Temperature-programmed Desorption Mass Spectrometry Research Articles

Direct synthesis of dilithium tetraphenylporphyrin: facile reaction of a free-base porphyrin with vapor-deposited lithium.

A solvent-free dilithium porphyrin was synthesized by direct reaction of free-base meso-tetraphenylporphyrin with elemental lithium in ultra-high vacuum. The reaction product dilithium tetraphenylporphyrin was studied by temperature-programmed desorption mass spectrometry (TPD-MS) and hard X-ray photoelectron spectroscopy (HAXPES). The solid-state reaction is thermodynamically favored, according to density functional theory (DFT) calculations.

Measuring the water content in freshly-deposited fingermarks

The literature view regarding the composition of deposited fingermarks has long been that the average water content is in the range of 98–99wt.%. This value has recently been challenged by Kent, claiming that it should be 20wt.% at most. Herein we have measured the weight percentage of water content in freshly-deposited fingermarks, with and without hand pre-washing. Two complementary techniques were utilized for the measurements, namely quartz crystal microbalance (QCM) for determining the relative mass-loss and its rate at ca. 37°C, and temperature-programmed desorption-mass spectrometry (TPD-MS) for establishing that the mass loss arises solely from the complete evaporation of all the water content in the fingermarks (done with hand pre-washing only). Unlike the traditional narrow-range values of 98–99% and the limiting value of 20wt.% suggested by Kent, our measurements indicate the occurrence of a broad 20–70% water content. Higher contents of water in fingermarks were found post hand pre-washing, most probably due to removal of the sebum from the fingertips, but none of the results exceeded 90%.

In Ukrainian

The study of the thermochemical properties of caffeic acid and its surface complexes is important for the pharmaceutical and food industries, medicine and for development of technologies of heterogeneous catalytic pyrolysis of the renewable plant biomass components. In this work, the structure of the surface complexes of caffeic acid on the surface of nanosized cerium dioxide was investigated using FTIR spectroscopy, depending on the degree of the surface coverage (0.1–1.2 mmol/g). Thermal transformations of surface complexes were studied using temperature-programmed desorption mass spectrometry (TPD MS). The analysis of the magnitude of the difference between the assymmetric and symmetric carboxylate stretches СОО - (...) and in case of monodentate coordination, between the C=O and CO stretches (...) was carried out. Based on the obtained values of D, it can be assumed that bidentate chelating complexes ( ≈ 72 cm –1 ), bidentate bridging complexes ( ≈ 110 cm –1 ), and monodentate bound complexes ( ≈ 236 cm –1 ) of caffeic acid are present on the nanoceria surface. In addition, complexes bound through the phenolic hydroxyl groups are present on the surface. This is due to the ability of the nanoceria to generate basic hydroxyl groups that are able to deprotonate the phenolic groups to form phenolates on the surface. The analysis of mass spectrometric data allowed identification of products of thermal transformation and suggested possible ways of forming 3,4-dihydroxyphenylethylene, pyrocatechol, and phenol from surface complexes of caffeic acid, the structure of which was confirmed by data of IR spectroscopy. The kinetic parameters of the phenol formation reaction were calculated. It was established that on the surface of CeO 2 the decarboxylation, dehydration and decarbonylation reactions of caffeic acid occur effectively. These reactions are the desirable processes in biomass conversion technologies.

Non-isothermal hydrogen desorption from β-UH3: Kinetics and mechanism

Non-isothermal hydrogen desorption kinetics from β-UH3 powder was investigated by means of temperature programmed desorption - mass spectrometry (TPD-MS). The hydride phase of the synthesized powder was determined by X-ray diffraction (XRD); particles size and morphology were characterized by scanning electron microscopy (SEM). The thermal decomposition (dehydrogenation) of β-UH3 is found to follow a zero-order kinetics with an activation energy of 104 kJ/(mol H2). By accounting for the observed kinetics and comparing the activation energy against reported density functional theory (DFT) values, a surface controlled mechanism, limited by surface recombination of hydrogen atoms is proposed.

