Search

This paper demonstrates that nanospace engineering of KOH activated carbon is possible by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. High specific surface areas, porosities, sub-nanometer (<1 nm) and supra-nanometer (1–5 nm) pore volumes are quantitatively controlled by a combination of KOH concentration and activation temperature. The process typically leads to a bimodal pore size distribution, with a large, approximately constant number of sub-nanometer pores and a variable number of supra-nanometer pores. We show how to control the number of supra-nanometer pores in a manner not achieved previously by chemical activation. The chemical mechanism underlying this control is studied by following the evolution of elemental composition, specific surface area, porosity, and pore size distribution during KOH activation and preceding H3PO4 activation. The oxygen, nitrogen, and hydrogen contents decrease during successive activation steps, creating a nanoporous carbon network with a porosity and surface area controllable for various applications, including gas storage. The formation of tunable sub-nanometer and supra-nanometer pores is validated by sub-critical nitrogen adsorption. Surface functional groups of KOH activated carbon are studied by microscopic infrared spectroscopy.

We report Fourier transform infrared spectroscopy (FTIR) studies of boron-doped activated carbons. The functional groups for hydrogen adsorption in these materials, the boron-related chemical bonds, are studied by comparing the activated carbon materials with and without boron doping. The activated carbon materials are prepared from corncob biomass waste feedstock through KOH activation, yielding adsorbents with a high surface area. Boron atoms are doped into the activated carbon by vapor deposition of decaborane up to a solubility of 6.8 wt.%. Extra boron atoms (2–3 wt.%) are located on the surface of the carbon matrix. Results from conventional FTIR show serious spectral broadenings and band overlaps. To overcome the spectral broadenings and band overlaps, the sample concentration is reduced to a very low weight percent (0.03%) of activated carbon in KBr, and spectra are acquired by using microscopic FTIR. Activated boron carbide is used as a reference material to validate the boron–carbon bond in the nanoporous materials. For activated carbon doped via vapor deposition of decaborane, the substitutions of carbon atoms with boron atoms is confirmed using microscopic FTIR through the appearance of boron–carbon bonds, although it cannot be observed with conventional FTIR.

The synthesis, characterization, and performance of a new low pressure, monolithic, activated carbon adsorbent developed for methane storage is discussed and compared to other adsorbents. The effect of particle packing density on the storage capacity of tanks filled with commercially available and developmental adsorbents is quantified. 20 kg of the developed monolithic material is tested using a custom built, 40 L, space conformable tank test assembly. The performance is found to be superior to metal organic frameworks and other activated carbons reported in literature based on high tank volumetric and gravimetric storage capacities. The developed material has a pore structure and external dimensions that allow for rapid adsorption/desorption with gas being able to reach the center of the 40 L tank within ∼3 s. The developed material delivers 151 V/V of methane between 35 bar and 1 bar in the 40 L tank. A continuous discharge flow rate of 2 g/s at 5 bar for a 10 gge system was demonstrated.

This paper covers the optimization of methane volumetric storage capacity by controlling the sub-nanometre (<1 nm) and supra-nanometre (1–5 nm) pore volumes. Nanospace engineering of KOH activated carbon generates an ideal structure for methane storage in which gas molecules are adsorbed as a high-density fluid by strong van der Waals forces into pores that are a few molecules in diameter. High specific surface areas, porosities, sub-nanometre (<1 nm) and supra-nanometre (1–5 nm) pore volumes are quantitatively selected by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. The formation of tuneable sub-nanometre and supra-nanometre pores is validated by sub-critical nitrogen adsorption. Aberration-corrected scanning transmission electron microscopy data show the atomic structure of high-surface-area activated carbon (2600 m2/g). While high surface area and high porosity are optimal for gravimetric methane storage, the results indicate that an exclusive sub-nanometre region, a low porosity and an acceptable surface area (approximately 2000 m2/g) are ideal for methane volumetric storage, storing 120 g CH4/l (184 vol/vol) at 35 bar and room temperature (22 °C). High-pressure methane isotherms up to 150 bar at 30, −25 and −50 °C on optimal activated carbons are presented. Methane volumetric storage capacity at 35 bar reaches 176 g/l (269 vol/vol) and 202 g/l (309 vol/vol) at −25 and −50 °C, respectively.

