14 results on '"John M. Griffin"'
Search Results
2. Efficient solid-state photoswitching of methoxyazobenzene in a metal–organic framework for thermal energy storage
- Author
-
Kieran Griffiths, Nathan R. Halcovitch, and John M. Griffin
- Subjects
General Chemistry - Abstract
Efficient photoswitching in the solid-state remains rare, yet is highly desirable for the design of functional solid materials. In particular, for molecular solar thermal energy storage materials high conversion to the metastable isomer is crucial to achieve high energy density. Herein, we report that 4-methoxyazobenzene (MOAB) can be occluded into the pores of a metal-organic framework Zn
- Published
- 2022
3. Na2.4Al0.4Mn2.6O7 anionic redox cathode material for sodium-ion batteries – a combined experimental and theoretical approach to elucidate its charge storage mechanism
- Author
-
Cindy Soares, Begoña Silván, Yong-Seok Choi, Veronica Celorrio, Valerie R. Seymour, Giannantonio Cibin, John M. Griffin, David O. Scanlon, and Nuria Tapia-Ruiz
- Subjects
Renewable Energy, Sustainability and the Environment ,General Materials Science ,General Chemistry - Abstract
Al substitution and subsequent Na excess in Na2Mn3O7 were achieved by a ceramic method, realizing the high-performance Na2.4Al0.4Mn2.6O7 oxygen-redox cathode for Na-ion batteries. A comparison between the two cathodes revealed the role of Al doping.
- Published
- 2022
4. Permselective ion electrosorption of subnanometer pores at high molar strength enables capacitive deionization of saline water
- Author
-
Sheng Bi, Volker Presser, Yuan Zhang, Luca Cervini, Tangming Mo, Guang Feng, and John M. Griffin
- Subjects
Fuel Technology ,Materials science ,Chemical engineering ,Renewable Energy, Sustainability and the Environment ,Ionic strength ,Capacitive deionization ,Drop (liquid) ,Electrode ,Energy Engineering and Power Technology ,Water treatment ,Microstructure ,Saline water ,Ion - Abstract
Capacitive deionization with porous carbon electrodes is an energy-efficient water treatment technique limited to the remediation of only brackish water due to the severe efficiency drop at high molar strength. Combining experiment and simulation, our work demonstrates the ability of subnanometer pores for permselective ion electrosorption, which enables capacitive deionization for saline media with high concentrations. Molecular dynamics simulations reveal the origin of permselective ion electrosorption in subnanometer pores at high molar strength. Within the subnanometer range, carbon pores with smaller size become more ionophobic and then express a higher ability of permselective ion electrosorption. This can be understood by the effects of the pore size on the microstructure of in-pore water and ions and the nanoconfinement effects on the ion hydration. These findings provide a new avenue for capacitive deionization of saline water (seawater-like ionic strength) to enable the application of highly concentrated saline media by direct use of porous carbons.
- Published
- 2020
5. Drug orientations within statin-loaded lipoprotein nanoparticles by 19F solid-state NMR
- Author
-
Sophie Lau, David A. Middleton, Naomi E. Stanhope, Eleri Hughes, and John M. Griffin
- Subjects
Drug ,Statin ,medicine.drug_class ,media_common.quotation_subject ,Nanoparticle ,010402 general chemistry ,01 natural sciences ,Catalysis ,Materials Chemistry ,medicine ,Molecule ,media_common ,010405 organic chemistry ,Chemistry ,Metals and Alloys ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Combinatorial chemistry ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Solid-state nuclear magnetic resonance ,Drug delivery ,Ceramics and Composites ,lipids (amino acids, peptides, and proteins) ,Lipoprotein - Abstract
NMR measurements of 19F chemical shift anisotropy and 1H-19F dipolar couplings provide unprecedented information on the molecular orientations of two fluorine-containing statin drugs within the heterogeneous environment of reconstituted high-density lipoprotein (rHDL) nanoparticles, a drug delivery system under clinical investigation.
