Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “desorption”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Phosphorus transformation response to soil properties changes induced by manure application in a calcareous soil

Management of phosphorus (P) loss in soils with heavy manure application requires improved understanding of the transformation characteristics of soil P. Influences of manure application on the forms and sorption-desorption characteristics of P in surface (0–30 cm) and subsurface (30–60 cm) layer of a calcareous soil were investigated in this paper in a six-year field trial in comparison to chemical fertilizer application. Hedley fractionation and P K-edge X-ray absorption near-edge structure spectroscopy were used to determine the soil P forms. Manure (M) and chemical fertilizer (F) treatments resulted in P accumulation in two soil depths, but the total P accumulation in surface soil with M treatment was significantly lower than F treatment with similar P surplus. Compared to control, M and F treatments were significantly increased the proportion of labile P at both depths. In surface soil, M treatment significantly decreased stable Ca-associated P proportion and increased Fe-associated P and inositol hexakisphosphate proportions. The accumulation and transformation of P in M treatment distinctly decreased P sorption maximun, sorption coefficient and buffer capacity, and increased the degree of P saturation and P desorption relative to F treatment. The soil properties of pH, organic carbon (OC), total nitrogen (TN), Mehlich-3 extractable Ca and Fe, and phytase in surface soil and pH, OC, TN, Mehlich-3 extractable Ca and dehydrogenase in subsurface soil had significant effects on the compositions of soil P (P < 0.05), respectively. Finally, lowered pH due to manure application mainly contributed to P transformation and release in the calcareous soil.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Near-surface and bulk behavior of Ag in SiC

The diffusive release of fission products, such as Ag, from TRISO particles at high temperatures has raised concerns regarding safe and economic operation of advanced nuclear reactors. Understanding the mechanisms of Ag diffusion is thus of crucial importance for effective retention of fission products. Two mechanisms, i.e., grain boundary diffusion and vapor or surface diffusion through macroscopic structures such as nano-pores or nano-cracks, remain in debate. In the present work, an integrated computational and experimental study of the nearsurface and bulk behavior of Ag in silicon carbide (SiC) has been carried out. The ab initio calculations show that Ag prefers to adsorb on the SiC surface rather than in the bulk, and the mobility of Ag on the surface is high. The energy barrier for Ag desorption from the surface is calculated to be 0.85~1.68 eV, and Ag migration into bulk SiC through equilibrium diffusion process is not favorable. Experimentally, Ag ions are implanted into SiC to produce Ag profiles buried in the bulk and peaked at the surface. High-temperature annealing leads to Ag release from the surface region instead of diffusion into the interior of SiC. It is suggested that surface diffusion through mechanical structural imperfection, such as vapor transport through cracks in 2 SiC coatings, may be a dominating mechanism accounting for Ag release from the SiC in the nuclear reactor.

Ag↗
DOE OSTI2011

Periodic mesoporous organosilicas with co-existence of diurea and sulfanilamide as an effective drug delivery carrier

In this article we report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. The materials possess hexagonal pores with a high degree of uniformity and show long-range order as confirmed by the measurements of small-angle X-ray scattering (SAXS), N{sub 2} adsorption isotherms, and transmission electron microscopy(TEM). FT-IR and solid state {sup 29}Si MAS and {sup 13}C CP MAS NMR spectroscopic analyses proved that the bridging groups in the framework are not cleaved and covalently attached in the walls of the PMOs. It was found that the organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 {sup o}C. The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4. -- Graphical Abstract: We report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. Display Omitted Highlights: {yields} Synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. {yields} The organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 {sup o}C. {yields} The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Silica-coated multi-walled carbon nanotubes impregnated with polyethyleneimine for carbon dioxide capture under the flue gas condition

