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This chapter covers a body of material that deals with movement of mass along gradients and between phases. It examines the commonalities and differences between linear driving forces, net rates of adsorption, and permeation. Each has the common feature that reaction is not involved but does involve transport between apparently well-defined regions. It focuses on chemically reactive systems in anticipation of eventually analyzing problems that involve mass transfer and reaction. Adsorption is a fundamental process of separation that is practiced for different purposes; removal of volatile organics contaminants (VOCs) from air is one, removal of water vapor from nitrogen is another. Adsorption is the process by which, molecules in the fluid phase in contact with a solid, move to the solid surface and interact with it. Once at the solid surface, these molecules may be reversibly or irreversibly adsorbed, that is, they may come back off the surface to the fluid phase with their full molecular integrity intact, or they may be so strongly bound that the rate of removal is for all purposes close enough to zero to be considered zero. True adsorption is a mass action process rather than a mass transfer process. What this means is that it will occur even in the absence of a concentration gradient between the bulk gas and the surface. It comes about due to the rapid and chaotic motion of the fluid phase molecules, and their impingement on the surface. From the elementary kinetic theory of an ideal gas one can compute the number of molecules impinging upon a surface per unit time per unit area at a given temperature and pressure.

This chapter extends the analyses that one can do well beyond the simple systems. It provides a fairly simple problem, the gravity-driven flow of fluid from a tank that led to Torricelli's Law. With this in the tool box, one would be able to step smartly through a series of systems with input and out fluid flows that are increasingly more complex, culminating in the proportional control of the level of a tank with sinusoidally driven input flow. This chapter uses Mathematica in ever more sophisticated ways and provides new problem-solving techniques. In the models based on analyses of systems that had simple inputs, the right hand side was either a constant or it was simple function of time. In those systems, one cannot consider the cause of the mass flow; it was literally external to both the control volume and the problem. The case of the flow was left implicit. The pump or driving device was upstream from the control volume, and all one needed to know was the magnitude of the flow that the device caused, and its time dependence. Given that information, one could replace the right hand side of the balance equation and integrate to the functional description of the system.

Sixty years ago, cupric acetate was proposed as one of the first homogeneous, heterolytic hydrogen activation catalysts. Later on, it was demonstrated that dihydrogen complexation is unequivocally the first step preceding H H bond cleavage. In this study, using a home-made, high-pressure adsorption setup working at different temperatures, we examined the carbon-nanoconfined counterparts of the former in order to elucidate the nature of H 2 -metal complex interaction inside the nanosized space provided by the porous support. In this regard, we found that by lowering temperature from 100 °C to room temperature, a marked alteration would take place in the nature of interaction. By doing so, we moved from what appeared to be (H 2 )CuH 2 , a dihydride-dihydrogen complex, to a Kubas compound releasing H 2 in a fully reversible manner. The nanoconfined metal complex discussed here may serve either as a prototypical, room-temperature hydrogen storage medium with optimum heat of interaction, or as a solid-phase hydrogen activation catalyst operating under mild conditions.

Spherical micron-sized carbon powders were synthesized from feedstock furfuryl alcohol and tested as anodes in sodium ion batteries (SIBs). A long cycle life of 1000 cycles is achievable with this carbon at C rate (3–4 mg cm−2 loading and i = 200 mA g−1) yielding a steady capacity of ca. 115 mA h g−1. The results from solid-state 23Na MAS NMR analyses of cycled electrodes indicate no correlation in voltage profiles with sodium site nature (graphene or nanopores), which is a new observation in SIB carbon anodes.