The formation of peptide-like molecules on interstellar dust grains

Molecules with an amide functional group resemble peptide bonds, the molecular bridges that connect amino acids, and may thus be relevant in processes that lead to the formation of life. In this study, the solid state formation of some of the smallest amides is investigated in the laboratory. To this end, CH$_{4}$:HNCO ice mixtures at 20 K are irradiated with far-UV photons, where the radiation is used as a tool to produce the radicals required for the formation of the amides. Products are identified and investigated with infrared spectroscopy and temperature programmed desorption mass spectrometry. The laboratory data show that NH$_{2}$CHO, CH$_{3}$NCO, NH$_{2}$C(O)NH$_{2}$, CH$_{3}$C(O)NH$_{2}$ and CH$_{3}$NH$_{2}$ can simultaneously be formed. The NH$_{2}$CO radical is found to be key in the formation of larger amides. In parallel, ALMA observations towards the low-mass protostar IRAS 16293-2422B are analysed in search of CH$_{3}$NHCHO (N-methylformamide) and CH$_{3}$C(O)NH$_{2}$ (acetamide). CH$_{3}$C(O)NH$_{2}$ is tentatively detected towards IRAS 16293-2422B at an abundance comparable with those found towards high-mass sources. The combined laboratory and observational data indicates that NH$_{2}$CHO and CH$_{3}$C(O)NH$_{2}$ are chemically linked and form in the ice mantles of interstellar dust grains. A solid-state reaction network for the formation of these amides is proposed.

Controlling the Surface Oxygen Groups of Polyacrylonitrile-Based Carbon Nanofiber Membranes While Limiting Fiber Degradation

Enhancing the performance of nanofibrous carbons requires the specific chemical functionalization of the surface, while limiting material degradation or causing other detrimental changes in the surface area and pore structures. We compare traditional oxidation protocols using HNO3, HNO3/H2SO4, and KMnO4 with the much less used oxidants RuO4 and OsO4, in tandem with secondary oxidants (such as KMnO4 or Oxone®), for their ability to form carboxylic acids on the surface of polyacrylonitrile-based activated carbon nanofiber membrane (ACNF) materials. While the traditional methods increased the carboxylic acid contents, they also destroyed the macrostructure of the ACNF, concomitant with the loss of up to 17 wt.% of the material. RuO4-mediated oxidations proved also to be too harsh. On the contrary, some of the OsO4-based protocols were characterized by very high mass yields; significant increase in carboxylic acid functionalization (6.3 µmol/mg) compared with the unmodified ACNF (1.7 µmol/mg), but with no concomitant loss of macrostructure, as measured by the retention of the Brunauer-Emmett-Teller (BET) surface area; and average pore width. While there was some reduction in micropore volume, the microporosity of the material remained high. The temperature-programmed desorption mass spectrometry (up to 1000 °C) indicated the presence of both single and adjacent carboxylic acid groups. We thus identified mild and highly effective reaction conditions for the functionalization of carbon nanomaterials without undue degradation of their physical properties.

Study on speciation of HgCl2 supported over activated carbon in simulated flue gases by temperature-programmed decomposition desorption mass spectrometry

HgCl2 that was homogenously dispersed over activated carbon was prepared by an HCl solution method (HgCl2(HCl)/AC), in the present study. The speciation of HgCl2(HCl)/AC in simulated flue gases was further investigated by a temperature-programmed decomposition desorption mass spectroscopy method, to clarify its transformation mechanism. It was found that HgCl2 sublimation occurred after Hg-H2O pretreatment, evidenced by the disappearance of the desorption peak of HgCl2 at 80 °C. After Hg-H2O pretreatment, new species of HgCl2 were formed, as confirmed by similar peak intensities of HgCl2 at mass numbers 270 and 272 at 335 °C. The SO2-H2O or H2S-H2O pretreatment helped stabilize the HgCl2 species supported over the AC, as evidenced by the weaker desorption peak of HgCl2 at around 80 °C. For the HgCl2(HCl)/AC pretreated with SO2-H2O, four desorption peaks of mercury were found, at 280, 335, 380 and 480 °C, indicating that new mercury compounds were formed during pretreatment or the TPDD process. The mercury desorbed at 280 °C was derived from a mercury complex of [HgCl]2SO4⋯A-C, while the mercury desorbed at 480 °C resulted from HgSO4. Some HgO species might be formed and stabilized over the AC during the TPDD process, corresponding to two mercury desorption peaks at 335 and 380 °C. After the pretreatment of HgCl2(HCl)/AC with H2S-H2O, some HgCl2 were transformed to HgS and HgO species, as evidenced by the mercury desorption peaks at 280, 305 and 380 °C.

