Infrared Reflection Absorption Spectroscopy Spectra Research Articles

The quantitative study of methane adsorption on the Pt(997) step surface as the initial process for reforming reactions

The adsorption states and thermal process of methane on a stepped Pt surface were investigated using temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations including van der Waals interactions. By estimating the activation energies of methane desorption from the TPD data, it was revealed that the adsorption energy for methane on the step site (0.19 eV) was higher than that on the terrace site (0.15 eV). The IRAS spectrum after multilayer adsorption and subsequent 70 K heating showed two peaks at 3009 and 1305 cm−1, which were assigned to the antisymmetric stretching and the deformation modes for adsorbed methane on the step site, respectively. The present DFT calculations show that the most stable adsorption structure for methane on the step site is a “2H” structure, where two C-H bonds point toward Pt atoms. Based on the electronic structure analysis, we conclude that the stability of the 2H structure originates from the mixing between the methane molecular orbitals and the orbitals of step Pt atoms. As a result, the length of the C-H bond pointing toward the Pt step atom is elongated compared with that of other C-H bonds. Thus, the Pt step site already activates the adsorbed methane slightly.

Incorporation of the New anti-Octadecaborane Laser Dyes into Thin Polymer Films: A Temperature-Dependent Photoluminescence and Infrared Spectroscopy Study.

New anti-octadecaborane(22) laser dyes have been recently introduced. However, their application in solid thin films is limited, despite being very desirable for electronics. Spectroscopic methods, photoluminescence (PL), and infrared reflection–absorption spectroscopy (IRRAS), are here used to reveal structural responses to a temperature change in thin polymer films made of π- and σ-conjugated and non-conjugated polymers and anti-octadecaborane(22) and its tetra-alkylatedderivatives. It has been observed that borane clusters are not firmly fixed within polymer matrices and that their ability for diffusion out of the polymer film is unprecedented, especially at higher temperatures. This ability is related to thermodynamic transitions of polymer macromolecular chains. PL and IRRAS spectra have revealed a clear correlation with β-transition and α-transition of polymers. The influence of structure and molecular weight of a polymer and the concentration and the substitution type of clusters on mobility of borane clusters within the polymer matrix is demonstrated. A solution is proposed that led to an improvement of the temperature stability of films by 45 °C. The well-known spectroscopic methods have proved to be powerful tools for a non-routine description of the temperature behavior of both borane clusters and polymer matrices.

Infrared Activities of Adsorbed Species on Metal Surfaces: The Puzzle of Adsorbed Methyl (CH3).

Reflection-absorption infrared spectroscopy (RAIRS) is widely used to identify molecular adsorbates on metals during surface chemical reactions, but the interpretation of RAIRS data can be difficult with experiment alone. Here, we reveal from first-principles calculations the origin of the contrasting RAIRS spectra of methyl adsorbed on Pt(111) and Ni(111). We find that the dynamic dipole associated with the symmetric C-H stretch vibration of CH3 along surface normal is significant on Pt(111) but negligibly small on Ni(111), explaining the strong IR activity in the former and the absence of any RAIRS peaks in the latter. This difference is correlated to different charge transfer patterns between metals and the adsorbate, which are determined by the different preferred adsorption sites of methyl on the two surfaces. This work highlights the need of electronic structure calculations in interpreting RAIRS spectra of adsorbates on metal surfaces.

(Invited) Enhancement of the ORR Activity By Hydrophobic Species Analyzed Using Single Crystal Electrodes

