One-Step Synthesis of Sulfur-Doped Nanoporous Carbons from Lignin with Ultra-High Surface Area, Sulfur Content and CO2 Adsorption Capacity.

Lignin is the second-most available biopolymer in nature. In this work, lignin was employed as the carbon precursor for the one-step synthesis of sulfur-doped nanoporous carbons. Sulfur-doped nanoporous carbons have several applications in scientific and technological sectors. In order to synthesize sulfur-doped nanoporous carbons from lignin, sodium thiosulfate was employed as a sulfurizing agent and potassium hydroxide as the activating agent to create porosity. The resultant carbons were characterized by pore textural properties, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The nanoporous carbons possess BET surface areas of 741-3626 m2/g and a total pore volume of 0.5-1.74 cm3/g. The BET surface area of the carbon was one of the highest that was reported for any carbon-based materials. The sulfur contents of the carbons are 1-12.6 at.%, and the key functionalities include S=C, S-C=O, and SOx. The adsorption isotherms of three gases, CO2, CH4, and N2, were measured at 298 K, with pressure up to 1 bar. In all the carbons, the adsorbed amount was highest for CO2, followed by CH4 and N2. The equilibrium uptake capacity for CO2 was as high as ~11 mmol/g at 298 K and 760 torr, which is likely the highest among all the porous carbon-based materials reported so far. Ideally adsorbed solution theory (IAST) was employed to calculate the selectivity for CO2/N2, CO2/CH4, and CH4/N2, and some of the carbons reported a very high selectivity value. The overall results suggest that these carbons can potentially be used for gas separation purposes.

Direct Ink 3D Printing of Porous Carbon Monoliths for Gas Separations.

Additive manufacturing or 3D printing is the advanced method of manufacturing monolithic adsorbent materials. Unlike beads or pellets, 3D monolithic adsorbents possess the advantages of widespread structural varieties, low heat and mass transfer resistance, and low channeling of fluids. Despite a large volume of research on 3D printing of adsorbents having been reported, such studies on porous carbons are highly limited. In this work, we have reported direct ink 3D printing of porous carbon; the ink consisted of commercial activated carbon, a gel of poly(4-vinylphenol) and Pluronic F127 as plasticizer, and bentonite as the binder. The 3D printing was performed in a commercial 3D printer that has been extensively modified in the lab. Upon 3D printing and carbonization, the resultant 3D printed porous carbon demonstrated a stable structure with a BET area of 400 m2/g and a total pore volume of 0.27 cm3/g. The isotherms of six pure-component gases, CO2, CH4, C2H6, N2, CO, and H2, were measured on this carbon monolith at 298 K and pressure up to 1 bar. The selectivity of four gas pairs, C2H6/CH4, CH4/N2, CO/H2, and CO2/N2, was calculated by Ideally Adsorbed Solution Theory (IAST) and reported. Ten continuous cycles of adsorption and desorption of CO2 on this carbon confirmed no loss of working capacity of the adsorbent.

Understanding the Adsorption of Rare-Earth Elements in Oligo-Grafted Mesoporous Carbon.

Rare-earth elements (REEs) are 17 elements of the periodic table primarily consisting of lanthanides. In modern society, the usage of REEs is ubiquitous in almost all modern gadgets and therefore efficient recovery and separation of REEs are of high importance. Selective adsorption and chelation of REEs in solid sorbents is a unique and sustainable process for their recovery. In this work, single-stranded oligos with 100 units of thymine were grafted onto carboxylated mesoporous carbon to synthesize a sorbent with phosphorus and oxygen functionalities. The sorbent was characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Three different REEs with varying atomic radii and densities, Lu, Dy, and La, were adsorbed onto the carbon from aqueous solutions. It was observed that the adsorbed amounts increased with the increase in the atomic radius or decrease in the atomic density. Calculation of the distribution coefficients for all the equilibrium adsorption amounts suggested that adsorption is more effective in the lower concentration region. The L3-edge X-ray absorption near-edge structure confirmed a 3+ oxidation state of REEs in the adsorbed phase. Extended X-ray absorption fine structure (EXAFS) confirmed the binding of REEs with oxygen functionalities in the adsorbed phase. The radial distribution functions calculated from the EXAFS data suggest a longer RE-O distance for La compared to those for Lu and Dy. The coordination numbers and Debye-Waller factors have typical values of about 8-9 atoms and 0.01-0.02 Å2, respectively.