- Published
- 2019
6. Average orientation of a fluoroaromatic molecule in lipid bilayers from DFT-informed NMR measurements of 1H–19F dipolar couplings
- Author
-
David A. Middleton, Eleri Hughes, Michael P. Coogan, and John M. Griffin
- Subjects
Bilayer ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Crystallography ,Membrane ,chemistry ,Lipophilicity ,Fluorine ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Lipid bilayer ,Magnetic dipole–dipole interaction - Abstract
Fluorine is often incorporated into the aromatic moieties of synthetic bioactive molecules such as pharmaceuticals and disease diagnostics in order to alter their physicochemical properties. Fluorine substitution may increase a molecule's lipophilicity, thereby enabling its diffusion across cell membranes to enhance bioavailability or to exert a direct physiological effect from within the lipid bilayer. Understanding the structure, dynamics and orientation of fluoroaromatic molecules in lipid bilayers can provide useful insight into the effect of fluorine on their mode of action, and their interactions with membrane-embedded targets or efflux proteins. Here we demonstrate that NMR measurements of 19F chemical shift anisotropy combined with 1H–19F dipolar coupling measurements together report on the average orientation of a lipophilic fluoroaromatic molecule, 4-(6-fluorobenzo[d]thiazol-2-yl)aniline (FBTA), rapidly rotating within a lipid bilayer. The 19F chemical shift tensor orientation in the molecular frame was calculated by density functional theory and corroborated by 1H–19F PISEMA NMR. It was then possible to analyse the line shapes of proton-coupled and proton-decoupled 19F spectra of FBTA in chain perdeuterated dimyristoylphosphatidylcholine (DMPC-d54) bilayers to restrict the average axis of molecular reorientation of FBTA in the bilayer to a limited range orientations. This approach, which exploits the high sensitivity and gyromagnetic ratios of 19F and 1H, will be useful for comparing the membrane properties of related bioactive fluoroaromatic compounds.
- Published
- 2018
7. Continuous silicon oxycarbide fiber mats with tin nanoparticles as a high capacity anode for lithium-ion batteries
- Author
-
Aura Tolosa, John M. Griffin, Benjamin Krüner, Mathias Widmaier, and Volker Presser
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Electrospinning ,0104 chemical sciences ,Anode ,chemistry.chemical_compound ,Fuel Technology ,chemistry ,Silicon carbide ,Lithium ,Fiber ,Composite material ,0210 nano-technology ,Tin - Abstract
Continuous fiber mats are attractive electrodes for lithium-ion batteries, because they allow operation at high charge/discharge rates in addition to being free of polymer binders and conductive additives. In this work, we synthesize and characterize continuous Sn/SiOC fibers (diameter ca. 0.95 mu m), as a Li-ion battery anode. Our synthesis employs electrospinning of a low-cost silicone resin, using tin acetate in a dual role both as a polymer crosslinker and as a tin precursor (6-22 mass%). The hybrid electrodes present very high initial reversible capacities (840-994 mA h g(-1)) at 35 mA g(-1), and retain 280310 mA h g(-1) at 350 mA g(-1). After 100 cycles at 70 mA g(-1), the hybrid fibers maintained 400-509 mA h g(-1). Adding low amounts of Sn is beneficial not just for the crosslinking of the polymer precursor, but also to decrease the presence of electrochemically inactive silicon carbide domains within the SiOC fibers. Also, the metallic tin clusters contribute to a higher Li+ insertion in the first cycles. However, high amounts of Sn decrease the electrochemical performance stability. In SiOC fibers synthesized at high temperatures (1200 degrees C), the C-free phase has a significant influence on the stability of the system, by compensating for the volume expansion from the alloying systems (Sn and SiO2), and improving the conductivity of the hybrid system. Therefore, a high amount of carbon and a high graphitization degree are crucial for a high conductivity and a stable electrochemical performance.
