Wasserstoffadsorption in Metall-organischen Gerüststoffen

In this thesis hydrogen adsorption is measured in ten MOFs with pores ranging from 3.4A to 34A and ultra-high surface areas of up to 5000 m2/g. Adsorption and desorp- tion isotherms are measured in two different regimes. First, at temperatures between 77K and room temperature and pressure up to 2MPa. From these measurements the isosteric heat of adsorption is determined in dependence of the hydrogen uptake for the whole range important for technical application. Second, hydrogen adsorption is mea- sured at approximately 20K and pressure up to 0.1MPa. For this new measurement technique a cryostat was developed, tested and calibrated. Hydrogen adsorption at 20 K enables for the first time the determination of specific surface area and specific pore volume by hydrogen. From theoretical calculations there are indications that the specific surface area and specific pore volume depend on the gas used for the determination and that surface areas and pore volumes available for hydrogen are remarkably different from the surface area and pore volumes determined by nitrogen or argon adsorption. Therefore, for the characterization of hydrogen storage materials the surface area and pore volume should be determined by hydrogen adsorption which is done in this work for the first time. Furthermore, adsorbed hydrogen at 20 K is less mobile than at 77 K. Therefore, adsorp- tion sites with different adsorption energy in the framework are subsequently filled. This filling can be observed from steps in the low pressure isotherm. Similar observations have been made before for nitrogen at 77 K and argon at 87 K, but never for hydrogen. Finally the results of hydrogen storage experiments are discussed concerning the requirements for application in a tank system. This work on the relation of hydrogen storage properties to the structure of MOFs will enable tailored synthesis of optimized MOFs for hydrogen storage application.In dieser Arbeit wurden die Wasserstoffspeichereigenschaften von 10 verschiedenen MOFs untersucht und mit ihren strukturellen Eigenschaften korreliert. Die maximal aufgenommene Wasserstoffmenge steigt mit der Oberfläche der MOFs und ist unabhängig von ihrer chemischen Zusammensetzung. Die Bindungsenthalpie wird bei niedrigen Wasserstoffaufnahmen von den Metallzentren der MOFs bestimmt. Bei höheren Aufnahmen im technisch relevanten Bereich sind diese Metallzentren gesättigt und die Bindungsenthalpie hängt von der Porengröße der MOFs ab. Kleinere Poren zeigen eine höhere Bindungsenthalpie für Wasserstoffmoleküle. Durch einen für diese Arbeit neu entwickelten Kryostat konnten erstmals Wasserstoffadsorptionsisothermen bei 19,5 K gemessen und die Besetzung der verschiedenen Adsorptionsplätze direkt als Stufen im Niederdruckbereich der Isotherme beobachtet werden. Aus diesen Isothermen wurden erstmals Oberflächen und Porenvolumina aus Wasserstoffadsorptionsmessungen unterhalb der kritischen Temperatur bestimmt. Die Physisorption von Wasserstoff unter kryogenen Bedingungen ist eine vielversprechende Möglichkeit für die Speicherung von Wasserstoff in mobilen Anwendungen. Die Korrelation der Speichereigenschaften zu den strukturellen Parametern ermöglicht die Synthese von MOFs mit optimalen Wasserstoffspeichereigenschaften

Elucidating gating effects for hydrogen sorption in MFU-4-type triazolate-based metal-organic frameworks featuring different pore sizes

10sinoneA highly porous member of isoreticular MFU-4-type frameworks, [Zn 5Cl4(BTDD)3] (MFU-4l(arge)) (H 2-BTDD=bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1, 4]dioxin), has been synthesized using ZnCl2 and H2-BTDD in N,N-dimethylformamide as a solvent. MFU-4l represents the first example of MFU-4-type frameworks featuring large pore apertures of 9.1a Å Here, MFU-4l serves as a reference compound to evaluate the origin of unique and specific gas-sorption properties of MFU-4, reported previously. The latter framework features narrow-sized pores of 2.5a Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU-4l has been solved ab initio by direct methods from 3D electron-diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron-beam precession. Independently, it has been solved using powder X-ray diffraction. Thermogravimetric analysis (TGA) and variable-temperature X-ray powder diffraction (XRPD) experiments carried out on MFU-4l indicate that it is stable up to 500°C (N2 atmosphere) and up to 350°C in air. The framework adsorbs 4a wt% hydrogen at 20a bar and 77a K, which is twice the amount compared to MFU-4. The isosteric heat of adsorption starts for low surface coverage at 5a kJmol-1 and decreases to 3.5a kJmol -1 at higher H2 uptake. In contrast, MFU-4 possesses a nearly constant isosteric heat of adsorption of ca. 7a kJmol-1 over a wide range of surface coverage. Moreover, MFU-4 exhibits a H2 desorption maximum at 71a K, which is the highest temperature ever measured for hydrogen physisorbed on metal-organic frameworks (MOFs). © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.noneDenysenko, D.;Grzywa, M.;Tonigold, M.;Streppel, B.;Krkljus, I.;Hirscher, M.;MUGNAIOLI, E.;Kolb, U.;Hanss, J.;Volkmer, D.Denysenko, D.; Grzywa, M.; Tonigold, M.; Streppel, B.; Krkljus, I.; Hirscher, M.; Mugnaioli, E.; Kolb, U.; Hanss, J.; Volkmer, D