Effect of Dimethallyl Carbonate Addition on Thermal Stability of Lithium Ion Batteries

The role of dimethallyl carbonate (DMAC), which has a multiple functional group, as an additive in electrolyte have been studied for improving thermal stability of lithium ion batteries (LIB). During the initial charging of the negative electrode with an electrolyte that contains the DMAC additive, film formation occurs near 1 V vs. Li/Li+. Furthermore, increases in the amount of DMAC additive are accompanied by increases in the height of the dq/dV peaks and film formation progresses. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) results show that increasing the amount of DMAC additive promotes the formation of aliphatic hydrocarbons of C5 or more in the Solid-Electrolyte-Interfase (SEI) and polymerization proceeds. The temperature programmed desorption mass spectrometry (TPD-MS) results show that the DMAC additive raises the peak temperature for CO2 generation to 100°C or higher. The DMAC additive suppresses self discharge of LIB and suppresses the increase in direct current resistance (DCR) after storage at 50°C.

Propane and propane-water interactions: a study at cryogenic temperatures.

The phase transition of solid propane and a propane-water mixture under ultrahigh vacuum has been investigated using reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption mass spectrometry (TPD-MS). Here, the investigation is divided into two sections: the phase transition of pure propane and the interaction of propane with water. RAIR spectra of pure propane reveal an unknown crystalline phase at 50 K (phase I), which gradually converts to a known crystalline phase (phase II) at higher temperature. This conversion is associated with certain kinetics. Co-deposition of water and propane restricts the amorphous to crystalline phase transition, while sequential deposition (H2O@C3H8; propane over predeposited water) does not hinder it. For an alternative sequential deposition (C3H8@H2O; water over predeposited propane), the phase transition is hindered due to diffusional mixing within the given experimental time, which is attributed to the reason behind the restricted phase transition.

Size and Surface Chemistry Tuning of Silicon Carbide Nanoparticles.

Chemical transformations on the surface of commercially available 3C-SiC nanoparticles were studied by means of FTIR, XPS, and temperature-programmed desorption mass spectrometry methods. Thermal oxidation of SiC NPs resulted in the formation of a hydroxylated SiO2 surface layer with C3Si-H and CHx groups over the SiO2/SiC interface. Controllable oxidation followed by oxide dissolution in HF or KOH solution allowed the SiC NPs size tuning from 17 to 9 nm. Oxide-free SiC surfaces, terminated by hydroxyls and C3Si-H groups, can be efficiently functionalized by alkenes under thermal or photochemical initiation. Treatment of SiC NPs by HF/HNO3 mixture produces a carbon-enriched surface layer with carboxylic acid groups susceptible to amide chemistry functionalization. The hydroxylated, carboxylated, and aminated SiC NPs form stable aqueous sols.

Adsorption properties of shungite in purification of water–alcohol solutions

Shungite adsorption properties to remove higher alcohols and other impurities from water–alcohol solutions is studied by the methods of nitrogen adsorption, thermogravimetric analysis, wetting, temperature-programmed desorption mass spectrometry, and FTIR spectroscopy. Shungite is shown to be able to effectively sorb impurities from water-alcohol solutions to form fairly strong adsorption systems. Heat treatment 180°C in vacuum results in almost complete decomposition of the adsorption systems, thus providing recovery and a slight increase of the specific surface and sorptive volume of shungite. The present findings demonstrate the theoretical possibility of recovery of adsorption centers on the shungite surface, which would extend its usable life as a sorbent.

Efficient Thermal Reactions of Sulfur Dioxide on Ice Surfaces at Low Temperature: A Combined Experimental and Theoretical Study

The interaction of sulfur dioxide (SO2) gas with a crystalline ice surface at low temperature was studied by analyzing the surface species with low energy sputtering (LES) and reactive ion scattering methods and the desorbing gases with temperature-programmed desorption mass spectrometry. The study gives direct evidence for the occurrence of efficient hydrolysis of SO2 with low energy barriers on the ice surface. Adsorbed SO2 molecules react with the ice surface at temperatures above ∼90 K to form anionic molecular species, which can be detected by OH–, SO2–, and HSO3– emission signals in the LES experiments. Heating the sample above ∼120 K causes the desorption of SO2 gas from the surface-bound hydrolysis products. As a result, the hydrolysis of SO2 on an ice surface is most efficient at 100–120 K. The surface products formed at these temperatures correspond to metastable states, which are kinetically isolated on the cold surface. Quantum mechanical calculations of a model ice system suggest plausible me...