In this study, silica-coated multi-walled carbon nanotubes impregnated with polyethyleneimine (PEI) were prepared via a two-step process: (i) hydrolysis of tetraethylorthosilicate onto multi-walled carbon nanotubes, and (ii) impregnation of PEI. The adsorption properties of CO{sub 2} were investigated using CO{sub 2} adsorption–desorption isotherms at 298 K and thermogravimetric analysis under the flue gas condition (15% CO{sub 2}/85% N{sub 2}). The results obtained in this study indicate that CO{sub 2} adsorption increases after impregnation of PEI. The increase in CO{sub 2} capture was attributed to the affinity between CO{sub 2} and the amine groups. CO{sub 2} adsorption–desorption experiments, which were repeated five times, also showed that the prepared adsorbents have excellent regeneration properties. - Graphical abstract: Fabrication and CO{sub 2} adsorption process of the S-MWCNTs impregnated with PEI. - Highlights: • Silica coated-MWCNT impregnated with PEI was synthesized. • Amine groups of PEI gave CO{sub 2} affinity sites on MWCNT surfaces. • The S-MWCNT/PEI(50) exhibited the highest CO{sub 2} adsorption capacity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Supramolecular hybrids of polytungstates and their adsorption properties for methylene blue

Two supramolecular hybrids [Ni(mbpy){sub 3}]{sub 2}[V{sub 2}W{sub 4}O{sub 19}]·6H{sub 2}O (1) and [Ni(mbpy){sub 3}]{sub 2}[VW{sub 12}O{sub 40}] (2) (mbpy=4,4′-dimethyl-2,2′-bipyridyl) had been synthesized and characterized. Single crystal X-ray diffraction analyses revealed that the anionic moieties in two hybrids belong to typical Lindqvist and α-Keggin-type structures, respectively. The counter ion [Ni(mbpy){sub 3}]{sup 2+} units were anchored to the polyanions via non-covalent intermolecular interactions. These supramolecular hybrids exhibit reversible adsorption–desorption performance for organic dye methylene blue (MB). Hybrid 2 shows a fast adsorption behavior towards MB and a relatively high value can be reached within 5 min in dark. Both 1 and 2 are structurally stable and can be easily separated from the reaction system for reuse. - Graphical abstract: Supramolecular hybrids of polytungstates have been synthesized and characterized, which exhibit the reversible adsorption–desorption performance for organic dye methylene blue.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Phase equilibria in the Tb-Mg-Co system at 500 °C, crystal structure and hydrogenation properties of selected compounds

The isothermal section of the Tb–Mg–Co phase diagram at 500 °C has been built on the basis of XRD analysis of forty samples prepared by powder metallurgy. The existence of two ternary compounds Tb{sub 4}Mg{sub 3}Co{sub 2} and Tb{sub 4}MgCo was confirmed. The formation of two solid solutions, Tb{sub 1−x}Mg{sub x}Co{sub 3} (0≤x≤0.4) and Tb{sub 1-−x}Mg{sub x}Co{sub 2} (0≤x≤0.6), was found for the first time. It is shown that Tb{sub 5}Mg{sub 24} also dissolves a small amount of Co. Other binary compounds do not dissolve the third component. The Tb{sub 4}MgCo and TbMgCo{sub 4} compounds form hydrides (12.7 and 5.3 at.H/f.u. capacity, respectively) that retain the original structure of metallic matrices. Upon thermal desorption the Tb{sub 4}MgCoH{sub 12.7} hydride was stable up to 300 °C and disproportionated at higher temperature. Two other hydrides, Tb{sub 4}Mg{sub 3}Co{sub 2}H{sub ∼4} and Tb{sub 2}MgCo{sub 9}H{sub 12}, are unstable in air and decompose into the initial compounds. - Highlights: • The phase equilibria at 500 °°C in the Tb–Mg–Co system has been studied. • The existence of two ternary compounds, Tb{sub 4}Mg{sub 3}Co{sub 2} and Tb{sub 4}MgCo, was confirmed. • The formation of two solid solutions, Tb{sub 1−x}Mg{sub x}Co{sub 3} and Tb{sub 1−x}Mg{sub x}Co{sub 2}, was found. • Hydrogen sorption–desorption properties have been studied for the selected alloys.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Effects of hydrogen adsorption on the properties of double wall BN and (BN){sub x}C{sub y} nanotubes

