Walker, Rebecca C.Stokes, Jamesa L.Hurwitz, Frances, IGuo, Haiquan...
8页
查看更多>>摘要：Aerogels can be used in spaceflight applications as thermal insulators due to their low density, low thermal conductivity, and tortuous path for solid conduction. However, the aerogel formulation must be optimized to increase the thermal stability of the aerogels, as a drastic densification and decrease in surface area often is exhibited after high-temperature exposure. This work considers yttria-stabilized zirconia (YSZ) aerogels, which have low thermal conductivity and are expected to be used for temperatures between 600 degrees C and 1000 degrees C. It is anticipated that new sol-gel chemistries will yield YSZ aerogels that exhibit retained mesoporous structure, increased surface area, and minimized shrinkage upon exposure to higher temperatures in the expected use range. This work investigates the addition of surfactant to 20 mol% YSZ aerogels. The cationic surfactant, cetrimonium bromide (CTAB), was used as the templating agent, preventing the collapse of the mesoporous structure upon gelation and drying. It was determined that adding one-half times the critical micelle concentration of CTAB increased the surface area of the aerogels by 72% and 41% and increased the pore volume following exposure to 600 degrees C and 1000 degrees C, respectively. This level of CTAB had the greatest increase in surface area and pore volume as compared to aerogels without CTAB or with twice the critical micelle concentration of CTAB. By optimizing the concentration of CTAB, the thermal stability of YSZ aerogels can be enhanced to make these materials more efficient when used as thermal management systems.
Othman, Ismail M. M.Li, JianshengEl-Bahy, Salah M.Gomaa, H....
14页
查看更多>>摘要：Herein, a hybrid chitosan-derived mesoporous spongy carbon (HCMSC) bio-adsorbent was prepared and used for efficient and extremely selective removal of Fe3+ toxins (>99%) from real water samples to generate Fe-free water for human usage. HCMSC bio-adsorbent was fabricated through direct grafting of 4-(2-(3-Methyl-5-oxo1-tosyl-1H-pyrazol-4(5H)-ylidene) hydrazinyl)-N-(pyrimidin-2-yl) benzenesulfonamide (PHBS) onto the chitosan-derived mesoporous spongy carbon (CMSC). The finding data demonstrated superior adsorption efficiency (>99%) and capacity (165 mg/g) of used HCMSC bio-captors toward Fe3+ ions at pH 4.5. The offered outcomes suggested that the batch-adsorption model kept their functionality to adsorb Fe3+ toxins even after numerous reuse periods effectively using 0.2 mol/L of HCl as eluent agent. Furthermore, the real applicability of HCMSC bio-adsorbent was achieved to remove Fe3+ ions from real water samples under optimum removal conditions.
查看更多>>摘要：Municipal solid waste contains essential building blocks of transportation fuel but is often deposited into landfills. Available conversion processes are still in their infancy; thus, requiring foundational knowledge to control reaction pathways and transform waste macromolecules into desired products. Active, robust, and low-cost catalysts with highly accessible active sites are needed for selective cleavage of certain bonds. The rapid deactivation and diffusion limitations are the major challenges to date which can be controlled by the catalyst pore structure and acidity. In this paper, we developed novel mesoporous ZSM-5 catalysts to maximise levoglucosan conversion, the dominant product of cellulose pyrolysis, into furfural. The concentration of levoglucosan dropped from 12.1% to 3.8% over the mesoporous ZSM-5. Furthermore, the pyrolysis of plastic materials that existed in the waste provided supplementary hydrogen, which synergistically contributed to the hydrodeoxygenation of some compounds like 5-hydroxymethylfurfural and 4-methyl-1,2-Benzenediol. The total amount of non-oxygenated compounds over the mesoporous catalyst reached 77% compared to 59.7% in non catalytic pyrolysis based on C-13 NMR results. The integration of C-13 NMR and GC-MS results provided an effective tool in identifying key reaction pathways and linking that to the catalyst's textural and acidic properties.
