IR Photoacoustic Spectroscopy Research Articles

Analysis of Carbon Materials with Infrared Photoacoustic Spectroscopy.

Measurement of infrared spectroscopy has emerged as a significant challenge for carbon materials due to the sampling problem. To overcome this issue, in this work, we performed measurements of IR spectra for carbon materials including C60, C70, diamond powders, graphene, and carbon nanotubes (CNTs) using the photoacoustic spectroscopy (PAS) technique; for comparison, the vibrational patterns of these materials were also studied with a conventional transmission method, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, or Raman spectroscopy. We found that the IR photoacoustic spectroscopy (IR-PAS) scheme worked successfully for these carbon materials, offering advantages in sampling. Interestingly, the profiles of IR-PAS spectra for graphene and CNTs exhibit negative bands using carbon black as the reference; the negative spectral information may provide valuable knowledge about the storage energy, production, structure, defect, or impurity of graphene and CNTs. Thus, this approach may open a new avenue for analyzing carbon materials.

Remote mid IR Photoacoustic Spectroscopy for the detection of explosive materials

Standoff photoacoustic detection of explosives using quantum cascade laser has been studied. The laser beam has been focused on to the target molecules adsorbed on metallic surfaces. A 25 kHz microphone, a resonator cavity in form of a cylinder, and a parabolic acoustic reflector have been used to demonstrate the method. The experimental results have been compared with the theoretical calculations in three different experimental conditions. The photoacoustic signals have been found to decrease with increase in the standoff range. The sensitivity of 2.0 µg/cm2 has been achieved at ~4.0 m.

Non-invasive individual methane measurement in dairy cows

Attempts to lower the environmental footprint of milk production needs a sound understanding of the genetic and nutritional basis of methane (CH4) emissions from the dairy production systems. This in turn requires accurate and reliable techniques for the measurement of CH4 output from individual cows. Many of the available measurement techniques so far are either slow, expensive, labor intensive and are unsuitable for large-scale individual animal measurements. The main objectives of this study were to examine and validate a non-invasive individual cow CH4 measurement system that is based on photoacoustic IR spectroscopy (PAS) technique implemented in a portable gas analysis equipment (F10), referred to as PAS-F10 method and to estimate the magnitude of between-animal variations in CH4 output traits. Data were collected from 115 Nordic Red cows of the Minkiö experimental dairy farm, at the Natural Resources Institute Finland (Luke). Records on continuous daily measurements of CH4, milk yield, feed intake and BW measurements over 2 years period were compiled for data analysis. The daily CH4 output was calculated using carbon dioxide as a tracer method. Estimates from the non-invasive PAS-F10 technique were then tested against open-circuit indirect respiration calorimetric chamber measurements and against estimates from other widely used prediction models. Concordance analysis was used to establish agreement between the chamber and PAS-F10 methods. A linear mixed model was used for the analysis of the large continuous data. The daily CH4 output of cows was 555 l/day and ranged from 330 to 800 l/day. Dry matter intake, level of milk production, lactation stage and diurnal variation had significant effects on daily CH4 output. Estimates of the daily CH4 output from PAS-F10 technique compared relatively well with the other techniques. The concordance correlation coefficient between combined weekly CH4 output estimates of PAS-F10 and chamber was 0.84 with lower and upper confidence limits of 0.65 and 0.93, respectively. Similarly, when chamber CH4 measurements were predicted from PAS-F10 measurements, the mean of two separate weekly PAS-F10 measurements gave the lowest prediction error variance than either of the separate weekly PAS-F10 measurements alone. This suggests that every other week PAS-F10 measurements when combined would improve the estimation of CH4 output with PAS-F10 technique. The repeatability of daily CH4 output from PAS-F10 technique ranged from 0.40 to 0.46 indicating that some between-animal variation exist in CH4 output traits.