In the present contribution, we apply first-principles calculations, based on the density functional theory, to study the effects of hydrogen adsorption on the structural and electronic properties of boron nitride and hybrid carbon–boron nitride double wall nanotubes. The results demonstrate that the hydrogen decoration induces significant structural deformation and an appreciable reduction in the gap energy. When the number of hydrogen atoms introduced on the outer wall is increased, desorption of hydrogen pairs are observed. The calculations indicate that each adsorbed hydrogen atom induces a structural deformation with an energetic cost of about 68 meV/atom. It is also found that the introduction of hydrogen atoms can be applied as an efficient tool for tuning the electronic properties of such structures. - Graphical abstract: Localized density of states of a hydrogenated double wall boron nitride nanotube. Some hydrogen pairs are desorbed, forming H{sub 2} molecules. - Highlights: • Hydrogenation induces structural deformation and reduction in the gap energy. • Each H atom induces a deformation with an energetic cost of about 68 meV/atom. • In some cases, desorption of H pairs from the outer wall is observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Study on glass-forming ability and hydrogen storage properties of amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) alloys

Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) amorphous alloys were prepared by rapid solidification, using a melt-spinning technique. X-ray diffraction and differential scanning calorimetry analysis were employed to measure their microstructure, thermal stability and glass-forming ability, and hydrogen storage properties were studied by means of PCTPro2000. Based on differential scanning calorimetry results, their glass-forming ability and thermal stability were investigated by Kissinger method, Lasocka curves and atomic cluster model, respectively. The results indicate that glass-forming ability, thermal properties and hydrogen storage properties in the Mg-rich corner of Mg–Ni–La–Co system alloys were enhanced by Co substitution for La. It can be found that the smaller activation energy (ΔΕ) and frequency factor (υ{sub 0}), the bigger value of B (glass transition point in Lasocka curves), and higher glass-forming ability of Mg–Ni–La–Co alloys would be followed. In addition, atomic structure parameter (λ), deduced from atomic cluster model is valuable in the design of Mg–Ni–La–Co system alloys with good glass-forming ability. With an increase of Co content from 0 to 4, the hydrogen desorption capacity within 4000 s rises from 2.25 to 2.85 wt.% at 573 K. - Highlights: • Amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0 and 4) alloys were produced by melt spinning. • The GFA and hydrogen storage properties were enhanced by Co substitution for La. • With an increase of Co content, the hydrogen desorption capacity rises at 573 K.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Development of efficient amine-modified mesoporous silica SBA-15 for CO{sub 2} capture

Graphical abstract: - Highlights: • A secondary amine AN-TEPA is used to modify the SBA-15. • CO{sub 2} adsorption capacity (180.1 mg g{sup −1}-adsorbent for 70% amine loading) is high. • The sorbent exhibits a high stability after 12 cycling runs. • The modified SBA-15 achieves complete desorption at low temperature (100 °C). - Abstract: A novel CO{sub 2} sorbent was prepared by impregnating mesoporous silica, SBA-15, with acrylonitrile (AN)-modified tetraethylenepentamine (TEPA) in order to increase CO{sub 2} adsorption capacity and improve cycling stability. The mesoporous silica with pre- and post-surface modification was investigated by X-ray diffraction characterization (XRD), N{sub 2} adsorption–desorption test (N{sub 2}-BET), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The adsorption/desorption performance of S-TN (TN: AN modified TEPA) and S-TEPA was studied by dynamic adsorption. Test results showed that the solid base-impregnated SBA-15 demonstrated high CO{sub 2} adsorption capacity (180.1 mg g{sup −1}-adsorbent for 70% amine loading level). Compared to S-TEPA (24.1% decrease of initial capacity), S-TN with 50% amine loading exhibited improved cycling stability, 99.9% activity reserved (from initial 153.0 mg g{sup −1} to 151.3 mg g{sup −1}) after 12 cycles of adsorption/desorption at 100 °C. A mechanism of molecular structure of the loaded amine was attributed to the improved performance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and characterization of mesoporous MgO by template-free hydrothermal method

