I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[10038]
Open Access
Abstract: Magnesium potassium phosphate cements (MKPC) were investigated to determine their efficacy towards retardation of reactive uranium metal corrosion. Optimised low-water content, fly ash (FA) and blast furnace slag (BFS) blended MKPC formulations were developed and their fluidity, hydration behaviour, strength and phase assemblage investigated. In-situ time resolved synchrotron powder X-ray diffraction was used to detail the early age (~60 h) phase assemblage development and hydration kinetics, where the inclusion of BFS was observed to delay the formation of struvite-K by ~14 h compared to FA addition (~2 h). All samples set within this period, suggesting the possible formation of a poorly crystalline binding phase prior to struvite-K crystallisation. Long-term corrosion trials using metallic uranium indicated that MKPC systems are capable of limiting uranium corrosion rates (reduced by half), when compared to a UK nuclear industry grout, which highlights their potential application radioactive waste immobilisation.
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May 2021
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[22322]
Abstract: The lithium-exchanged form of a merlinoite zeolite (MER) with Si/Al = 4.2 (unit cell composition Li6.2Al6.2Si25.8O64) possesses a strongly contracted framework when dehydrated (the unit cell volume decreases by 12.9% from the hydrated “wide-pore” form to the dehydrated “narrow-pore” form). It shows cooperative adsorption behavior for CO2, leading to two-step isotherms with the second step at elevated pressure (>2.5 bar at 298 K). Partially exchanging Na and K cations to give single-phase Li,Na- and Li,K-MER materials reduces the pressure of this second adsorption step because the transition from narrow- to wide-pore forms upon CO2 adsorption occurs at lower partial pressures compared to that in Li-MER: partial exchange with Cs does not reduce the pressure of this transition. Exsolution effects are also seen at K cation contents >2.2 per unit cell. The phase transitions proceed via intermediate structures by complex phase behavior rarely seen for zeolitic materials. The strongly distorted narrow-pore structures adopted upon dehydration give one-dimensional channel structures in which the percolation of CO2 through the material requires cation migration from their locations in ste sites. This is slow in Li3.4Cs2.8-MER where Cs cations occupy these critical ste cavities in the channels, causing very slow adsorption kinetics. As the partial pressure of CO2 increases, a threshold pressure is reached where cooperative adsorption and Cs cation migration occur and the wide-pore form results, with a three-dimensionally connected pore system, leading to a sharp increase in uptake. This is far in excess of the increase of unit cell volume because more of the pore space becomes accessible. Strong hysteretic effects occur upon desorption, leading to CO2 encapsulation. CO2 remaining within the material after repeated adsorption/desorption cycles without heated activation improves sorption kinetics and modifies the stepped isotherms.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Ashok S.
Menon
,
Seda
Ulusoy
,
Dickson O.
Ojwang
,
Lars
Riekehr
,
Christophe
Didier
,
Vanessa K.
Peterson
,
German
Salazar-alvarez
,
Peter
Svedlindh
,
Kristina
Edström
,
Cesar Pay
Gomez
,
William R.
Brant
Diamond Proposal Number(s):
[21804]
Open Access
Abstract: Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol–gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Tatchamapan
Yoskamtorn
,
Pu
Zhao
,
Xin-ping
Wu
,
Kirsty
Purchase
,
Fabio
Orlandi
,
Pascal
Manuel
,
James
Taylor
,
Yiyang
Li
,
Sarah
Day
,
Lin
Ye
,
Chiu C.