查看更多>>摘要：In this present work, two task specific ionic liquids (TSILs) were encapsulated into the framework of a Zeolite imidazolate framework-8 (ZIF-8) to enhance its CO2 capture capacity and CO2/N-2 selectivity at post-combustion conditions. 1-Ethyl-3-methylimidazolium amino-acetate {[EMIM][glycine (Gly)]} and 1-Ethyl-3-methylimidazolium (S)-2-aminopropionate {[EMIM][alanine (Ala)]} were selected as TSILs. TSIL@ZIF-8 composites sorbents were prepared by varying the loading of TSIL, and properties such as sorbent thermal stability, porous structure and crystal nature of the composite were investigated. Incorporation of TSIL into ZIF-8 led to a dramatic rise in CO2 uptake particularly at pressures lower than 1.0 bar. At this low-pressure range, CO2 uptake was greater than in pristine ZIF-8 for all TSIL loadings and TSIL@ZIF-8 composites with 30 wt% [Emim][Gly] reached a CO2 uptake capacity of 0.76 mmol.g(-1) solid at 0.1 bar, and 0.88 mmol/g-solid at 0.2 bar at 303 K. These values were 13 and 7 times higher that CO2 uptake in pristine ZIF-8 at identical conditions. TSIL functionalized composites also exhibited much higher selectivity than pristine ZIF-8 at all pressures. For instance, at 30 wt% [EMIM][Gly] loading, CO2/N-2 ideal selectivities at 313 K were 28 and 19 at 0.1 and 0.2 bar, respectively. This synthesized composite sorbent, with significantly high CO2 uptake, better CO2/N-2 selectivity at the low-pressure region (<1.0 bar), and low isosteric heat of adsorption (Q(st)), confirms that TSIL@ZIF-8 composites can be potential candidates for post-combustion CO2 capture processes and opens the door for the further development of suitable TSIL@MOF composite sorbent to be deployed in the CO2 capture process.
查看更多>>摘要：It was first demonstrated that under liquid-phase conditions, an increase in the mesoporosity of ZSM-5 zeolite boosts a rhodium-containing catalyst activity in the oxidative carbonylation of methane to acetic acid (the acetic acid yield is 570 mu mol gcat(-1)). To increase the mesoporosity of zeolite, two approaches were used: ultrasonic treatment and desilication of zeolite. The ultrasonic pretreatment leads to an increase in the acetic acid yield with a decrease in the total yield of oxygenates (methanol/acetic acid molar ratio is 0.2). On the contrary, preliminary desilication contributes to an increase in the total yield of oxygenates, mainly due to methanol (methanol/acetic acid molar ratio is 1.8). The combination of ultrasonic pretreatment and desilication of zeolite improves the total yield of oxygenates with an increase in the acetic acid yield. Such a change in the catalytic properties is attributed both to the acidity of the parent zeolite and the local atomic environment of rhodium. XAS spectroscopy showed that rhodium can be present on the zeolite surface either as nanoclusters giving rise to methanol or as isolated rhodium atoms, which promote the acetic acid formation.
查看更多>>摘要：In this study, Fe3O4@HMPDA@HA core-shell submicron particles with a large specific surface area and total pore volumes were prepared. A large cavity structure was constructed between the core and the shell, so the core-shell particles as drug carriers have a large loading capacity. The adsorption properties and mechanism of organic dyes RhB and MB on particles were studied. The results showed that the adsorption capacities of the particles to RhB and MB were 830.65 mg/g and 380.66 mg/g respectively. And doxorubicin (DOX) was used as a targeted drug to research the delivery and sustained-release properties of the particles, the results showed that the loading capacity of DOX was up to 624.75 mg/g. In addition, Hyaluronic acid (HA) can specifically recognize the cancer cells, so the above prepared particles combined magnetic targeting and receptor-mediated targeting. In vitro experiments, the DOX loaded particles had a significant inhibitory effect on HeLa cells.
查看更多>>摘要：The inevitable use of FAU-type zeolites and long synthesis time bottleneck the mass production of SSZ-39 zeolite, a next-generation catalyst for selective catalytic reduction of NOx by ammonia (NH3-SCR). Herein, fast synthesis of SSZ-39 zeolites directly from colloidal silica and sodium aluminate is achieved with various reactant compositions, including a cost-effective low organic structure-directing agent-consuming condition and a scarcely reported KOH-containing condition. The reactant alkalinity and NaOH content are critical to the phase selectivity and fast crystallization, and partially replacing Na+ with K+ can eliminate the formation of gmelinite impurity. With optimized conditions, synthesis can be completed within 4 h without aging process in an autoclave, and even within 80 min by fast heating in a tubular reactor. Outstanding hydrothermal stability and NH3-SCR activity of the Cu-exchanged samples prove such fast and direct synthesis route a promising way to efficiently produce high-quality SSZ-39 zeolites for further applications.