Highlights: • A simple synthesis of porous MgO with diameter size from 3 to 10 μm without any templates. • Effect of temperature and time were investigated. • Systematic characterization by TG/DTA, XRD, SEM, TEM, and nitrogen adsorption–desorption isotherm of MgO. • A possible formation and crystal growth mechanism of mesopores MgO is proposed. - Abstract: Mesoporous MgO particles have been synthesized through a novel template-free hydrothermal co-precipitation method using a Mg(NO{sub 3}){sub 2} solution as the magnesium source and NaCO{sub 3} as precipitant. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N{sub 2} adsorption–desorption analysis. The results indicate that the MgO samples have a disordered mesoporous structure, a large BET surface area, and a large pore volume. The effect of reaction temperature on the MgO product BET surface area was studied. A possible formation and crystal growth mechanism for mesoporous MgO is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Resistive sensing of gaseous nitrogen dioxide using a dispersion of single-walled carbon nanotubes in an ionic liquid

Graphical abstract: Ionic liquid ([C6-mim]PF6) used as dispersant agent for SWCNTs: An investigations were carried out to find the structural quality and surface modification for sensor application. - Highlights: • An effective technique based on Ionic liquids (IL) and their use as a dispersant. • Electron microscopy and spectroscopy for structure characterization. • Covalent linkage of ILs with SWNTs and dispersion of SWCNTs. • The IL-wrapped sensing film, capable for detecting trace levels of gas. - Abstract: Single-walled carbon nanotubes (SWCNTs) were dispersed in an imidazolium-based ionic liquid (IL) and investigated in terms of structural quality, surface functionalization and inter-CNT force. Analysis by field emission electron microscopy and transmission electron microscopy shows the IL layer to coat the SWNTs, and FTIR and Raman spectroscopy confirm strong binding of the ILs to the SWNTs. Two kinds of resistive sensors were fabricated, one by drop casting of IL-wrapped SWCNTs, the other by conventional dispersion of SWCNTs. Good response and recovery to NO{sub 2} is achieved with the IL-wrapped SWCNTs material upon UV-light exposure, which is needed because decrease the desorption energy barrier to increase the gas molecule desorption. NO{sub 2} can be detected in the 1–20 ppm concentration range. The sensor is not interfered by humidity due to the hydrophobic tail of PF6 (ionic liquid) that makes our sensor highly resistant to moisture.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Three-dimensional MoO3 nanoflowers assembled with nanosheets for rhodamine B degradation under visible light

Highlights: • The orthorhombic three-dimensional MoO{sub 3} nanoflowers were synthesized by the modified hydrothermal method. • Using different amount of HCl to transfer from the h-MoO{sub 3} to the α-MoO{sub 3} was well discussed. • Better pore sizes and surface areas of the three-dimensional MoO{sub 3} nanoflowers accelerate the photodegradation process of RhB. • The three-dimensional MoO{sub 3} nanoflowers showed the photocatalytic activity (91.57%). • This methodology should be useful for preparing other nanostructured catalysts. - Abstract: Three-dimensional hierarchical nanoflowers self-assembled with the orthorhombic molybdenum oxide (α-MoO{sub 3}) nanoflowers were synthesized by the modified hydrothermal method. The structure characterizations of the three-dimensional α-MoO{sub 3} nanoflowers were carried out by scanning electron microscope (SEM), Energy Disperse Spectroscopy (EDS), X-ray diffraction (XRD) and nitrogen adsorption-desorption measurement. Moreover, the three-dimensional α-MoO{sub 3} nanoflowers as photocatalyst exhibited enhanced photocatalytic activity towards photodegradation of Rhodamine B (RhB) under xenon (Xe) lamp irradiation. The results of SEM, EDS, XRD and nitrogen adsorption-desorption measurement showed the three-dimensional α-MoO{sub 3} nanoflowers have a better morphology, pore size (7.99 nm) and surface areas (50.788 m{sup 2} g{sup −1}) than hexagonal MoO{sub 3} (h-MoO{sub 3}) nanosheets, photocatalytic activity studies confirmed that the three-dimensional α-MoO{sub 3} nanoflowers photocatalyst exhibits a high visible-light-driven activity for photodegradation of RhB solution of 91.57% within 160 min under Xe lamp irradiation. A mechanism was also proposed for the degradation of RhB by three-dimensional α-MoO{sub 3} nanoflowers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Oxidation of H 2 S by coadsorbed oxygen on the α-Cr 2 O 3 (0001) surface

