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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Triazoloisoquinoline-based dual functional dyestuff for dye-sensitized solar cells

Graphical abstract: They consist of treating triazoloisoquinolines substituted tetramethyl-dioxaborolane (2) with 5-formyl-2-bromothiophene under conditions for Suzuki coupling to produce 5-(4-(3-oxo-[1,2,4]triazolo[3,4-a]isoquinolin-2(3H)-yl)phenyl) thiophene-2-carbaldehyde (3). Knoevenagel condensation of compound 3 with cyanoacrylic acid is carried out in the presence of piperidine, and after precipitation and purification with silica gel chromatography, the final dyestuff 4L is obtained as a yellow powder. This product has been characterized by spectroscopic analyses. Display Omitted Highlights: ► This new dyestuff investigated the role of triazoloisoquinoline dyestuffs as co-adsorbents and co-sensitizers with N719. ► The results show that co-adsorption of N719 sensitizer with dyestuff 5 increases the photocurrent in 1–0.25 molar ratio. ► This improved conversion efficiency is attributed to the insulating molecular layer, and the light harvesting effect at shorter-wavelength regions. -- Abstract: Triazoloisoquinoline contains electron-rich nitrogen and oxygen heteroatoms in a heterocyclic structure with high electron-donating ability. By utilizing this feature, two organic dyesutffs containing triazoloisoquinoline were synthesized and used in the fabrication of dye-sensitized solar cells (DSSCs), overcoming the deficiency of ruthenium dyestuff absorption in the blue part of the visible spectrum. This method also fills the blanks of ruthenium dyestuff sensitized TiO{sub 2} film, and forms a compact insulating molecular layer due to the nature of small molecular organic dyestuffs. The incident photon-to-electron conversion efficiency of N719 at shorter wavelength regions is 35%. After addition of triazoloisoquinoline-based dyestuff for co-sensitization, the IPCE at 350–500 nm increased significantly. This can be attributed to the increased photocurrent of the cells, which improves the dye-sensitized photoelectric conversion efficiency from 4.49% to 5.15%, which the overall conversion efficiency increased by about 15%. As a consequence, this low molecular weight organic dyestuff is a promising candidate as co-adsorbent and co-sensitizer for highly efficient dye-sensitized solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Simple solvothermal synthesis of hydrophobic magnetic monodispersed Fe{sub 3}O{sub 4} nanoparticles

Graphical abstract: A facile method to produce monodispersed magnetite nanoparticles is based on the solvothermal reaction of iron acetylacetonate (Fe(acac)3) decomposition. The sizes ranged from 7 to 12 nm, which could be controlled by adjusting the volume ratio of oleylamine to n-hexane. Display Omitted Highlights: ► The solvethermal reaction of Fe(acac){sub 3} decomposition was carried out at mild temperature in the presence of oleylamine and n-hexane. ► The size of nanocrystals is controlled by adjusting the volume ratio of oleylamine to n-hexane. ► The low-boiling-point solvent n-hexane offered autogenous pressure parameter after gasified in the reaction temperature. ► The as prepared hydrophobic monodisperse Fe{sub 3}O{sub 4} NPs can be used to prepare the magnetic micelles for future biomedical applications. -- Abstract: A new solvothermal method is proposed for the preparation of Fe{sub 3}O{sub 4} nanoparticles (NPs) from iron acetylacetonate in the presence of oleylamine and n-hexane. The products are characterized by X-ray powder diffraction, infrared (IR) spectroscopy, transmission electron microscopy, thermogravimetry/differential thermogravimetry (TG/DTG) analysis, and vibrating sample magnetometery. The new procedure yields superparamagnetic monodispersed Fe{sub 3}O{sub 4} particles with sizes ranging from 7 nm to 12 nm. The nanocrystal sizes are controlled by adjusting the volume ratio of oleylamine to n-hexane. IR and TG/DTG analyses indicate that the oleylamine molecules, as stabilizers, are adsorbed on the surface of Fe{sub 3}O{sub 4} NPs as bilayer adsorption models. The surface adsorption quantities of oleylamine on 7.5 and 10.4 nm-diameter Fe{sub 3}O{sub 4} NPs are 18% and 11%, respectively. The hydrophobic surface of the obtained nanocrystals is passivated by adsorbed organic solvent molecules. These molecules provide stability against agglomeration, enable solubility in nonpolar solvents, and allow the formation of magnetic polymer micelles.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of electrolytes and surfactants on the morphology and stability of advanced silver nano-materials

