FTIR Spectroelectrochemistry: Optimization of Experimental Setup

This study describes a systematic investigation of the electrocatalytic activity of poly[Ni(salen)] films, as catalysts for the electro-oxidation of Cn alcohols (Cn = methanol, ethanol, and glycerol) in alkaline medium. The [Ni(salen)] complex was electropolymerized on a glassy carbon surface and electrochemically activated in NaOH solution by cyclic voltammetry. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy results indicate that during the activation step the polymeric film hydrolyzes, leading to the formation of β-Ni(OH)2 spherical nanoparticles, with an average size of 2.4 ± 0.5 nm, encapsulated with the poly[Ni(salen)] film. Electrochemical results obtained together with the in situ Fourier transform infrared spectroscopy confirm that the electro-oxidation of methanol, ethanol, and glycerol occurs by involving a cycling oxidation of β-Ni(OH)2 with the formation of β-NiOOH species, followed by the charge transfer to the alcohols, which regenerates β-Ni(OH)2. Analyses of the oxidation products at low potentials indicate that the major product obtained during the oxidation of methanol and glycerol is the formate, while the oxidation of ethanol leads to the formation of acetate. On the other hand, at high potentials (E = 0.6 V), there is evidence that the oxidation of Cn alcohols leads to carbonate ions as an important product.

This study explores the development of core–shell electrocatalysts for efficient glycerol oxidation in alkaline media. Carbon-supported M@Pt/C (M = Co, Ni, Sn) catalysts with a 1:1 atomic ratio of metal (M) to platinum (Pt) were synthesized using a facile sodium borohydride reduction method. The analysis confirmed the formation of the desired core–shell structure, with Pt dominating the surface as evidenced by energy-dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) revealed the presence of a face-centered cubic (fcc) Pt structure for Co@Pt/C and Ni@Pt/C. Interestingly, Sn@Pt/C displayed a PtSn alloy formation indicated by shifted Pt peaks and the presence of minor Sn oxide peaks. Notably, no diffraction peaks were observed for the core metals, suggesting their amorphous nature. Electrocatalytic evaluation through cyclic voltammetry (CV) revealed superior glycerol oxidation activity for Co@Pt/C compared to all other catalysts. The maximum current density followed the order Co@Pt/C > Ni@Pt/C > Sn@Pt/C > Pt/C. This highlights the effectiveness of the core–shell design in enhancing activity. Furthermore, Sn@Pt/C displayed remarkable poisoning tolerance attributed to a combined effect: a bifunctional mechanism driven by Sn oxides and an electronic effect within the PtSn alloy. These findings demonstrate the significant potential of core–shell M@Pt/C structures for designing highly active and poisoning-resistant electrocatalysts for glycerol oxidation. The presented approach paves the way for further development of optimized catalysts with enhanced performance and stability aiming at future applications in direct glycerol fuel cells.

Tilt angles of liquid crystal molecules, 5CB, have been investigated in the liquid crystal cells with the polyimide (PI) LB alignment films on the aluminum electrodes using the attenuated total reflection (ATR) measurement. The ATR properties were evaluated from the surface plasmon polariton (SPP) and the guided wave excitation modes (GWEM) when various DC voltages were applied to the cell. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones using a three layers model. Furthermore, the electric field intensities in the cell were calculated at several incident angles.

An apparatus for the study of solution phase kinetics using FT-IR spectroscopy has been developed. The observation chamber consists of an integrated tangential mixer-flow cell and a ZnSe element permitting attenuated total reflectance (ATR) measurements. The short optical pathlength afforded by ATR allows mid-IR observation of chemical reactions in aqueous solution, including the spectral region near the water bending vibration (1640 cm−1). High hydraulic backpressures required to force solution rapidly through a thin layer flow cell are not necessary with the ATR flow cell because the optical pathlength and the flow cross-section have been decoupled, allowing for a relativity large flow chamber when compared with instruments incorporating a transmission flow cell. Overall system performance has been evaluated using the hydrolysis of methylchloroacetate as a test reaction. The feasibility of observing reactions with initial half-lives of approximately 250 ms is demonstrated. The system is very robust, with little risk of damaging the optics during routine maintenance.

