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Abstract: We report the guest-anion-induced photoluminescence enhancement of metal–organic frameworks (UiO-66-NH2), first based upon diffraction and computational evidence. We found that only limited anions, namely, carbonate and fluoride, can lead to a significant enhancement in photoluminescence, whereas their related anions, such as acetate and chloride, cannot. The optimized crystal structures reveal that the guest carbonate and fluoride ions interact with four framework amino functional groups through hydrogen bonding (ca. 1.6–1.7 Å) that ultimately forms a quaternary (−N(H))4···X– molecular bridge around the nodal center. Hence, the hydrogen-bonded molecular bridge not only restricts the intermolecular C–C rotation of the linker molecules but also greatly perturbs the electronic densities between the guest anions and the framework amino groups.
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Jul 2021
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I11-High Resolution Powder Diffraction
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Guangchao
Li
,
Christopher
Foo
,
Xianfeng
Yi
,
Wei
Chen
,
Pu
Zhao
,
Pan
Gao
,
Tatchamapan
Yoskamtorn
,
Yao
Xiao
,
Sarah
Day
,
Chiu C.
Tang
,
Guangjin
Hou
,
Anmin
Zheng
,
Shik Chi Edman
Tsang
Abstract: There has been a long debate on how and where active sites are created for molecular adsorption and catalysis in zeolites, which underpin many important industrial applications. It is well accepted that Lewis acidic sites (LASs) and basic sites (LBSs) as active sites in pristine zeolites are generally believed to be the extra-framework Al species and residue anion (OH–) species formed at fixed crystallographic positions after their synthesis. However, the dynamic interactions of adsorbates/reactants with pristine zeotype materials to “create” sites during real conditions remain largely unexplored. Herein, direct experimental observation of the establishment of induced active sites in silicoaluminophosphate (SAPO) by an adsorbate is for the first time made, which contradicts the traditional view of the fixed active sites in zeotype materials. Evidence shows that an induced frustrated Lewis pair (FLP, three-coordinated framework Al as LAS and SiO (H) as LBS) can be transiently favored for heterolytic molecular binding/reactions of competitive polar adsorbates due to their ineffective orbital overlap in the rigid framework. High-resolution magic-angle-spinning solid-state NMR, synchrotron X-ray diffraction, neutron powder diffraction, in situ diffuse reflectance infrared Fourier transform spectroscopy, and ab initio molecular dynamics demonstrate the transformation of a typical Brønsted acid site (Al(OH)Si) in SAPO zeolites to new induced FLP structure for hetereolytic binding upon adsorption of a strong polar adsorbate. Our unprecedented finding opens up a new avenue to understanding the dynamic establishment of active sites for adsorption or chemical reactions under molecular bombardment of zeolitic structures.
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Jun 2021
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I11-High Resolution Powder Diffraction
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Martin
Schroeder
,
Louis
Kimberley
,
Alena M.
Sheveleva
,
Jiangnan
Li
,
Joseph H.
Carter
,
Xinchen
Kang
,
Gemma L.
Smith
,
Xue
Han
,
Sarah J.
Day
,
Chiu C.
Tang
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
Sihai
Yang
Abstract: Selective oxidation of benzylic C‐H compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metals catalysts. Here, we report the efficient oxidation of benzylic C‐H groups in a broad range of substrates under mild conditions over a robust metal‐organic framework material, MFM‐170, incorporating redox‐active [Cu2II(O2CR)4] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X‐ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant tBuOOH (t‐butyl hydroperoxide) via partial reduction to [CuIICuI(O2CR)4] species.