Introduction Enhancement of the oxygen reduction reaction (ORR) is important for the development of fuel cells. Pt oxides are blocking species of the ORR on Pt electrodes.1,2 Theoretical calculation predicts that the change of adsorbed water structure inhibits the formation of Pt oxides on n(111)−(111) series of Pt, resulting in the high ORR activity of this series.3 In the notation of high index planes n(hkl)−(mno), n, (hkl) and (mno) show the number of terrace atomic rows, structures of terrace and step, respectively.Hydrophobic species also changes water structure around electrode surfaces. Modification with alkyl amines (OA/PA) and melamine enhances the ORR activity of Pt nanoparticles.4,5 This paper summarized the structural effects on the enhancement of the ORR by hydrophobic species on single crystal electrodes of Pt6 and Pt x Pd y Co z . Experimental Linear sweep voltammograms were measured using rotating disk electrode (RDE) in 0.1 M HClO4 saturated with O2. Potential was scanned positively from 0.05 V(RHE) at scanning rate of 0.010 V s−1. The ORR activity was estimated using the specific activity at 0.90 V(RHE). Hydrophobic species examined were alkyl amines (OA/PA), tetraalkyl ammonium cation (THA+) and melamine. The structure formulae and the hard sphere models of single crystal electrodes are shown in Fig. 1. Results and Discussion <Pt single crystal electrodes> Alkyl amines (OA/PA) enhance the ORR activity on n(111)-(111) series of Pt with 7 ≤ n.7 This fact indicates that wide (111) terrace (7 ≤ n) is necessary for the ORR activation by OA/PA. The ORR activity on flat Pt(111) is most activated by OA/PA. However, OA/PA markedly deactivates the ORR on flat Pt(100). Wide flat hexagonal terrace plays a key role in the activation by OA/PA. Modification with OA/PA decreases the charges of Pt oxide formation of voltammograms of all the single crystal electrodes, even on the surfaces of which ORR activity decreases after the modification. Infrared reflection absorption spectroscopy (IRAS) shows that the formation of ice-like water with smaller cluster size enhances the ORR activity after OA/PA modification.8 The ORR activity of Pt(111) is enhanced with the increase of the alkyl chain length of tetraalkyl ammonium cation. The ORR activity of Pt(111) modified with THA+ is 8 times as high as that of bare Pt(111).9 IRAS band intensity of PtOH decreases markedly after THA+ modification. This fact indicates that the ORR activity of Pt(111) is extremely high without Pt oxides. THA+ slightly enhanced the activity of Pt(331) = 3(111)-(111) that has the highest ORR activity in single crystal Pt electrodes. Melamine enhances the ORR activity on all the n(111)-(111) series of Pt.10 The activity on Pt(111) is enhanced most markedly again after melamine modification. Melamine also increases the activity of Pt(331) twice, giving the highest activity in the Pt single crystal electrodes examined. IRAS spectra show that the enhancement of the activity was attributed to the decrease of the coverage of PtOH. <Pt x Pd y Co z single crystal electrodes> Pt x Pd y Co z single crystal electrodes have higher ORR activity than Pt and Pt3Co single crystal electrodes.11 THA+ enhances the ORR activity of Pt x Pd y Co z (111) electrodes. The ORR activity of PtPd0.1Co0.2(111) modified with THA+ is 3.7 and 19 times as high as that of bare PtPd0.1Co0.2(111) and Pt(111), respectively. However, THA+ deactivates the ORR on Pt x Pd y Co z (100) and Pt x Pd y Co z (110) electrodes. Melamine increases the ORR activity of all the Pt x Pd y Co z single crystal electrodes. The enhancement ratio of PtPd0.1Co0.2(111) (2.1) is the highest in Pt x Pd y Co z single crystal electrodes examined. Acknowledgements This study was supported by New Energy and Industrial Technology Development Organization (NEDO). References N. M. Marković, H. A. Gasteiger, B. N. Grgur, and P. N. Ross, J. Electroanal. Chem., 467, 157 (1999). T. Ueno, H. Tanaka, S. Sugawara, K. Shinohara, A. Ohma, N. Hoshi, and M. Nakamura, J. Electroanal. Chem., 800, 162 (2017). R. Jinnouchi, K. Kodama, and Y. Moromoto, J. Electroanal. Chem., 716, 31 (2014).K. Miyabayashi, H. Nishihara, and M. Miyake, Langmuir, 30, 2936 (2014). M. Asahi, S. Yamazaki, N. Taguchi, and T. Ioroi, J. Electrochem. Soc., 166, F498 (2019). N. Hoshi, and M. Nakamura, Chem. Lett., 50, 72 (2021). K. Saikawa, M. Nakamura, and N. Hoshi, Electrochem. Commun., 87, 5 (2018). N. Hoshi, K. Saikawa, and M. Nakamura, Electrochem. Cummun., 106, 106536 (2019). T. Kumeda, H. Tajiri, O. Sakata, N. Hoshi, and M. Nakamura, Nat. Commun., 9, 4378 (2018). N. Wada, M. Nakamura, and N. Hoshi, Electrocatalysis, 11, 275 (2020). M. Torihata, M. Nakamura, N. Todoroki, T. Wadayama, and N. Hoshi, Electrochem. Commun., 125, 107007 (2021). Figure 1