Tang
,
Yufei
Zhao
,
S. C. Edman
Tsang
Abstract: Understanding structural responses of metal–organic frameworks (MOFs) to external stimuli such as the inclusion of guest molecules and temperature/pressure has gained increasing attention in many applications, for example, manipulation and manifesto smart materials for gas storage, energy storage, controlled drug delivery, tunable mechanical properties, and molecular sensing, to name but a few. Herein, neutron and synchrotron diffractions along with Rietveld refinement and density functional theory calculations have been used to elucidate the responsive adsorption behaviors of defect-rich Zr-based MOFs upon the progressive incorporation of ammonia (NH3) and variable temperature. UiO-67 and UiO-bpydc containing biphenyl dicarboxylate and bipyridine dicarboxylate linkers, respectively, were selected, and the results establish the paramount influence of the functional linkers on their NH3 affinity, which leads to stimulus-tailoring properties such as gate-controlled porosity by dynamic linker flipping, disorder, and structural rigidity. Despite their structural similarities, we show for the first time the dramatic alteration of NH3 adsorption profiles when the phenyl groups are replaced by the bipyridine in the organic linker. These molecular controls stem from controlling the degree of H-bonding networks/distortions between the bipyridine scaffold and the adsorbed NH3 without significant change in pore volume and unit cell parameters. Temperature-dependent neutron diffraction also reveals the NH3-induced rotational motions of the organic linkers. We also demonstrate that the degree of structural flexibility of the functional linkers can critically be affected by the type and quantity of the small guest molecules. This strikes a delicate control in material properties at the molecular level.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Abstract: The structure and reorientational dynamics of KB3H8 were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the α′- and β-polymorphs. Furthermore, it was found that the [B3H8]− anion undergoes different reorientational motions in the three polymorphs α, α′, and β. In α-KB3H8, the [B3H8]− anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C2 symmetry axis of the [B3H8]− anion upon transitioning to α′-KB3H8. After transitioning to β-KB3H8, the [B3H8]− anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of β-KB3H8 deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B3H8]− anion facilitates the K+ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K+ conductivity.
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Feb 2021
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I11-High Resolution Powder Diffraction
I20-EDE-Energy Dispersive EXAFS (EDE)
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Longfei
Lin
,
Mengtian
Fan
,
Alena M.
Sheveleva
,
Xue
Han
,
Zhimou
Tang
,
Joseph H.
Carter
,
Ivan
Da Silva
,
Christopher
Parlett
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
German
Sastre
,
Svemir
Rudic
,
Hamish
Cavaye
,
Stewart F.
Parker
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Anibal J.
Ramirez-cuesta
,
Martin P.
Attfield
,
Yueming
Liu
,
Chiu C.
Tang
,
Buxing
Han
,
Sihai
Yang
Diamond Proposal Number(s):
[2359]
Open Access
Abstract: Optimising the balance between propene selectivity, propene/ethene ratio and catalytic stability and unravelling the explicit mechanism on formation of the first carbon–carbon bond are challenging goals of great importance in state-of-the-art methanol-to-olefin (MTO) research. We report a strategy to finely control the nature of active sites within the pores of commercial MFI-zeolites by incorporating tantalum(V) and aluminium(III) centres into the framework. The resultant TaAlS-1 zeolite exhibits simultaneously remarkable propene selectivity (51%), propene/ethene ratio (8.3) and catalytic stability (>50 h) at full methanol conversion. In situ synchrotron X-ray powder diffraction, X-ray absorption spectroscopy and inelastic neutron scattering coupled with DFT calculations reveal that the first carbon–carbon bond is formed between an activated methanol molecule and a trimethyloxonium intermediate. The unprecedented cooperativity between tantalum(V) and Brønsted acid sites creates an optimal microenvironment for efficient conversion of methanol and thus greatly promotes the application of zeolites in the sustainable manufacturing of light olefins.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Abstract: Electronic phase separation into charge-ordered (CO) and charge-averaged (CA) phases in
Ca
Fe
3
−
x
M
x
O
5
samples for dopants
M
=
Mn
and Co has been investigated using powder neutron and x-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. Electronic phase separation is observed in lightly doped
Ca
Fe
3
O
5
samples, where
4
–
10
%
Ca is replaced by Mn, Fe, or Co, and the CA ground state is stabilized at higher doping levels. The CO and CA phases are found to emerge below a common magnetic ordering temperature at
300
–
320
K
providing strong evidence for a lattice strain-driven mechanism that couples their magnetic transitions.
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Feb 2021
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B18-Core EXAFS
B22-Multimode InfraRed imaging And Microspectroscopy
I11-High Resolution Powder Diffraction
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Shaojun
Xu
,
Xue
Han
,
Yujie
Ma
,
Thien D.
Duong
,
Longfei
Lin
,
Emma K.
Gibson
,
Alena
Sheveleva
,
Sarayute
Chansai
,
Alex
Walton
,
Duc-the
Ngo
,
Mark D.
