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2D layered nanomaterials have attracted considerable attention for their potential for highly efficient separations, among other applications. Here, a 2D lamellar membrane synthesized using hexagonal boron nitride nanoflakes (h-BN...
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2D layered nanomaterials have attracted considerable attention for their potential for highly efficient separations, among other applications. Here, a 2D lamellar membrane synthesized using hexagonal boron nitride nanoflakes (h-BNF) for highly efficient ion separation is reported. The ion-rejection performance and the water permeance of the membrane as a function of the ionic radius, ion valance, and solution pH are investigated. The nonfunctionalized h-BNF membranes show excellent ion rejection for small sized salt ions as well as for anionic dyes (>97%) while maintaining a high water permeability, ≈1.0 × 10~(-3) L m m~(-2) h~(-1) bar~(-1)). Experiments show that the ion-rejection performance of the membrane can be tuned by changing the solution pH. The results also suggest that the rejection is influenced by the ionic size and the electrostatic repulsion between fixed negative charges on the BN surface and the mobile ions, and is consistent with the Donnan equilibrium model. These simple-to-fabricate h-BNF membranes show a unique combination of excellent ion selectivity and high permeability compared to other 2D membranes.
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Correspondingstates correlations have been developed for the viscosity and thermal conductivity of aqueous electrolyte solutions for a wide range of temperatures, pressures, and concentrations. For viscosity, the Vogel-Tamann-Fulc...
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Correspondingstates correlations have been developed for the viscosity and thermal conductivity of aqueous electrolyte solutions for a wide range of temperatures, pressures, and concentrations. For viscosity, the Vogel-Tamann-Fulcher equation has been generalized using the corresponding states theory, and extended to include pressure effects. Twenty six aqueous electrolyte solutions, including both monovalent and multivalent electrolytes, have been studied and a generalized correlation has been developed for viscosity, with four system dependent parameters. For thermal conductivity, a similar corresponding states based correlation has been developed. Twenty three aqueous electrolyte solutions were studied for thermal conductivity and a generalized equation was obtained that requires only two-system dependent parameters. With both correlations, the maximum error is usually within 10% of the experimental values, with the average errors being much less. Additional systems can also be included in both correlations in a straight-forward manner.
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Pt nano-particles from about 1 to 10 nm have been prepared on silica, alkali-silica, alumina, silica-alumina, carbon and SBA-15 supports. EXAFS spectra of the reduced catalysts in He show a contraction of the Pt-Pt bond distance a...
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Pt nano-particles from about 1 to 10 nm have been prepared on silica, alkali-silica, alumina, silica-alumina, carbon and SBA-15 supports. EXAFS spectra of the reduced catalysts in He show a contraction of the Pt-Pt bond distance as particle size is decreased below 3 nm. The bond length decreased as much as 0.13 A for 1 nm Pt particles. Adsorption of CO and H2 lead to a increase in Pt-Pt bond distance to that near Pt foil, e.g., 2.77 A. In addition to changes in the Pt bond distance with size, as the particle size decreases below about 5 nm there is a shift in the XANES to higher energy at the L3 edge, a decrease in intensity near the edge and an increase in intensity beyond the edge. We suggest these features correspond to effects of coordination (the decrease at the edge) and lattice contraction (the increase beyond the edge). At the L2 edge, there are only small shifts to higher energy at the edge. However, beyond the edge, there are large increases in intensity with decreasing particle size. At the Li edge there are no changes in position or shape of the XANES spectra. Adsorption of CO and H2 also lead to changes in the L3 and L2 edges, however, no changes are observed at the L1 edge. Density Functional Theory and XANES calculations show that the trends in the experimental XANES can be explained in terms of the states available near the edge. Both CO and H2 adsorption result in a depletion of states at the Fermi level but the creation of anti-bonding states above the Fermi level which give rise to intensity increases beyond the edge.
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The chemical pathway for synthesizing covalent organic frameworks(COFs)involves a complex medley of reaction sequences over a rippling energy landscape that cannot be adequately described using existing theories.Even with the deve...
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The chemical pathway for synthesizing covalent organic frameworks(COFs)involves a complex medley of reaction sequences over a rippling energy landscape that cannot be adequately described using existing theories.Even with the development of state-of-the-art experimental and computational tools,identifying primary mechanisms of nucleation and growth of COFs remains elusive.Other than empirically,little is known about how the catalyst composition and water activity affect the kinetics of the reaction pathway.Here,for the first time,we employ time-resolved in situ Fourier transform infrared spectroscopy(FT-IR)coupled with a six-parameter microkinetic model consisting of ~10 million reactions and over 20 000 species.The integrated approach elucidates previously unrecognized roles of catalyst pKa on COF yield and water on growth rate and size distribution.COF crystalline yield increases with decreasing pKa of the catalysts,whereas the effect of water is to reduce the growth rate of COF and broaden the size distribution.The microkinetic model reproduces the experimental data and quantitatively predicts the role of synthesis conditions such as temperature,catalyst,and precursor concentration on the nucleation and growth rates.Furthermore,the model also validates the second-order reaction mechanism of COF-5 and predicts the activation barriers for classical and non-classical growth of COF-5 crystals.The microkinetic model developed here is generalizable to different COFs and other multicomponent systems.
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Sodium naphthenates(NaNs),found in crude oils and oil sands process-affected water(OSPW),can act as surfactants and stabilize undesirable foams and emulsions.Despite the critical impact of soap-like NaNs on the formation,propertie...