Unraveling interfacial properties of organic-coated marine aerosol with lipase incorporation

Marine aerosols are believed to have an organic surface coating on which fatty acids act as an important component due to their high surface activity. In addition, various kinds of enzyme species are abundantly found in seawater, some of which have been identified to exist in marine aerosols. Herein, from the perspective of marine aerosol interface simulation, we investigate the effect of Burkholderia cepacia lipase on the surface properties of stearic acid (SA) monolayer at the air-water interface by using surface-sensitive techniques of Langmuir trough and Infrared reflection-absorption spectroscopy (IRRAS). Our findings indicate that the stearic acid film undergoes a significant expansion, especially when the lipase concentration is 500 nM, because of the incorporation of lipase as observed from the surface pressure-area (π-A) isotherms. IRRAS spectra also show reduced intensities and ordering in the methylene stretching vibration region of stearic acid as a result of low surface density and disordered packing as the enzyme concentration increases. In particular, when the concentration of lipase is 500 nM, the lowest Ias/Is values are shown on both pure water subphase and artificial seawater subphase, indicating more gauche conformations for SA. Furthermore, SA films with lipase incorporation were also studied at three different pH of subphase environment, considering the decrease of pH caused by the reaction with acidic gases during the aerosol aging process. The results reflect a more pronounced expansion of SA monolayer in acidic environment at pH 2.5, suggesting that hydrophobic interaction plays an important role in the disorder of the SA monolayer. In view of the coexistence of fatty acids and enzymes in the marine environment, this study provides a further understanding of the surface organization and behavior of organic-coated marine aerosols and deepen the knowledge of lipid-enzyme interfacial interactions occurring in the atmosphere.

A time domain study of surfactin penetrating a phospholipid monolayer at the air-water interface investigated using sum frequency generation spectroscopy, infrared reflection absorption spectroscopy, and AFM-nano infrared microscopy

We have investigated the interaction of surfactin with a monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at the air-water interface as a function of time, following its injection into the sub-phase, using non-linear Sum Frequency Generation (SFG) vibrational spectroscopy and Infrared Reflection Absorption Spectroscopy (IRRAS). SFG resonances from the phospholipid and from the surfactin were distinguished from each other by using selective deuteration. The surface pressure at the interface was measured concurrently for up to 8 h. After an induction period, the spectra from the lipid diminished and those of surfactin gradually appeared whilst at the same time the surface pressure increased. However, eventually the surfactin signals disappeared and those of the lipid reappeared. Although the SFG spectra of the lipid disappeared at intermediate times, the IRRAS spectra of the lipid were always present at the interface. Variation in the temporal SFG behaviour was investigated as the pH of the sub-phase, the initial surface pressure of the lipid, and the surfactin concentration were changed. Samples of the surface film were transferred onto mica substrates at selected times along the temporal profile and imaged by Atomic Force Microscopy - nano Infrared Spectroscopy (nano-IR). A model is proposed to account for the results from the four different experimental techniques used.

Desorption Kinetics of Carbon Dioxide from a Graphene-Covered Pt(111) Surface.

