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Results for “ADSORPTION”
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.
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The inhibition of methane hydrate formation by water alignment underneath surface adsorption of surfactants
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Ammonia Adsorption and Co-adsorption with Water in HKUST-1: Spectroscopic Evidence for Cooperative Interactions
Ammonia interactions and competition with water at the interface of nanoporous metal organic framework thin films of HKUST-1 (Cu 3 Btc 2 , Btc = 1,3,5-benzenedicarboxylate) are investigated with ambient pressure X-ray photoelectron spectroscopy (APXPS). In the absence of water, ammonia adsorption at the Cu 2+ metal center weakens the metal-linker bond of the framework. In the presence of water, due to the higher binding energy (adsorption strength) of ammonia compared to water, ammonia replaces water at the unsaturated Cu 2+ metal centers. The water molecules remaining in the pores are stabilized by hydrogen bonding to ammonia. Hydrogen bonding between the water and ammonia strengthens the metal-ammonia interaction due to cooperative interactions. Cooperative interactions result in a reduction in the metal center oxidation state facilitating linker replacement by other species explaining the previously reported structure degradation.
Iron Ion and Iron Hydroxide Adsorption to Charge-Neutral Phosphatidylcholine Templates
Abstract not provided
Adsorption and Reaction of Methanol over CeO X (100) Thin Films
Methanol was adsorbed on oxidized and reduced CeO X (100) thin films to probe the active sites and reaction selectivity of these surfaces compared to those of CeO X (111). Roughly twice as much methoxy was formed on oxidized CeO 2 (100) compared to that formed on CeO 2 (111). In addition to more methoxy, hydroxyl is also more stable on CeO 2 (100). Unlike on CeO 2 (111), however, methanol on CeO 2 (100) produced CO, CO 2 , and H 2 in addition to water and formaldehyde. The behavior of CeO 2 (100) is related to its surface structure, which provides greater access to Ce cations and therefore more active adsorption sites and more highly undercoordinated Ce and O. The undercoordinated O may explain the enhanced dehydrogenation activity leading to CO and H 2 formation. The reduction of ceria leads to increased methanol uptake on both CeO 2 – X (100) and CeO 2 – X (111). However, although the uptake doubled on reduced CeO 2 – X (111) compared to the oxidized surface, it increased by only 10% on reduced CeO 2 – X (100) compared to that on fully oxidized CeO 2 (100). Reduction of both surfaces leads to a greater production of CO and H 2 . Reaction on all surfaces progresses rapidly from methoxy to products. Lastly, there is no spectroscopic evidence of formyl or formate intermediates. On CeO X (100), carbonate is detected that decomposes into CO 2 at high temperature.
Porous materials with pre-designed single-molecule traps for CO2 selective adsorption
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Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters
Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe 2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
Investigation of trimethylacetic acid adsorption on stoichiometric and oxygen-deficient CeO 2 (111) surfaces
We studied the interactions between the carboxylate anchoring group from trimethylacetic acid (TMAA) and CeO 2 (111) surfaces as a function of oxygen stoichiometry using in situ X-ray photoelectron spectroscopy (XPS). The stoichiometric CeO 2 (111) surface was obtained by annealing the thin film under 2.0 × 10 –5 Torr of oxygen at ~550 °C for 30 min. In order to reduce the CeO 2 (111) surface, the thin film was annealed under ~5.0 × 10 –10 Torr vacuum conditions at 550 °C, 650 °C, 750 °C and 850 °C for 30 min to progressively increase the oxygen defect concentration on the surface. The saturated TMAA coverage on the CeO 2 (111) surface determined from XPS elemental composition is found to increase with increasing oxygen defect concentration. This is attributed to the increase of under-coordinated cerium sites on the surface with the increase in the oxygen defect concentrations. Furthermore, XPS results were in agreement with periodic density functional theory (DFT) calculations and indicate a stronger binding between the carboxylate group from TMAA and the oxygen deficient CeO 2–δ (111) surface through dissociative adsorption.
Structural tuning of zinc–porphyrin frameworks via auxiliary nitrogen-containing ligands towards selective adsorption of cationic dyes
Three novel zinc–porphyrin MOFs have been synthesized by using versatile N-containing ligands. The open Watson–Crick pair in the interior surface in one Zn-MOF has been presented, which could endow the related MOF with excellent selective adsorption of dye molecules.
A generalized van der Waals model for light gas adsorption prediction in IRMOFs
A generalized van der Waals model for predicting the adsorption isotherms in IRMOFs by defining different attractive regions.
Privileged zeolitic sites for humid CO 2 adsorption: K + in double eight-membered rings
A proficient site for humid CO 2 adsorption in zeolites: K + -D8R structures can selectively adsorb CO 2 over H 2 O.
Cooperative Gas Adsorption without a Phase Transition in Metal-Organic Frameworks
Cooperative adsorption of gases by porous frameworks, which permits more efficient uptake and removal than the more usual noncooperative (Langmuir-type) adsorption, usually results from a phase transition of the framework. Here in this paper, we show how cooperativity emerges in the class of metal-organic frameworks mmen-M 2 (dobpdc) in the absence of a phase transition. Our study provides a microscopic understanding of the emergent features of cooperative binding, including the position, slope, and height of the isotherm step, and indicates how to optimize gas storage and separation in these materials.
Semi-adsorption-controlled growth window for half-Heusler FeVSb epitaxial films
The electronic, magnetic, thermoelectric, and topological properties of Heusler compounds (composition XYZ or X 2 YZ) are highly sensitive to stoichiometry and defects. Here we establish the existence and experimentally map the bounds of a semi-adsorption-controlled growth window for semiconducting half-Heusler FeVSb films, grown by molecular beam epitaxy (MBE). We show that due to the high volatility of Sb, the Sb stoichiometry is self-limiting for a finite range of growth temperatures and Sb fluxes, similar to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within this window are nearly structurally indistinguishable by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). Here, the highest electron mobility and lowest background carrier density are obtained towards the Sb-rich bound of the window, suggesting that Sb vacancies may be a common defect. Similar semi-adsorption-controlled bounds are expected for other ternary intermetallics that contain a volatile species Z = {Sb, As, Bi}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges remain in controlling the remaining Fe/V (X/Y) transition metal stoichiometry.
Adsorption and excess fission Xe - Adsorption of Xe on vacuum crushed minerals
It is hypothesized that adsorption is not likely to provide a sufficiently precise mechanism for the concentration of excess fission Xe in the entire lunar regolith, in view of laboratory analogs of the lunar soil and calculations of the residence times of noble gases in the present day regolith. Lunar cold trap and episodic degassing models are difficult to reconcile, however, with the generality of excess fission Xe in all gas-rich highland breccias. It is concluded that the high Xe concentration in such highland breccias is not the result of Xe adsorption prior to the trapping of this component.
Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation
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