Electrocatalytic Activity of Co-4,4′dimethyl-2,2′-bipyridine Supported on Ketjenblack for Reduction of CO2 to CO Using PEM Reactor

Electrochemical reduction of CO2 was carried out to synthesize CO by using a gas-electrolysis cell. Heat treatment of Co(dmbpy)3 (dmbpy: 4,4′-dimethyl-2,2′-bipyridine) complex on Ketjenblack (KB) in a He stream at 673 K provided an effective electrocatalyst, as denoted Co-dmbpy/KB, for selective reduction of CO2 to CO. Both Co loadings and dmbpy/Co ratios in the Co-dmbpy/KB precusors played important roles in determining their electrocatalytic activities. Under potentiostatic electrolysis at −0.70 V (standard hydrogen electrode (SHE)), Co-dmbpy/KB (Co loading 1 wt%, dmbpy/Co = 5) showed an excellent CO2 reduction activity, a formation rate of CO 254 μmol h−1 cm−2 and a faradic efficiency of CO 78.0%. By localizing the electrocatalyst at the interface between cathode and Nafion, the electrocatalyst was efficiently utilized and a high turn-over number 1183 h−1 was achieved. Temperature-programmed desorption mass spectrometry for CO2 (CO2 TPD-MS) indicated that CO2 adsorption capacity of the electrocatalyst was irreverent to their electroreduction activity for CO2.

Catalyst Shelf Life: Its Effect on Nitrogen-Doped Carbon Nanotubes

In this work is presented a study of the shelf life of an iron-impregnated MgO (Fe/MgO) sample and an explanation of the effect of its aging on morphology and electroactivity of nitrogen-doped carbon nanostructures prepared by using this catalyst at different ages. Characterizations of Fe/MgO by thermogravimetric analysis (TGA), temperature-programmed desorption mass spectroscopy (TPD-MS), high-resolution X-ray powder diffraction (HR-XRPD), and X-ray photoelectron spectroscopy (XPS) have been performed at different aging times. The catalyst is formed by crystalline MgO, Mg(OH)2, and FeO phases. During aging, CO2 adsorption induces the formation of amorphous carbonate, resulting in a decrease of specific surface area, a redistribution of porosity, a reduction of the iron percentage at the surface, and an increase of iron oxide particle size. Different surface and bulk properties are used to explain different morphologies and electroactivities of the nitrogen-doped carbon nanotubes synthesized at different ...

Kinetics of Valeric Acid Ketonization and Ketenization in Catalytic Pyrolysis on Nanosized SiO2 , γ-Al2 O3 , CeO2 /SiO2 , Al2 O3 /SiO2 and TiO2 /SiO2.

Valeric acid is an important renewable platform chemical that can be produced efficiently from lignocellulosic biomass. Upgrading of valeric acid by catalytic pyrolysis has the potential to produce value added biofuels and chemicals on an industrial scale. Understanding the different mechanisms involved in the thermal transformations of valeric acid on the surface of nanometer-sized oxides is important for the development of efficient heterogeneously catalyzed pyrolytic conversion techniques. In this work, the thermal decomposition of valeric acid on the surface of nanoscale SiO2 , γ-Al2 O3 , CeO2 /SiO2 , Al2 O3 /SiO2 and TiO2 /SiO2 has been investigated by temperature-programmed desorption mass spectrometry (TPD MS). Fourier transform infrared spectroscopy (FTIR) has also been used to investigate the structure of valeric acid complexes on the oxide surfaces. Two main products of pyrolytic conversion were observed to be formed depending on the nano-catalyst used-dibutylketone and propylketene. Mechanisms of ketene and ketone formation from chemisorbed fragments of valeric acid are proposed and the kinetic parameters of the corresponding reactions were calculated. It was found that the activation energy of ketenization decreases in the order SiO2 >γ-Al2 O3 >TiO2 /SiO2 >Al2 O3 /SiO2 , and the activation energy of ketonization decreases in the order γ-Al2 O3 >CeO2 /SiO2 . Nano-oxide CeO2 /SiO2 was found to selectively catalyze the ketonization reaction.