Electrochemistry and electrochemical reactions are increasingly important in the transition to a sustainable chemical industry. The electron transfer that drives such reactions takes place within nanometers of the electrode surface, and follow-up chemical reactions take place within the diffusion layer. Hence, understanding electrochemical reactions requires time-, potential-, and spatially resolved analysis. The confocal nature of Raman spectroscopy provides high spatial resolution, in addition to detailed information on molecular structure. The intrinsic weakness of nonresonant Raman scattering, however, is not sensitive enough for relatively minor changes to the solution resulting from reactions at the electrode interface. Indeed, the limit of detection is typically well above the concentrations used in electrochemical studies. Here, we show that surface-enhanced Raman scattering (SERS) and resonance Raman (rR) spectroscopy allow for spatially and time-resolved analysis of solution composition at (<1-2 nm) and near (within 5 μm) the electrode surface, respectively, in a selective manner for species present at low (<1 mM) concentrations. We show changes in concentration of species at the electrode surface, without the need for labels, specific adsorption, or resonance enhancement, using a SERS-active gold electrode prepared readily by electrochemical surface roughening. A combination of smooth and roughened gold electrodes is used to distinguish between surface and resonance enhancement using the well-known redox couples ferrocene and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). We discuss the impact of specific adsorption on the spectral analysis with the ruthenium(II) polypyridyl complex, [Ru(bpy)3]2+. The dual function of the electrode (surface enhancement and electron transfer) in the analysis of solution processes is demonstrated with the reversible oxidation of TMA (4,N,N-trimethylaniline), where transient soluble species are identified in real time, with rapid spectral acquisition, making use of localized enhancement. We anticipate that this approach will find use in elucidating electro(catalytic) reactions at electrode interfaces.

Ruthenium‐based Pd and Pt nanoparticles were prepared by mild microwave‐assisted heating and were characterized by X‐ray diffraction and transmission electron microscopy. The activities of these catalysts during the oxidation of glycerol in alkaline media were studied by electrochemical, analytical, and in situ spectroscopy techniques. Changing the noble metal (Pd or Pt) allowed the selectivity of the catalysts to be tailored during the electrooxidation of glycerol. This introduces the possibility of utilizing the catalysts in cogeneration processes for renewable energy sources and also of employing the catalysts to produce value‐added molecules selectively. High‐performance liquid chromatography evidenced that the PtRu material had excellent catalytic activity in the selective oxidation of glycerol to dihydroxyacetone, whereas the PdRu anode favored the production of glycerate.

A dialkylsubstituted imidazolium iodide ionic liquid (1-methyl-3-[3-(trimethoxy-lambda4-silyl)propyl]imida-zolium iodide, MTMSPIm+I-) was prepared with the intention of using it as a quasi-solid-state electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of Grätzel design, while the analogous electrolyte in a gel state was made by the addition of tetramethoxysilane (TMOS) in the molar ratio MTMSPIm+I-:TMOS = 1:1. The structure of the MTMSPIm+I- in its non-hydrolyzed and hydrolyzed states and in its fully condensed form, obtained after ageing the sols for various times (from a few hours to a few weeks) and heating them at 200 degrees C (fully condensed form), was studied employing time-dependent infrared attenuated total reflection (ATR) and 29Si NMR spectroscopic measurements. The structure of the condensed species was correlated with the viscosity and the specific conductivity measurements of MTMSPIm+I- sols and TMOS/MTMSPIm+I- gels during their ageing. The final product of the condensation of MTMSPIm+I- sols was described as a positively-charged ladder-like polysilsesquioxane with Tn end groups exhibiting a single T3 signal in 29Si NMR spectra and characteristic doublet bands at 1138 and 1049 cm(-1) in IR. This structure was retained to a large extent in TMOS/MTMSPIm+I- gels, confirming their nanocomposite structure. The results of the ATR infrared time-dependent spectroscopic studies showed that in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to shifts in the vibrational band positions in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined and the results applied in this work.