Highlights: ► Stoichiometric ratio of S{sub 2}O{sub 3}{sup 2−} and Ag{sup +} ions are responsible to the formation of prefect transparent yellow colored silver sol. ► Higher S{sub 2}O{sub 3}{sup 2−} concentrations has damping effect. ► Head group of the surfactants and nature of the electrolytes have significant effect on the stability of silver nanoparticles. - Abstract: The impact of electrolytes, stabilizing and/or capping agents on morphology of colloidal silver nano-materials (AgNPs) has been studied spectroscopically. Sodium thiosulfate acts as reducing-, stabilizing- and damping-agents. Stoichiometric ratios of S{sub 2}O{sub 3}{sup 2−} and Ag{sup +} ions were responsible to the formation stable and prefect transparent dark yellow colored AgNPs. The S{sub 2}O{sub 3}{sup 2−}-stabilized AgNPs were significantly more stable in inorganic electrolytes (NaNO{sub 3}, Na{sub 2}SO{sub 4}, Na{sub 2}CO{sub 3} and KBr). S{sub 2}O{sub 3}{sup 2−} is adsorbed more strongly than the used other anions. The addition of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) has significant effects on the absorbance of S{sub 2}O{sub 3}{sup 2−}-stabilized AgNPs which can be rationalized in terms of electrostatic attraction and repulsion between the adsorbed S{sub 2}O{sub 3}{sup 2−} ions on to the surface of AgNPs and cationic and/or anionic head groups of used surfactants, respectively. Transmission electron microscopy images suggest that AgNPs are polydispersed, spherical and exhibiting an interesting irregular morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis and characterization of LTA nanozeolite using barley husk silica: Mercury removal from standard and real solutions

Highlights: ► Silica extraction from barley husk with high purity for the synthesis of A nanozeolite. ► Free template A nanozeolite synthesized via new source of silica at low temperature. ► Optimization of SiO{sub 2}/Al{sub 2}O{sub 3}, Na{sub 2}O/SiO{sub 2} ratios, temperature and time of the synthesis. ► Utilizing of synthesized A nanozeolite for mercury removal from aqueous solutions. ► Mercury removal at optimized pH, contact time and adsorbent dose from real solution. - Abstract: In this study, synthesized Lined Type A (LTA) nanozeolite from barley husk silica (BHS) was used for mercury removal from standard and real aqueous solutions. The BHS in amorphous phase with 80% purity was extracted from barley husk ash (BHA), and used effectively as a new source of silica for the synthesis of NaA nanozeolite. The NaA nanocrystal in pure phase has been synthesized at low temperature, without adding any organic additives. The effects of heating time, reaction temperature, SiO{sub 2}/Al{sub 2}O{sub 3}, and Na{sub 2}O/SiO{sub 2} mole ratios on the crystallization of NaA nanozeolite were studied. The adsorption capacity of mercury (II) was studied as a function of pH, contact time, and amount of adsorbent. The crystallization of NaA nanozeolite from BHS was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Brunauer–Emmett–Teller (BET), and FTIR techniques. Moreover, concentration of Hg{sup 2+} ions in the aqueous solutions was analyzed by hydride generation atomic absorption spectroscopy method (HG-AAS). The standard and real samples analysis showed that NaA nanozeolite is capable of Hg{sup 2+} ions removal from the aqueous solutions. Efficiency of mercury (II) adsorption from real solutions onto the nano-sized NaA zeolite was 98%.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Preparation and electrochemical performance of sulfur-alumina cathode material for lithium-sulfur batteries