- Published
- 2018
8. Ion counting in supercapacitor electrodes using NMR spectroscopy
- Author
-
John M. Griffin, Alexander C. Forse, Hui Wang, Clare P. Grey, Pierre-Louis Taberna, Patrice Simon, Nicole M. Trease, University of Cambridge [UK] (CAM), Stony Brook University [SUNY] (SBU), State University of New York (SUNY), Centre interuniversitaire de recherche et d'ingenierie des matériaux (CIRIMAT), Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC), Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), University of Cambridge (UNITED KINGDOM), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Stony Brook University (USA), Centre Interuniversitaire de Recherche et d'Ingénierie des Matériaux - CIRIMAT (Toulouse, France), and Institut National Polytechnique de Toulouse - INPT (FRANCE)
- Subjects
spectroscopy ,Supercapacitor ,education.field_of_study ,Tetrafluoroborate ,Ion exchange ,Chemistry ,Matériaux ,Population ,Inorganic chemistry ,Analytical chemistry ,Nuclear magnetic resonance spectroscopy ,Electrolyte ,Alkali metal ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Ion ,chemistry.chemical_compound ,NMR spectroscopy ,Adsorption ,supercapacitor electrodes ,[SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering ,Physical and Theoretical Chemistry ,education - Abstract
19F NMR spectroscopy has been used to study the local environments of anions in supercapacitor electrodes and to quantify changes in the populations of adsorbed species during charging. In the absence of an applied potential, anionic species adsorbed within carbon micropores (in-pore) are distinguished from those in large mesopores and spaces between particles (ex-pore) by a characteristic nucleus-independent chemical shift (NICS). Adsorption experiments and two-dimensional exchange experiments confirm that anions are in dynamic equilibrium between the in- and ex-pore environments with an exchange rate in the order of tens of Hz.19Fin situNMR spectra recorded at different charge states reveal changes in the intensity and NICS of the in-pore resonances, which are interpreted in term of changes in the population and local environments of the adsorbed anions that arise due to the charge-storage process. A comparison of the results obtained for a range of electrolytes reveals that several factors influence the charging mechanism. For a tetraethylammonium tetrafluoroborate electrolyte, positive polarisation of the electrode is found to proceed by anion adsorption at a low concentration, whereas increased ion exchange plays a more important role for a high concentration electrolyte. In contrast, negative polarization of the electrode proceeds by cation adsorption for both concentrations. For a tetrabutylammonium tetrafluoroborate electrolyte, anion expulsion is observed in the negative charging regime; this is attributed to the reduced mobility and/or access of the larger cations inside the pores, which forces the expulsion of anions in order to build up ionic charge. Significant anion expulsion is also observed in the negative charging regime for alkali metal bis(trifluoromethane)sulfonimide electrolytes, suggesting that more subtle factors also affect the charging mechanism.
- Published
- 2014
9. A novel structural form of MIL-53 observed for the scandium analogue and its response to temperature variation and CO2adsorption
- Author
-
David Fairen-Jimenez, Stephen P. Thompson, Sharon E. Ashbrook, Paul A. Wright, Valerie R. Seymour, Tina Düren, Alexandra M. Z. Slawin, John P. S. Mowat, and John M. Griffin
- Subjects
Materials science ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Co2 adsorption ,01 natural sciences ,0104 chemical sciences ,3. Good health ,Inorganic Chemistry ,Crystallography ,chemistry ,Thermal ,Molecule ,Scandium ,0210 nano-technology ,Porosity - Abstract
The scandium analogue of the flexible terephthalate MIL-53 yields a novel closed pore structure upon removal of guest molecules which has unusual thermal behaviour and stepwise opening during CO(2) adsorption. By contrast, the nitro-functionalised MIL-53(Sc) cannot fully close and the structure possesses permanent porosity for CO(2).
- Published
- 2012
10. Nuclear magnetic resonance study of ion adsorption on microporous carbide-derived carbon
- Author
-
Nicole M. Trease, Patrice Simon, Hui Wang, Clare P. Grey, John M. Griffin, Alexander C. Forse, Yury Gogotsi, and Volker Presser
- Subjects
Magnetic Resonance Spectroscopy ,Surface Properties ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,01 natural sciences ,Ion ,Adsorption ,Nuclear magnetic resonance ,Particle Size ,Physical and Theoretical Chemistry ,Ions ,Supercapacitor ,Chemistry ,Microporous material ,021001 nanoscience & nanotechnology ,Carbon ,0104 chemical sciences ,NMR spectra database ,Carbide-derived carbon ,0210 nano-technology ,Porosity - Abstract
A detailed understanding of ion adsorption within porous carbon is key to the design and improvement of electric double-layer capacitors, more commonly known as supercapacitors. In this work nuclear magnetic resonance (NMR) spectroscopy is used to study ion adsorption in porous carbide-derived carbons. These predominantly microporous materials have a tuneable pore size which enables a systematic study of the effect of pore size on ion adsorption. Multinuclear NMR experiments performed on the electrolyte anions and cations reveal two main environments inside the carbon. In-pore ions (observed at low frequencies) are adsorbed inside the pores, whilst ex-pore ions (observed at higher frequencies) are not adsorbed and are in large reservoirs of electrolyte between carbon particles. All our experiments were carried out in the absence of an applied electrical potential in order to assess the mechanisms related to ion adsorption without the contribution of electrosorption. Our results indicate similar adsorption behaviour for anions and cations. Furthermore, we probe the effect of sample orientation, which is shown to have a marked effect on the NMR spectra. Finally, we show that a (13)C →(1)H cross polarisation experiment enables magnetisation transfer from the carbon architecture to the adsorbed species, allowing selective observation of the adsorbed ions and confirming our spectral assignments.