Nanoporous carbons were synthesized and treated with nitric acid after which the change in their propensities for ammonia adsorption was determined. The adsorbents had mean pore sizes ranging from 0.5 to 12 nm and they included polyfurfuryl alcohol (PFA)-derived carbons, commercial activated carbons, and both soft and hard-templated mesoporous carbons. The carbons were treated with concentrated nitric acid at elevated temperatures (e.g. 90 °C) and for time spans between 15 and 240 min. The textural properties of carbons, before and after nitric acid treatment, were determined using CO2 adsorption at 0 °C. Ammonia adsorption uptakes were measured at 25 °C and at pressures up to 9.5 bar. The highest total uptake of ammonia on the native carbons, that is prior to nitric acid treatment, was ∼10 mmol/g at 1 bar and 25 °C; this was obtained on a microporous carbon derived from the pyrolysis of polyfurfuryl alcohol and polyethylene glycol blends followed by CO2 oxidation. Nitric acid treatment of this carbon significantly increased its total uptake of ammonia to 17 mmol/g. This sample provided a reversible uptake of 14 mmol/g after it was outgassed at 160 °C and 10−5 bar under dynamic vacuum. This is 2 mmol/g higher than state-of-the-art ammonia adsorbents such as COF-10. An x-ray photoelectron spectrum (XPS) showed that the oxygen content of the carbon increased from 3 at.% to 16.4 at.% after the nitric acid treatment. Heats of adsorption profiles, calculated from adsorption isotherms, started from 165 kJ/mol and quickly dropped to 40 kJ/mol with ammonia loading. This showed that the isosteric heat of adsorption on the remaining surface was still higher than the native carbon sample resulting in high reversible adsorption uptake, even after excluding the irreversible adsorption on the very high energy sites.

In this article, we report the results of careful, room-temperature, high-pressure adsorption studies, in which simple complexes of copper and silver reversibly adsorb hydrogen when dispersed within nanoporous carbon. Whereas these complexes alone did not adsorb hydrogen, when they were nanoconfined within carbon, they adsorbed 1–3 mol of H2 per metal center. As a figure of merit, nanoconfined cupric formate adsorbed ∼2.6 H2/Cu at 100 bar and 20 °C, much larger than any reported metal-containing adsorption medium. On carbon alone, the heat of hydrogen adsorption decreased with an increase in adsorption extent, limiting to insufficient levels of uptake. By contrast, when these metal salts were dispersed within the carbon, the heats of adsorption increased markedly in a linear manner, meaning that the thermodynamics has moved in the right direction and is not self-limiting. Such thermodynamic behavior is associated with side-on dihydrogen binding onto a metal center, the so-called Kubas binding. Such intera...

The effect of boron substituted carbon (BC x , x ∼ 3–5) coatings on the hydrogen adsorption properties of porous carbons was investigated via spectroscopic characterization and hydrogen adsorption measurements. Thin films of BC x were synthesized by reacting BCl 3 and benzene in a chemical vapor and then depositing the product as a solid (CVD). The BC x deposits were collected on microporous carbon substrates and mesoporous silica aerogel. High-resolution solid-state boron NMR, 11 B HR-NMR, detected boron atoms in a symmetric chemical environment with trigonal coplanar coordination. Results from analyses based on NMR, X-ray photoelectron spectroscopy (XPS), and d-spacings, calculated from electron diffraction and X-ray diffraction (XRD) patterns, indicated that 17 at.% boron was substitutionally incorporated into the carbon framework. Thus the material has an empirical formula of BC 4.9 . Hydrogen adsorption data were collected at 100 bar and 25 °C. The BC x coatings reduced the surface area of the porous substrates by 30–50%. However, at the same time, they increased the heat of adsorption and the adsorption capacities per unit area by as much as a factor of five. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) revealed wagging energies at 1190 cm −1 attributable to hydrogen interactions with C–B–C bonds.

There are new and interesting adsorbents that show very high levels of adsorption on a mass basis. As one looks for viable new materials that can be moved from the bench to a pilot and then to full-scale units, a gap in adsorption results of these adsorbents immediately emerges. There has been a lack of consideration given to adsorbent density. When the transition is made from science to technology, density is critical because this variable will control the volume of the adsorbent bed and the size of the unit, both of which determine capital outlay.

Carbon materials with bimodal porosity have shown enhanced performance in a wide variety of applications including catalysis, energy storage and fluid separation. Presence of mesoporosity is essential to lower the mass transfer limitation imposed by the microporous nature of the carbons. The synthesis approaches used to prepare bimodal carbons with controlled micro/mesopore size and narrow pore size distribution, usually involve multi step processes and the use of harsh chemicals and solvents. Herein, we present a simple one step method that can be used to synthesize carbon with bimodal pore size distribution. Simultaneous polymerization of furfuryl alcohol and phloroglucinol-formaldehyde in the presence of a structure-directing agent (Pluronic F-127) was carried out and the resultant polymer was pyrolyzed to yield the bimodal carbon. Effect of polymerization conditions such as concentrations of monomer, initiator and surfactant on the bimodal pore size distribution of the carbon was studied in detail. Pyrolyzed precursors form carbons with narrow mean micropore size of 0.5 nm and mean mesopores ranging from 3.5 to 6 nm. The range of the mesopore size could be altered by varying the polymerization parameters (acid and surfactant concentration) as well as selective oxidation using CO 2 gas.