Elucidating the mechanisms of Paraffin-Olefin separations using nanoporous adsorbents: An overview.

Light olefins are the precursors of all modern-day plastics. Olefin is always mixed with paraffins in the time of production, and therefore it needs to be separated from paraffins to produce polymer-grade olefin. The state-of-the-art separation technique, cryogenic distillation, is highly expensive and hazardous. Adsorption could be a novel, sustainable, and inexpensive separation strategy, provided a suitable adsorbent can be designed. There are different types of mechanisms that were harnessed for the separation of olefins by adsorption, and in this review, we have focused our discussion on those mechanisms. These mechanisms include, (a) Affinity-based separation, like pi complexation and hydrogen bonding, (b) Separation based on pore size and shape, like size-exclusion and gate-opening effect, and (c) Non-equilibrium separation, like kinetic separation. In this review, we have elaborated each of the separation strategies from the fundamental level and explained their roles in the separation processes of different types of paraffins and olefins.

Adsorption of Rare Earth Elements onto DNA-Functionalized Mesoporous Carbon.

The recovery and separation of rare earth elements (REEs) are of national importance owing to the specific usages, high demand, and low supply of these elements. In this research, we have investigated the adsorption of rare earth elements onto DNA-functionalized mesoporous carbons with a BET surface area of 605 m2/g and a median mesopore width of 48 Å. Three types of single-stranded DNA, one with 100 base units of thymine, another with 20 units of thymine, and the third, a 2000 unit long DNA from salmon milt were grafted on the carboxylated mesoporous carbon surface. All of the DNA-functionalized mesoporous carbons demonstrated higher adsorption of REEs compared to pristine mesoporous carbon and DNA grafted with 100 units of thymine demonstrated slightly higher adsorbed amounts compared to others. Pure neodymium (Nd(III)) adsorption in the aqueous phase demonstrated an adsorbed amount of 110.4 mg/g with respect to the initial concentration of 500 mg/g. A pH variation study with pure Nd(III) demonstrated that the adsorbed amount is higher at elevated pH compared to that at lower pH, thereby suggesting possible recovery at lower pH. Adsorption of a mixture of 16 REEs, including Sc, Lu, Tm, Yb, Er, Ho, Tb, Dy, Y, Eu, Gd, Sm, Ce, Nd, Pr, and La revealed that the adsorbed amount increased with an increase in the atomic weight and metallic radii of elements within the lanthanides. The calculation of the distribution coefficients for all of the equilibrium adsorption amounts suggested that adsorption is more effective in the lower concentration region. The Nd L3-edge X-ray absorption near edge structure (XANES) confirmed a 3+ oxidation state of Nd in the adsorbed phase. The extended X-ray absorption fine structure (EXAFS) confirmed the local atomic structure relaxation of Nd complexes in the adsorbed phase and shortening of the Nd-O bond distance by about 0.03-0.04 Å, which may be associated with their local complexation at the carbon surface.

Electrospun, flexible and reusable nanofiber mat of graphitic carbon nitride: Photocatalytic reduction of hexavalent chromium.

