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The 3D chemical structure (4D spectromicroscopy) of nanoporous Al2O3 aerogels coated with ZnO by atomic layer deposition (ALD) was studied by multienergy scanning transmission X-ray microscopy. The...

Multi-functional membranes with high permeance and selectivity that can mimic nature's designs have tremendous industrial and bio-medical applications. Here, we report a novel concept of a 3D nanometer (nm)-thin membrane that can overcome the shortcomings of conventional membrane structures. Our 3D membrane is composed of two three-dimensionally interwoven channels that are separated by a continuous nm-thin amorphous TiO2 layer. This 3D architecture dramatically increases the surface area by 6000 times, coupled with an ultra-short diffusion distance through the 2–4 nm-thin selective layer that allows for ultrafast gas and water transport, ∼900 l m−2 h−1 bar−1. The 3D membrane also exhibits a very high ion rejection (R ∼ 100% for potassium ferricyanide) due to the combined size- and charge-based exclusion mechanisms. The combination of high ion rejection and ultrafast permeation makes our 3DM superior to the state-of-the-art high-flux membranes whose performances are limited by the flux-rejection tradeoff. Furthermore, its ultimate Li+ selectivity over polysulfide or gas can potentially solve major technical challenges in energy storage applications, such as lithium–sulfur or lithium–O2 batteries.

Herein we report the fabrication of ultralight gold aerogel monoliths with tunable densities and pore structures. Gold nanowires are prepared at the gram scale by substrate-assisted growth with uniform size, ultrathin diameters, high purity, and a high aspect ratio. Freeze-casting of suspensions of these nanowires produces free-standing, monolithic aerogels with tunable densities from 6 to 23 mg/cm3, which to the best of our knowledge represents the lowest density monolithic gold material. We also demonstrate that the pore geometries created during freeze-casting can be systematically tuned across multiple length scales by the selection of different solvents and excipients in the feedstock suspension. The mechanical behavior of porous materials depends on relative density and pore architectures.

We demonstrate the synthesis of high-surface-area, low-density refractory aerogels. The monolithic hafnium boride (HfB2) and zirconium boride (ZrB2) aerogels are prepared via borothermal reduction ...

Experiments on the National Ignition Facility (NIF) to study hohlraums lined with a 20-mg/cc $400\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ aerogel at full scale (hohlraum diameter = 6.72 mm) are reported. Driven with a 1.6-MJ, 450-TW laser pulse, the performance of the foam liner is diagnosed using implosion hot-spot symmetry measurements of the high-density carbon (HDC) capsule and measurement of inner beam propagation through a thin-wall $8\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ Au window in the hohlraum. Results show an improved capsule performance due to laser energy deposition further inside the hohlraum, leading to a modest increase in x-ray drive and reduced preheat due to changes in the x-ray spectrum when the foam liner is included. In addition, the outer cone bubble uniformity is improved, but the predicted improvement in inner beam propagation to improve symmetry control is not realized for this foam thickness and density.

The measurement of the density of materials, especially ultralow-density foams, is difficult in that the measurement must be precise and localizable. The density of the material is often governed b...

Carbon aerogels (CAs) are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first CAs were made via pyrolysis of resorcinol–formaldehyde (RF)-based organic aerogels in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous CAs, several other carbon allotropes have been realized in aerogel form: carbon nanotubes (CNTs), graphene, graphite, and diamond. Furthermore, the popularity of graphene aerogels has inspired research into aerogels made of a host of graphene analog materials (e.g., boron nitride, transition metal dichalcogenides, etc.), with potential for an even wider array of applications. Finally, the development of three-dimensional-printed aerogels provides the potential for CAs to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of RF-derived, CNT, graphene, graphite, diamond, and graphene analog aerogels.