Surface Response of Brominated Carbon Media on Laser and Thermal Excitation: Optical and Thermal Analysis Study

The present study is objected to develop an analytical remote optical diagnostics of the functionalized carbons surface. Carbon composites with up to 1 mmol g−1 of irreversibly adsorbed bromine were produced by the room temperature plasma treatment of an activated carbon fabric (ACF) derived from polyacrylonitrile textile. The brominated ACF (BrACF) was studied by elastic optical scattering indicatrix analysis at wavelength 532 nm. The obtained data were interpreted within results of the thermogravimetric analysis, X-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry. The bromination dramatically reduces the microporosity producing practically non-porous material, while the incorporated into the micropores bromine induces the dielectric and structural impact on surface polarizability and conductivity due to the charging effect. We have found that the elastic optical scattering in proper solid angles in the forward and the backward hemispheres is sensitive to the kind of the bromine bonding, e.g., physical adsorption or chemisorption, and the bromination level, respectively, that can be utilized for the express remote fabrication control of the nanoscale carbons with given interfaces.

Chemical State of Nitrogen in Nitrogen-Doped Hydroxyapatite Ceramics with Enhanced Bioactivity

The chemical state of nitrogen which was induced into crystal structure of hydroxyapatite by nitrogen-doping method (N-doping method) was examined. Determination of lattice constants by powder X-ray diffraction (XRD) showed that the nitrogen species induced by N-doping method substituted the OH- ion in the crystal structure of hydroxyapatite. In addition, Fourier transform infrared spectroscopy (FT-IR) and temperature programmed desorption-mass spectroscopy (TPD-MS) determined that the chemical state of nitrogen induced by N-doping method was N2O.

In English

Gelatin-based films with silica-to-gelatin weight ratio 1:5 or 8:5, containing either hydrophilic or hydrophilic-hydrophobic silica, have been prepared and studied by means of thermogravimetric analysis and temperature-programmed desorption mass spectrometry. It has been shown that silica presence has no effect on the mechanism of thermal decomposition of gelatin; however, it affects the kinetics of gelatin thermolysis both in vacuum and in air, including an increase in the activation energy of the volatile products formation at hydrophilic silica content about 17 wt. %. Hydrophobization of silica surface as well as an increase in hydrophilic silica concentration in the film from 17 to 62 wt. % decreases the activation energy of the volatile products formation during gelatin thermolysis. This effect is explained by reduced binding of gelatin with silica owing to either substitution of some surface silanol groups upon partial hydrophobization of silica, or their involving into interparticle rather than in silica-gelatin interactions at higher silica content.

Dimethylsilanone Generation from Pyrolysis of Polysiloxanes Filled with Nanosized Silica and Ceria/Silica.

Temperature-programmed desorption mass spectrometry (TPD MS) was used to study the pyrolysis of PDMS and its composites with nanosized silica and ceria/silica. The results suggest that the elusive organosilicon compound, dimethylsilanone, is generated from PDMS over a broad temperature range (in some cases starting at 70 °C). The presence of nano-oxides catalyzes this process. Ions characteristic of the fragmentation of dimethylsilanone under electron ionization are assigned with the aid of DFT structure calculations. Possible reaction mechanisms for dimethylsilanone generation are discussed in the context of the calculated kinetic parameters. Observed accompanying products of PDMS pyrolysis, such as tetramethylcyclodisiloxane and hexamethylcyclotrisiloxane, indicate that multiple channels are involved in the dimethylsilanone release.

Thermal transformation of bioactive caffeic acid on fumed silica seen by UV–Vis spectroscopy, thermogravimetric analysis, temperature programmed desorption mass spectrometry and quantum chemical methods

Thermochemical studies of hydroxycinnamic acid derivatives and their surface complexes are important for the pharmaceutical industry, medicine and for the development of technologies of heterogeneous biomass pyrolysis. In this study, structural and thermal transformations of caffeic acid complexes on silica surfaces were studied by UV–Vis spectroscopy, thermogravimetric analysis, temperature programmed desorption mass spectrometry (TPD MS) and quantum chemical methods. Two types of caffeic acid surface complexes are found to form through phenolic or carboxyl groups. The kinetic parameters of the chemical reactions of caffeic acid on silica surface are calculated. The mechanisms of thermal transformations of the caffeic chemisorbed surface complexes are proposed. Thermal decomposition of caffeic acid complex chemisorbed through grafted ester group proceeds via three parallel reactions, producing ketene, vinyl and acetylene derivatives of 1,2-dihydroxybenzene. Immobilization of phenolic acids on the silica surface improves greatly their thermal stability.