In heterogeneous catalysis, pore size exerts an influence on reaction pathway, selectivity, equilibrium and adsorption constants. This effect can in principle cause noticeable changes in selectivity. Here, we present an analysis of a diffusion–reaction process in the pores of a catalyst comprised of platinum nanoparticles embedded within a molecular sieving carbon. When the alkenes are hydrogenated over this catalyst, the reaction takes place within the ultramicropores of the carbon. Experimental data for the liquid phase hydrogenation of different alkenes over platinum supported on the carbon versus platinum embedded within the same carbon were collected. From these data kinetic parameters and diffusion coefficients for reactions were evaluated. The forward rate constant for 2-methyl-1-pentene hydrogenation was found to be almost one order of magnitude larger within the embedded platinum catalyst versus the supported platinum catalyst. The variation in pore size and reactant molecule dimension, were also found to affect the adsorption equilibrium constants and diffusion coefficients. For 2-methyl-1-pentene molecule with the highest steric hindrance, K increased to 500 g/mol in embedded catalyst compared to 100 g/mol on supported catalyst. At the same time the diffusion coefficient for 2-methyl-1-pentene was one order of magnitude smaller than 1-hexene.

Reactant shape selective catalysis occurs when substrates of different sizes and shapes are consumed at different rates over catalysts that combine molecular sieving transport processes with reaction. By contrast the same substrates react at nearly equivalent rates over catalysts that have large, open pores that do not induce any form of molecular sieving. Here we describe the design and synthesis of reactant shape selective catalysts for liquid phase hydrogenation reactions. Using an emulsion polymerization of furfuryl alcohol, we have made catalysts that consist of microporous carbon nanospheres within which are embedded platinum nanoparticles. The porosity of the carbon spheres was found to be a key parameter affecting catalyst activity and selectivity; porosity was varied by adding pore forming agents, such as polyethylene glycol with different molecular weights, during synthesis, or by mild oxidation of the as-synthesized catalyst using carbon dioxide. In addition to increasing porosity to reduce mass transfer limitations, a synthesis of smaller carbon spheres (

We present a simple method to synthesize shape selective carbon catalysts for large alkene hydrogenation reactions by tailoring porosity of platinum embedded in polyfurfuryl alcohol derived carbons. A small amount of mesoporosity, in addition to the intrinsic microporous nature of the carbon, shortens the diffusion length for the reactant molecule, enabling these materials to be used for catalysis in the liquid phase. A systematic study of hydrogenation reactions of liquid phase alkenes is reported. The molecular sieving effect of the catalyst was examined by varying molecular length, size, double bond position, stereoregularity and the number of double bonds in the alkenes.

Carbon spheres were synthesized by emulsion polymerization and pyrolysis of polyfurfuryl alcohol. Pluronic F-127 was used as the structure-directing agent to synthesize polymer spheres that after pyrolysis led to carbon spheres with average sizes from 50 nm to few micrometers in diameter depending upon the conditions of polymerization. As-synthesized carbon spheres possess high surface areas of around 480 m2/g with an average mean pore size of 0.5 nm. These spheres can be activated using carbon dioxide to create much higher surface areas (>1500 m2/g). Different compositional regions of the pseudo-ternary phase diagram of surfactant/monomer/solvent were explored in order to determine the effects of changes in the emulsion polymerization variables on the kinds of carbon morphologies that could be derived from polyfurfuryl alcohol after pyrolysis. The diameter of the carbon spheres was found to be sensitive to monomer and surfactant concentrations, acid molarity and solvent composition. In general, the diameter of the spheres grew with increasing furfuryl alcohol concentration and decreasing surfactant concentration, respectively. By varying the acid concentration and solvent composition, a minimum diameter for spheres was found. The formation and size of the spheres are strongly influenced both by micelle growth and the polymerization mechanism.