Experiments using a single 527 nm wavelength beam interacting with sub- and supercritical density SiO2 and Ta2O5 foams examined laser propagation and backscatter from laser–plasma instabilities such as Stimulated Brillouin Scattering (SBS). Two densities of each material were examined, and multiple diagnostics were used to characterize the propagation and backscatter. For 5 mg/cc SiO2 (ne/nc = 0.375), the laser propagation distance was well approximated by treating the foam as a gas. However, for the 2 mg/cc SiO2 foam (ne/nc = 0.15), the same model over-predicts the propagation distance by ∼40%. Existing analytical theories on propagation through subcritical foams were able to account for this difference. The laser heat wave propagated ∼1/2 as far in Ta2O5 than SiO2 foams with similar electron density. We showed that this difference is due to the increased radiation losses in the higher Z foam. The fraction of backscattered light scales linearly with incident laser intensity for the range of intensities examined. Ta2O5 foams had significantly lower levels of backscatter (1–3%) than the SiO2 (4–8%), which is consistent with estimates of large Landau damping due to the presence of the oxygen atoms. The measured fraction of SBS backscattered laser energy for a 2 mg/cc SiO2 foam shot was ∼4 times lower than predicted by simulations assuming a gas-like foam. We found that we needed to assume increased ion heating such that Ti/Te ∼ 1.2–1.5 in the plasma to agree with the measured SBS reflectivity. Analytical models of laser-heated foams predict preferential heating of the ions as has been observed in previous experiments.

The ablative expansion of laser-heated materials is important for determining how hohlraum cavities can be utilized for inertial confinement fusion. The utility of a low-density foam layer to reduce the density of the expanding heated hohlraum wall is demonstrated in a series of experiments on the National Ignition Facility. X-ray radiography measurements of the expanding foam-lined Au wall in low aspect-ratio cylindrical geometry are used to compare the impact of Au-doped CH and Ta2O5 foams between 10 and 40 mg/cc on the wall expansion. HYDRA Simulations are used to estimate the x-ray transmission at the 1/4 nc surface, which is important in understanding the absorption of laser light by the plasma. These demonstrate for the first time that a foam layer reduces the expansion of a hohlraum-like target and illustrate that the interplay between the expanding foam plasma and the shock reflected by the hohlraum wall is critical in optimizing foam-liner parameters to achieve the maximum time for a symmetric drive on a capsule.

Functional porous materials are of increasing importance in energy conversion and catalysis. Improved analysis is needed to guide optimization. Four-dimensional (4D) imaging [chemical mapping in three-dimensional (3D) by spectro-tomography] of an Al2O3 aerogel coated with ZnO by atomic layer deposition was performed using soft X-ray ptychography at the Zn L-edge. A two-dimensional spatial resolution of 14(2) nm was achieved. Visualizations of the 3D chemical structure are provided. The degree of ZnO coverage of the surface of the Al2O3 aerogel framework in two different samples was estimated and found to be both thicker and less homogeneous than expected. Other analyses of the 4D results, including the degree of contact between Al2O3 and ZnO, were extracted from the reconstructed 3D data. This pioneering soft X-ray spectro-ptycho-tomography study will anchor further studies of functional porous materials.

Compared to tedious, multi-step treatments for electroless gold plating of traditional thermoplastics, this communication describes a simpler three-step procedure for 3D printed crosslinked polyacrylate substrates. This allows for the synthesis of ultralight gold foam microlattice materials with great potential for architecture-sensitive applications in future energy, catalysis, and sensing.

Capacitive deionization (CDI) is a promising desalination technology, which operates at low pressure, low temperature, requires little infrastructure, and has the potential to consume less energy for brackish water desalination. However, CDI devices consume significantly more energy than the theoretical thermodynamic minimum, and this is at least partly due to resistive power dissipation. We here report our efforts to characterize electric resistances in a CDI system, with a focus on the resistance associated with the contact between current collectors and porous electrodes. We present an equivalent circuit model to describe resistive components in a CDI cell. We propose measurable figures of merit to characterize cell resistance. We also show that contact pressure between porous electrodes and current collectors can significantly reduce contact resistance. Lastly, we propose and test an alternative electrical contact configuration which uses a pore-filling conductive adhesive (silver epoxy) and achieves significant reductions in contact resistance.