The interaction of carbon dioxide (CO2) with a graphene-covered Pt(111) surface was investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). The TPD spectra show monolayer and multilayer desorption peaks; however, the multilayer peak is not well-separated from the monolayer peak. The TPD spectra for submonolayer and multilayer coverages align on separate common leading edges. This alignment is a signature of zero-order desorption kinetics. The RAIRS spectra for submonolayer coverages have a relatively sharp peak at ∼2350 cm-1, which is assigned to the ν3 asymmetric stretch. The peak is observed at the onset of CO2 adsorption, and the area of the peak increases linearly with coverage. This suggests that CO2 does not lie flat on the surface but instead has a component of its bond axis perpendicular to the graphene surface.

In Situ Infrared Spectroelectrochemistry for Understanding Structural Transformations of Precisely Defined Ions at Electrochemical Interfaces.

Understanding the intrinsic properties of electroactive species at electrode-electrolyte interfaces (EEIs) is essential to the rational design of high-performance solid-state energy conversion and storage systems. In situ spectroscopy combined with cyclic voltammetry (CV) provides insights into structural changes of electroactive species at functioning EEIs. Ion soft landing enables precisely controlled deposition of mass- and charge-selected ions onto electrode surfaces thereby avoiding the contamination inherent with conventional electrode preparation techniques. In this contribution, we describe a new approach for the simultaneous electrochemical and spectroscopic characterization of soft-landed ions at operating solid-state EEIs. The technique exploits a specially fabricated three-electrode cell that is compatible with in situ infrared reflection absorption spectroscopy (IRRAS) characterization of the soft-landed ions. Keggin polyoxometalate (POM) anions, PW12O403-, were selected as a model system for these experiments due to their multielectron redox activity, structural stability, and well-characterized IRRAS spectrum. In situ CV measurements indicated continuous multielectron transfer processes of the soft-landed PW12O403- anions over a large potential range of -2.1 to -0.3 V. A distinct shift in the wavenumber of the terminal W═Ot stretching vibration in the IRRAS spectra was observed during the multielectron reduction process. The results demonstrate the capabilities of the in situ spectroelectrochemical approach for examining structural changes of well-defined electroactive species during electron-transfer processes at operating solid-state EEIs.

Adsorption geometry of methyl chloride weakly interacting with Ag(111)

The adsorption structure of CH3Cl on Ag(111) was investigated by temperature programmed desorption (TPD), infrared reflection-absorption spectroscopy (IRAS), and density functional theory (DFT) calculation. The saturation coverage of CH3Cl at the first layer was estimated to be 0.22 ML by TPD spectra. In the IRAS spectra before the first layer was completed, a CH3 asymmetric deformation mode was observed, while a CH3 symmetric deformation mode and a CH3 symmetric stretching mode were not observed. This result suggests that CH3Cl at the first layer is almost parallel to the surface, which was confirmed by DFT calculations. In contrast, a CH3Cl at the second layer was concluded to be inclined from the surface parallel.

SO2 adsorption on rutile TiO2(110): An infrared reflection-absorption spectroscopy and density functional theory study

The adsorption of SO2 on single crystalline TiO2(110) has been investigated by means of polarized infrared reflection-absorption spectroscopy (IRRAS) experiments and density functional theory (DFT) calculations. IR absorption bands were detected at 1324 cm−1 and 985 cm−1 with p-polarized light incident along both the [11¯0] and [001] crystallographic directions at 123 K. When the temperature was increased to 153 K, the peak at 1324 cm−1 disappears, while a new, weak band appears at 995 cm−1. Simultaneously, a band at 995 cm−1 also emerges with s-polarized light along the [11¯0] direction. Based on the symmetry properties of the IRRAS spectra and accompanying ab initio simulations of the spectra employing a three layer model (vacuum-adsorbate-substrate), it is shown that the low temperature absorption IRRAS bands can be attributed to an SO3-like adsorbate structure. This is also the most stable adsorption structure (Ead = −0.58 eV) on the stoichiometric surface. The combined IRRAS and DFT results show that the band appearing at 995 cm−1 is associated with a surface sulfite specie which is stabilized by residual surface water. The DFT calculations also revealed that a stable adsorption structure exists on a reduced TiO2 surface, where SO2 binds strongly to an oxygen vacancy site. It is suggested that this is an intermediate that form surface sulfate upon further reactions with water, although it was not observed on the stoichiometric surface studied in this work.