Carbons can be engineered to achieve exceptional storage capacities: the ALL-CRAFT (www.all-craft.missouri.edu) nanoporous carbon achieves gravimetric excess adsorption of 0.073 kg H2/kg C, gravimetric storage capacity of 0.106 kg H2/kg C, and volumetric storage capacity of 0.040 kg H2/l C (80 K, 100 bar). The nanopores generate high storage capacity by having: high surface area (2,600 m^2/g); high H2-wall interaction; and multi-layer H2 adsorption (cryogenic). We we show how the experimental characteristics of the ALL-CRAFT carbon correlate to the observed H2 storage, with help from theoretical considerations and GCMC simulations. The ALL-CRAFT carbon is composed of a large variety of pore sizes which generates substantial heterogeneity. We explain most features observed by considering superpositions of low- and high-binding energy sites (9 kJ and 5 kJ/mol), corresponding to wide and narrow (< 1 nm) pores. We further explain: exceptional low-temperature storage (in excess of the usual Chahine's rule); and absence of an excess adsorption peak (for 0 < P < 100 bar)

Activated carbons made from corn cob show promise as materials for high-capacity hydrogen storage. As part of our characterization of these materials, we are interested in learning how different production methods affect the adsorption energies. In this talk, we will present experimentally measured isosteric heats of adsorption for various activated carbons calculated using the Clausius-Clayperon equation and hydrogen isotherms at temperatures of 80 and 90K and pressures up to 100 bar measured on a volumetric instrument. We discuss differences observed between isosteric heats determined from Gibbs excess adsorption vs. absolute adsorption curves.

The Alliance for Collaborative Research in Alternative Fuel Technology (ALL-CRAFT) has been optimizing high surface area activated carbon nanospaces for high capacity hydrogen storage. Boron doped samples have been prepared by vapor deposition of decaborane. Neutron irradiation of Boron doped activated carbon was done at the University of Missouri Research Reactor (MURR). Ultrananopores created by alpha particle fission tracks from Boron-neutron capture alter the surface and the adsorption properties of activated Carbons. A detailed theoretical model of the creation and the structure of defects on graphene sheets was developed. BET surface areas, porosity, and pores size distributions of modified activated carbons were measured using sub-critical nitrogen isotherms. Hydrogen adsorption isotherms of irradiated samples were indicative of record fraction of high binding energies and record fraction of sub-nm pores compared to their unirradiated parent samples.

The Alliance for Collaborative Research in Alternative Fuel Technology (ALL-CRAFT) has developed activated carbons from corn cob as adsorbent materials for methane gas storage by physisorption at low pressures. KOH activated carbons were compressed into carbon monolith using chemical binders. High pressure methane isotherms up to 250 bar at room temperature on monolithic and powdered activated carbons were measured gravimetrically and volumetrically. Record methane storage capacities of 250 g CH4/kg carbon and 130 g CH4/liter carbon at 35 bar and 293 K have been achieved. BET surface area, porosity, and pore size distributions were measured from sub-critical nitrogen isotherms. Pore entrances were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A prototype adsorbed natural gas (ANG) tank, loaded with carbon monoliths, was tested in Kansas City.

Adsorption mechanism depends on adsorbent geometry. The most important factors defined by geometry are: the surface accessible for adsorption and the distribution of energy of adsorption. In a particular type of pores with walls built from graphene layer fragments, we observe a competition between these two factors: an increase of adsorption due to the additional adsorption surface introduced by the walls' edges and a decrease of adsorption uptake due to smaller adsorption energy near the edges. We present the results of Monte Carlo simulations of N2 and H2 adsorption in model, finite size carbon slit pores. This model mimics real carbon samples better than usually used infinite pore models, whatever is the assumed pore shape (slit-like, tubular, curved etc). In particular, it allows us to account for the adsorption at the pore edges, totally neglected in infinite models. We show that the contribution of edges to the total adsorption is not negligible: in smallest pores, with the diameters comparable with the pore width, the edge contribu-tion can be even equally or more important than that of the pore inside. We discuss and compare Monte Carlo simulations and DFT approach in similar pore geometries

Binding energy between adsorbent and adsorbate strongly affects the mechanism of adsorption. Porous systems are usually characterized by a distribution of this energy, which is not easy to determine experimentally. A coupled experimental-simulation procedure to estimate binding energy directly from experimental adsorption isotherms is proposed. This new approach combines experimental information (pore size distribution determined from nitrogen adsorption at 77 K) and numerical data (grand canonical Monte Carlo simulations of adsorption in pores) to explain an influence of binding energy on adsorption isotherms. The procedure has been validated by analysis of hydrogen adsorption in a series of carbons activated with KOH:C ratio varying from 3 to 6. These carbons show high capacity of hydrogen storage both at 80 and 303 K (115 gH2/kgC and 23 gH2/kgC at p = 100 bar, respectively, for carbon activated during 1 h at T = 790 C (T = 1361 K) with KOH:C ratio equal to 3, having the surface area above 2600 m2/g, 0.77 porosity, and large fraction (31%) of pores with average width below 1 nm). An additional energetic parameter has been introduced into the conventional fitting procedure to account for the distribution of adsorption energy in measured samples. The observed high consistency between experimental and simulated results validates/correlates the characterization procedures and proves the coherence and robustness of both the experimental results and the numerical simulations.