- Published
- 2013
11. Ionothermal 17O enrichment of oxides using microlitre quantities of labelled water
- Author
-
Russell E. Morris, Dinu Iuga, Daniel M. Dawson, Sharon E. Ashbrook, Valerie R. Seymour, David W. Aldous, John M. Griffin, and Lucy Clark
- Subjects
Coupling constant ,Stereochemistry ,Isotropy ,Oxide ,Analytical chemistry ,General Chemistry ,Spectral line ,law.invention ,Bond length ,NMR spectra database ,chemistry.chemical_compound ,chemistry ,law ,Calcination ,Topology (chemistry) - Abstract
We present an ionothermal-based method for the simple and low-cost enrichment in 17O of oxide materials. This is demonstrated for the case of SIZ-4, an ionothermally-prepared aluminophosphate framework with the CHA topology. A preliminary study of unenriched samples of SIZ-4 highlights the importance of the careful choice of template in order to obtain an ordered structure. We then show how an ionothermal synthesis procedure incorporating microlitre quantities of 17O-enriched H2O enables as-prepared and calcined samples of SIZ-4 to be obtained with 17O enrichment levels that are sufficient to enable the recording of high-quality 17O solid-state NMR spectra. While second-order quadrupolar-broadened resonances are unresolved in 17O MAS NMR spectra, 17O double-rotation (DOR) and multiple-quantum (MQ)MAS NMR spectra reveal distinct resonances that are partially assigned by comparison with NMR parameters derived using first-principles calculations. The calculations also enable an investigation of the dependence of 17O NMR parameters on the local structural environment. We find that both the 17O isotropic chemical shift and quadrupolar coupling constant show clear dependencies on Al–O–P bond lengths, and angles and will therefore provide a sensitive probe of structure and geometry in aluminophosphate frameworks in future studies.
- Published
- 2012
12. 93Nb NMR and DFT investigation of the polymorphs of NaNbO3
- Author
-
Daniel M. Dawson, Richard I. Walton, Karen E. Johnston, Sharon E. Ashbrook, John M. Griffin, and Philip Lightfoot
- Subjects
Phase transition ,Magnetic Resonance Spectroscopy ,Chemistry ,Niobium ,Sodium ,Temperature ,General Physics and Astronomy ,Oxides ,Nuclear magnetic resonance spectroscopy ,Spectral line ,Pseudopotential ,Nuclear magnetic resonance ,Chemical physics ,Phase (matter) ,Metastability ,Physical and Theoretical Chemistry ,Crystallization ,Phase diagram ,Perovskite (structure) - Abstract
Sodium niobate (NaNbO(3)) has a particularly complex phase diagram, with a series of phase transitions as a function of temperature and pressure, and even at room temperature a number of different structural variations have been suggested. Recent work has demonstrated that bulk powders of NaNbO(3), prepared using a variety of synthetic approaches, contain a mixture of perovskite phases; the commonly reported Pbcm phase and a second, polar phase tentatively identified as belonging to space group P2(1)ma. The two phases exhibit very similar (23)Na MAS NMR spectra, although high-resolution MQMAS spectra were able to distinguish between them. Here, we investigate whether different perovskite polymorphs can be distinguished and/or identified using a variety of (93)Nb NMR methods, including MAS, MQMAS and wideline experiments. We compare the experimental results obtained for these more common perovskite materials to those for the metastable ilmenite polymorph of NaNbO(3). Our experimental results are supported by first-principles calculations of NMR parameters using a planewave pseudopotential approach. The calculated NMR parameters appear very different for each of the phases investigated, but high forces on the atoms indicate many of the structural models derived from diffraction require optimisation of the atomic coordinates. After geometry optimisation, most of these perovskite phases exhibit very similar NMR parameters, in contrast to recent work where it was suggested that (93)Nb provides a useful tool for distinguishing NaNbO(3) polymorphs. Finally, we consider the origin of the quadrupolar coupling in these materials, and its dependence on the deviation from ideality of the NbO(6) octahedra.