(2012). A New Approach to Intellectual Property Management and Industrially Funded Research at Penn State. Research-Technology Management: Vol. 55, No. 5, pp. 12-17.

In the present work, design and operation of a high pressure gas adsorption apparatus at room temperature and at pressures up to 100 bar are discussed. A theoretical and experimental error analysis is done to determine accuracy and robustness of the measurements. For this study, activated carbon was selected as the adsorbent and hydrogen as the adsorbate gas. A sensitivity analysis was done by taking into account the effects of temperature, pressure, volume and weight of the sample. The analysis shows that the volumes of the sample and reference cells as determined by helium-free space measurements have significant effect on the accuracy of the adsorption uptake measurement. For instance, a 0.1% error in the measurement of either volume led to approximately a 3% error in hydrogen uptake measurement at 298 K and 100 bar.

n contrast to almost every other artifact produced bymodern industrial society, (automobiles, jet aircraft,locomotives, ocean going vessels, etc.) the design,construction and operation of buildings is still highly frag-mented and comparatively unsophisticated. This is thecase even though the construction industry amounts toover one trillion dollars of the US economy. Materials ofconstruction, coatings, cladding, as well as electrical,mechanical and other components (windows, roofing,heating, ventilation, air conditioning etc.) may be selectedindependently with little, or no, thought given to theirinteractions and the effects of their coupling on the build-ing’s performance. For some architects and building own-ers, especially of high-end structures for urban officespace, the principal goal of design has often been visualimpact, which is to say that form dominates function.This kind of architectural statement is accomplished onlywith enormous up-front capital investments and with hugepenalties in downstream operating costs due to low effi-ciencies inherent to the design. To say that energy effi-ciency suffers most in such buildings is an understatement.The financial model in such cases is that the architecturalstatement will be afforded with collection of very highrents. In some cases, little or no consideration is or waspaid to the habitability of the space in other words thebuilding’s indoor ecology was at best of secondary impor-tance.There are notable examples of such extravagant buildingsin almost every large American city, as well as around theworld; they are not hard to find, but they are emblematic of aby-gone era. These buildings, constructed in the 20th century,symbolize much of what must be changed in the 21st centurybuilding industry; functionality and performance must trumpexcesses of form. As evidence that the society’s view of thesebuildings and buildings in general is changing rapidly, thepremier icon of the ‘‘sky-scraper era’’, the Empire StateBuilding, has undergone a deep retrofit to bring its efficiencyto the level of LEED Gold and this symbolizes the new stand-ards that can be achieved for older commercial buildings aswe move further into the 21st century

The Greater Philadelphia Innovation Cluster (GPIC) for Energy-Efficient Buildings is breaking new ground on how public-private research partnerships are conducted. A consortium of public, private, ...

Boron/nitrogen substituted carbons were synthesized by co-pyrolysis of polyborazylene/coal tar pitch blends to yield a carbon with a boron and nitrogen content of 14 at% and 10 at%, respectively. The presence of heteroatoms in these carbons shifted the hydrogen evolution overpotential to −1.4 V vs Ag/AgCl in aqueous electrolytes, providing a large electrochemical potential window (∼2.4 V) as well as a specific capacitance of 0.6 F/m2. An asymmetric capacitor was fabricated using the as-prepared low surface area carbon as the negative electrode along with a redox active manganese dioxide as the positive electrode. The energy density of the capacitor exceeded 10 Wh/kg at a power density of 1 kW/kg and had a cycle life greater than 1000 cycles.

Asymmetric aqueous electrochemical capacitors with energy densities as high as 22 Wh kg −1 , power densities of 11 kW kg −1 and a cell voltage of 2 V were fabricated using cost effective, high surface carbon derived from coal tar pitch and manganese dioxide. The narrow pore size distribution of the activated carbon (mean pore size ∼0.8 nm) resulted in strong electroadsorption of protons making them suitable for use as negative electrodes. Amorphous manganese dioxide anodes were synthesized by chemical precipitation method with high specific capacitance (300 F g −1 ) in aqueous electrolytes containing bivalent cations. The fabricated capacitors demonstrated excellent cyclability with no signs of capacitance fading even after 1000 cycles.