Ring opening metathesis polymerization (ROMP) using Grubbs second generation catalyst generates aliphatic gels from norbornene based crosslinkable monomers with a functionality of 2 or 3. Supercritical drying of these gels (CO 2 ) leads to the formation of aerogels with densities as low as 4 mg mL − 1 . The microstructure was analyzed by SEM, and pore analyses by nitrogen adsorption. The use of crosslinkable monomers allows the straightforward synthesis of aerogels consisting of only carbon and hydrogen with C:H ratios up to ca. CH 1.58 with a finer microstructure than that of DCPD.

Lightweight composites achieved by the incorporation of voids or pores are limited by their notoriously poor mechanical properties. Reinforcement of these composites by the incorporation of high aspect ratio nanofibers/tubes is challenging due to the difficulty and expense of efficiently dispersing the reinforcing elements in the desired matrix. Here, we present a method to fabricate preformed, porous fiber networks that can be infiltrated by the matrix of choice. First, we demonstrate the synthesis of mechanically robust, electrically conductive low-density carbon nanotube-based aerogels with macroscopic dimensions. The nanotube aerogels are prepared by the sol–gel polymerization of resorcinol with formaldehyde in an aqueous suspension containing a dispersion of highly purified single-walled carbon nanotubes. Subsequent drying and pyrolysis result in free-standing monoliths consisting of a random network of carbon nanotube bundles decorated and cross-linked by graphitic carbon nanoparticles. Such nanotube-based aerogels exhibit electrical conductivities improved by an order of magnitude compared to those of foams without nanotubes and elastic behavior up to compressive strains as large as ~80%. Finally, we show how these aerogels can be infiltrated by a wide range of matrix materials to form lightweight composites with enhanced mechanical and electrical properties.

The synthesis of ultralow-density (>5 mg/cm(3) ) bulk materials with interconnected nanotubular morphology and deterministic, fully tunable feature size, composition, and density is presented. A thin-walled nanotubular design realized by employing templating based on atomic layer deposition makes the material about 10 times stronger and stiffer than aerogels of the same density.

Realization of macroscale three-dimensional isotropic carbons that retain the exceptional electrical and mechanical properties of graphene sheets remains a challenge. Here, a method for fabricating graphene-derived carbons (GDCs) with isotropic properties approaching those of individual graphene sheets is reported. This synthesis scheme relies on direct cross-linking of graphene sheets via the functional groups in graphene oxide to maximize electronic transport and mechanical reinforcement between sheets and the partial restacking of the sheets to increase the material density to about 1 g cm-3. These GDCs exhibit properties 3–6 orders of magnitude higher than previously reported 3D graphene assemblies.

Carbon nanotube-carbon aerogel (CNT-CA) networks are a member of a novel class of ultra-low density, high surface area, hierarchically structured, carbon-based materials possessing unique mechanical and physical properties. Through the secondary incorporation of a polymer matrix into these aerogel systems it is now possible to form intercalated polymeric hybrid CNT-CA composite materials with polymer to carbon surface internal surface contact areas in the order of ∼600 m2 g−1 at carbon loadings as low as ∼1.5 wt %. Reported here is the synthesis of a series of well-defined poly(dimethylsiloxane) (PDMS)/CNT-CA composite systems, their characterization and the in-depth analysis of the effects of the carbon architecture on the thermal stability and degradation behaviour of the of the PDMS matrix. The results of degradative thermal analysis using both pyrolysis gas-chromatography/mass spectrometry (py-GC/MS) and thermogravimetric analysis (TGA), clearly demonstrate that the presence of the CNT-CA scaffold within the PDMS matrix greatly increases the thermal stability of the system and drives the matrix towards calcination at temperatures above 600 °C. Subsequent characterization of the residual materials using a combination of fast magic angle spinning solid-state nuclear magnetic resonance (Fast-MAS NMR), energy dispersive X-ray spectroscopy (EDAX) and electron microscopy have demonstrated that the improvements in thermal stability are concurrent with the relative loading of carbon nanotubes within the aerogel matrix, that the PDMS matrix is being driven towards the formation of increased levels of SiO2 on degradation and that the preferential calcination effect is a function of the unique high surface area fibular network structure of the CNT-CA monoliths.