Nanofiber mat of graphitic carbon nitride (g-C3N4) was fabricated from g-C3N4/polyvinylidene fluoride (PVDF) composite using an electrospinning technique. The mat was characterized with SEM, AFM, XRD, FTIR and photoluminescence (PL) spectroscopy. This nanofiber mat is flexible and can be folded or rolled without losing any structural integrity. The nanofiber mat also demonstrates self-cleaning properties in aqueous medium as demonstrated with two dyes, methylene blue and rhodamine B. Hexavalent chromium was successfully reduced by the nanofiber mat of g-C3N4 under visible light. Although the rate of reduction of Cr(VI) was very slow in presence of nanofiber mat of g-C3N4 alone, it was enhanced significantly in presence of trace amounts (0.3%) formic acid. Formic acid played the dual role of hole scavenging agent of g-C3N4 to make the photogenerated electrons more available to the reaction and generating H2 and CO in the system that can also directly reduce Cr(VI) onto Cr(III). The nanofiber mat demonstrated excellent cyclability for photocatalytic reduction of Cr(VI) and self-cleaning properties in presence of visible light.

Soft-Templating of Sulfur and Iron Dual-Doped Mesoporous Carbons: Lead Adsorption in Mixtures.

Lead pollution in drinking water is one of the most common problems worldwide. In this research, sulfur and iron dual-doped mesoporous carbons are synthesized by soft-templating with sulfur content 4.4-6.1 atom% and iron content 7.8-9 atom%. Sulfur functionalities of the carbons are expected to enhance the affinity of the carbon toward lead whereas iron content is expected to separate the carbon from water owing to its magnetic properties. All the carbons were characterized by pore textural properties, x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). In order to study the Pb(II) removal efficiently of this carbon in competitive mode and to mimic the real-world use, one additional heavy-metal, including Cr(III), and four other commonly occurring metals-Na(I), K(I), Ca(II) and Fe (III)-are added with lead prior to adsorption experiments. It was observed that Pb(II) adsorption capacity of this carbon was not influenced by the presence of other metals. A highly elevated concentration of Na(I), K(I), Ca(II) and Fe(III) in the eluting solution compared to the initial dose suggested possible leaching of those metals from other salts as impurities, water source or even from the carbon itself, although the XPS analysis of the carbon confirmed negligible adsorption of those metals in carbon. From the equilibrium and kinetic data of adsorption, few parameters have been calculated, including distribution coefficient, diffusive time constant and pseudosecond order rate constant. The overall results suggest that these iron and sulfur dual-doped mesoporous carbons can serve as potential adsorbents for removal of lead from drinking water in the presence of other competing metals.

Photocatalytic and photo-fenton activity of iron oxide-doped carbon nitride in 3D printed and LED driven photon concentrator.

We have synthesized iron oxide doped carbon nitride with 0.5 to 2 wt.% iron oxide and characterized by XPS, TGA, FTIR, SEM, photoluminescence spectroscopy and photoelectrochemical measurements. A herbicide, dicamba was employed as model organic pollutant for degradation in presence with the catalyst and hydrogen peroxide. A 3D printed photon concentrator with two chips on board (COB) LEDs with visible light spectra and two complex parabolic mirror surfaces was used as photo-reactor. The findings revealed that both photocurrent and degradation of dicamba were functions of light intensity and concentrator geometry. The rapid degradation of dicamba can be attributed to the holistic and individual actions of structural components of the photocatalyst. Four distinct phenomena, including photocatalytic activity of carbon nitride, quenching of electron/hole pairs and generation of additional reactive hydroxyl radicals by hydrogen peroxide, Fenton and photo-Fenton activity of iron oxide component of carbon nitride in presence of hydrogen peroxide and photocatalytic activity of iron oxide alone in conjuncture with carbon nitride can contribute to the overall photocatalytic activity of the system. Liquid Chromatography-Mass spectrometry (LCMS) analysis of the degradation products showed loss of chlorine from the aromatic ring and evidence of free radical addition reactions in the course of photocatalysis.

One-step conversion of agro-wastes to nanoporous carbons: Role in separation of greenhouse gases.

