Electrospray film deposition for solvent-elimination infrared spectroscopy

The application of electrospray (ES) for quantitative transfer of analytes from solution to an internal reflection element for analysis by Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy has been developed in this work. The method (ES-ATR-FTIR) is evaluated with nonvolatile and semivolatile organic and inorganic compounds dissolved in pure organic solvents, or organics in mixture with water. The technique demonstrates the capability for rapid solvent evaporation from dilute solutions, facilitating the creation of thin films that allow ATR-FTIR to generate transmission-mode-like spectra. ES-ATR-FTIR with multiple reflections displays a linear response (R2 = 0.95–0.99) in absorbance with the deposited mass and instrumental detection limit below 100 ng, which demonstrates potential for quantitative applications. The method is applicable when crystalline substances are present, even though the formation of particles restricts the upper limit of mass loadings relative to substances forming homogeneous films. In addition to the solvent, semivolatile compounds can evaporate during the ES process; the magnitude of losses will depend on solution composition and temperature.

Nitrous Oxide Abatement over Fe-Zeolite

Bryan Bromley

The use of zeolites for catalytic reactions is a field in continuous development. Since it was demonstrated that metal-zeolites are efficient catalysts for NOx abatement, decomposition of nitrous oxide (N2O) over Fe-containing zeolites has attracted great interest by the scientific community mainly due: N2O is the third most important gas contributing to global warming, its concentration in atmosphere is still on the rise and direct N2O decomposition to N2 and O2 is a sustainable alternative. N2O interaction with Fe-zeolite leads to the formation of "special" adsorbed oxygen (often called α-oxygen) with great potential for selective oxidation. Although the focus of a number of studies, the nature of the actives sites for the formation of this adsorbed oxygen is still unclear. The main objectives of this work are: 1) study the decomposition mechanism of N2O over isomorpously substituted Fe-ZSM-5 zeolite aiming on catalyst optimization and 2) optimization and further use of structured Fe-zeolite in novel micro-structured reactor. A number of refined transient kinetics methods were intensively used such as transient response, Temperature Programmed Desorption (TPD) and Temporal Analysis of Product (TAP). Density Functional Theory (DFT) and in situ IR spectroscopy studies were conducted in collaboration and our results support the following: In chapter 3, quantitative measurements have been carrier out to analyze the effect of temperature on the activation (under helium flow) and the irreversible deactivations that can happen during the pretreatment. The results obtained indicate that high temperature treatment (1273 K) results in the formation of a high amount of α-sites. The addition of a very low fraction of oxygen (2%) in the feed demonstrates that the catalyst is sensitive to its presence. Certain sites can be irreversibly destroyed, a result ascribed to the oxidation of active Fe(II) to Fe2O3 clusters which contain inactive Fe(III). Catalyst treatment at high temperature (1273 K) in He for up to 3 hours, also reduced irreversibly the concentration of α-sites. TPD measurements have shown desorption of oxygen at 3 different temperatures. Desorption at the lowest temperature (650 K) was assign to the α-oxygen recombination. The oxygen which desorbs at 700 K was associated to the oxygen from the deactivated sites. Oxygen which desorbs at the highest temperature (730 K) is originated from the surface NOx that desorbed as NO and O2. After a comparison of the concentration of the molecules accumulated, we propose that NO2 is the adsorbed specie. The mechanism of N2O decomposition on the binuclear oxo-hydroxo bridged extraframework iron core site [FeII(μ-O)(μ-OH)FeII]+ inside the ZSM-5 zeolite has been studied by combining theoretical and experimental approaches (see chapter 4). Rate parameters computed using standard statistical mechanics and transition state theory reveal that elementary catalytic steps involved into N2O decomposition are strongly dependent on the temperature. This theoretical result was contrasted with the experimentally observed steady state kinetics of the N2O decomposition and TPD experiments. As predicted by the theoretical study, the switch of the reaction order with respect to N2O pressure (from zero to one) occurs at around 800 K which confirms a change of the rate determining step from the α-oxygen recombination to α-oxygen formation. The proposed mechanism was also confirmed by O2-TD which confirmed the viability of the binuclear complex. The α-oxygen recombination at low temperature (

EPFL2010

Broadband Optical Spectrum Downconversion to RF Using Integrated Dual-Comb Source

Andrey Voloshin

Combining all the benefits of Fourier transform infrared (FTIR) spectroscopy in a chip scale spectroscopic sensor looks promising for mobile and wearable platform development. Dual-comb spectroscopy enables downconversion of optical absorption spectra into the RF range for fast measurement using single photodetector [1] . Some cases of dual-comb spectroscopy based on laser-pumped MRs were successfully demonstrated [2] – [4] . The early attempts at combining LD-pumped integrated frequency combs into dual-comb were also reported [5] . However, to demonstrate viability of the technology for applications, it is important to integrate LD and SiN-chip with the MR into the compact autonomously operated device generating at least one optical frequency comb.

IEEE2021

Identification of Isomeric Biomolecules by Infrared Spectroscopy of Solvent-Tagged Ions

Andrei Zviagin

The difference in functionality of many isomeric biomolecules requires their analytical identification for life science studies. We present a universal approach for quantitative identification of different small- to medium-sized isomeric biomolecules that can be brought to the gas phase from solution by electrospray ionization (ESI). The method involves infrared (IR) fragment cold ion spectroscopy of analyte molecules that are incompletely desolvated by soft ESI. The use of solvent molecules as natural tags removes a need for adding to solutions any special compounds, which may interfere with liquid chromatography or mass spectrometric measurements. The tested peptides and especially monosaccharides and lipids exhibit highly isomerspecific IR fragment spectra of such noncovalent complexes, which were produced from water, methanol, acetonitrile, and 2butanol solutions. The relative concentrations in solution mixtures of, for instance, two isomeric dipeptides can be quantified with the accuracy of 1.6% and 2.9% for the acquisition time of 25 min and, potentially, 5 s, respectively; for three isomeric phosphooctapeptides, the accuracy becomes 4.1% and 11% for 17 min and, potentially, 10 s measurements, respectively.

AMER CHEMICAL SOC2022

Nitrous Oxide Abatement over Fe-Zeolite

Bryan Bromley

EPFL2010