Evaluation of liquid crystal molecules on polyimide LB films using attenuated total reflection measurement

Nano‐sized Au and Pd catalysts are favorable for oxidations with molecular oxygen, and the preparation of this kind of nanoparticles with high catalytic activities is strongly desirable. We report a successful synthesis of bimetallic Au‐Pd nanoparticles with rich edge and corner sites on unique support of Mg‐Al mixed oxides (Au‐Pd/MAO), which are favorable for producing metal nanoparticles with high degree of coordinative unsaturation of metal atoms. The systematic microscopic characterizations confirm the bimetallic Au‐Pd nanoparticles are present as Au‐Pd alloy. The irregular shape of the bimetallic nanoparticles are directly observed in HRTEM images. As we expected, Au‐Pd/MAO gives very excellent catalytic performances in the aerobic oxidation of benzyl alcohol and glycerol. For example, Au‐Pd/MAO shows very high TOF of 91000 h−1 at 433 K with molecular oxygen at air pressure in solvent‐free oxidation of benzyl alcohol; this catalyst also shows relatively high selectivity for tartronic acid (TARAC, 36.6%) at high conversion (98.5%) in aerobic oxidation of glycerol. The superior catalytic properties of Au‐Pd/MAO would be potentially important for production of fine chemicals.

The Microbiologically Induced Corrosion (MIC) of concrete sewer pipes is a commonly known problem that can lead to the destruction of the system, creating multiple public health issues and the need for costly repair investments. The present study focuses on the development of a magnesium hydroxide coating, with optimized properties to protect concrete against MIC. The anti-corrosion properties of the respective coating were evaluated by using short and long duration accelerated sulfuric acid spraying tests. The coating presented satisfying adhesion ability, based on pull-off and Scanning Electron Microscopy (SEM) analysis measurements. The surface pH of the coated concrete was maintained at the alkaline region (i.e., >8.0) throughout the duration of all acid spraying tests. The consumption of the coating, due to the reaction (neutralization) with sulfuric acid, was confirmed by the respective mass and thickness measurements. The protection ability of this coating was also evaluated by recording the formation of gypsum (i.e., the main corrosion product of concrete) during the performed tests, by X-ray Diffraction (XRD) analysis and by the Attenuated Total Reflectance (ATR) measurements. Finally, a long duration acid spraying test was additionally used to evaluate the behavior of the coating, simulating better the conditions existing in a real sewer pipe, and the obtained results showed that this coating is capable of offering prolonged protection to the concrete substrate.

Virgin coconut oil (VCO) may be adulterated with cheaper oils, such as palm oil (PO). Thus, the detection and quantification of VCO adulteration with PO was monitored using Fourier transform infrared (FTIR) spectroscopy, combined with chemometrics of partial least square (PLS) and discriminant analysis at frequency regions of 3,010–3,000, 1,660–1,650 and 1,120–1,105/cm. Attenuated total reflectance (ATR) measurements were made on pure VCO and that adulterated with varying concentrations of PO (0.5–50% w/w in VCO). PLS calibration exhibited a good relationship between actual and FTIR‐predicted values with coefficient of determination (R2) of 0.999 and standard error of calibration of 0.533. The cross validation was performed by removing one standard at a time, and the final R2 value of 0.996 and standard error of prediction of 0.953 were obtained. The discriminant analysis using seven principal components was able to classify pure VCO and that adulterated with PO.PRACTICAL APPLICATIONSThe adulteration of virgin coconut oil (VCO) with cheaper oils is a serious matter, not only for food suppliers but also for consumers. Therefore, an analytical technique offering fast and reliable detection of such adulteration must be developed. Fourier transform infrared spectroscopy combined with chemometrics of partial least square for quantitative analysis of adulterant, and discriminant analysis for classification between VCO and that adulterated with palm oil, can be employed for detection of palm oil as an adulterant in VCO for quality assurance purposes.