Predicting the Possibility for Deep Hydroprocessing of Some Kuzbass Coals

Using thermal analysis and photoacoustic IR spectroscopy techniques, the abilities to be hydrogenated for some low-metamorphosed Kuzbass coals have been estimated in the aim of studying the possibilities of their deep industrial processing to obtain liquid fuels and valuable chemical products. Two independent parameters for quick assessment of solid fuel suitability for hydrogenation processes under high pressure of hydrogen have been proposed: 1) the relative maximal rate of coal pyrolysis in the 300-500°C temperature range, [(1/m o ) • dm/dT] (calculated from thermal analysis data), and 2) the intensity of aliphatic IR absorption bands (the sum of their optical densities), normalized to the optical density of an IR absorption band associated with aromatic ring C=C-bonds [i.e., (D 2920 +D 2860 )/D 1600 ] (obtained from photoacoustic FTIR spectra of coal materials). It has been shown that for a number of low-metamorphosed Kuzbass coals (Barzas sapromixite, Itatsky lignite and Karakansky longflame coal) the above mentioned parameters were in good consistency with generally accepted hydrogenation ability parameters of solid fossil fuels – atomic H/C ratios and volatile matter values.

Theoretical and practical limitations of the acetylene inhibition technique to determine total denitrification losses

Abstract. The loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. Flux monitoring of N2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient method, is impossible due to the large atmospheric N2 background (78%). The acetylene (C2H2) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N2 losses from intact soil cores. In principle, AIT allows an estimation of total denitrification at high temporal resolution and on small spatial scales, with limited workload and costs involved. To investigate its potential and limitations, a laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed simultaneous measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with automated C2H2 injection. A survey of total denitrification losses (N2 + N2O) over 1.5 yr in soil cores from an intensively managed, cut grassland system in central Switzerland supports previous reports on severe limitations of the AIT, which precluded reliable estimates of total denitrification losses. Further, the unavoidable sampling and transfer of soil samples to the laboratory causes unpredictable deviations from the denitrification activity in the field.

Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy, photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is supported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data have demonstrated that the composition and structure of the rhodium complexes that form on the titanium dioxide surface during different heat treatments later determine the state of the supported rhodium particles forming in the sodium tetrahydroborate reaction medium.

The influence of the copolymerization conditions on the polymer structure. FT-IR/PAS studies

Preparation of porous copolymers of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) by suspension-emulsion and bulk polymerization is presented. The influence of polymerization technique, type and amount of porogen on the copolymer structure has been investigated. The porous structure of MAA-EGDMA copolymers has been examined. Porous structure was determined for all of the obtained copolymers. Chemical nature of the copolymers surfaces was characterized by Fourier transform infrared (FT-tR) and IR photoacoustic spectroscopy (FT-IR/PAS).

Rotational influence on multiphoton absorption efficiency in SF6-N2mixtures

The results of pulsed IR photoacoustic spectroscopy measurements of multiphoton absorption and rotational relaxation processes in SF 6 -N 2 mixtures are presented. Total average number ( total ) of absorbed photons per one absorbing molecule (SF 6 ) during the laser pulse was compared with average number of absorbed photons ( v ) really stored in SF 6 vibrational modes, using generalized coupled two-level model. Obtained results can be used to confirm or predict the excitation level ( v ) of absorbing molecule during the laser pulse, as a function of added buffer-gases. This approach could allow one to control laser field - molecule interaction in different gas mixtures, understand the efficiency of collisional effects (especially rotational relaxation) and their positive and negative influence on absorption characteristics of irradiated polyatomic molecule.