Structural and optical properties of a-C:H:O:Cl and a-C:H:Si:O:Cl films obtained by Plasma Enhanced Chemical Vapor Deposition

Amorphous hydrogenated oxygenated chlorinated carbon materials with and without silicon were produced by PECVD at deposition rates of up to 150 nm min−1. Surface roughness, morphology and contact angle were almost independent of the main system parameter, namely the partial pressure of CHCl3 in the plasma feed, CCl. Infrared reflection absorption spectroscopy (IRRAS) of the films revealed the presence of C=O and C=C bonding in all the chlorinated films. IRRAS spectra also showed the presence of C-Cl bonds in the most chlorinated a-C:H:O:Cl films. Hydration of Si-Cl to Si-OH occurs in the a-C:H:Si:O:Cl films. As revealed by Energy-dispersive X-ray spectroscopy (EDS) the Cl content increases and the O content decreases as CCl increases. Under the range of conditions used, [Cl] reached maxima of ∼32 at.% and 25 at.%, respectively, for the series of a-C:H:O:Cl and the a-C:H:Si:O:Cl films. For the a-C:H:Si:O:Cl films the Si content decreases with increasing CCl. Optical properties were calculated from Ultraviolet-visible near infrared spectral data. Refractive indices varied between ∼1.52 and 1.78, depending on CCl. The Tauc gaps can be selected by a suitable choice of CCl in the range of roughly 1.3–2.6 eV.

The interaction of trace heavy metal with lipid monolayer in the sea surface microlayer

Lipid molecules and trace heavy metals are enriched in sea surface microlayer and can be transferred into the sea spray aerosol. To better understand their impact on marine aerosol generation and evolution, we investigated the interaction of trace heavy metals including Fe3+, Pb2+, Zn2+, Cu2+, Ni2+, Cr3+, Cd2+, and Co2+, with dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface. Phase behavior of the DPPC monolayer on heavy metal solutions was probed with surface pressure–area (π–A) isotherms. The conformation order and orientation of DPPC alkyl chains were characterized by infrared reflection–absorption spectroscopy (IRRAS). The π–A isotherms show that Zn2+ and Fe3+ strongly interact with DPPC molecules, and induce condensation of the monolayers in a concentration-dependent manner. IRRAS spectra show that the formation of cation-DPPC complex gives rise to conformational changes and immobilization of the headgroups. The current results suggest that the enrichment of Zn2+ in sea spray aerosols is due to strong binding to the DPPC film. The interaction of Fe3+ with DPPC monolayers can significantly influence their surface organizations through the formation of lipid-coated particles. These results suggest that the sea surface microlayer is capable of accumulating much higher amounts of these metals than the subsurface water. The organic and metal pollutants may transfer into the atmosphere by this interaction.

Emerging investigator series: exploring the surface properties of aqueous aerosols coated with mixed surfactants.

Mixed Langmuir monolayers of cholesterol with both saturated and unsaturated fatty acids, stearic acid (SA), and oleic acid (OA) spread at the air-seawater surface were studied. The phase behavior, molecular interaction, and conformational order of the monolayers were investigated by surface pressure-area (π-A) isotherms and infrared reflection-absorption spectroscopy (IRRAS) measurements. The thermodynamic parameters of the mixed films, including excess molecular area and excess Gibbs free energy were calculated by using the isotherm data. The interaction between SA (or OA) and cholesterol varied with the molar fraction of the fatty acids and surface pressure. OA/chol monolayers showed the characteristics of miscibility, but they acted as nonideal systems. Cholesterol has been observed to have a stabilizing effect on OA monolayers. The negative values of the excess Gibbs free energy in the entire composition range demonstrated that mixed OA/chol monolayers were thermodynamically stable. IRRAS spectra showed that mixing with cholesterol changes the ordering of fatty acid monolayers at the air-seawater surface. The findings provide general information regarding the structural changes in the monolayer induced by lateral packing. These results help in the understanding of the mixing behavior of fatty acids and cholesterol and provide insights into the fate of the mixed-monolayer-coated sea salt aerosol in the ocean environment.

