors, such as copper(I) (hexafluoroacetylacetonato) vinyltrimethylsilane, Cu(hfac)VTMS, is a gas-phase reduction with molecular hydrogen. Here we present an alternative method to copper film and nanostructure growth using the well-defined silicon surface. Nearly ideal hydrogen termination of silicon single-crystalline substrates achievable by modern surface modification methods provides a limited supply of a reducing agent at the surface during the initial stages of metal deposition. Spectroscopic evidence shows that the Cu(hfac) fragment is present upon room-temperature adsorption and reacts with H-terminated Si(100) and Si(111) surfaces to deposit metallic copper. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to follow the initial stages of copper nucleation and the formation of copper nanoparticles, and X-ray energy dispersive spectroscopy (XEDS) confirms the presence of hfac fragments on the surfaces of nanoparticles. As the surface hydrogen is consumed, copper nanoparticles are formed; however, this growth stops as the accessible hydrogen is reacted away at room temperature. This reaction sets a reference for using other solid substrates that can act as reducing agents in nanoparticle growth and metal deposition.

Chemical control of interfaces formed on silicon surfaces is important for many practical applications. In this work, the reaction of nitrosobenzene with a clean Si(100)- 2 × 1 surface by [2 + 2] cycloaddition at room temperature is investigated. This reaction is compared to the 1,3-dipolar cycloaddition reaction of nitrobenzene on the same surface and to the cyclocondensation reaction of nitrobenzene with hydrogen-terminated Si(100) surfaces. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) methods were used for this study. For both nitrosobenzene and nitrobenzene on Si(100)- 2 × 1, oxygen migrates subsurface, despite substantial kinetic barriers. The effects of oxygen migration are addressed by combining DFT cluster modeling and XPS in the N 1s region. The reaction pathways of these nitrogen-containing bifunctional molecules on a clean Si(100)- 2 × 1 surface lead to the phenylnitrene adduct as the dominant surface species, while ...

The molecular level chemistry of 2,2,6,6-tetramethyl-3,5-heptanedione (dpmH) has been investigated on a Si(1 0 0)-2 × 1 surface. The dpmH compound is a β-diketone, whose deprotonated form is used as a ligand in chemical precursors for metal-organic chemical vapor deposition (MOCVD). A combination of multiple internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR), temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and density functional theory (DFT) were employed to analytically detect and monitor surface species under different thermal conditions. Upon adsorption at cryogenic temperatures dpmH was shown to be present in the enolic form, while primarily OH dissociation and [2 + 2] carbonyl cycloaddition were revealed at room temperature. Upon heating from room temperature to 900 K, isobutene evolution into the gas phase was found to be a minor reaction pathway. The remainder of dpmH decomposes on the surface to release hydrogen into the gas phase.

The thermal decomposition of hydroxyl-terminated generation-4 polyamidoamine dendrimer (G4OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating an approximately 40-atom Pt particle (Pt-G4OH). Infrared absorption reflection spectroscopy studies showed that, when the films were heated in air to various temperatures up to 275 degrees C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres. For the G4OH dendrimer, complete decomposition was achieved in air at 500 degrees C, while decomposition of the Pt-G4OH dendrimer was completed at 400 degrees C, leaving only platinum metal behind. In a nonoxidizing argon atmosphere, a greater fraction of the G4OH decomposed below 300 degrees C, but all of the dendrimer fragments were not removed until heating above 550 degrees C. In contrast, Pt-G4OH decomposition in argon was similar to that in air, except that decomposition occurred at temperatures approximately 15 degrees C higher. Thermal decomposition of the dendrimer films on Au surfaces was also studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. Heating the G4OH films to 250 degrees C during the TPD experiment induced the desorption of large dendrimer fragments at 55, 72, 84, 97, 127, 146, and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much greater intensities for H(2) desorption were detected compared to that of the G4OH film. XPS studies of the G4OH films demonstrated that significant bond breaking in the dendrimer did not occur until temperatures above 250 degrees C and heating to 450 degrees C caused dissociation of C=O, C-O, and C-N bonds. For the Pt-G4OH dendrimer films, carbon-oxygen and carbon-nitrogen bond scission was observed at room temperature, and further decomposition to atomic species occurred after heating to 450 degrees C. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that decomposition of the dendrimer to gaseous hydrogen is the dominant reaction pathway compared to desorption of the larger dendrimer fragments observed in the absence of Pt particles.

As the cornerstone of multiple practical applications, silicon single crystal surfaces have attracted the interest of scientific and engineering communities for several decades. The most recent advances employ the surfaces precovered with a specific functionality to extend into the realm of organic and metal–organic films with well-defined interfaces, to protect the surfaces from oxidation and other contaminations, and to build the components of present and future molecular electronics and sensing devices. This critical review will focus on the reactivity of the selectively terminated Si(100) and Si(111) surfaces. The hydrogen and halogen-terminated surfaces are the most widely used and most heavily reviewed previously, thus only a brief summary will be given here with the emphasis of the most recent thermal approaches to functionalization of hydrogen-terminated silicon. The silicon surfaces precovered with NHx functionality are emerging as a very likely candidate both for the production of sharp interfaces and for coadsorption, co-assembly, and potential molecular templating of patterns on single crystalline surfaces. A brief overview of recent advances in achieving control over the hydroxyl-termination of silicon will be given. Some future directions for further development of chemistry, reactivity, and assembly on these surfaces, as well as potential applications, are highlighted in the last section (152 references).

As the cornerstone of multiple practical applications, silicon single crystal surfaces have attracted the interest of scientific and engineering communities for several decades. The most recent advances employ the surfaces precovered with a specific functionality to extend into the realm of organic and metal-organic films with well-defined interfaces, to protect the surfaces from oxidation and other contaminations, and to build the components of present and future molecular electronics and sensing devices. This critical review will focus on the reactivity of the selectively terminated Si(100) and Si(111) surfaces. The hydrogen and halogen-terminated surfaces are the most widely used and most heavily reviewed previously, thus only a brief summary will be given here with the emphasis of the most recent thermal approaches to functionalization of hydrogen-terminated silicon. The silicon surfaces precovered with NH(x) functionality are emerging as a very likely candidate both for the production of sharp interfaces and for coadsorption, co-assembly, and potential molecular templating of patterns on single crystalline surfaces. A brief overview of recent advances in achieving control over the hydroxyl-termination of silicon will be given. Some future directions for further development of chemistry, reactivity, and assembly on these surfaces, as well as potential applications, are highlighted in the last section (152 references).