Highlights: ► Micron-sized alumina was synthesized as adsorbent for lithium-sulfur batteries. ► Sulfur-alumina material was synthesized via crystallizing nucleation. ► The Al{sub 2}O{sub 3} can provide surface area for the deposition of Li{sub 2}S and Li{sub 2}S{sub 2}. ► The discharge capacity of the battery is improved during the first several cycles. - Abstract: Nano-sized sulfur particles exhibiting good adhesion with conducting acetylene black and alumina composite materials were synthesized by means of an evaporated solvent and a concentrated crystallization method for use as the cathodes of lithium-sulfur batteries. The composites were characterized and examined by X-ray diffraction, environmental scanning electron microscopy and electrochemical methods, such as cyclic voltammetry, electrical impedance spectroscopy and charge–discharge tests. Micron-sized flaky alumina was employed as an adsorbent for the cathode material. The initial discharge capacity of the cathode with the added alumina was 1171 mAh g{sup −1}, and the remaining capacity was 585 mAh g{sup −1} after 50 cycles at 0.25 mA cm{sup −2}. Compared with bare sulfur electrodes, the electrodes containing alumina showed an obviously superior cycle performance, confirming that alumina can contribute to reducing the dissolution of polysulfides into electrolytes during the sulfur charge–discharge process.

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 OSTI2013

Influence of In doping on the structural, photo-luminescence and alcohol response characteristics of the SnO{sub 2} nanoparticles

Graphical abstract: When the sample is exposed to air, the atmospheric oxygen O{sub 2} adsorbs on the sample surface in the form of ionic species O{sup −} by capturing electrons from the conduction band. The adsorbed ionic species O{sup −} react with the test alcohol molecules and are responsible for sensing mechanism. - Highlights: • In-doped SnO{sub 2} samples show smaller crystallinity with crystallite size: ∼7–9 nm. • EDX analyses confirm the incorporation of indium ions in the SnO{sub 2} lattice. • Raman spectra are consistent with the results of XRD and SAED pattern. • Alcohol response has been found to increase with the indium dopant concentration. • 3 at% In-doped sample exhibits maximum response (96.5%) to propan-2-ol at 250 °C. - Abstract: Undoped and In-doped SnO{sub 2} nanoparticles were synthesized by the co-precipitation method. Upon In doping, the samples exhibit reduced crystallinity as compared to the undoped SnO{sub 2}. The Raman spectra of the undoped samples exhibit three fundamental peaks at 467.3, 633.4 and 774.6 cm{sup −1} corresponding to E{sub g}, A{sub 1g} and B{sub 2g} vibration modes, respectively. The PL spectra show two strong emission bands at the wavelengths 417 nm and 479 nm, along with five weak emission peaks in the visible region. Alcohol response characteristics of the In-doped SnO{sub 2} samples were investigated for various concentrations (10–50 ppm) at different operating temperatures (150–250 °C). Among all the samples examined, the 3 at% In-doped SnO{sub 2} sample shows maximum response (96.5%) to propan-2-ol, followed by ethanol (92%) and methanol (90%) at the operating temperature of 250 °C for 50 ppm concentration. For each test alcohol, the response has been found to increase with the In dopant concentration.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and photocatalytic property of BiOBr/palygorskite composites

Graphical abstract: - Highlights: • BiOBr/palygorskite composite photocatalysts were prepared for the first time. • The synchronous role of adsorbability and photocatalytic oxidation was studied. • BiOBr/palygorskite composite exhibit enhanced photocatalytic activities. • The optimal ratio of [Bi]/palygorskite was identified. - Abstract: BiOBr/palygorskite composite photocatalysts were prepared by a hydrothermal method for the first time, which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR), N{sub 2}-sorption and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by decomposition of methyl orange (MO) under visible light irradiation. The results revealed that BiOBr/palygorskite composites had strong photoabsorption in the visible light region. All BiOBr/palygorskite composites possessed higher photocatalytic activity than pure BiOBr. The highest activity was obtained by S5.0 sample. The enhanced photocatalytic performance was attributed to strong photoabsorption, the synchronous role of adsorbability and photocatalytic oxidation on BiOBr/palygorskite composites and the efficient separation of photogenerated electron–hole pairs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of the both texture and electrical properties of activated carbon on the CO{sub 2} adsorption capacity