Study on phase separation in an ultra-thin poly(methyl methacrylate)/poly(4-vinyl phenol) film by infrared reflection absorption spectroscopy

The phase separation of poly(methyl methacrylate) (PMMA)/poly(4-vinyl phenol) (PVPh) (50/50 wt%) ultra-thin films was investigated by infrared reflection absorption spectroscopy (IR-RAS). Of particular note is that we succeeded in measuring the IR-RAS spectra of ultra-thin films of PMMA/PVPh (50/50 wt%) polymer blend with a film thickness of only 2.14 nm. It was found from the present study that the PMMA/PVPh polymer blends were clearly separated as the film thickness was thinner than the radius of gyration of PMMA. The IR-RAS spectra reveal that the hydrogen bond between the C=O group of PMMA and the OH group of PVPh is broken upon the phase separation in the ultra-thin film. In the spectra, many peaks are observed in the OH stretching region of the ultra-thin PMMA/PVPh films, indicating the existence of several weak hydrogen bonds with slightly different interactions, presumably due to the quasi-stable molecular chain configurations resulting from the strong confinement. This is in sharp contrast to the corresponding bulk sample for which a broad band is usually observed in this region because of the continuous distribution of the hydrogen bonding, which is typical for the blends.

Adsorption of Water, Methanol, and Formic Acid on Fe2NiP, a Meteoritic Mineral Analogue

The surface of an analogue to the meteoritic mineral schreibersite or (Fe,Ni)3P was investigated to provide insight into the interaction of the mineral surface with prebiotic molecules such as water, methanol, and formic acid. A protocol for creating synthetic metal-phosphide samples with a surface reflectivity suitable for reflection–absorption infrared spectroscopy (RAIRS) was developed and is outlined in this paper. Scanning electron microscopy coupled with energy dispersive spectroscopy revealed an average defect size less than 1 μm and evidence of subsurface phosphorus segregation. At surface temperatures between 120 and 140 K, RAIRS spectra indicate that water and formic acid interact molecularly with surface atoms, while methanol appears to dissociate into methoxy and protons upon adsorption. The observed infrared spectra provide insight into the adsorption geometries of these prebiotic molecules on synthetic schreibersite. This data suggests the importance of the schreibersite mineral surface in a...

Preparation and Characterization of New Pt/Rh/SnO2 Nanoparticle Catalysts for Ethanol Oxidation Reaction to CO2