An overview is given of the development of nanoporous graphene monolith as storage materials for molecular hydrogen for next-generation low-pressure tanks. Compacting activated carbon powder into monolith is an efficient space-filling technique to increase the volumetric storage capacity. Monolith has been synthesized with a packing density of 0.7 g/cm3 using MSC30 and Polyvinyl alcohol (PVA). The presence of the pyrolyzed binder decreased the excess adsorption by 34 % and the gravimetric storage capacity by 48%. Despite the decrease in excess adsorption, the volumetric storage capacity increased by 30% due the high packing configuration of monolith.

Activated carbons made from corn cob show promise as materials for high-capacity hydrogen storage. As part of our characterization of these materials, we are interested in learning how different production methods affect the adsorption energies. In this talk, we will show how hydrogen adsorption isotherms may be used to calculate these adsorption energies at zero coverage using Henry's law. We will additionally discuss differences between the binding energy and the isosteric heat of adsorption by applying this analysis at different temperatures.

Early results on optimization of gravim. excess adsorption for undoped carbons, with KOH activation: 1.Excess adsorption and gravimetric storage capacity both increase with increasing KOH:C ratio and activation temperature. Excess adsorption dominated by KOH:C ratio. 2.Volumetric storage capacity decreases with increasing activation temperature. 3. 2.5K activated at 700 oC has record volumetric storage capacity of 132 g CH4/liter carbon at 35 bar and 22 oC (200 V/V, 110% of DOE target of 118 g/liter). Has only micropores (< 2nm). Large surface area and low porosity is key to volumetric storage capacity. 4. 4K activated at 790 oC has record gravimetric storage capacity of 256 g CH4/kg carbon at 35 bar and 22 oC. Presence of mesopores raises gravimetric storage capacity. 5. Langmuir and Ono-Kondo analysis of CH4 excess isotherms at 295 K gives surface area (2400-2700 m2/g, agree with BET area), film thickness (~0.4 nm), saturated film density (320-440 g/cm3), and average binding energy (8-9 kJ/mol). 6.Briquetting can increase volumetric storage capacity by factor of 2 if surface area remains constant.

There is significant interest in the properties of boron-doped activated carbons for their potential to improve hydrogen storage. Boron-doped activated carbons have been produced using a novel process involving the pyrolysis of a boron containing compound and subsequent high-temperature annealing. In this talk we will present a systematic study of the effect of different boron doping processes on the samples' surface area, micropore structure, and hydrogen sorption. Experimental results include boron content from prompt gamma neutron activation analysis, boron-carbon chemistry from Fourier transform infrared spectroscopy (FTIR), nitrogen subcritical adsorption, and 80K and 90K hydrogen adsorption isotherms which allow us to evaluate the hydrogen binding energy for each sorptive material.

In this talk we will present an overview of our new Hydrogen Test Fixture (HTF) constructed by the Midwest Research Institute for The Alliance for Collaborative Research in Alternative Fuel Technology to test activated carbon monoliths for hydrogen gas storage. The HTF is an automated, computer-controlled volumetric instrument for rapid screening and manipulation of monoliths under an inert atmosphere (to exclude degradation of carbon from exposure to oxygen). The HTF allows us to measure large quantity (up to 500 g) of sample in a 0.5 l test tank, making our results less sensitive to sample inhomogeneity. The HTF can measure isotherms at pressures ranging from 1 to 300 bar at room temperature. For comparison, other volumetric instruments such as Hiden Isochema's HTP-1 Volumetric Analyser can only measure carbon samples up to 150 mg at pressures up to 200 bar.

There is significant interest in the properties of boron-doped activated carbons for their potential to improve hydrogen storage. ootnotetextMultiply Surface-Functionalized Nanoporous Carbon for Vehicular Hydrogen Storage, P. Pfeifer et al. DOE Hydrogen Program 2011 Annual Progress Report, IV.C.3, 444-449 (2011). Boron-doped activated carbons have been produced using a process involving the pyrolysis of decaborane (B10H14) and subsequent high-temperature annealing. In this talk, we will present a systematic study of the effect of different boron doping processes on the samples' structure, hydrogen sorption, and surface chemistry. Initial room temperature experiments show a 20% increase in the hydrogen excess adsorption per surface area compared to the undoped material. Experimental enthalpies of adsorption will be presented for comparison to theoretical predictions for boron-doped carbon materials. Additionally, results from a modified version of the doping process will be presented.