The value of electrode density is often overlooked in the pursuit of impressive supercapacitor metrics. Low-density electrodes deliver the best performance in terms of gravimetric energy and power densities when only the mass of the electrodes is considered. However, energy and power values with respect to the total system mass (electrode + electrolyte) or volume are more meaningful for practical application. Low-density electrodes are impractical due to both large mass contributions by the electrolyte and large system volumes. Here, we use highly compressible graphene aerogel electrodes (up to 87.5% volumetric compression) to systematically characterize the effects of electrode density on energy and power metrics. The results reveal that electrode density is similar to electrode thickness in that both parameters have a squared effect on power. Accounting for the aqueous electrolyte's mass lowered the gravimetric energy and power by almost an order of magnitude for 0.144 g cm−3 dense carbon electrodes but only by a factor of 1.5 when the electrode density was increased to 1.15 g cm−3 through compression. The high-density electrodes achieve 8 W h kg−1, 70 000 W kg−1, and 144 F cm−3 in a symmetric electrode setup after factoring in the aqueous electrolyte's mass. Therefore, in the pursuit of high energy per mass, it can be just as effective to lower the system's mass with smaller electrolyte fractions as it is to use electrolytes with larger voltage ranges. High electrode densities allow aqueous electrolyte supercapacitors to attain energy densities per the system mass comparable to those of commercially-available organic electrolyte supercapacitors while maintaining 10–100× greater power.

Binder-free, monolithic, high surface area graphene macro-assemblies (GMAs) are promising materials for supercapacitor electrodes, but, like all graphitic carbon based supercapacitor electrodes, still lack sufficient energy density for demanding practical applications. Here, we demonstrate that the energy storage capacity of GMAs can be increased nearly 3-fold (up to 23 W h kg−1) by facile, non-covalent surface modification with anthraquinone (AQ). AQ provides battery-like redox charge storage (927 C g−1) without affecting the conductivity and capacitance of the GMA support. The resulting AQ-GMA battery/supercapacitor hybrid electrodes demonstrate excellent power performance, show remarkable long-term cycling stability and, by virtue of their excellent mechanical properties, allow for further increases in volumetric energy density by mechanical compression of the treated electrode. Our measured capacity is very close to the theoretical maximum obtained using detailed density functional theory calculations, suggesting nearly all incorporated AQ is made available for charge storage.

A robust, millimeter-sized low-density Cu foam with ∼90% (v/v) porosity, ∼30 nm thick walls, and ∼1 μm diameter spherical pores is prepared by the slip-casting of metal-coated polymer core-shell particles followed by a thermal removal of the polymer. In this paper, we report our key findings that enable the development of the low-density Cu foams. First, we need to synthesize polystyrene (PS) particles coated with a very thin Cu layer (in the range of tens of nanometers). A simple reduction in the amount of Cu deposited onto the PS was not sufficient to form such a low-density Cu foams due to issues related to foam collapse and densification upon the subsequent polymer removal step. Precise control over the morphology of the Cu coating on the particles is essential for the synthesis of a lower density of foams. Second, improving the dispersion of PS-Cu particles in a suspension used for the casting as well as careful optimization of a baking condition minimize the formation of irregular large voids, leading to Cu foams with a more uniform packing and a better connectivity of neighboring Cu hollow shells. Finally, we analyzed mechanical properties of the Cu foams with a depth-sensing indentation test. The uniform Cu foams show a significant improvement in mechanical properties (∼1.5× modulus and ∼3× hardness) compared to those of uncontrolled foam samples with a similar foam density but irregular large voids. Higher surface areas and a good electric conductivity of the Cu foams present a great potential to future applications.

Porous electrode capacitors are used extensively in systems which store energy, harvest mixing energy, or desalinate water. These electrodes can possess a hierarchical pore structure with larger macroscale pores allowing for facile ion and fluid transport, and smaller, nanometer-scale pores enabling significant ion storage. We here present a combined theoretical (linear circuit model) and experimental (electrochemical impedance spectroscopy) study of porous carbon electrode capacitors which integrate nanoscale pores into a micron-scale porous network. Our experiments are performed on a set of customfabricated hierarchical carbon aerogel electrodes with varying pore structure, including electrodes with sub-nanometer (sub-nm) pores. Our combined theory and experimental approach allows us to demonstrate the utility of our model, perform detailed characterizations of our electrodes, study the effects of pore structure variations on impedance, and propose hierarchical electrode design and characterization guidelines. Further, we demonstrate that our approach is promising toward the detailed study of ion storage mechanisms in sub-nm pores.