查看更多>>摘要：Based on the "double Debye" theory, the microvoid and amorphous structure parameters of T and MJ series carbon fibers could be obtained by SAXS analysis. Results indicated that tensile strength of T and MJ series carbon fibers increased with the decrease of microvoid size, and the relationship between them basically followed the Griffith microcrack theory. Importantly, it was found that the fitting result from the Griffith formula which was supplemented by introducing amorphous structure parameters was much better than the reports before, and it indicated that tensile strength of MJ series increased with the increase of amorphous size, but T series showed an opposite trend. It was because that amorphous region in MJ series provided the path for the propagation of crack and consumed more energy, which increased the tensile strength. For T series, nitrogen atoms in amorphous region might cause the distortion and deformation of graphite lamellar, thus introducing more defects. And the effect on tensile strength caused by defects from nitrogen atoms might be much greater than the contribution of crack propagation in amorphous region. Therefore, the decrease of amorphous size might represent the reduction of defects, thus increasing the tensile strength.
查看更多>>摘要：Amine-functionalized porous adsorbent is one kind of important materials in carbon dioxide capture due to its stability and efficiency. In this study, a copolymer (polyHIPE) with interconnected macropore networks, hierarchical porous structure and abundant branched amino groups was prepared by high internal phase emulsion (HIPE) strategy via copolymerization of styrene (St), divinylbenzene (DVB), tetraethyl orthosilicate (TEOS), and triethoxyvinylsilane (VTEO), and then a novel amine-functionalized CO2 adsorbent was synthesized by in situ ring-opening grafting copolymerization of aziridine with the polyHIPE. The structure, morphology, and physicochemical properties of the polyHIPEs were characterized by FTIR, TEM, TGA, and SEM. The key roles of VTEO and TEOS in introducing active hydroxyl groups onto the surface of the inert polymer was evaluated, which was essential to improve the hydrophilicity of the polyHIPE and to provide reactive sites to combine with amine agents. The contact angle of the polyHIPE while copolymerized with TEOS and VTEO significantly was decreased from 144 degrees to 72 degrees. In order to further increase the specific surface area of the polyHIPEs, post crosslinking of polyHIPEs was implemented through a Friedel-Crafts reaction. The specific surface area of post-crosslinked polyHIPE could reach 513 m(2)/g, which was proven to be effective to enhance its CO2 adsorption capacity. Finally, the abundant branched amino sites via aziridine grafting and high surface area greatly enhanced CO2 adsorption capacity of the amino-modified polyHIPEs. The adsorption capacity of 2.40 and 3.25 mmol CO2/g could be achieved under dry and humid conditions in 0.1 atm partial pressure of CO2, respectively.
Vayssilov, Georgi N.Kubota, YoshihiroKatada, NaonobuYamamoto, Kana...
12页
查看更多>>摘要：YNU-5 zeolite has the YFI-type framework with a 12-12-8 ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated 8-ring channels separated from the system by a thin (mono-atomic silicate) wall. In this study, the acidic property of YNU-5 zeolite was analyzed mainly by means of the ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. In addition, the accessibility of acid sites was evaluated through adsorption of pyridine. The number of Br:misted acid sites approximately agreed with the number of Al atoms, and the amount of Lewis acid sites was negligible, indicating that most acid sites have the nature of bridging Si(OH)Al group in the YFI framework. Most of the Br:misted acidic OH groups on the YNU-5 zeolites (including the dealuminated samples) reacted with pyridine vapor at 343 K to form pyridinium cations, indicating that the Br:misted acid sites are highly accessible through the 12-12-8-ring system. Enthalpy of ammonia desorption from the Br:misted acid site, which can be an index of acid strength or reactivity of the acid site with a basic reactant, was in the following order: FAU < MOR (12-ring) approximate to *BEA < MFI < MWW approximate to YFI < MOR (8-ring), indicating the markedly large ammonia desorption enthalpy on the YNU-5 zeolite compared to the other 12-ring zeolites. The DFT calculations suggest that the Br:misted acidic protons with especially high ammonia desorption enthalpy are located in the isolated 8-ring but accessible from the 12-12-8-ring system side. In addition, dealumination at a high temperature under the reflux conditions with nitric acid resulted in the preferential removal of Br:misted acid sites with low ammonia desorption enthalpy, probably in the 12-12-8-ring system. The presence of reactive Br:misted acid sites in the isolated 8-ring, accessibility to them from the 12-12-8-ring system, and preferential removal of the Br:misted acid sites from the 12-12-8-ring system are reasonably consistent with the previously reported catalytic properties for dimethyl ether-to-olefin reaction.
NSTL
Elsevier