Highlights: • A series of activated carbon pellet without binder was prepared by chemical activation. • Carbon dioxide storage isotherm at 30 °C and up to 25 bars was measured for the microporous carbon. • Adsorption enthalpies have been correlated with the carbon dioxide uptake. • Pyrolysis temperature effect on the electrical conductivity of the samples. • Impact of the both texture and electrical properties on CO{sub 2} adsorption capacity have been deducted - Abstract: A series of activated carbon pellets (ACP) based on olive stones were studied for CO{sub 2} storage application. The surface area, pore volume, and pore diameter were evaluated from the analysis of N{sub 2} adsorption isotherm data. The characterization of carbon materials was performed by scanning electron microscopy (SEM), the powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). The adsorption enthalpies were obtained by microcalorimetry. The effect of pyrolysis temperature on textural, electrical conductivity and gas adsorption capacities of the ACP were investigated by adsorbing CO{sub 2} at 303 K in the pressure range of 0–2.3 MPa. In fact the electrical conductivity is strongly affected by the microporosity of the samples and the size of the micropore. It increases when the pore size decreases which affect the CO{sub 2} adsorption. Also with increases temperature the free electrons concentration on the surface increases which affect the interaction of the adsorbed gas molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Improvement of charge separation in TiO{sub 2} by its modification with different tungsten compounds

Highlights: • Ammonium m-tungstate doped to TiO{sub 2} highly improved charge separation in TiO{sub 2}. • Negative electrokinetic potential of TiO{sub 2} facilitates holes migration to its surface. • Fast migration of holes to TiO{sub 2} surfaces increased yield of OH radicals formation. • Adsorption of dyes on photocatalyst increased its decomposition under visible light. - Abstract: Three different tungsten precursors were used for TiO{sub 2} modification: H{sub 2}WO{sub 4}, WO{sub 2}, and ammonium m-tungstate. It was proved that modification of TiO{sub 2} with tungsten compounds enhanced its photocatalytic activity through the improvement of charge separation. This effect was obtained by coating of TiO{sub 2} particles with tungsten compound, which changed their surficial electrokinetical potential from positive onto negative. The most efficient tungsten compound, which caused enhanced separation of free carriers was ammonium m-tungstate (AMT). Two dyes with different ionic potential were used for the photocatalytic decomposition. It appeared that cationic dye—Methylene Blue was highly adsorbed on the negatively charged surface of TiO{sub 2} modified by AMT and decomposed, however this photocatalyst was quickly deactivated whereas anionic dye—acid red was better adsorbed on the less acidic surface of TiO{sub 2} and was rapidly decomposed with almost the same rate in the five following cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnesium diboride (MgB2): An effective and novel precursor for the synthesis of vertically aligned BNNTs