Ring opening metathesis polymerization (ROMP) of cycloolefins is a promising new route for the preparation of polymeric aerogels. The resulting unsaturation in the polymer backbone, however, makes these particular systems susceptible to oxidative degradation under ambient conditions. One method to increase the oxidative stability of these aerogels is to hydrogenate the material. In the present study, hydrogenation of poly(dicyclopentadiene) gels was achieved through thermolysis of para-toluenesulfonyl hydrazide in the presence of tripropylamine followed by solvent exchange and supercritical drying to form the hydrogenated aerogel (H- p DCPD). Aerogels were prepared with varying densities and were characterized by FTIR-ATR, elemental analysis, BET, SEM, XPS, DSC and TGA. The oxidative stability of H- p DCPD aerogels over p DCPD was investigated through thermolysis in the presence of atmospheric oxygen. We report herein the synthesis and characterization of this new material.

In this study, synthesis and characterization of thick carbon nanotube (CNT) electrodes with impressive electrical conductivity, mechanical properties, and large surface area is presented. The electrodes are made by effectively cross-linking the CNTs with graphitic carbon particles. The random network of cross-linked CNTs results in a bulk conductivity of >60 S/cm, large Young’s modulus (∼1.2 GPa), and high surface area (>500 m2/g). Electrochemical characterization of these thick CNT electrodes (100–1000 μm) shows a capacitance of 90 F/g (40 F/cm3) in an aqueous electrolyte (5 M KOH). Furthermore, much of this capacitance is maintained at fast scan rates up to 1000 mV/s. This high rate performance leads to a simultaneous display of large energy densities (>10 Wh/kg) and power densities (>40 kW/kg) for the thick, binderless CNT electrode. © 2013 The Electrochemical Society. [DOI: 10.1149/2.020310jss] All rights reserved.

A novel nanoporous carbon/electrolyte hybrid material is reported for use in actuation. The nanoporous carbon matrix provides a 3D network that combines mechanical strength, light weight, and low cost with an extremely high surface area. In contrast to lower dimensional nanomaterials, the nanoporous carbon matrix can be prepared in the form of macroscopic monolithic samples that can be loaded in compression. The hybrid material is formed by infiltrating the free internal pore volume of the carbon with an electrolyte. Actuation is prompted by polarizing the internal interfaces via an applied electric bias. It is found that the strain amplitude is proportional to the Brunauer-Emmett-Teller (BET) mass specific surface area, with reversible volume strain amplitudes up to the exceptionally high value of 6.6%. The mass-specific strain energy density compares favorably to reported values for piezoceramics and for nanoporous metal actuators.

Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

The ultra low density, high electrical conductivity, and mechanical robustness of carbon nanotube aerogels (SWNT-CA) make them ideal scaffolds around which to create novel composites. Here we report on the synthesis and characterization of oxide/carbon nanotube composites fabricated through the sol–gel deposition of oxide coatings (SiO2, SnO2 or TiO2) on SWNT-CA. The porous network of the SWNT-CA scaffold is retained after the deposition and drying process. In each case, the deposited oxide appears to form a uniform coating on the surfaces of aerogel ligaments. The composite materials exhibit high electrical conductivity (∼100 S/m) and enhanced mechanical properties relative to the uncoated SWNT-CA support. In addition, the oxide/SWNT-CA composites possess high surface areas (as high as 742 m2/g) and large mesopore volumes (as high as 2.2 cm3/g). This approach offers viability in engineering new oxide/CNT composites for applications such as energy storage, sensing, and catalysis.