Highly microporous carbons have been synthesized from four types of agro-wastes of lignin, walnut shells, orange peels and apricot seeds by one-step carbonization/activation with potassium hydroxide (KOH) in varying ratios. The resultant carbons demonstrated BET specific surface areas of 727-2254 m2/g, and total pore volumes 0.34-1.14 cm3/g. These are higher than the majority of agro-waste derived carbons reported in the literature. For all the carbons, CO2 adsorption at 298 K was higher than SF6 followed by N2 suggesting a possible separation of CO2 and SF6 from N2. The adsorbed amounts of CO2 at 298 K and 273 K and at pressures up to 760 Torr were 7.24 and 9.4 mmol/g, respectively which, to the best of our knowledge, are the highest CO2 uptakes in these temperatures by any carbon material reported so far. For all the gases, selectivity, mixed adsorption isotherms and adsorption breakthrough have been simulated from experimental data.

Synthesis of Nitrogen and Sulfur Codoped Nanoporous Carbons from Algae: Role in CO2 Separation.

Nitrogen and sulfur codoped and completely renewable carbons were synthesized from two types of algae, Spirulina Platensis and Chlorella Vulgaris, without any additional nitrogen fixation reaction. The type of activation agents, char-forming temperature, activation agent-to-char ratio, and activation temperature were all varied to optimize the reaction conditions for this synthesis. The maximum Brunauer-Emmett-Teller surface area and total pore volumes of the carbons were 2685 m2/g and 1.4 cm3/g, respectively. The nitrogen and sulfur contents of the carbons were in the range of 0.9-5.69 at. % and 0.05-0.2 at. %, respectively. The key nitrogen functionalities were pyridinic, amino, and pyridonic/pyrrolic groups, whereas the key sulfur functionalities were S-C, O-S-C, and SO x groups. CO2 adsorption isotherms were measured at 273, 298, and 313 K, and the ideal adsorbed solution theory was employed to calculate the selectivity of adsorption of CO2 over N2 and simulate binary adsorption isotherms. The adsorption results demonstrated that the CO2 adsorption amount and the heat of CO2 adsorption were higher for carbons with higher nitrogen content, confirming the influence of nitrogen functionality in CO2 adsorption. The overall results suggested that these algae-derived renewable carbons can serve as potential adsorbents for CO2 separation from N2.

Nanoporous Boron Nitride as Exceptionally Thermally Stable Adsorbent: Role in Efficient Separation of Light Hydrocarbons.

In this work, nanoporous boron nitride sample was synthesized with a Brunauer-Emmett-Teller (BET) surface area of 1360 m2/g and particle size 5-7 µm. The boron nitride was characterized with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron microscopy (TEM and SEM). Thermogravimetric analysis (TGA) under nitrogen and air and subsequent analysis with XPS and XRD suggested that its structure is stable in air up to 800 °C and in nitrogen up to 1050 °C, which is higher than most of the common adsorbents reported so far. Nitrogen and hydrocarbon adsorption at 298 K and pressure up to 1 bar suggested that all hydrocarbon adsorption amounts were higher than that of nitrogen and the adsorbed amount of hydrocarbon increases with an increase in its molecular weight. The kinetics of adsorption data suggested that adsorption becomes slower with the increase in molecular weight of hydrocarbons. The equilibrium data suggested that that boron nitride is selective to paraffins in a paraffin-olefin mixture and hence may act as an "olefin generator". The ideal adsorbed solution theory (IAST)-based selectivity for CH4/N2, C2H6/CH4, and C3H8/C3H6 was very high and probably higher than the majority of adsorbents reported in the literature. IAST-based calculations were also employed to simulate the binary mixture adsorption data for the gas pairs of CH4/N2, C2H6/CH4, C2H6/C2H4, and C3H8/C3H6. Finally, a simple mathematical model was employed to simulate the breakthrough behavior of the above-mentioned four gas pairs in a dynamic column experiment. The overall results suggest that nanoporous boron nitride can be used as a potential adsorbent for light hydrocarbon separation.

