Functionalized MOFs for Enhanced CO2 Capture Torrisi, Antonio; Bell, Robert G; Mellot-Draznieks, Caroline
Crystal growth & design,
07/2010, Letnik:
10, Številka:
7
Journal Article
Recenzirano
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Based on computational studies, we propose new metal−organic framework materials, in which the bridging ligands have been functionalized by different substituents, with the aim of improving the CO2 ...adsorption capacity of the material. The materials are based on the large-pore form of MIL-53(Al3+), with the following functional groups: OH-, COOH-, NH2-, and CH3-. For each form, adsorption heats and isotherms were simulated using the Grand Canonical Monte Carlo method which were found to be consistent with DFT calculations. The study illustrates the enormous impact of the functional groups in enhancing CO2 capture in the pressure range 0.01−0.5 bar and at room temperature. It also provides important insights into the structural factors which play a key role in the CO2 adsorption process in the functionalized MOFs. We propose the material (OH)2-MIL-53(Al3+) as an optimal candidate for improved CO2 capture at low pressures.
Use the Force: A force field for the MIL‐53(Cr) framework was derived and validated by molecular dynamics simulations. This approach allows the “breathing” of the framework in the presence of CO2 to ...be captured and gives insight into the structural switching mechanism from a narrow‐ to a large‐pore form (see picture). This force field can be used directly in studies of many guest molecules and, with a minimum adjustment, for other MOF systems.
Dynamic adaptive policy pathways (DAPP) is emerging as a 'fit-for-purpose' method for climate-change adaptation planning to address widening future uncertainty and long planning timeframes. A key ...component of DAPP is to monitor indicators of change such as flooding and storm events, which can trigger timely adaptive actions (change pathway/behavior) ahead of thresholds. Signals and triggers are needed to support DAPP-the signal provides early warning of the emergence of the trigger (decision-point), and the trigger initiates the process to change pathway before a harmful adaptation-threshold is reached. We demonstrate a new approach to designing signals and triggers using the case of increased flooding as sea level continues to rise. The flooding frequency is framed in terms of probable timing of several events reaching a specific height threshold within a set monitoring period. This framing is well suited to adaptive planning for different hazards, because it allows the period over which threshold exceedances are monitored to be specified, and thus allows action before adaptation-thresholds are reached, while accounting for the potential range of timing and providing a probability of premature warning, or of triggering adaptation too late. For our New Zealand sea level case study, we expect early signals to be observed in 10 year monitoring periods beginning 2021. Some urgency is therefore required to begin the assessment, planning and community engagement required to develop adaptive plans and associated signals and triggers for monitoring. Worldwide, greater urgency is required at tide-dominated sites than those adapted to large storm-surges. Triggers can be designed with confidence that a change in behavior pathway (e.g. relocating communities) will be triggered before an adaptation-threshold occurs. However, it is difficult to avoid the potential for premature adaptation. Therefore, political, social, economic, or cultural signals are also needed to complement the signals and triggers based on coastal-hazard considerations alone.
Coastal flooding is a major global hazard, yet few
studies have examined the spatial and temporal characteristics of extreme
sea level and associated coastal flooding. Here we analyse sea-level ...records
around the coast of New Zealand (NZ) to quantify extreme storm-tide and
skew-surge frequency and magnitude. We identify the relative magnitude of
sea-level components contributing to 85 extreme sea level and 135 extreme
skew-surge events recorded in NZ since 1900. We then examine the spatial and
temporal clustering of these extreme storm-tide and skew-surge events and
identify typical storm tracks and weather types associated with the spatial
clusters of extreme events. We find that most extreme storm tides were
driven by moderate skew surges combined with high perigean spring tides. The
spring–neap tidal cycle, coupled with a moderate surge climatology,
prevents successive extreme storm-tide events from happening within 4–10 d of each other, and generally there are at least 10 d between extreme
storm-tide events. This is similar to findings from the UK (Haigh et al.,
2016), despite NZ having smaller tides. Extreme events more commonly
impacted the east coast of the North Island of NZ during blocking weather
types, and the South Island and west coast of the North Island during trough
weather types. The seasonal distribution of both extreme storm-tide and
skew-surge events closely follows the seasonal pattern of mean sea-level
anomaly (MSLA) – MSLA was positive in 92 % of all extreme storm-tide events and
in 88 % of all extreme skew-surge events. The strong influence of
low-amplitude (−0.06 to 0.28 m) MSLA on the timing of extreme events shows
that mean sea-level rise (SLR) of similarly small height will drive rapid
increases in the frequency of presently rare extreme sea levels. These
findings have important implications for flood management, emergency
response and the insurance sector, because impacts and losses may be
correlated in space and time.