Without any catalyst or pressure, bulk non-graphitizing carbon does not exhibit any change in its atomic order (or graphitize) even at 3000 °C. We propose a route for significant graphitization in polymer-derived disordered carbon materials at moderate temperatures by pre-aligning the precursor polymer chains. Accordingly, we employ a template-based fabrication process, where the capillary forces align the polyfurfuryl alcohol chains in the form of nanowires with diameter from 100–200 nm. The nanowires are pyrolyzed at temperatures ranging from 600 °C to 2000 °C and characterized with transmission electron and Raman microscopy as well as electrical conductivity measurements. The observed significant change in atomic rearrangement is explained by the alignment of precursor chains during the templated synthesis.

Composites of nanoporous carbon and single wall carbon nanotubes were heat treated in vacuum at temperatures ranging from 1200 to 2000 °C. The resultant interface between the two allotropes of carbon was characterized using high resolution transmission electron microscopy and Raman spectroscopy. At the interface between the nanoporous carbon and the nanotube, the nanotube served as a template for ordering and orientation of the normally disordered nanoporous carbon along the nanotube axis during high temperature treatment. When annealed at 2000 °C, the nanoporous carbon transformed to graphitic nanoribbon which in turn crushed the nanotube to form a nanoscale carbon “bulb”. This result is interesting since at these temperatures, the native nanoporous carbon is well known to resist ordering and is therefore referred to as being a “non-graphitizing” carbon. That the nanotube should act as a template for the incipient graphitization suggests that bonding and strength for load transfer may be developed at these interfaces.

Nanofibers of poly(ethyl 2-cyanoacrylate) were directly grown via a template-less vapor phase polymerization technique directly on surface modified glass substrates. Several commercially available glass slides were investigated for polymer nanofiber deposition. In addition, glass substrates were also modified in the laboratory using silanes with different functional groups. The growth of nanofibers at different relative humidities was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that nanofiber formation is favored when the polymerization occurs at relative humidities greater than 68%. The diameter and the number density of the nanofibers were examined in terms of the wettability of cyanoacrylate monomer on the modified glass substrates.

The type of anionic initiator used to polymerize ethyl 2-cyanoacrylate was found to influence the morphology of the polymer formed via vapor phase polymerization. Depending upon the type of initiator, polymerization of ethyl 2-cyanoacrylate resulted in either the formation of neat polymer nanofibers (∼200 nm in diameter) or thin films. Based on the classification of anions using Hard Soft Acid Base principles, we found that harder anions favored polymer film formation while softer ones favored polymer nanofibers. Infrared (IR) spectroscopy, scanning electron microscopy (SEM) and gel permeation chromatography (GPC) were used to characterize the structure, morphology and molecular weight of the synthesized polymers, respectively. Finally, a mechanism of formation of different polymer morphologies is proposed.

A new pathway to synthesize a carbon with both nanoporosity and pre-graphitic structures has been discovered by annealing at 2000 °C a CO 2 activated, non-graphitizing, nanoporous carbon originally derived from polyfurfuryl alcohol. The activation process with CO 2 overcomes the barrier to graphitization normally present in this carbon even when treated at high temperature. Gas adsorption analysis, skeletal density measurements, X-ray diffraction, and transmission electron microscopy are utilized to probe the structure of both the non-activated and the activated carbons at 800, 1200, 1800, and 2000 °C. The influence of activation time is also examined. Prior to activation the nanopore walls are comprised of several layers of disordered graphenes. Activation eliminates the barrier to graphitization by reducing the number of layers below the limit of detection and by removing carbon material highly susceptible to oxidation. Annealing at 2000 °C of the carbon activated to 84% burnoff induces the formation of pre-graphitic domains amongst the nanoporous carbon. The (0 0 2) bands corresponding to 2 θ = 24.3°, 26°, and 26.5° are identified and assigned to amorphous, turbostratic, and graphitic morphologies. A pore volume of 0.50 cm 3 g −1 localized in pores below 2 nm in size is preserved after annealing.