Highlights: • Discovered Magnesium diboride (MgB{sub 2}) as an effective and novel precursor for the synthesis of BNNTs. • Synthesized vertically aligned BNNTs directly on SiO{sub 2} substrate at 1000{sup °}C. • Magnesium (Mg) from MgB{sub 2} in partially melted form diffuses on SiO{sub 2} substrate. • The adsorbed Boron with Mg reacts with Nitrogen from decomposed ammonia and synthesized vertically aligned BNNTs. - Abstract: Vertically aligned Boron nitride nanotubes (BNNTs) have exceptional electrical, mechanical and thermal properties suitable for its potential applications without any further purification. However, the synthesis of aligned BNNTs via previously reported techniques is not only complicated, lengthy and misleading but also result in useless impurities in the final product. Here, we report Magnesium diboride (MgB{sub 2}) as an effective and novel precursor for the synthesis of vertically aligned BNNTs directly on SiO{sub 2} substrate at 1000 {sup °}C. Magnesium (Mg) from MgB{sub 2} in partially melted form diffuses on SiO{sub 2} substrate whereas the adsorbed Boron with Mg reacts with Nitrogen from decomposed ammonia and synthesized vertically aligned BNNTs. The morphology, alignment, structure and compositions of the as-synthesized BNNTs are studied via field emission scanning electron microscope, high resolution transmission electron microscope, energy dispersive x-ray spectroscopy, x-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Au nanoparticles and graphene oxide co-loaded graphitic carbon nitride: Synthesis and photocatalytic application

Highlights: • The 0.5%Au/GO/g-C3N4 composite exhibites excellent photocatalytic activity. • GO nanoslice acts as an e- transporter and acceptor Au/GO/g-C3N4 composite. • Au particles in Au/GO/g-C3N4 composite act as electron trap to separate e- and h{sup +}. • Adsorbed OH and h{sup +} are involved in reducing and oxidizing process, respectively. - Abstract: Inhibition of charge-carrier recombination in semiconductors is one of the most efficient methods to enhance the photocatalytic performance in visible light irradiation. Noble metals and graphene oxide (GO) are currently regarded as fine channels to enhance the charge-carrier transfer efficiency. Herein, novel Au nanoparticles and GO co-loaded graphitic carbon nitride (Au/GO/g-C{sub 3}N{sub 4}) composite was obtained by a single step ultrasonic chemical process, and the photocatalytic activity was tested in Rhodamine B (Rh B) photodegradation in visible light region. The Au/GO/g-C{sub 3}N{sub 4} composite containing 0.5%Au (molar Au per unit molar of g-C{sub 3}N{sub 4}) exhibited excellent photocatalytic activity and might be attributed to the important part of GO nanoslices and Au nanoparticles. An electron transporter and acceptor have been acted by the GO nanoslices to facilitate the charge transfer and against the recombination of photoexcited electron-hole pairs. In the meantime, an electron trap was formed on the Au nanoparticles to separate the charges. Furthermore, it was found that the reactive species of adsorbed OH and holes took part in the reduction and oxidization actions in the photocatalytic process, respectively. The design of the Au/GO/g-C{sub 3}N{sub 4} composite provides a novel route to synthesis of highly efficient photocatalysts in environmental application.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Insight into the oxidation mechanism of Nb3Si(111) surface: First-principles calculations

Highlights: • Oxygen adsorption behavior on Nb{sub 3}Si(111) is studied by using first-principles. • O atom tends to be adsorbed on the NbSi bridge site. • The capacity of oxidation follow the order of Cr > Al > Si. • Cr can improve the Nb{sub 3}Si’s oxidation resistance because of Cr d-orbital effect. - Abstract: The oxidation resistance plays an important role in high-temperature ceramics. Although transition metal silicides exhibit the better oxidation behavior, the improvement of oxidation resistance is still a great challenge for their applications. Here, we apply first-principles calculations to investigate the oxidation mechanism and the influence of alloying elements (Cr and Al) on the oxidation resistance of Nb{sub 3}Si(111) surface. The calculated results show that the O atom is adsorbed on the NbSi-bridge site because of the charge interaction between O-2p state, Si-3p state and Nb-4d state. We further find that Cr-doping is more thermodynamically stable than that of Al-doping. In particular, the capacity of oxidation resistance follows the order of Cr > Al > Si. Finally, we conclude that Cr-doping can effectively improve the oxidation resistance of Nb{sub 3}Si(111) surface. The calculated electronic structure shows that Cr d-orbital plays a crucial role in oxidation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Solution combustion synthesis of LaxSm1−xMn2O5 nanoparticles and their electrocatalytic performances for Al-air batteries