Introduction PtSnRh ternary catalysts have been proved to be useful for ethanol oxidization reaction (EOR).1 We demonstrated that when Rh was deposited on Pt adjacent to the SnO2 on SnO2–modified Pt substrate, the selectivity of CO2 was greatly improved,2 suggesting that these three elements play an essential role for the complete EOR to produce CO2. In this study, to confirm this conclusion with nanoparticles, we prepared two kinds of Pt/Rh/SnO2 nanoparticle catalysts, in which the position of the Rh atoms was controlled by the partial CO stripping. The resultant Pt/Rh/SnO2 nanoparticle catalysts were evaluated the EOR activity as well as the CO2 selectivity by electrochemical and spectroscopic methods. Experimental Pt/SnO2(3:1) nanoparticle-loaded carbon black was prepared according to ref. 3. The Rh deposition on the Pt/SnO2/C nanoparticle catalyst was conducted in a three-electrode cell with a Pt plate (2x3 cm) as the counter electrode (CE), reversible hydrogen electrode (RHE) as reference electrode, and a Pt mesh as the working electrode (WE). The Pt/SnO2/C powder was sonicated in an Ar-saturated 0.5 M H2SO4 solution at 30 oC for 1 h to get the well-dispersed suspension. In the first method, Rh was directly deposited on the Pt/SnO2 nanoparticles. Hydrogen was bubbled in the Pt/SnO2/C suspension containing 0.1 mM RhCl3 with stirring to deposit Rh on the Pt surface of the nanoparticles. The ternary catalyst was obtained after filtering, washing, and evaporating, which is named Ter-1. In the second method, the Rh deposition site was controlled by the partial CO stripping. CO was bubbled in the Pt/SnO2/C suspension to adsorb CO on the Pt surface of the Pt/SnO2 nanoparticles. Then the adsorbed CO on Pt neighboring to Sn was selectively desorbed while the potential was set at 0.5V vs. RHE for 15 min. After that, Rh was deposited on the exposed Pt surface of the Pt/SnO2 nanoparticles by using the same process as in the first method, which is named Ter-2. For electrochemical measurements, each ternary catalyst was casted on a glassy carbon (GC) electrode as described in ref. 3. Linear sweep voltammetry (LSV) in 1 M C2H5OH/0.1 M HClO4 was performed to evaluate EOR activity. Products and intermediates of EOR were identified by infrared reflection absorption spectroscopy (IRRAS). Results and discussion From X-ray diffraction spectroscopy, the size of Pt/SnO2 and ternary nanoparticles was estimated as 2.5 nm and 2.8 nm, respectively. Energy-dispersive X-ray spectroscopy revealed the similar metal composition for the two ternary catalysts, in which the Rh content was ca. 5%. Figure 1 illustrates that Ter-2 has the lowest onset potential and the highest current density toward EOR, whereas the current density of Ter-1 is even lower than Pt/SnO2/C. Figure 2 shows the IRRAS spectra of the Pt/SnO2, Ter-1 and Ter-2. In comparison with Pt/SnO2/C, Ter-2 greatly facilitated the formation of CO2 (2343 cm-1) as opposed to acetic acid (1277 cm-1). In contrast, Ter-1 exhibited the similar product distribution for EOR to Pt/SnO2/C. References A. Kowal, M. Li, M. Shao, K. Sasaki, M.B. Vukmirovic, J. Zhang, N.S. Marinkovic, P. Liu, A.I. Frenkel and R.R. Adzic. Nature Materials, 8, 325 (2009).M. P. Tu, M. Chiku, E. Higuchi and H. Inoue, ECS Transactions, 69 (17) 675-681 (2015)E. Higuchi, K. Miyata, T. Takase, H. Inoue, J. of Power Sources, 196 (2001), 1730 – 1737. Figure 1

Highly Ordered Self-Assembled Monolayers of Carboxy- and Ester-Terminated Alkanethiols on Au(111): Infrared Absorption and Hyperthermal-Deposition Experiments with Cr(benzene)2 Ions

The physical and chemical properties of carboxy- and ester-terminated alkanethiolate self-assembled monolayers (SAMs) on a gold (Au) substrate (Au(111)), which were prepared in a one-pot reaction, were investigated by means of infrared reflection absorption spectroscopy (IRAS) and hyperthermal-deposition experiments with Cr(benzene)2 ions. IRAS spectra showed that the vibrational modes of hydrogen-bonded COOH and CH2 wagging are sensitive to the flatness and cleanness of Au substrates for COOH-SAM and COOMe-/COOEt-SAM, respectively. The intensities of CH2 wagging modes are temperature dependent, which is relevant to the alkyl chain ordering in the highly ordered SAM. The terminal groups of the highly ordered SAM are dissociated by hyperthermal collision events of gas-phase-synthesized Cr(benzene)2 sandwich complex ions, and the adsorption properties of deposited Cr(benzene)2 are discussed in relation to IRAS and temperature-programmed desorption (TPD) measurements.