Noncompetitive and Competitive Adsorption of Heavy Metals in Sulfur-Functionalized Ordered Mesoporous Carbon.

In this work, sulfur-functionalized ordered mesoporous carbons were synthesized by activating the soft-templated mesoporous carbons with sulfur bearing salts that simultaneously enhanced the surface area and introduced sulfur functionalities onto the parent carbon surface. XPS analysis showed that sulfur content within the mesoporous carbons were between 8.2% and 12.9%. The sulfur functionalities include C-S, C═S, -COS, and SOx. SEM images confirmed the ordered mesoporosity within the material. The BET surface areas of the sulfur-functionalized ordered mesoporous carbons range from 837 to 2865 m2/g with total pore volume of 0.71-2.3 cm3/g. The carbon with highest sulfur functionality was examined for aqueous phase adsorption of mercury (as HgCl2), lead (as Pb(NO3)2), cadmium (as CdCl2), and nickel (as NiCl2) ions in both noncompetitive and competitive mode. Under noncompetitive mode and at a pH greater than 7.0 the affinity of sulfur-functionalized carbons toward heavy metals were in the order of Hg > Pb > Cd > Ni. At lower pH, the adsorbent switched its affinity between Pb and Cd. In the noncompetitive mode, Hg and Pb adsorption showed a strong pH dependency whereas Cd and Ni adsorption did not demonstrate a significant influence of pH. The distribution coefficient for noncompetitive adsorption was in the range of 2448-4000 mL/g for Hg, 290-1990 mL/g for Pb, 550-560 mL/g for Cd, and 115-147 for Ni. The kinetics of adsorption suggested a pseudo-second-order model fits better than other models for all the metals. XPS analysis of metal-adsorption carbons suggested that 7-8% of the adsorbed Hg was converted to HgSO4, 14% and 2% of Pb was converted to PbSO4 and PbS/PbO, respectively, and 5% Cd was converted to CdSO4. Ni was below the detection limit for XPS. Overall results suggested these carbon materials might be useful for the separation of heavy metals.

A study on the cytotoxicity of carbon-based materials.

With an aim to understand the origin and key contributing factors towards carbon-induced cytotoxicity, we have studied five different carbon samples with diverse surface area, pore width, shape and size, conductivity and surface functionality. All the carbon materials were characterized with surface area and pore size distribution, X-ray photoelectron spectroscopy (XPS) and electron microscopic imaging. We performed cytotoxicity study in Caco-2 cells by colorimetric assay, oxidative stress analysis by reactive oxygen species (ROS) detection, cellular metabolic activity measurement by adenosine triphosphate (ATP) depletion and visualization of cellular internalization by TEM imaging. The carbon materials demonstrated a varying degree of cytotoxicity in contact with Caco-2 cells. The lowest cell survival rate was observed for nanographene, which possessed the minimal size amongst all the carbon samples under this study. None of the carbons induced oxidative stress to the cells as indicated by the ROS generation results. Cellular metabolic activity study revealed that the carbon materials caused ATP depletion in cells and nanographene caused the highest depletion. Visual observation by TEM imaging indicated the cellular internalization of nanographene. This study confirmed that the size is the key cause of carbon-induced cytotoxicity and it is probably caused by the ATP depletion within the cell.

Postextraction Separation, On-Board Storage, and Catalytic Conversion of Methane in Natural Gas: A Review.