Developing three-dimensional (3D) graphene assemblies with properties similar to those individual graphene sheets is a promising strategy for graphene-based electrodes. Typically, the synthesis of 3D graphene assemblies relies on van der Waals forces for holding the graphene sheets together, resulting in bulk properties that do not reflect those reported for individual graphene sheets. Here, we report the use of sol-gel chemistry to introduce chemical bonding between the graphene sheets and control the bulk properties of graphene-based aerogels. Adjusting synthetic parameters allows a wide range of control over surface area, pore volume, and pore size, as well as the nature of the chemical cross-links (sp(2) vs sp(3)). The bulk properties of the graphene-based aerogels represent a significant step toward realizing the properties of individual graphene sheets in a 3D assembly with surface areas approaching the theoretical value of an individual sheet.

The effects of nanoconfinement on the structural phase transition, H2 release and uptake, and the emission of toxic diborane (B2H6) on desorption of LiBH4 have been comprehensively investigated in the presence of various porous hard carbon templates at a variety of pore sizes. Calorimetry signatures of both the structural phase transition and melting of nanoconfined LiBH4 shifted to a lower temperature with respect to the bulk, finally vanishing below a pore size around 4 nm. The desorption of LiBH4 confined in these nanoporous carbons shows a systematic and monotonic decrease in the desorption temperature and concomitantly, mass spectroscopic analysis indicated a gradual reduction of the partial pressure of B2H6 with decreasing pore size, suggesting that formation of stable closoborane salts may be avoided by interrupting the reaction pathway. This represents a major breakthrough in the reversibility of boron-based hydrogen storage systems, where capacity is lost in the formation of stable B−H species on...

We demonstrated the synthesis of high surface area ZnO–ACA composites with well-crystallized ZnO nanoparticles by simple sol–gel process. The coverage of ZnO nanoparticles on the carbon framework of ACA is very uniform, with no exposed carbon framework. Thermal removal of carbon produces ZnO replica structure mimicking the original ACA framework.

Here, we present the synthesis and characterization of low-density single-walled carbon nanotube-based aerogels (SWNT-CA). Aerogels with varying nanotube loading (0–55 wt.%) and density (20–350 mg cm −3 ) were fabricated and characterized by four-probe method, electron microscopy, Raman spectroscopy and nitrogen porosimetry. Several properties of the SWNT-CAs were highly dependent upon nanotube loading. At nanotube loadings of 55 wt.%, shrinkage of the aerogel monoliths during carbonization and drying was almost completely eliminated. Electrical conductivities are improved by an order of magnitude for the SWNT-CA (55 wt.% nanotubes) compared to those of foams without nanotubes. Surface areas as high as 184 m 2 g −1 were achieved for SWNT-CAs with greater than 20 wt.% nanotube loading.

We report that nanoparticulate zirconia (ZrO(2)) catalyzes both growth of single-wall and multiwall carbon nanotubes (CNTs) by thermal chemical vapor deposition (CVD) and graphitization of solid amorphous carbon. We observe that silica-, silicon nitride-, and alumina-supported zirconia on silicon nucleates single- and multiwall carbon nanotubes upon exposure to hydrocarbons at moderate temperatures (750 degrees C). High-pressure, time-resolved X-ray photoelectron spectroscopy (XPS) of these substrates during carbon nanotube nucleation and growth shows that the zirconia catalyst neither reduces to a metal nor forms a carbide. Point-localized energy-dispersive X-ray spectroscopy (EDAX) using scanning transmission electron microscopy (STEM) confirms catalyst nanoparticles attached to CNTs are zirconia. We also observe that carbon aerogels prepared through pyrolysis of a Zr(IV)-containing resorcinol-formaldehyde polymer aerogel precursor at 800 degrees C contain fullerenic cage structures absent in undoped carbon aerogels. Zirconia nanoparticles embedded in these carbon aerogels are further observed to act as nucleation sites for multiwall carbon nanotube growth upon exposure to hydrocarbons at CVD growth temperatures. Our study unambiguously demonstrates that a nonmetallic catalyst can catalyze CNT growth by thermal CVD while remaining in an oxidized state and provides new insight into the interactions between nanoparticulate metal oxides and carbon at elevated temperatures.

Mixed aromatic-alkyne molecules have been designed to scavenge and remove hydrogen in unwanted situations. Such materials in powdered solid form are mixed with catalytic metal particles that dissociate H2 molecules into H radicals. However, many details of the H uptake mechanism remain poorly understood. Here we report molecular modeling studies, using both classical force fields and first-principles density functional theory, aimed at providing enhanced understanding of the uptake kinetics. Such insights are important in improving the H scavenging efficiency of the present and next-generation materials, as well as to provide molecular-scale interpretation of supporting experiments.