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Sodium naphthenates(NaNs),found in crude oils and oil sands process-affected water(OSPW),can act as surfactants and stabilize undesirable foams and emulsions.Despite the critical impact of soap-like NaNs on the formation,properties,and stability of petroleum and OSPW foams,there is a significant lack of studies that characterize foam film drainage,motivating this study.Here,we contrast the drainage of aqueous foam films formulated with NaN with foams containing sodium dodecyl sulfate(SDS),a well-studied surfactant system,in the relatively low concentration regime(c/CMC<12.5).The foam films exhibit drainage via stratification,displaying step-wise thinning and coexisting thick-thin regions manifested as distinct shades of gray in reflected light microscopy due to thickness-dependent interference intensity.Using IDIOM(interferometry digital imaging optical microscopy)protocols that we developed,we analyze pixel-wise intensity to obtain thickness maps with high spatiotemporal resolution(thickness<1 nm,lateral ~500 nm,time ~10 ms).The analysis of interference intensity variations over time reveals that the aqueous foam films of both SDS and NaN possess an evolving,dynamic,and rich nanoscopic topography.The nanoscopic thickness transitions for stratifying SDS foam films are attributed to the role played by damped supramolecular oscillatory structural disjoining pressure contributed by the confinement-induced layering of spherical micelles.In comparison with SDS,we find smaller concentration-dependent step size and terminal film thickness values for NaN,implying weaker intermicellar interactions and oscillatory structural disjoining pressure with shorter decay length and periodicity.
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PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably m...
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PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably more expensive than Cu catalysts. Therefore, we explore NiZn as a potentially cheaper alternative to PdZn. Both PdZn(111) and NiZn(111) have similar potential energy surfaces for WGS as previous work on Cu(111) suggesting that they may be effective WGS catalysts. However, unlike PdZn (and Cu), the primary mechanism for WGS shifts from the carboxyl mechanism to a redox mechanism over NiZn(111) (although they are similar in magnitude).
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摘要 :
PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably m...
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PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably more expensive than Cu catalysts. Therefore, we explore NiZn as a potentially cheaper alternative to PdZn. Both PdZn(111) and NiZn(111) have similar potential energy surfaces for WGS as previous work on Cu(111) suggesting that they may be effective WGS catalysts. However, unlike PdZn (and Cu), the primary mechanism for WGS shifts from the carboxyl mechanism to a redox mechanism over NiZn(111) (although they are similar in magnitude).
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The conversion of synthesis gas to hydrocarbon fuels by Co catalysts through the Fischer-Tropsch process has received renewed attention particularly with regard to the role of promoters. In this letter, we utilize scanning transmi...
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The conversion of synthesis gas to hydrocarbon fuels by Co catalysts through the Fischer-Tropsch process has received renewed attention particularly with regard to the role of promoters. In this letter, we utilize scanning transmission electron microscopy imaging and electron energy-loss spectroscopy to elucidate the interaction between the Mn promoter, the Co nano-catalysts, and the TiO2 support. In-situ heating experiments show the diffusion of Mn and Ti-support onto the Co particle under reducing conditions.
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Surface wettability characteristics of commercially pure titanium (CP-Ti/Ti-II) and titanium Grade 5 alloy (Ti-6A1-4V/Ti-V) with 10 nm-thick atomic layer deposited (ALD) TiO_2 from Tetrakis DiEthyl Amino Titanium and water vapor w...
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Surface wettability characteristics of commercially pure titanium (CP-Ti/Ti-II) and titanium Grade 5 alloy (Ti-6A1-4V/Ti-V) with 10 nm-thick atomic layer deposited (ALD) TiO_2 from Tetrakis DiEthyl Amino Titanium and water vapor were studied in conjunction with cleaning steps before and after the ALD treatment. The wettability characteristics of rough Ti-II and Ti-V samples were investigated after each step, that is, as received, after de-ionized (DI) water rinse followed by N_2 drying, sonication in methanol, ALD treatment, and post-ALD DI water rinse. Samples without ALD or cleaning treatments were hydrophobic to variable extents, depending on exposure to different environments, surface impurities, roughness, and aging. Surface treatments reported in the literature resulted in hydrophilic/hydrophobic surfaces likely due to organic and/or inorganic impurities. In this study, (i) it is established that it is critically important to probe surface wettability after each substrate treatment; (ii) both Ti-II and Ti-V surfaces are found to become more hydrophilic after each one of the sequential treatments used; and (iii) independently of the initial wettability characteristics of Ti-II and Ti-V surfaces, the aforementioned treatments result in a water contact angle well below 10?, which is an important factor in cellular response. X-ray photoelectron spectroscopy of ALD titania films indicated trace impurities in them. Grazing incidence X-ray diffraction suggested amorphous ALD TiO_2 at 200°C; anatase TiO2 was obtained with as little as 5 min annealing at 600°C in nitrogen.
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Atomic layer deposition (ALD) of TiO_2 using tetrakis(diethylamino)titanium precursor and H_2O was studied on silicon and copper surfaces in order to examine differences in nucleation. Both surfaces were patterned on the same subs...
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Atomic layer deposition (ALD) of TiO_2 using tetrakis(diethylamino)titanium precursor and H_2O was studied on silicon and copper surfaces in order to examine differences in nucleation. Both surfaces were patterned on the same substrate to assure identical deposition conditions. Spectral ellipsometry, X-ray photoelectron spec-troscopy and surface profilometry were used to probe nucleation phenomena, growth rates, and surface morphology on both surfaces. The TiO_2 deposition on copper was found to exhibit a significant induction period of about 20-25 ALD cycles with no observable TiO_2 during the first 10-15 cycles on the copper side; in contrast, no such inhibited growth was observed in the TiO_2 deposition on silicon. This result opens up potential for selective ALD of TiO_2 films on silicon-based substrates patterned with a metal without the use of a mask, a self-assembled monolayer or soft lithography which is impractical for some nanoscale semiconductor fabrication processes. After film nucleation, the TiO-2 growth rate on both surfaces was found to be 0.10 nm/cycle.
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