In today's perspective, natural gas has gained considerable attention, due to its low emission, indigenous availability, and improvement in the extraction technology. Upon extraction, it undergoes several purification protocols including dehydration, sweetening, and inert rejection. Although purification is a commercially established technology, several drawbacks of the current process provide an essential impetus for developing newer separation protocols, most importantly, adsorption and membrane separation. This Review summarizes the needs of natural gas separation, gives an overview of the current technology, and provides a detailed discussion of the progress in research on separation and purification of natural gas including the benefits and drawbacks of each of the processes. The transportation sector is another growing sector of natural gas utilization, and it requires an efficient and safe on-board storage system. Compressed natural gas (CNG) and liquefied natural gas (LNG) are the most common forms in which natural gas can be stored. Adsorbed natural gas (ANG) is an alternate storage system of natural gas, which is advantageous as compared to CNG and LNG in terms of safety and also in terms of temperature and pressure requirements. This Review provides a detailed discussion on ANG along with computation predictions. The catalytic conversion of methane to different useful chemicals including syngas, methanol, formaldehyde, dimethyl ether, heavier hydrocarbons, aromatics, and hydrogen is also reviewed. Finally, direct utilization of methane onto fuel cells is also discussed.

Biocompatibility of soft-templated mesoporous carbons.

Soft-templated mesoporous carbon is morphologically a non-nano type of carbon. It is a relatively newer variety of biomaterial, which has already demonstrated its successful role in drug delivery applications. To investigate the toxicity and biocompatibility, we introduced three types of mesoporous carbons with varying synthesis conditions and pore textural properties. We compared the Brunauer-Emmett-Teller (BET) surface area and pore width and performed cytotoxicity experiments with HeLa cells, cell viability studies with fibroblast cells and hemocomapatibility studies. Cytotoxicity tests reveal that two of the carbons are not cytotoxic, with cell survival over 90%. The mesoporous carbon with the highest surface area showed slight toxicity (∼ 70% cell survival) at the highest carbon concentration of 500 µg/mL. Fibroblast cell viability assays suggested high and constant viability of over 98% after 3 days with no apparent relation with materials property and good visible cell-carbon compatibility. No hemolysis (<1%) was confirmed for all the carbon materials. Protein adsorption experiments with bovine serum albumin (BSA) and fibrinogen revealed a lower protein binding capacity of 0.2-0.6 mg/m(2) and 2-4 mg/m(2) for BSA and fibrinogen, respectively, with lower binding associated with an increase in surface area. The results of this study confirm the biocompatibility of soft-templated mesoporous carbons.

Studies on supercapacitor electrode material from activated lignin-derived mesoporous carbon.

We synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and then activated the carbon through physical and chemical methods to obtain activated mesoporous carbon. The activated mesoporous carbons exhibited 1.5- to 6-fold increases in porosity with a maximum Brunauer-Emmett-Teller (BET) specific surface area of 1148 m(2)/g and a pore volume of 1.0 cm(3)/g. Both physical and chemical activation enhanced the mesoporosity along with significant microporosity. Plots of cyclic voltammetric data with the capacitor electrode made from these carbons showed an almost rectangular curve depicting the behavior of ideal double-layer capacitance. Although the pristine mesoporous carbon exhibited a range of surface-area-based capacitance similar to that of other known carbon-based supercapacitors, activation decreased the surface-area-based specific capacitance and enhanced the gravimetric specific capacitance of the mesoporous carbons. A vertical tail in the lower-frequency domain of the Nyquist plot provided additional evidence of good supercapacitor behavior for the activated mesoporous carbons. We have modeled the equivalent circuit of the Nyquist plot with the help of two constant phase elements (CPE). Our work demonstrated that biomass-derived mesoporous carbon materials continue to show potential for use in specific electrochemical applications.

Sustainable mesoporous carbons as storage and controlled-delivery media for functional molecules.

Here, we report the synthesis of surfactant-templated mesoporous carbons from lignin, which is a biomass-derived polymeric precursor, and their potential use as a controlled-release medium for functional molecules such as pharmaceuticals. To the best of our knowledge, this is the first report on the use of lignin for chemical-activation-free synthesis of functional mesoporous carbon. The synthesized carbons possess the pore widths within the range of 2.5-12.0 nm. In this series of mesoporous carbons, our best result demonstrates a Brunauer-Emmett-Teller (BET) surface area of 418 m(2)/g and a mesopore volume of 0.34 cm(3)/g, which is twice the micropore volume in this carbon. Because of the dominant mesoporosity, this engineered carbon demonstrates adsorption and controlled release of a representative pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale utilization of these sustainable mesoporous carbons in applications involving adsorption, transport, and controlled release of functional molecules is desired for industrial processes that yield lignin as a coproduct.