Highlights: • Pure-phase La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} were firstly achieved through one step calcined solution combustion synthesis with high yield. • The main impact of La/Sm is the amount of surface adsorbed oxygen and surface Mn{sup 4+} ions as revealed by XPS results. • The La{sub 0.1}Sm{sub 0.9}Mn{sub 2}O{sub 5} exhibited the highest activity, which has an appropriate ratio between oxygen vacancies and Mn{sup 3+}. • The cell produced with La{sub 0.1}Sm{sub 0.9}Mn{sub 2}O{sub 5} exhibits flat discharge curves in 40 h above 1.5 V. - Abstract: Compared the most reported synthesis methods, a series of La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) catalysts were first synthesized through sol-gel solution combustion synthesis with a short cycle and high yield. The main impact of different La/Sm molar ratios is the amount of surface adsorbed oxygen (O{sub ads}) and surface Mn{sup 4+} ions as revealed by XPS results. Electrochemical properties are characterized by rotating disk electrode (RDE) and the full dischargeable Al-air battery with 4 M NaOH electrolyte. The measurements of RDE reveal that the electron transfer number of La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) are all closed to 4, and the sample prepared with x = 0.1 possesses the most excellent electrocatalytic activity for oxygen reduction reaction (ORR) and good discharge performance in alkaline medium. All of the above results indicate that the La{sub x}Sm{sub 1−x}Mn{sub 2}O{sub 5} (x = 0, 0.1, 0.3, 0.5) are promising catalysts with a high catalytic activity toward ORR.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Effect of carbon dioxide and nitrogen on the diffusivity of methane confined in nano-porous carbon aerogel

The microscopic diffusivity of methane (CH{sub 4}) confined in nano-porous carbon aerogel was investigated as a function of added carbon dioxide (CO{sub 2}) and nitrogen (N{sub 2}) pressure using quasi-elastic neutron scattering (QENS). In the range of the external pressure of 1-2.5 MPa, the self-diffusivity of methane was found to increase with CO{sub 2} pressure and remain practically unchanged in the N{sub 2} environment. Increasing mobility of methane with CO{sub 2} pressure suggests that the adsorbed CH4 molecules become gradually replaced by CO{sub 2} on the surface of carbon aerogel pores, whereas the presence of N{sub 2} does not induce the replacement. The molecular mobility of the methane, with or without added carbon dioxide and nitrogen, is described by the unrestricted diffusion model, which is characteristic of methane compressed in small pores. On the other hand, both nitrogen and carbon dioxide molecules in carbon aerogel, when studied alone, with no methane present, follow a jump diffusion process, characteristic of the molecular mobility in the densified adsorbed layers on the surface of the aerogel pores.

03 NATURAL GAS↗
DOE OSTI2017

Adsorptive separation of CO 2 in sulfur-doped nanoporous carbons: Selectivity and breakthrough simulation

In this research, we have synthesized two sulfur functionalized nanoporous carbons by post-synthesis modifications with sulfur bearing activating agents that simultaneously enhanced the surface area and introduced sulfur functionalities on the carbon surface. The Brunauer–Emmett–Teller (BET) surface areas of these materials were 2865 and 837 m 2 /g with total sulfur contents of 8.2 and 12.9 %, respectively. The sulfur-functionalized carbons were characterized with pore textural properties, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and electron microscopy (SEM and TEM). In both the carbons, CO 2 adsorption isotherms and kinetics were measured in three different temperatures of 298, 288 and 278 K and pressures up to 760 torr. The gravimetric CO 2 uptake followed the trend with BET surface area but the surface area-based uptake was reversed and it followed the trend of sulfur content. The heat of adsorption of CO 2 in low uptake was 60-65 kJ/mol, which is the highest for CO 2 adsorption in porous carbons. In order to investigate the adsorptive separation of CO 2 , N 2 and CH 4 adsorption isotherms were also measured at 298 K and 760 torr. The selectivity of separation for CO 2 /N 2 and CO 2 /CH 4 was calculated based on the Ideal Adsorbed Solution Theory (IAST) and all the results demonstrated the high CO 2 selectivity for the carbon with higher sulfur content. The adsorption isotherms were combined with mass balances to calculate the breakthrough behavior of the binary mixtures of CO 2 /N 2 and CO 2 /CH 4 . The simulation results demonstrated that the dimensionless breakthrough time is a decreasing function of the mole fraction of CO 2 in the feed stream. The overall results suggest that the sulfurfunctionalized carbons can be employed as potential adsorbents for CO 2 separation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis of high-surface area tungstated zirconia by atomic layer deposition on mesoporous silica