High-surface-area activated carbons for hydrogen storage were investigated as a function of post-synthesis surface treatment. Thermal treatment of the initial carbon in high vacuum at temperatures 200-1000 C leads to materials with significantly different surface chemistries and hydrogen storage capacities. Results from nitrogen pore-structure analyses, FT-IR spectroscopy before and after the treatment, and thermogravimetric analysis and mass spectroscopy of volatile reaction products during treatment, are reported. For treatment at 600 C, excess hydrogen adsorption at 80 K and 303 K is found to be 20-30% higher than for the untreated sample. At temperatures below 450 C, volatiles are mostly water and air; volatiles above 450 C are mostly carbon dioxide and carbon monoxide. The results are interpreted as that high-temperature treatment produces materials with a large fraction of high-binding-energy sites.

Background The majority of coeliac disease (CD) patients are not being properly diagnosed and therefore remain untreated, leading to a greater risk of developing CD-associated complications. The major genetic risk heterodimer, HLA-DQ2 and DQ8, is already used clinically to help exclude disease. However, approximately 40% of the population carry these alleles and the majority never develop CD. Objective We explored whether CD risk prediction can be improved by adding non-HLA-susceptible variants to common HLA testing. Design We developed an average weighted genetic risk score with 10, 26 and 57 single nucleotide polymorphisms (SNP) in 2675 cases and 2815 controls and assessed the improvement in risk prediction provided by the non-HLA SNP. Moreover, we assessed the transferability of the genetic risk model with 26 non-HLA variants to a nested case-control population (n=1709) and a prospective cohort (n=1245) and then tested how well this model predicted CD outcome for 985 independent individuals. Results Adding 57 non-HLA variants to HLA testing showed a statistically significant improvement compared to scores from models based on HLA only, HLA plus 10 SNP and HLA plus 26 SNP. With 57 non-HLA variants, the area under the receiver operator characteristic curve reached 0.854 compared to 0.823 for HLA only, and 11.1% of individuals were reclassified to a more accurate risk group. We show that the risk model with HLA plus 26 SNP is useful in independent populations. Conclusions Predicting risk with 57 additional non-HLA variants improved the identification of potential CD patients. This demonstrates a possible role for combined HLA and non-HLA genetic testing in diagnostic work for CD., Collaborators:PreventCD GroupHär ingår Lotta Högberg och Lars Stenhammar från Barn-och ungdomskliniken, VrinneviFunding Agencies|5R1DK084568-02, NIH, National Institutes of Health

BACKGROUND A window of opportunity has been suggested for reducing the risk of celiac disease by introducing gluten to infants at 4 to 6 months of age. METHODS We performed a multicenter, randomized, double-blind, placebo-controlled dietary-intervention study involving 944 children who were positive for HLA-DQ2 or HLA-DQ8 and had at least one first-degree relative with celiac disease. From 16 to 24 weeks of age, 475 participants received 100 mg of immunologically active gluten daily, and 469 received placebo. Anti-transglutaminase type 2 and antigliadin antibodies were periodically measured. The primary outcome was the frequency of biopsy-confirmed celiac disease at 3 years of age. RESULTS Celiac disease was confirmed by means of biopsies in 77 children. To avoid underestimation of the frequency of celiac disease, 3 additional children who received a diagnosis of celiac disease according to the 2012 European Society for Pediatric Gastroenterology, Hepatology, and Nutrition diagnostic criteria (without having undergone biopsies) were included in the analyses (80 children; median age, 2.8 years; 59% were girls). The cumulative incidence of celiac disease among patients 3 years of age was 5.2% (95% confidence interval [CI], 3.6 to 6.8), with similar rates in the gluten group and the placebo group (5.9% [95% CI, 3.7 to 8.1] and 4.5% [95% CI, 2.5 to 6.5], respectively; hazard ratio in the gluten group, 1.23; 95% CI, 0.79 to 1.91). Rates of elevated levels of anti-transglutaminase type 2 and antigliadin antibodies were also similar in the two study groups (7.0% [95% CI, 4.7 to 9.4] in the gluten group and 5.7% [95% CI, 3.5 to 7.9] in the placebo group; hazard ratio, 1.14; 95% CI, 0.76 to 1.73). Breast-feeding, regardless of whether it was exclusive or whether it was ongoing during gluten introduction, did not significantly influence the development of celiac disease or the effect of the intervention. CONCLUSIONS As compared with placebo, the introduction of small quantiti