- Published
- 2011
13. Complete 1H resonance assignment of β-maltose from 1H–1H DQ-SQ CRAMPS and 1H (DQ-DUMBO)–13C SQ refocused INEPT 2D solid-state NMR spectra and first principles GIPAW calculations
- Author
-
Jonathan R. Yates, Lyndon Emsley, Chris J. Pickard, Tran N. Pham, Amy L. Webber, Anne Lesage, Bénédicte Elena, Francesco Mauri, John M. Griffin, Ana M. Gil, Robin S. Stein, and Steven P. Brown
- Subjects
NMR spectra database ,Nuclear magnetic resonance ,fisica ,Solid-state nuclear magnetic resonance ,Chemistry ,Chemical shift ,General Physics and Astronomy ,Resonance ,Pulse sequence ,Nuclear magnetic resonance spectroscopy ,Physical and Theoretical Chemistry ,Two-dimensional nuclear magnetic resonance spectroscopy ,Homonuclear molecule - Abstract
A disaccharide is a challenging case for high-resolution (1)H solid-state NMR because of the 24 distinct protons (14 aliphatic and 10 OH) having (1)H chemical shifts that all fall within a narrow range of approximately 3 to 7 ppm. High-resolution (1)H (500 MHz) double-quantum (DQ) combined rotation and multiple pulse sequence (CRAMPS) solid-state NMR spectra of beta-maltose monohydrate are presented. (1)H-(1)H DQ-SQ CRAMPS spectra are presented together with (1)H (DQ)-(13)C correlation spectra obtained with a new pulse sequence that correlates a high-resolution (1)H DQ dimension with a (13)C single quantum (SQ) dimension using the refocused INEPT pulse-sequence element to transfer magnetization via one-bond (13)C-(1)H J couplings. Compared to the observation of only a single broad peak in a (1)H DQ spectrum recorded at 30 kHz magic-angle spinning (MAS), the use of DUMBO (1)H homonuclear decoupling in the (1)H DQ CRAMPS experiment allows the resolution of distinct DQ correlation peaks which, in combination with first-principles chemical shift calculations based on the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach, enables the assignment of the (1)H resonances to the 24 distinct protons. We believe this to be the first experimental solid-state NMR determination of the hydroxyl OH (1)H chemical shifts for a simple sugar. Variable-temperature (1)H-(1)H DQ CRAMPS spectra reveal small increases in the (1)H chemical shifts of the OH resonances upon decreasing the temperature from 348 K to 248 K.
- Published
- 2010
14. Dynamics on the microsecond timescale in hydrous silicates studied by solid-state 2H NMR spectroscopy
- Author
-
Stephen Wimperis, John M. Griffin, Andrew J. Miller, Sharon E. Ashbrook, and Andrew J. Berry
- Subjects
Deuterium NMR ,Carbon-13 NMR satellite ,Chemistry ,Analytical chemistry ,General Physics and Astronomy ,Transverse relaxation-optimized spectroscopy ,Phosphorus-31 NMR spectroscopy ,Fluorine-19 NMR ,Nuclear magnetic resonance spectroscopy ,Nuclear magnetic resonance crystallography ,Physical and Theoretical Chemistry ,Carbon-13 NMR - Abstract
Solid-state (2)H NMR spectroscopy has been used to probe the dynamic disorder of hydroxyl deuterons in a synthetic sample of deuterated hydroxyl-clinohumite (4Mg(2)SiO(4).Mg(OD)(2)), a proposed model for the incorporation of water within the Earth's mantle. Both static and magic angle spinning (MAS) NMR methods were used. Static (2)H NMR appears to reveal little evidence of the dynamic process, yielding results similar to those obtained from deuterated brucite (Mg(OD)(2)), where no dynamics on the relevant timescale are expected to be present. However, in (2)H MAS NMR spectra, considerable line broadening is observed for hydroxyl-clinohumite and a (2)H double-quantum (DQ) MAS NMR spectrum confirms that this is due to motion on the microsecond timescale. Using a model for dynamic exchange of the hydroxyl deuterons between two sites identified in previous diffraction studies, first-principles density functional theory (DFT) calculations of (2)H (spin I = 1) quadrupolar NMR parameters, and a simple analytical model for dynamic line broadening in MAS NMR experiments, we were able to reproduce the observed motional line broadening and use this to estimate a rate constant for the dynamic process. From analysis of the observed (2)H linewidths in variable-temperature MAS experiments, an activation energy for the exchange process was also determined. A simulated static (2)H NMR lineshape based on our dynamic model is consistent with the observed experimental static NMR spectrum, confirming that the motion present in this system is not easily detectable using a static NMR approach. Finally, a (2)H DQMAS NMR spectrum of fluorine-substituted (2)H-enriched hydroxyl-clinohumite shows how the dynamic exchange process is inhibited by O-DF(-) hydrogen-bonding interactions.
- Published
- 2010
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.