Porous carbons with tunable porosity and electrical conductivity have received considerable attention due to their potential application as anodes in lithium ion batteries, electrocatalysts in fuel cells, and high surface area electrodes in electrical double layer capacitors [1,2]. High porosities and surface areas are critical to the performances of these materials. Significant porosity and surface area are easily created by activation of non-graphitizing carbon, yet the material lacks in conductivity [3–5]. Whereas graphitic carbon possesses high conductivity, it strongly resists activation by traditional methods [5]. Recently graphitic carbons with controlled pore sizes have been obtained by pyrolysis of graphitizing carbon precursors deposited in mesoporous silica templates [2,6,7]. However, the preparation of carbon with nanopores, width less than 2 nm, is unattainable by this method, thus limiting its ultimate surface area, porosity, and performance. Graphitization of non-graphitizing carbon occurs in the presence of a variety metals, but the product is contaminated with the catalyst [8–11]. Stress graphitization of pure carbon has been reported at temperatures in excess of 2000 C [12,13]. Porosity is not preserved. Herein we describe the discovery of a new route to the synthesis of a pure nanoporous carbon containing pre-graphitic structures with both high surface area and high nanoand mesoporosity from the readily available polymer precursor polyfurfuryl alcohol. Nanoporous carbon (NPC) is synthesized by pyrolysis of polymers, such as polyfurfuryl alcohol (PFA). Due to its strong resistance to transformation to graphite even when annealed at temperature above 2000 C, it is classified as non-graphitizing, which was defined by Franklin [14]. This resistance is attributed to the presence of extensive cross-linking in the precursor, which creates kinetically frozen disorder through a chaotic misalignment of the graphenes in the carbon that result during pyrolysis [15– 17]. Disorder in NPC gives rise to porosity and the majority of pores are narrowly distributed in the range from 0.4 to 0.5 nm width [16,18,19]. The pore volume and surface area of NPC can be further developed by simple activation with CO2 [20,21]. We have found that the pre-graphitic ordering of PFA-derived NPC can be accomplished after CO2 treatment at 900 C, which generates activated NPC (a-NPC). The a-NPC provides an unexpected pathway to pre-graphitic carbon with nanoporosity by subsequent annealing at 2000 C. First, p-toluenesulfonic acid monohydrate (0.048 gm, Sigma–Aldrich) was dissolved in 5 ml of Triton X-100 (Sigma–Aldrich) by heating mildly. Then to this solution, 5 ml of furfuryl alcohol (99% Sigma–Aldrich) was added. The reaction mixture was stirred magnetically at 10 C. After polymerization for 48 h the product was transferred to a quartz boat and pyrolyzed under flowing argon in a quartz tube furnace. The sample was heated at a rate of 10 C min 1 to 800 C and held for 1 h. The carbon product was pure, without inorganic contaminants. It was ground and sieved to a particle size of < 38 lm. Activated NPC was prepared in a quartz tube furnace. 0.5 gm of carbon was heated to 900 C over 1 h in flowing argon. After 1 h of soak time the gas was switched to CO2 and soaked for an additional 3.5 h. The sample was cooled back to room temperature under argon. High temperature

The preparation of porous stainless steel supports was found to have a significant impact on the properties of nanoporous carbon membranes fabricated upon them. Nanofillers were incorporated into porous stainless steel supports to modify the pore structure by reducing the average pore size and porosity. Carbon membrane properties were examined as a function of support variables such as filler content, shape, size and nature of the particles. Optimum performances, in terms of the ideal selectivity ratio for oxygen to nitrogen permeances ( S O 2 / N 2 ∼ 3 – 6 ) and the oxygen permeance (10−8 mol m−2 s−1 Pa−1), were obtained when the filler completely saturated the support. This represents about a two order of magnitude improvement in oxygen permeance when compared to carbon membranes prepared on unmodified porous stainless steel supports. The origin of the improvement in the permeance is due to the formation of carbon membranes which are on average two orders of magnitude thinner than those formed on unmodified supports, i.e., the carbon membranes exists as very thin layers around and between the silica nanoparticles. A simple geometric model based on the packing of silica particles inside the porous stainless steel support is proposed to visualize and quantify this effect. The generality of the support modification concept is also demonstrated by the ability to employ different types of nanofillers and support geometries to obtain carbon membranes with high flux. Air separation experiments show that these membranes can produce both oxygen rich streams enriched to as much as 48% by volume and nitrogen rich streams enriched to over 90% by volume at reasonable operating conditions.