Atomic layer deposition (ALD) was used to prepare ZrO 2 films on the surface of the mesoporous silica, SBA-15, and to modify the surface of these films with WO 3 in order to form tungstated zirconia. Adsorption-desorption isotherms, pore size distributions, and transmission electron microscopy demonstrated that the ALD synthesis produced zirconia films that were conformal to the SBA-15 pores. DRIFT spectroscopy of pyridine adsorbed on the tungstated-zirconia SBA-15 samples showed adsorbed pyridinium ions, confirming the presence of Brønsted-acid sites on this material, consistent with what has been reported for bulk tungstated zirconia. Here, the ALD-synthesized, tungstated-zirconia SBA-15 was also shown to be active in the acid-catalyzed H-D exchange between toluene and D 2 O.

Brønsted acid site↗
DOE OSTI2019

Silver clusters tune up electronic properties of graphene nanoflakes: A comprehensive theoretical study

Graphene-silver composites reflect a synergic effect of both components with enhanced electronic, adsorption and catalytic properties. We introduce here the detailed theoretical study on geometric, thermodynamic and electronic properties of silver clusters Ag n (n=2–10) adsorbed on graphene nanoflakes as a model for silver-graphene composites. First, a benchmark study is performed on Ag n …coronene complexes (n=2, 4) by evaluating various functional against reported high level ab-initio method for the selection of best functional for further calculations. Then, density functional theory study at the best chosen level is performed to inquire how clustering of adsorbate attached with carbon surface can impact geometric, electronic and thermodynamic properties of silver-graphene composites. Furthermore, the interaction energies are corrected for dispersion and basis set superposition error in order to get more realistic estimate of interaction energies. In progression, we investigated the dependence of interaction energy upon cluster size and dimensionality. For Ag n …coronene, the binding energies increase monotonically as the number of atoms in the cluster increases. However, for Ag n …dodecabenzocoronene, the interaction energies show a sudden drop at Ag 7 …dodecabenzocoronene. The difference in behavior between Ag n …dodecabenzocoronene and Ag n …coronene for interaction energy is attributed to edge effect present in coronene. Furthermore, coplanar orientations of the silver clusters on polyaromatic hydrocarbons have higher interaction energies. The 2D-3D transition of the silver cluster is observed for Ag 7 …coronene. CDA analysis reveals that backdonation from dodecabenzocoronene to silver clusters is more dominant in Ag 4 –Ag 7 whereas other clusters have dominant charge transfer to dodecabenzocoronene. Charge transfer analysis via constrained density functional theory (CDFT) reveals significant energy lowering from charge donor-acceptor interactions. Further energy decomposition analysis (EDA) using absolutely-localized molecular orbitals (ALMO) suggests that, while charge-transfer is important in these systems, the sum of electrostatics, Pauli repulsion, and London dispersion are far more significant as silver cluster size increases. NCI results also support the presence of van der Waals and electrostatic interactions. The hollow top is most favorite interaction sites compared to bridge top and head top binding sites over coronene lattice. The ionization potential, electron affinity, frontier molecular orbital analysis, chemical hardness, softness, chemical potential, and Fermi levels are deliberated to verify the stability and reactivity of most stable silver-graphene composites. The remarkable outcome of the current findings makes our silver-graphene composite as a potential applicant for high performance electronic and catalytic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