Abstract
The criteria and assumptions that were used to derive the steady-state tropical cyclone intensity and structure theory of Emanuel and Rotunno are assessed using three-dimensional ...convection-allowing simulations using the Weather Research and Forecasting Model. One real-data case of Hurricane Patricia (2015) and two idealized simulations with and without vertical wind shear are examined. In all three simulations, the gradient wind balance is valid in the inner-core region above the boundary layer. The angular momentum M and saturation entropy surfaces s* near the top of the boundary layer, in the outflow region and along the angular momentum surface that passes the low-level radius of maximum wind MRMW are nearly congruent, satisfying the criterion of slantwise moist neutrality in the vicinity of MRMW. The theoretically derived maximum wind magnitude above the boundary layer compares well with the simulated maximum tangential wind and gradient wind using the azimuthally averaged pressure field during the intensification and quasi-steady state of the simulated storms. The Richardson number analysis of the simulated storms shows that small Richardson number (0 < Ri ≤1) exists in the outflow region, related to both large local shear and small static stability. This criticality of the Richardson number indicates the existence of small-scale turbulence in the outflow region. We also show that the stratification of temperature along the M surfaces at the outflow region for steady-state hurricanes is approximately applicable in these three-dimensional simulations, while the radial distribution of gradient wind is qualitatively comparable to the theoretical radial profiles. Some caveats regarding the theory are also discussed.
Despite aggressive therapies, median survival for malignant gliomas is less than 15 months. Patients with unmethylated O(6)-methylguanine-DNA methyltransferase (MGMT) fare worse, presumably because ...of temozolomide resistance. AdV-tk, an adenoviral vector containing the herpes simplex virus thymidine kinase gene, plus prodrug synergizes with surgery and chemoradiotherapy, kills tumor cells, has not shown MGMT dependency, and elicits an antitumor vaccine effect.
Patients with newly diagnosed malignant glioma received AdV-tk at 3 × 10(10), 1 × 10(11), or 3 × 10(11) vector particles (vp) via tumor bed injection at time of surgery followed by 14 days of valacyclovir. Radiation was initiated within 9 days after AdV-tk injection to overlap with AdV-tk activity. Temozolomide was administered after completing valacyclovir treatment.
Accrual began December 2005 and was completed in 13 months. Thirteen patients were enrolled and 12 completed therapy, three at dose levels 1 and 2 and six at dose level 3. There were no dose-limiting or significant added toxicities. One patient withdrew before completing prodrug because of an unrelated surgical complication. Survival at 2 years was 33% and at 3 years was 25%. Patient-reported quality of life assessed with the Functional Assessment of Cancer Therapy-Brain (FACT-Br) was stable or improved after treatment. A significant CD3(+) T-cell infiltrate was found in four of four tumors analyzed after treatment. Three patients with MGMT unmethylated glioblastoma multiforme survived 6.5, 8.7, and 46.4 months.
AdV-tk plus valacyclovir can be safely delivered with surgery and accelerated radiation in newly diagnosed malignant gliomas. Temozolomide did not prevent immune responses. Although not powered for efficacy, the survival and MGMT independence trends are encouraging. A phase II trial is ongoing.
Abstract
Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation. However, targeted synthesis of zeolites ...with new pore structures and compositions remains a key challenge. Here, we propose an approach based on a unique 3D-3D topotactic transformation, which takes advantage of weak bonding in zeolites. This is inspired by the structure transformation of PST-5, a new aluminophosphate molecular sieve, to PST-6 by calcination. The structure of nano-sized PST-5 crystals is determined by 3D electron diffraction. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. This method provides a concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.
Intermolecular interactions between the CO(2) molecule and a range of functionalized aromatic molecules have been investigated using density functional theory. The work is directed toward the design ...of linker molecules which could form part of new metal-organic framework materials with enhanced affinity for CO(2) adsorption at low pressure. Two classes of substituted benzene molecules were considered: (i) with halogen substituents (tetrafluoro-, chloro-, bromo-, and dibromobenzene) and (ii) with methyl substituents (mono-, di-, and tetramethylbenzene). In the benzene-CO(2) complex, the main interaction is between the delocalized pi aromatic system and the molecular quadrupole of CO(2). Halogen substituents have an electron-withdrawing effect on the ring which destabilizes the pi-quadrupole interaction. Weak "halogen-bond" and hydrogen bondlike interactions partially compensate for this, but not to the extent that any significant enhancement of the intermolecular binding energy is observed. Methyl groups, on the other hand, have a positive inductive effect which strengthens the CO(2)-aromatic interaction by up to 3 kJ mol(-1) in the case of tetramethylbenzene. Weak hydrogen bondlike interactions with methyl H also contribute to the stability of the complexes.
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