The interactions of H 2 S and oxygen have been explored on the α-Cr 2 O 3 (0001) surface using temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and sticking coefficient measurements. H 2 S adsorbs with near unity sticking on the clean α-Cr 2 O 3 (0001) surface at 125 K up to a coverage of ~1.6 ML (where 1 ML is defined as the surface areal density of Cr 3+ sites). Reversible adsorption is evidenced in TPD by three desorption states evolving between 150 and 315 K. Although no S-containing decomposition products were observed in TPD, AES detected S on the surface after TPD indicating that some degree of irreversible decomposition occurred. The level of H 2 S decomposition on the clean surface was estimated to be between 0.2-0.5 ML using water TPD as an indicator of S site blocking. In contrast, preadsorbed O 2 at three temperatures (125, 400 and 800 K) exerted drastic changes on the surface chemistry of H 2 S seen on the clean surface. At 400 and 800 K, O 2 adsorption on clean α-Cr 2 O 3 (0001) is dissociative, populating the surface with chromyl groups (Cr=O) in the former case (corresponding to roughly 1 O per Cr 3+ surface site) and resulting in a nearly complete O-termination sheet (~3 O per Cr 3+ ) in the latter case. Little or no H2S chemistry is observed on the O-terminated surface based on TPD and AES. However, availability of Cr-coordination sites on the chromyl-terminated surface facilitated H 2 S adsorption and oxidation during TPD to SO 2 (445-470 K) and H 2 O (320 K). Isotopic-labeling studies suggest that the oxygen atom in the water product originates from dosed oxygen whereas that in the SO 2 product comes from the lattice. Similar results were obtained from H 2 S dosed on the surface pretreated with O 2 at 125 K, where O 2 adsorption is predominately molecular, except that S 2 was also detected in TPD at 525 K and the amount of SO 2 produced at 445 K decreased. These results suggest that atomically adsorbed oxygen effectively oxidizes H 2 S, but that molecularly adsorbed O 2 is key to the partial oxidation of H 2 S to elemental sulfur.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

CO oxidation on nanoporous gold: A combined TPD and XPS study of active catalysts

Disks of nanoporous gold (np-Au), produced by leaching of silver from AgAu alloy and prepared as active catalysts for CO oxidation in a continuous-flow reactor, were investigated in detail by x-ray photoelectron spectroscopy and temperature-programmed desorption spectroscopy in ultra-high vacuum. Np-Au exhibits several oxygen species on and in the surface: Chemisorbed oxygen (O act ), probably generated at residual silver sites at the surface, is readily available after np-Au preparation and consumed by CO oxidation. It can be replenished on activated np-Au by exposure to O 2 . In addition, strongly bound oxygen, probably at subsurface sites, is present as a major species and not consumed by CO oxidation. Pronounced CO desorption at temperatures above 200 K observed after exposing np-Au to CO at 105 K indicates an additional, more stable type of CO binding sites on np-Au as compared to pure gold. Only CO at these binding sites is consumed by oxidation reaction with O act . In conclusion, we propose that the presence of strongly bound subsurface oxygen stabilizes CO adsorption on np-Au, thereby being as crucial for the observed catalytic activity of np-Au as residual silver.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Surface and bulk crystallization of amorphous solid water films: Confirmation of “top-down” crystallization