Impact of anions on the surface organisation of lipid monolayers at the air–water interface

Environmental contextLipids released from lysis of phytoplankton cells are enriched in the sea surface microlayer. Such surface-active organics can be transferred through bursting bubbles to sea-spray aerosols where they can influence atmospheric chemistry. The results presented here suggest that phospholipids combine more readily with SO42− than with Br−, leading to enrichment of organic-coated sulfate salts in marine aerosols. AbstractInorganic salts and organic matter are known to be present at higher levels in the sea surface microlayer and marine aerosols; however, the impact of common anions on their surface properties is not well understood. Here, a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer was enriched with the sodium and ammonium salts of different anions (Br−, Cl−, NO3−, SO42−, CH3COO−, and HCO3−), and the effects on the surface properties of the monolayer were investigated. The monolayer phase behaviour and the structure of the lipid phases were studied by surface pressure–area (π–A) isotherms and infrared reflection-absorption spectroscopy (IRRAS). The presence of salts in the subphase was found to increase the surface pressure of the DPPC monolayer at a fixed area per molecule. The effect of the anions follows the order of the Hofmeister series. The higher concentration of salt solution caused the π–A isotherm to shift to larger area. The IRRAS spectra demonstrate that the ordering of the DPPC molecules in the liquid condensed phase remains essentially unaffected, even at higher electrolyte concentrations. DPPC molecules combined with SO42− could be transferred from the ocean to sea spray aerosol. The present study finds that the anions have significant influence on the surface organisation and, consequently, the interfacial properties, of the surface-active species at the air–water interface, a finding that has further implications for atmospheric aerosol nucleation.

Aqueous-phase aerosols on the air-water interface: Response of fatty acid Langmuir monolayers to atmospheric inorganic ions.

Atmospheric aerosol particles composed of a mixture of organic and inorganic compounds are common and constitute an important fraction of air pollutants. In this study, the activities of common atmospheric inorganic ions (Ag+, Zn2+, Fe3+, Fe2+, Ca2+ and Al3+) and fatty acid molecules (stearic acid and arachidic acid) at air-aqueous interface were investigated by Langmuir methods and infrared reflection-absorption spectroscopy (IRRAS). In the presence of different inorganic ions, surface pressure-area isotherms of the Langmuir films showed compressed or expanded characteristics. IRRAS spectra confirmed that the existence of inorganic ions in the fatty acid monolayer changes the surface properties of aqueous-phase aerosols. Formation of different coordination types of carboxylates at the air-water interface alters the dissolution and partitioning behavior, which has significant influence of Raoult effect on nucleating cloud droplets. Our work displays the relationship between structure and surface properties for aqueous-phase aerosols and implies an efficient method for further understanding of their formation mechanism and potential atmospheric implications.

A spectroscopic membrane permeation cell for in-situ infrared-reflection absorption spectroscopic analysis of membrane surfaces and simultaneous measurement of trans-membrane gas permeation rates

In this work, we describe a spectroscopic membrane permeation cell that we have designed and fabricated to enable—for the first time—the surface of metal membranes to be analyzed by infrared-reflection absorption spectroscopy (IRAS) while simultaneously measuring the rate of hydrogen permeation across the membrane under realistic permeation conditions. As a proof-of-concept, we demonstrate that the permeation cell can (1) accurately measure the rate of H2 permeation across a 25µm-thick Pd foil membrane, (2) detect sub-monolayer coverages of CO on the membrane surface in the 333–533K temperature range, and (3) measure the rate of H2 permeation across the membrane while simultaneously detecting surface-adsorbed CO during exposure to H2/CO gas mixtures at 533K. IRAS spectra recorded during exposure to H2/CO gas mixtures at 533K indicate that CO dissociates on the membrane surface, and C–H bonds are formed, which modify the surface adsorption properties of the membrane and result in irreversible losses in the H2 flux across the membrane. With this spectroscopic membrane permeation cell, it is possible to correlate microscopic surface processes to macroscopic rates of permeation across the membrane, which will enable the rational design of new membrane materials that are resistant to deactivation.