Investigation of Fungal Deterioration of Synthetic Paint Binders Using Vibrational Spectroscopic Techniques

The deterioration of synthetic polymers caused by biological process is usually evaluated by visual inspection and measuring physical effects. In contrast to this approach, we have applied vibrational spectroscopies to study the biodegradation of the synthetic resins. 29 synthetic resins used as paint binding media, including acrylic, alkyd and poly(vinyl acetate) polymers, were examined for potential susceptibility to fungal degradation using the standard method ASTM G21-96(2002). In addition, the degraded resins were analysed by Raman spectroscopy, FT-IR and FT-IR photoacoustic spectroscopy. Almost all the acrylic resins studied proved to be resistant to microbial attack, while all alkyd resins and some poly(vinyl acetates) turned out to be biodegradable. Within a few days of inoculation Aspergillus niger was the most copious fungus on the biodegraded resins. A comparison of the IR and Raman spectra of control and biodegraded resins did not show any differences, but photoacoustic spectroscopy revealed additional bands for the fungal-degraded resins, consistent with the presence of fungal-derived substances. The additional bands in the photoacoustic spectra were due to the presence of Aspergillus niger and melanin, a fungal pigment. Since IR photoacoustic spectroscopy can be also a suitable technique for the chemical characterisation of binding media, the same spectroscopic analysis can be employed to both characterise the material and obtain evidence for fungal colonization. Microbial growth on Sobral 1241ML (alkyd resin) after 28 d (growth rating 4) compared with the non-inoculated resin.

Dehydrogenation of Ethylbenzene with Nitrous Oxide in the Presence of Mesoporous Silica Materials Modified with Transition Metal Oxides

The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites.

Mixed metal fluorides as doped Lewis acidic catalyst systems: a comparative study involving novel high surface area metal fluorides

MF3-doped/MgF2 systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid metal fluorides with dopant metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and 19F-MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions. The exemplarily investigated GaF3-doped/MgF2 system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.

Mixed metal fluorides as doped Lewis acidic catalyst systems: a comparative study involving novel high surface area metal fluorides

MF 3-doped/MgF 2 systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid metal fluorides with dopant metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and 19 F -MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions. The exemplarily investigated GaF 3-doped/MgF 2 system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.

Solid-phase synthesis of modified oligopeptides via Passerini multicomponent reaction

A Passerini multicomponent reaction of N-protected-α-aminoaldehydes, carboxylic acids and solid-supported isocyanides has been successfully performed on Lantern™. The initially formed N-protected-β-amino-α-acyloxyamides gave, by piperidine-promoted deprotection and concomitant acyl migration, β-acylamino-α-hydroxyamides which, by OH-oxidation and cleavage off the solid support, provided β-acylamino-α-oxoamides. Formation and disappearance of the isocyano group has been followed using photoacoustic IR spectroscopy, a fast, reliable and non-disruptive technique that has been successfully applied for the first time to macroscopic solid supports.

Buffer-gas pressure influence on multiphoton absorption in SF6–N2 mixtures

In this article the results of pulsed IR photoacoustic spectroscopy measurements of multiphoton absorption and relaxation processes in SF6–N2 mixtures are presented. The total average number of absorbed photons per one absorbing molecule (basic physical quantity which characterized multiphoton processes) during the laser pulse 〈n〉total is used and analyzed with a generalized coupled two-level model. This type of analysis is based on buffer-gas pressure (pbuff) functional behavior of 〈n〉total and calculation of its partial values depending on collisions, 〈n〉coll, and laser fluence, 〈n〉Φ, influence. Using different methods of photoacoustic spectroscopy, collisionaly induced rotational and vibrational to translational relaxation process parameters (τrot and τV-T, respectively) are quantitatively obtained and used to determine partial values of 〈n〉coll, 〈n〉rot, and 〈n〉V-T. It will be shown that a method based on ∂〈n〉total/∂p functional dependence on pbuff and laser fluence Φ can be used to confirm or predict the existence of some processes during the laser pulse, such as dissociation or strong vibrational to vibrational energy transfer, which can contribute to the total amount of energy absorbed into the investigated sample. This could allow one to apply this method and control laser field–molecule interaction in different gas mixtures, and help one to understand multiphoton absorption processes in detail.

Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

AbstractThe tert‐butoxy radical‐facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free‐radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP‐graft‐PMMA residues were detected by solid‐state 13C‐NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert‐butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1–2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 898–915, 2002

Structural and Electrochemical Characterization of Glassy Carbon Prepared from Silicon‐Doped Polymethacrylonitrile/Divinylbenzene Copolymer

There has been a great deal of discussion on the potential role of heteroatoms in carbons intended for lithium ion intercalation. Previous observations have been mixed, ranging from beneficial to detrimental effects on intercalation capacity, irreversible losses, and charge efficiencies. The introduction or substitution of silicon into a carbon matrix prepared by chemical vapor deposition has demonstrated a positive effect. The present study concerns substitutional effects in disordered carbons synthesized from polymer precursors. Solid‐state nuclear magnetic resonance, photoacoustic IR spectroscopy, X‐ray fluorescence, and high‐resolution transmission electron microscopy were used to follow the modified carbon synthesis. Silicon is successfully incorporated into the polymer matrix by copolymerizing the precursors with tetravinylsilane. On oxidative stabilization and pyrolysis, however, the Si‐C connectivity is replaced by Si‐O coordination. These silicon species appear to be discrete, and no evidence for either a crystalline or amorphous secondary phase is seen. These silicon species have a profound effect on the electrochemical performance. Irreversible loss processes are greatly increased, and charge efficiencies are decreased when compared to nonsubstituted controls. © 1999 The Electrochemical Society. All rights reserved.

Characterization of a TiCl4-modified silica surface by means of quantitative surface analysis

The reaction of TiCl4 with the surface of a silica gel has been investigated in detail using Fourier-transform IR photoacoustic spectroscopy (FTIR PAS) and elemental analysis. The hydroxy groups on the silica react with the TiCl4 giving rise to both monodentate and didentate surface groups. The parameters influencing the relative distribution of these groups have been studied. A quantitative description of the chemisorbed species has been obtained as a function of the pretreatment and the reaction temperatures.

Reactions at the interphase between an isocyanate and epoxy resins — infrared spectroscopic investigations

The formation of an interphase between an epoxy resin and an urethane is shown. The interphase is formed by the reaction of isocyanate groups with the hydroxyl groups of the already cured epoxy resin. The network density of the epoxy resin was controlled by the functionality of the curing agent. The examination of the interphase is carried out by photoacoustic IR-spectroscopy and the analysis of cross sections by IR-microscopy. It is shown, that the depth of interpenetration is controlled by the crosslinking density of the epoxy resin. Furthermore the depth of interpenetration is reduced, if additional hydroxyl groups are present in the epoxy resin.

Hydrogen cyanide polymers: from laboratory to space

Hydrogen cyanide polymers—heterogeneous solids ranging in color from yellow to orange to red to black—may be among the organic macromolecules most readily formed within the solar system The non-volatile black crust of comet Halley for example, may consist largely of such polymers. It seems likely. too, that HCN polymers are a major constituent of the dark. CN bearing solids identified tentatively by IR spectra in the dust of some other comets. HCN polymerization could also account for some of the yellow-orange-red coloration of Jupiter and Saturn, and perhaps for the orange haze high in Titan's atmosphere. Studies of these polymers show that a yellow-brown powder can be extracted by water and further hydrolyzed to vield α-amino acids. Several instrumental methods used for the separation and identification of these intriguing materials. including pyrolysis mass spectrometry, Fourier transform IR photoacoustic spectroscopy and supercritical fluid extraction chromatography, reveal fragmentation patterns and chemical functionalities consistent with the presence of polymeric peptide precursors—polyamidines—in HCN polymers. Implications for prebiotic chemistry are profound. Primitive Earth may have been covered by HCN polymers and other organic products through bolide bombardment or terrestrial synthesis, producing a proteinaceous matrix able to bring about the molecular interactions leading to the emergence or life. Cyanide polymerization could also he a preferred pathway beyond Earth and the solar system, on planetary bodies and satellites around other stars and in the dusty molecular clouds of spiral galaxies.

95/00238 Reactivity of coal according to photoacoustic IR spectroscopy data

95/00238 Reactivity of coal according to photoacoustic IR spectroscopy data