Route to a Family of Robust, Non interpenetrated Metal Organic Frameworks with pto like Topology

A combination of topological rules and quantum chemical calculations has facilitated the development of a rational metal organic framework MOF synthetic strategy using the tritopic benzene 1,3,5 tribenzoate btb linker and a neutral cross linker 4,4 bipyridine bipy . A series of new compounds, namely [M 2 bipy ] 3 btb 4 DUT 23 M , M Zn, Co, Cu, Ni , [Cu 2 bisqui 0.5 ] 3 btb 4 DUT 24, bisqui diethyl R,S 4,4 biquinoline 3,3 dicarboxylate , [Cu 2 py 1.5 H2O 0.5 ] 3 btb 4 DUT 33, py pyridine , and [Cu 2 H2O 2 ] 3 btb 4 DUT 34 , with high specific surface areas and pore volumes up to 2.03 m 3 g 1 for DUT 23 Co were synthesized. For DUT 23 Co , excess storage capacities were determined for methane 268 mg g 1 at 100 bar and 298 K , hydrogen 74 mg g 1 at 40 bar and 77 K , and n butane 99 mg g 1 at 293 K . DUT 34 is a non cross linked version of DUT 23 non interpenetrated pendant to MOF 14 that possesses open metal sites and can therefore be used as a catalyst. The accessibility of the pores in DUT 34 to potential substrate molecules was proven by liquid phase adsorption. By exchanging the N,N donor 4,4 bipyridine with a substituted racemic biquinoline, DUT 24 was obtained. This opens a route to the synthesis of a chiral compound, which could be interesting for enantioselective separatio

20 K H<sub>2</sub> Physisorption on Metal???Organic Frameworks with Enhanced Dormancy Compared to Liquid Hydrogen Storage

Liquid hydrogen (LH2) is the best way of transporting hydrogen, as its high volumetric energy density translates into a significant reduction in hydrogen transportation and refueling operations expenses. However, the phase transformation from liquid to gaseous hydrogen, due to heat leakage of the LH2 vessel, causes a considerable volume change, results in boil-off losses, and makes long-term storage/transportation problematic. These boil-off losses are a severe drawback for continental transportation through truck tube trailers having evaporative losses of about 3???15% per day (depending on the volume). Herein, hydrogen storage by cryo-adsorption using metal???organic frameworks (MOFs) is proposed as an alternative to reduce boil-off losses and enhance dormancy during continental transportation. The stronger van der Waals interaction operating between adsorbate and adsorbent leads to superdense H2 adsorption, which compensates for the space occupied by the adsorbent skeleton and results in a volumetric storage capacity comparable to that of LH2 tanks (???96%). Depending on the textural properties of MOFs, H2 desorption can start from 45 K, resulting in an extended dormancy time of the tank system. In addition, the observation of hindered rotational transition (J: 0 ??? 1) signal in neutron scattering analysis indicates that H2 are firmly attached and highly immobile on the adsorption sites. The hindered rotation by adsorption at 20 K on MOFs also suggests that the intermolecular separation is less than the bulk liquid (even solid) phase

Exploration of Time-Oriented Data in Immersive Virtual Reality Using a 3D Radar Chart Approach

In this paper, we present an approach to interact with time-oriented data in Virtual Reality within the context of Immersive Analytics. We implemented a Virtual Reality application that enables its user to explore data in an immersive environment (head-mounted display, 3D gestural input), utilizing potential advantages of immersive technologies, for instance, depth cues for better spatial understanding, natural interaction, and user engagement. The visualization design is inspired by the overall concept of a radar chart, and using the third dimension to represent time-series related data. We conducted a user study with 15 participants, encouraging them to examine a representative dataset within an explorative analysis scenario with no time constraints. Based on the results of usability and user engagement scores, task completion analysis, observations, and interviews, we were able to empirically validate the approach in general, and gain insights in the users’ interaction and data analysis strategies.DISA-DHOpen Data Exploration in Virtual Reality (ODxVR

"Oh, that's where you are!" : Towards a Hybrid Asymmetric Collaborative Immersive Analytics System

We present a hybrid Immersive Analytics system to support asymmetrical collaboration between a pair of users during synchronous data exploration. The system consists of an immersive Virtual Reality application, a non-immersive web application, and a real-time communication interface connecting both applications to provide features to facilitate the collaborators’ mutual understanding and their ability to make (spatial) references. We conducted a real world case study with pairs of language students, encouraging them to use the developed system to investigate a large multivariate Twitter dataset from a sociolinguistic perspective within an explorative analysis scenario. Based on the results of usability scores, log file analyses, observations, and interviews, we were able to validate the approach in general, and gain insights into the users’ collaboration with respect to awareness, deixis, and group dynamics.DISA-DHOpen Data Exploration in Virtual Reality (ODxVR