The pyrolysis of polyfurfuryl alcohol was studied up to 600 °C. Micropores appear in the carbon as early as 300 °C along with a significant amount of mesopores. As the pyrolysis temperature is increased, microporosity is retained, but the mesoporosity disappears. At 600 °C the material is microporous with a monodisperse pore size distribution centered at 4–5 A. Infrared, X-ray photoelectron, and nuclear magnetic resonance spectroscopies, in combination with thermogravimetric analysis provide evidence that between 300 and 400 °C, both polyaromatic domains decorated with hydrogen and oxygen (hetero) atoms and partially decomposed polymer chains coexist. The unreacted polymer and heteroatoms induce mesoporosity by buffering the micropores created by polyaromatic domains. Raising the pyrolysis above 400 °C releases the buffering material, thereby collapsing the mesopores.

Silica nanoparticles were slip cast into porous stainless steel supports, which were then coated with polyfurfuryl alcohol and pyrolyzed to make nanoporous carbon membranes. The single gas permeances of the membranes formed on modified stainless steel supports were found to be between two and three orders of magnitude larger than the permeances of nanoporous carbon membranes (

A novel type of thin-film catalyst has been developed that combines high activity with selective transport across a micron-scale membrane film. Nanoporous carbon was used as a support for 12-tungstophosphoric acid with composite films synthesized by two distinct approaches: in-situ polymerization and adsorption from solution. Ion sputtering and XPS were used in combination to characterize the high dispersion of the catalyst within the film in the former case and a gradient in catalyst concentration in the latter. Both methods produce intact Keggin structures as demonstrated by FTIR spectroscopy. Gas permeation experiments indicate a preservation of separation capacity with O2/N2 permeability ratios as high as 6.5. The catalytic films were benchmarked using the decomposition of methyl tert-butyl ether at 55 °C and demonstrate remarkable increases in both conversion and simultaneous separation of decomposition products. Integrated conversions in a semi-batch reactor configuration far exceed the thermodynam...

A model for the structure of a non-graphitizing carbon is built by randomly incorporating between 0.5% and 4% non-hexagonal rings into an extended sp2 carbon sheet. The sheets are created using Cerius2 Modeling software, optimized using a DREIDING force-field, and turbostratically layered to create a three-dimensional structure. We show that the calculated pair distribution function (PDF) for models containing approximately 1% non-hexagonal rings is remarkable similar to the experimental PDF obtained from neutron scattering by a non-graphitizing carbon prepared from polyfurfuryl alcohol pyrolyzed at 1200 °C. No attempt was made to fit the model to the experimental data, and the model has no adjustable parameters except for the fraction of non-hexagonal rings.

Porous solids are of great technological importance due to their ability to interact with gases and liquids not only at the surface, but throughout their bulk. Although large pores can be produced and well controlled in a variety of materials, nanopores in the range of 2 nm and below (micropores, according to IUPAC classification) are usually achieved only in carbons or zeolites. To date, major efforts in the field of porous materials have been directed towards control of the size, shape and uniformity of the pores. Here we demonstrate that porosity of carbide-derived carbons (CDCs) can be tuned with subångström accuracy in a wide range by controlling the chlorination temperature. CDC produced from Ti3SiC2 has a narrower pore-size distribution than single-wall carbon nanotubes or activated carbons; its pore-size distribution is comparable to that of zeolites. CDCs are produced at temperatures from 200-1,200 degrees C as a powder, a coating, a membrane or parts with near-final shapes, with or without mesopores. They can find applications in molecular sieves, gas storage, catalysts, adsorbents, battery electrodes, supercapacitors, water/air filters and medical devices.