This report demonstrates a chemical functionalization method for controlling TiO2 ALD in low-density nanoporous materials, i.e., aerogels. Functionalization of silica aerogel with trimethylsilane is shown to inhibit TiO2 growth on the aerogel via ALD. A proposed mechanism for the deactivation effect is the blocking of surface functional groups, such as hydroxyl (OH) moieties, which serve as chemisorption sites for the ALD precursors and hence are essential for nucleating the deposition process. Subsequent modification of the aerogel functionalization through the selective removal of hydrocarbon groups via heat or plasma treatment reactivates the aerogel towards deposition, thereby resulting in TiO2 growth. The results presented here demonstrate the use of ALD as a selective tool for creating novel nanoporous materials.

We report the synthesis and characterization of novel elastomeric nanocomposites containing polyhedral oligomeric silsesquioxanes (POSS) as both the cross-linker and filler within a polydimethylsiloxane (PDMS) polymer matrix. These polymer composites were prepared through the reaction of octasilane-POSS (OS-POSS) with vinyl-terminated PDMS chains using hydrosilylation chemistry. In addition, larger super-POSS cross-linkers, consisting of two pendant hepta(isobutyl)POSS molecules attached to a central octasilane-POSS core, were also used in the fabrication of the PDMS composites. The chemical incorporation of these POSS cross-linkers into the PDMS network was verified by solid-state 1 H magic angle spinning NMR. Based on dynamic mechanical analysis, the PDMS nanocomposites prepared with the octafunctional OS-POSS cross-linker exhibited enhanced mechanical properties relative to polymer systems prepared with the tetrafunctional TDSS cross-linker at equivalent loading levels. The observed improvements in mechanical properties can be attributed to the increased dimensionality of the POSS cross-linker. The PDMS elastomers synthesized from the larger super-POSS molecule showed improved mechanical properties relative to both the TDSS and OS-POSS composites due to the increased volume-fraction of POSS filler in the polymer matrix.

Atomic layer deposition (ALD) appears to be uniquely suited for coating substrates with ultrahigh aspect ratios (or similar 10(3)), including nanoporous solids. Here, we study the ALD of Cu and Cu3N on the inner surfaces of low-density nanoporous silica aerogel monoliths. Results show that Cu depth profiles in nanoporous monoliths are limited not only by Knudsen diffusion of heavier precursor molecules into the pores, as currently believed, but also by other processes such as the interaction of precursor and reaction product molecules with pore walls. Similar behavior has also been observed for Fe, Ru, and Pt ALD on aerogels. On the basis of these results, we discuss design rules for ALD precursors specifically geared for coating nanoporous solids.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

Monolithic nanocrystalline anatase titania aerogels are synthesized by the epoxide sol–gel method followed by thermal annealing at 550 ° C. These aerogels are formed by ∼ 10–20 nm size anatase nanoparticles which are randomly oriented and interconnected into an open-cell solid network. Aerogel monoliths have an apparent density of ∼ 10% and a surface area of ∼ 100 m 2 g −1 . High-resolution transmission electron microscopy and soft X-ray absorption near-edge structure spectroscopy reveal good crystallinity of the anatase nanoparticles forming the aerogel skeleton.

In this article, we report a detailed study of resorcinol-formaldehyde (RF) aerogels prepared under different processing conditions, [resorcinol]/[catalyst] (R/C) ratios in the starting sol-gel solutions, using continuous flow hyperpolarized (129)Xe NMR in combination with solid-state (13)C and two-dimensional wide-line separation (2D-WISE) NMR techniques. The degree of polymerization and the mobility of the cross-linking functional groups in RF aerogels are examined and correlated with the R/C ratios. The origin of different adsorption regions is evaluated using both coadsorption of chloroform and 2D EXSY (129)Xe NMR. A hierarchical set of Xe exchange processes in RF aerogels is found using 2D EXSY (129)Xe NMR. The exchange of Xe gas follows the sequence (from fastest to slowest): mesopores with free gas, gas in meso- and micropores, free gas with micropores, and, finally, among micropore sites. The volume-to-surface-area (V(g)/S) ratios for aerogels are measured for the first time without the use of geometric models. The V(g)/S parameter, which is related both to the geometry and the interconnectivity of the pore space, has been found to correlate strongly with the R/C ratio and exhibits an unusually large span: an increase in the R/C ratio from 50 to 500 results in about a 5-fold rise in V(g)/S.