Tetrahydrofuran-induced K and Li doping onto poly(furfuryl alcohol)-derived activated carbon (PFAC): influence on microstructure and H2 sorption properties.

We have doped poly(furfuryl alcohol)-derived activated carbon (PFAC) with two alkali metals, potassium (K) and lithium (Li), by previously reacting the metals with naphthalene in the presence of tetrahydrofuran (THF), followed by introducing them to pristine PFAC. The THF molecule causes a minor alteration of the microstructure of PFAC as confirmed by Raman spectra, X-ray diffraction, and pore textural analysis. Raman spectra and X-ray diffraction indicated a slight localized ordering toward the stacking defects of disordered carbon, as in PFAC, which can be attributed to the movement of THF molecules within the internal planes of graphene sheets. Pore textural analysis confirmed the lowering of the specific surface area and pore volume of both K- and Li-doped PFACs (BET SSA, 1378 m(2)/g (PFAC); 1252 m(2)/g (K-PFAC), 1081 m(2)/g (Li-PFAC)). Volumetric hydrogen adsorption measurements at temperatures of 298, 288, 273, and 77 K and pressures of up to 1 bar indicated the enhanced adsorption potential imposed by the presence of alkali metals, which can be reconfirmed by the elevated heats of adsorption of metal-doped PFACs (Li-PFAC, -(10-11) kJ/mol; K-PFAC, -(16-19) kJ/mol) compared to that of pristine PFAC (-9.6 kJ/mol).

Hydrogen confinement in carbon nanopores: extreme densification at ambient temperature.

In-situ small-angle neutron scattering studies of H(2) confined in small pores of polyfurfuryl alcohol-derived activated carbon at room temperature have provided for the first time its phase behavior in equilibrium with external H(2) at pressures up to 200 bar. The data were used to evaluate the density of the adsorbed fluid, which appears to be a function of both pore size and pressure and is comparable to the density of liquid H(2) in narrow nanopores at ∼200 bar. The surface-molecule interactions responsible for densification of H(2) within the pores create internal pressures that exceed the external gas pressure by a factor of up to ∼50, confirming the benefits of adsorptive storage over compressive storage. These results can be used to guide the development of new carbon adsorbents tailored for maximum H(2) storage capacities at near-ambient temperatures.

Hydrogen adsorption on Pd- and Ru-doped C60 fullerene at an ambient temperature.

Palladium- and ruthenium-doped C(60) fullerene compounds were synthesized by incipient wetness impregnation of C(60) fullerene with the corresponding metal acetylacetonate precursors. Transmission electron microscopy (TEM) imaging of the metal-doped C(60) fullerene samples showed different dispersion morphologies of palladium and ruthenium particles on the C(60) matrix. Raman spectra revealed a drastic decrease in peak intensity followed by disappearance of several bands indicating the distortion of the C(60) cage structure. The amorphous nature of the C(60) fullerene compounds was confirmed by the X-ray diffraction study. Hydrogen adsorption amount of 0.85 wt % and 0. 69 wt % on Pd-C(60) and Ru-C(60), respectively, as compared to 0.3 wt % on the pure C(60) fullerene were measured at 300 bar and 298 K. The enhancement in the hydrogen uptakes can be attributed to several factors, including adsorption of molecular H(2) on the defect sites, metallic hydride formation, spillover of hydrogen, and bond formation with atomic hydrogen with different active sites of carbon of host fullerene. The hydrogen adsorption isotherms are of type III and can be correlated by the Freundlich (for Ru-C(60)) and modified Oswin equations (for Pd-C(60) and pristine C(60)).