Frogley
,
Chiu C.
Tang
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
C. Richard A.
Catlow
,
Christopher
Hardacre
,
Sihai
Yang
,
Martin
Schroeder
Open Access
Abstract: Efficient catalytic conversion of NO2 to non-harmful species remains an important target for research. State-of-the-art deNOx processes are based upon ammonia (NH3)-assisted selective catalytic reduction (NH3-SCR) over Cu-exchanged zeolites at elevated temperatures. Here, we describe a highly efficient non-thermal plasma (NTP) deNOx process catalyzed by a Cu-embedded metal-organic framework, Cu/MFM-300(Al), at room temperature. Under NTP activation at 25°C, Cu/MFM-300(Al) enables direct decomposition of NO2 into N2, NO, N2O, and O2 without the use of NH3 or other reducing agents. NO2 conversion of 96% with a N2 selectivity of 82% at a turnover frequency of 2.9 h−1 is achieved, comparable to leading NH3-SCR catalysts that use NH3 operating at 250°C–550°C. The mechanism for the rate-determining step (NO→N2) is elucidated by in operando diffuse reflectance infrared Fourier transform spectroscopy, and electron paramagnetic resonance spectroscopy confirms the formation of Cu2+⋯NO nitrosylic adducts on Cu/MFM-300(Al), which facilitates NO dissociation and results in the notable N2 selectivity.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786, 17375]
Open Access
Abstract: Cadmium cyanide, Cd(CN)2, is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. Here we show that this NTE is actually X-ray-exposure dependent: Cd(CN)2 contracts not only on heating but also on irradiation by X-rays. This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion. We call this effect ‘negative X-ray expansion’ (NXE) and suggest its origin involves an interaction between X-rays and cyanide ‘flips’; in particular, we rule out local heating as a possible mechanism. Irradiation also affects the nature of a low-temperature phase transition. Our analysis resolves discrepancies in NTE coefficients reported previously on the basis of X-ray diffraction measurements, and we establish the ‘true’ NTE behaviour of Cd(CN)2 across the temperature range 150–750 K. The interplay between irradiation and mechanical response in Cd(CN)2 highlights the potential for exploiting X-ray exposure in the design of functional materials.
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Feb 2021
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B22-Multimode InfraRed imaging And Microspectroscopy
I11-High Resolution Powder Diffraction
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Lydia
Briggs
,
Ruth
Newby
,
Xue
Han
,
Christopher
Morris
,
Mathew
Savage
,
Cristina
Perez
,
Timothy L.
Easun
,
Mark
Frogley
,
Gianfelice
Cinque
,
Claire A.
Murray
,
Chiu C.
Tang
,
Sihai
Yang
,
Junliang
Sun
,
Martin
Schroeder
Diamond Proposal Number(s):
[22137, 22138]
Open Access
Abstract: We report the adsorption of C2H2, CO2 and SO2 in a new, ultra-stable Cr(III)-based MOF, MFM-300(Cr), {[Cr2(OH)2(L)], H4L = biphenyl-3,3',5,5'-tetracarboxylic acid}. MFM-300(Cr) shows uptakes of 7.37, 7.73 and 8.59 mmol g-1 for CO2, C2H2 and SO2, respectively, at 273 K, 1.0 bar, and shows a higher selectivity for SO2/CO2 compared with the Al(III) analogue MFM-300(Al) (selectivity of 79 vs. 45). In order to monitor the effects of changing metal centre on gas uptake and to integrate the properties of the homometallic analogues, the mixed metal MFM-300(Al0.67Cr0.33), [Al1.34Cr0.66(OH)2L] has been synthesised. In situ synchrotron micro-FTIR spectroscopy has identified distinct CO2 binding environments on Al-O(H)-Al, Cr-O(H)-Cr and Al-O(H)-Cr bridges in MFM-300(Al0.67Cr0.33), and we have determined the binding domains for these gases by in situ synchrotron X-ray diffraction in both MFM-300(Cr) and MFM-300(Al0.67Cr0.33). The capability of these materials for gas separation has been confirmed by dynamic breakthrough experiments. The incorporation of Al(III) and Cr(III) within the same framework allows tuning of the host-guest and guest-guest interactions within these functional porous materials.
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Feb 2021
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