The crystallization kinetics of nanoscale amorphous solid water (ASW) films are investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). TPD measurements are used to probe surface crystallization and RAIRS measurements are used to probe bulk crystallization. Isothermal TPD results show that surface crystallization is independent of the film thickness (from 100 to 1000 ML). Conversely, the RAIRS measurements show that the bulk crystallization time increases linearly with increasing film thickness. These results suggest that nucleation and crystallization begin at the ASW/vacuum interface and then the crystallization growth front propagates linearly into the bulk. This mechanism was confirmed by selective placement of an isotopic layer (5% D2O in H2O) at various positions in an ASW (H2O) film. In this case, the closer the isotopic layer was to the vacuum interface, the earlier the isotopic layer crystallized. These experiments provide direct evidence to confirm that ASW crystallization in vacuum proceeds by a “top-down” crystallization mechanism.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Oxygen adsorption on spontaneously reconstructed Au(511)

The four-fold site on {100} facets, which are potential catalytic sites on high-curvature gold nanoparticles, is difficult to prepare on a gold single crystal due to surface reconstruction. Here, the Au(511) surface with a high density of step edges and a well-maintained {100} local structure was studied by scanning tunneling microscopy (STM), temperature programmed reaction spectroscopy (TPRS), and density functional theory (DFT) calculations. Annealing at 550 K and 870 K induces reconstruction on the Au(511) surface to a mixture of (311) and (711) micro-terraces. At room temperature and low oxygen coverage, oxygen adsorbs at both three- and four-fold sites on the surface, leading to a well-ordered zig-zag structure. Oxygen atoms cause significant orbital hybridization and a slight displacement of the gold atoms to which they bind. High oxygen coverages induce the formation of clusters, which are not active towards oxidation of isopropanol at room temperature and a pressure of 10-10 mbar. Oxygen adsorption saturates at 1 monolayer (ML), and two separate oxygen recombinative desorption peaks were observed at coverages above 0.11 ML. Our characterization of this surface and the O adsorption structure allows future studies of {100} micro-terraces for oxidation reactions, which contributes to studies on gold-based catalysts with an irregular shape.

catalysis (heterogeneous), mesostructured material↗
DOE OSTI2013

Synchrotron based mass spectrometry to investigate the molecular properties of mineral-organic associations

Soil organic matter (OM) is important because its decay drives life processes in the biosphere. Analysis of organic compounds in geological systems is difficult because of their intimate association with mineral surfaces. To date there is no procedure capable of quantitatively separating organic from mineral phases without creating artifacts or mass loss. Therefore, analytical techniques that can (a) generate information about both organic and mineral phases simultaneously and (b) allow the examination of predetermined high-interest regions of the sample as opposed to conventional bulk analytical techniques are valuable. Laser Desorption Synchrotron Postionization (synchrotron-LDPI) mass spectrometry is introduced as a novel analytical tool to characterize the molecular properties of organic compounds in mineral-organic samples from terrestrial systems, and it is demonstrated that when combined with Secondary Ion Mass Spectrometry (SIMS), can provide complementary information on mineral composition. Mass spectrometry along a decomposition gradient in density fractions, verifies the consistency of our results with bulk analytical techniques. We further demonstrate that by changing laser and photoionization energies, variations in molecular stability of organic compounds associated with mineral surfaces can be determined. The combination of synchrotron-LDPI and SIMS shows that the energetic conditions involved in desorption and ionization of organic matter may be a greater determinant of mass spectral signatures than the inherent molecular structure of the organic compounds investigated. The latter has implications for molecular models of natural organic matter that are based on mass spectrometric information.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