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...

We describe a general procedure for the synthesis of ordered macroporous resorcinol–formaldehyde (RF) and carbon aerogels (CA) in which colloidal crystals of polystyrene (PS) spheres were used as templates. With this approach, ordered arrays of PS spheres are infused with a resorcinol–formaldehyde sol–gel solution. Following gelation of the sol, the RF/PS composite was washed with toluene to remove the template. Periodic macroporous RF aerogels were obtained after supercritical drying with liquid carbon dioxide. These materials can then be carbonized under a nitrogen atmosphere to afford the corresponding macroporous CAs. Scanning electron microscopic examination shows that both the organic and carbon materials consist of many hexagonally ordered domains of spherical cavities with different crystal orientations, reflecting the symmetry of the original PS template.

We report the synthesis and characterization for the first example of a low-density nanocrystalline thoria aerogel. The monolithic aerogels were prepared through the solgel polymerization of hydrated thorium nitrate in ethanol using ammonium hydroxide and propylene oxide as gelation initiators. The dried ThO{sub 2} aerogel was characterized by high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption/desorption analyses. The aerogel network was determined to be composed of spherical primary particles with features in the 5-20 nm range. These particles were also determined to be highly crystalline as evidenced by the higher magnification TEM examination. The thoria aerogel possesses high surface area (120 m{sup 2}/g) and pore diameters in the micro- and mesoporous range.

The carbon aerogels prepared by a new method through gelation and supercritical drying in isopropanol were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and a surface area analyzer. Their chemical structure, morphology, and pore structure are discussed. We found that all of these carbon aerogel (CA-IPA) samples have almost the same carbon and oxygen elemental states, as well as similar oxygen-containing groups. The curve fitting of the C1s XPS spectra of the samples for characterizing oxygen-containing surface groups can be performed by assuming the peak type to be a Gaussian–Lorentzian Cross Product, but we cannot obtain good results using a Gaussian lineshape. When the mass density of the CA-IPA decreases, the mesopores and macropores of the samples are found to grow, but the size and the shape of individual carbon nanoparticles in various CA-IPA samples do not apparently change. The micropore volume of the CA-IPA samples increases with a decrease in the mass density, while the mesopore volume has a maximum at a certain mass density. The CA-IPA samples have a very narrow micropore distribution at about 0.5 nm. The mesopore distribution of the CA-IPA is widened and the average pore size increases as the mass density of the sample decreases. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3060–3067, 2004

Activated carbon fiber/carbon aerogel (ACF/CA) composites were fabricated by gelling a mixture of ACF and resorcinol and furfural, followed by supercritical drying of the mixture in isopropanol. The product then went through carbonization in a nitrogen atmosphere. The fabrication conditions, such as the mass content of R–F, the content of the ACF added, and the gelation temperature, were explored. The textures and pore structures of the ACF/CA composites thus obtained were characterized using transmission electron microscopy, scanning electron microscopy, and a surface area analyzer. The mechanical properties of the samples were assessed primarily through compressive tests. The experimental results indicated that the added ACF disperses uniformly in the resulting ACF/CA composites. The carbon matrix of the ACF/CA composites also consisted of interconnected carbon nanoparticles with sizes in the range of 20 to 30 nm. The ACFs can reinforce the related carbon aerogels when they originally have low mass density and are weak in mechanical strength. When large amounts of ACF were added to the composites, the micropore area and micropore volume of the composites increased, but their external surface area decreased. The mesopore volumes and the related diameters and mesopore size distributions of the ACF/CA composites were mainly affected by the mass density of the composites. The micropore sizes of all the composites were sharply concentrated at about 0.5 nm.