Detection of petroleum hydrocarbons in continental areas using airborne hyperspectral thermal infrared data (SEBASS)

2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO, 1) and related aminoxyl derivatives are important catalysts for alcohol oxidation. They are featured in the synthesis of pharmaceuticals and recently found considerable attention for the conversion of hydroxyl bearing biomass-derived feedstocks to value-added products. Aminoxyl compounds undergo facile redox reactions at electrode surfaces, enabling them to mediate electrochemical oxidation of alcohols.The well-known electron transfer reaction of these persistent radicals involves a reversible one electron oxidation to the corresponding oxoammonium species (TEMPO+ , 3), which are relatively strong oxidants. Aminoxyl radicals can also undergo a proton coupled reduction to hydroxylamines (2), which is quasireversible and less known. However, for many of their electrosynthetic reactions, the catalytic cycle involves not only aminoxyl/oxoammonium redox couple, but also formation of hydroxylamines and regeneration of the oxoammonium from the hydroxylamine. This two steps oxidation has been proposed to occur via two distinct pathways: the comproportionation reaction between the hydroxylamine and a second oxoammonium cation to form aminoxyloxyl radical (two) followed by oxidation of aminoxyl radicals to oxoammonium (pathway b), or the two-electron oxidation of the hydroxylamine to the oxoammonium (pathway a). The electron transfer of the hydroxylamine, at the electrode surface, is a quasireversible ill-defined reaction that strongly depends on the electrode material and conditionings, and its detailed understanding is still lacking. Herein, we investigated the electron transfer reaction of TEMPO and its hydroxylamine, is formed during catalytic alcohol oxidation, using the glassy carbon electrodes that treated under different conditions. Well-treated electrode facilitates the electron transfer of hydroxylamine and enables two-electrons oxidation to oxoammonium, whereas on the untreated electrode, two separated one-electron oxidations are observed that enables measuring the rate of generation and consumption of hydroxylamine. Understanding of how each regeneration pathway affects the catalytic behavior made it possible to comprehensively understand all the features of the current profiles obtained under various alcohol oxidation conditions. Figure 1. Possible mechanism for regeneration of oxoammonium during aminoxyl catalyzed alcohol oxidation. Figure 1

Aggregation of silver colloidal particles in the hydrosol via chemisorption of octadecanethiol (ODT) molecules was investigated based on in situ UV–visible transmission and infrared attenuated total reflection (ATR) measurements. As‐prepared silver hydrosol exhibits a single absorption peak at 395 nm because of the plasma resonance of the metal particles. Upon addition of ODT‐dissolved ethanol to the hydrosol, the resonance band red‐shifts and broadens, the detailed features of which depend on the ODT concentration and elapsed time. Both the red‐shift and the broadening are attributed to particle aggregation in the solution via ODT chemisorption. Aggregation on a germanium prism surface by the addition of ODT‐dissolved ethanol to the hydrosol was investigated using infrared ATR spectroscopy. At moderate ODT concentrations, intense aggregation via ODT chemisorption occurs strongly on the prism surface, allowing observation of ODT absorption bands. Angle‐dependent infrared ATR measurements for the ethanol and ODT molecules at the prism/solution interface clearly show that aggregation on the prism surface proceeds via the exclusion of ethanol. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Electrochemical oxidation using renewable energy is an attractive strategy that provides a sustainable and mild approach for biomass transformation. Herein, the electrocatalytic oxidation of furfuryl alcohol in an aqueous solution was investigated using CuO nanorods. Two kinds of CuIII intermediates, namely, (CuO2)− and (Cu2O6)6–, were detected on the surface of the working electrode. (Cu2O6)6–, generated in the potential range of 1.35–1.39 V versus the reversible hydrogen electrode (RHE), induced the oxidation of furfuryl alcohol to furaldehyde with a yield of ≥98%. (CuO2)−, generated at a potential greater than 1.39 V versus RHE, which led to the oxidation of furfuryl alcohol to 2-furoic acid with a yield of ≥99%. Furthermore, the CuIII-catalyzed system exhibited a measure of universal applicability, wherein (Cu2O6)6– and (CuO2)− induced the highly selective electro-oxidation of benzyl alcohol, vanillyl alcohol, and 4-pyridinemethanol to yield the corresponding aldehydes and acids, respectively.