Vitamin D and mortality: meta-analysis of individual participant data from a large consortium of cohort studies from Europe and the United States

Objective To investigate the association between serum 25-hydroxyvitamin D concentrations (25(OH) D) and mortality in a large consortium of cohort studies paying particular attention to potential age, sex, season, and country differences. Design Meta-analysis of individual participant data of eight prospective cohort studies from Europe and the US. Setting General population. Participants 26 018 men and women aged 50-79 years Main outcome measures All-cause, cardiovascular, and cancer mortality. Results 25(OH) D concentrations varied strongly by season (higher in summer), country (higher in US and northern Europe) and sex (higher in men), but no consistent trend with age was observed. During follow-up, 6695 study participants died, among whom 2624 died of cardiovascular diseases and 2227 died of cancer. For each cohort and analysis, 25(OH) D quintiles were defined with cohort and subgroup specific cut-off values. Comparing bottom versus top quintiles resulted in a pooled risk ratio of 1.57 (95% CI 1.36 to 1.81) for all-cause mortality. Risk ratios for cardiovascular mortality were similar in magnitude to that for all-cause mortality in subjects both with and without a history of cardiovascular disease at baseline. With respect to cancer mortality, an association was only observed among subjects with a history of cancer (risk ratio, 1.70 (1.00 to 2.88)). Analyses using all quintiles suggest curvilinear, inverse, dose-response curves for the aforementioned relationships. No strong age, sex, season, or country specific differences were detected. Heterogeneity was low in most meta-analyses. Conclusions Despite levels of 25(OH) D strongly varying with country, sex, and season, the association between 25(OH) D level and all-cause and cause-specific mortality was remarkably consistent. Results from a long term randomised controlled trial addressing longevity are being awaited before vitamin D supplementation can be recommended in most individuals with low 25(OH) D levels

Overweight duration in older adults and cancer risk: a study of cohorts in Europe and the United States

Recent studies have shown that cancer risk related to overweight and obesity is mediated by time and might be better approximated by using life years lived with excess weight. In this study we aimed to assess the impact of overweight duration and intensity in older adults on the risk of developing different forms of cancer. Study participants from seven European and one US cohort study with two or more weight assessments during follow-up were included (n = 329,576). Trajectories of body mass index (BMI) across ages were estimated using a quadratic growth model; overweight duration (BMI ≥ 25) and cumulative weighted overweight years were calculated. In multivariate Cox models and random effects analyses, a longer duration of overweight was significantly associated with the incidence of obesity-related cancer [overall hazard ratio (HR) per 10-year increment: 1.36; 95 % CI 1.12–1.60], but also increased the risk of postmenopausal breast and colorectal cancer. Additionally accounting for the degree of overweight further increased the risk of obesity-related cancer. Risks associated with a longer overweight duration were higher in men than in women and were attenuated by smoking. For postmenopausal breast cancer, increased risks were confined to women who never used hormone therapy. Overall, 8.4 % of all obesity-related cancers could be attributed to overweight at any age. These findings provide further insights into the role of overweight duration in the etiology of cancer and indicate that weight control is relevant at all ages. This knowledge is vital for the development of effective and targeted cancer prevention strategies

Impact of smoking and smoking cessation on cardiovascular events and mortality among older adults: Meta-analysis of Individual participant data from prospective cohort studies of the CHANCES consortium

Objective: To investigate the impact of smoking and smoking cessation on cardiovascular mortality, acute coronary events, and stroke events in people aged 60 and older, and to calculate and report risk advancement periods for cardiovascular mortality in addition to traditional epidemiological relative risk measures. Design: Individual participant meta-analysis using data from 25 cohorts participating in the CHANCES consortium. Data were harmonised, analysed separately employing Cox proportional hazard regression models, and combined by meta-analysis. Results: Overall, 503?905 participants aged 60 and older were included in this study, of whom 37?952 died from Cardiovascular Diseases. Random effects meta-analysis of the association of smoking status with cardiovascular mortality yielded a summary hazard ratio of 2.07 (95% CI 1.82 to 2.36) for current smokers and 1.37 (1.25 to 1.49) for former smokers compared with never smokers. Corresponding summary estimates for risk advancement periods were 5.50 years (4.25 to 6.75) for current smokers and 2.16 years (1.38 to 2.39) for former smokers. The excess risk in smokers increased with cigarette consumption in a dose-response manner, and decreased continuously with time since smoking cessation in former smokers. Relative risk estimates for acute coronary events and for stroke events were somewhat lower than for cardiovascular mortality, but patterns were similar. Conclusions: Our study corroborates and expands evidence from previous studies in showing that smoking is a strong independent risk factor of cardiovascular events and mortality even at older age, advancing cardiovascular mortality by more than five years, and demonstrating that smoking cessation in these age groups is still beneficial in reducing the excess risk