Poly(ethylene glycol), which has a negligible carbon yield upon pyrolysis, was used as a template to study the controlled formation of mesoporosity in pyrolytic carbons. A series of carbons was produced from mixtures of poly(ethylene glycol) and poly(furfuryl alcohol) with 25, 50 and 75% composition by weight and an Mn of 300 to18 500 g/mol of template. Polydisperse dextran adsorption reveals a maximum in uptake for 8000 g/mol and 50% templated carbons, while materials from 75% mixtures or those from less than 2000 g/mol template yielded negligible dextran uptake. These results correlated well with the intensity ratio of a broad peak between 7 and 11° 2θ in the X-ray diffraction spectrum and the 002 diffraction peak and also qualitatively with micrographs of the internal microstructure of the carbons. The results suggest a templating process dominated by both the molecular size of the template and the rate of expulsion of decomposed template material during the formation of the solid.

Using a transient analysis of permeation, i.e. the time lag method, as a function of temperature and pressure, it is shown that each of the parameters needed to fully evaluate adsorption and diffusion can be obtained in situ. These experiments were conducted on a supported tubular nanoporous carbon membrane, 5.1 cm 2 in area and prepared by ultrasonic deposition of poly(furfuryl alcohol) onto a porous stainless steel support. The permeation experiments were conducted at temperatures ranging from 25 to 225°C and over a range of pressures from 100 to 700 kPa. Under these conditions the fluxes ranged from 10 −7 to 10 −4 mol/m 2 /s with permeances ranging between 10 −12 and 10 −9 mol/m 2 /s/Pa. Heats of adsorption were found to be 2.5, 2.21, 3.05 and 2.52 kcal/mol for N 2 , O 2, Ar and CO 2 , respectively, and generally lower than those reported for granular nanoporous carbons. The apparent activation barriers to diffusion were also found to be low at 2.06, 5.87, 4.12, 5.89 and 2.19 kcal/mol for He, N 2 , O 2 , Ar and CO 2 . These results point to the presence of two parallel pathways for transport — the major one through the nanopores but a second through a few defect pores. Assumed to be on the order of 50 nm in diameter, these defects were calculated to represent a total area fraction of 3.43×10 −9 .

A novel method for producing carbon membranes for ultrafiltration applications is presented using a spray deposition and pyrolysis of poly(furfuryl alcohol)/poly(ethylene glycol) mixtures on macroporous stainless steel supports. The poly(ethylene glycol) or PEG employed as a carbonization template creates a mesoporosity that leads to pores in the ultrafiltration range. Scanning electron microscopy (SEM) shows that the membranes consisted of 12- to 15-m thick carbon films. Gas permeation and water permeability data were used for the calculation of mean pore sizes, which were found to decrease with decreasing average molecular weight of the PEG template. Ultrafiltration of a polydisperse dextran solution was used to quantify the retention properties of the membranes. Molecular weight cutoffs determined from dextran retention data were shown to vary with template molecular weight: values of 2 × 10 4 ,3 .5 × 10 4 , and 6 × 10 4 gm ol −1 dextran were measured for respective templates of 2000, 3400, and 8000 g mol −1 PEG. For PEG molecular weights of 2000 or below, the templating effect was ill defined, membrane film cracking became more prominent, and membrane selectivity and reproducibility were adversely affected. © 2002 Published by Elsevier Science B.V.

Thermoelectric properties of single wall carbon nanotubes (SWNT) are quite sensitive to gases in contact with the tube walls. This effect makes possible a thermoelectric chemical sensor. Large, reversible swings in thermoelectric power (S), sometimes even involving sign changes in S, have been observed. Even contact of the SWNTs with He and N 2 and H 2 result in easily detectable and reversible changes in S. Smaller, polar alcohol molecules stimulate a large thermoelectric response, although H 2 O has no effect. For adsorption of six membered ring molecules C 6 H n in SWNTs, the large thermoelectric response observed for Benzene (n = 6) is seen to decrease as the π electrons in the molecule are removed, and the coupling between the molecules and the SWNT is thereby reduced. These effects are discussed in terms of the diffusion thermopower for a rope, and a new scattering channel associated with adsorbed molecules.

A theoretical model developed predicts the thickness of a polymer film, coated on a rotating and translating cylindrical support. A model for the deposition process can be used to determine optimal operating conditions. It was validated experimentally and shows that the film-thickness morphology is quite sensitive to certain operating parameters. For example, particular sets of operating parameter values can produce highly nonuniform film thicknesses. Selected examples of the model calculations are discussed, as well as their implications.