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Apr 2021
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I11-High Resolution Powder Diffraction
|
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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Diamond Proposal Number(s):
[14099]
Open Access
Abstract: Two-dimensional (2D) hexagonal boron nitride (h-BN) is becoming increasingly interesting for wider engineering applications. Thermal exfoliation is being suggested as a facile technology to produce large quantities of 2D h-BN. Further optimization of the process requires fundamental understanding of the exfoliation mechanism, which is hardly realized by ex-situ techniques. In this study, time resolved in-situ synchrotron X-ray powder diffraction experiments are conducted while heat treating bulk h-BN up to 1273 K. During the heating process, linear expansion of c-axis is observed and the contraction of a-axis up to around 750 K is consistent with previous research. However, a changing behavior from contraction to expansion in a- axis direction is newly observed when heating over 750 K. With the consideration of previous thermally oxidation studies, a hypothesis of thermal assisted exfoliation with oxygen interstitial and substitution of nitrogen at high temperature is proposed.
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Nov 2020
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I11-High Resolution Powder Diffraction
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Wei-Che
Lin
,
Simson
Wu
,
Guangchao
Li
,
Ping-Luen
Ho
,
Yichen
Ye
,
Pu
Zhao
,
Sarah
Day
,
Chiu
Tang
,
Wei
Chen
,
Anmin
Zheng
,
Benedict T. W.
Lo
,
Shik Chi Edman
Tsang
Diamond Proposal Number(s):
[16358]
Open Access
Abstract: Catalytic conversion of methanol to aromatics and hydrocarbons is regarded as a key alternative technology to oil processing. Although the inclusion of foreign metal species in H-ZSM-5 containing Brønsted acid site (BAS) is commonly found to enhance product yields, the nature of catalytically active sites and the rationalization for catalytic performance still remain obscure. Herein, by acquiring comparable structural parameters by both X-ray and neutron powder diffractions over a number of metal-modified ZSM-5 zeolites, it is demonstrated for the first time that active pairs of metal site-BAS within molecular distance is created when single and isolated transition metal cation is ion-exchanged with the zeolites. According to our DFT model, this could lead to the initial heterolytic cleavage of small molecules such as water and methanol by the pair with subsequent reactions to form products at high selectivity as that observed experimentally. It may account for their active and selective catalytic routes of small molecule activations.
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Oct 2020
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I11-High Resolution Powder Diffraction
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Qi
Xue
,
Yi
Xie
,
Simson
Wu
,
Tai-Sing
Wu
,
Yun-Liang
Soo
,
Sarah
Day
,
Chiu C.
Tang
,
Ho W.
Man
,
Sha T.
Yuen
,
Kwok-Yin
Wong
,
Yin
Wang
,
Benedict T. W.
Lo
,
Shik C. E.
Tsang
Diamond Proposal Number(s):
[23230]
Abstract: We investigate the geometric and electronic properties of single-atom catalysts (SACs) within metal–organic frameworks (MOFs) with respect to electrocatalytic CO2 reduction as a model reaction. A series of mid-to-late 3d transition metals have been immobilised within the microporous cavity of UiO-66-NH2. By employing Rietveld refinement of new-generation synchrotron diffraction, we not only identified the crystallographic and atomic parameters of the SACs that are stabilised with a robust M⋯N(MOF) bonding of ca. 2.0 Å, but also elucidated the end-on coordination geometry with CO2. A volcano trend in the FEs of CO has been observed. In particular, the confinement effect within the rigid MOF can greatly facilitate redox hopping between the Cu SACs, rendering high FEs of CH4 and C2H4 at a current density of −100 mA cm−2. Although only demonstrated in selected SACs within UiO-66-NH2, this study sheds light on the rational engineering of molecular interactions(s) with SACs for the sustainable provision of fine chemicals.
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Oct 2020
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[14555]
Open Access
Abstract: Temperature or pressure-swing sorption in porous metal-organic framework (MOF) materials has been proposed for new gas separation technologies. The high tuneability of MOFs toward particular adsorbates and the relatively low energy penalty for system regeneration means that reversible physisorption in MOFs has the potential to create economic and environmental benefits compared with state-of-the-art chemisorption systems. However, for MOF-based sorbents to be commercialised they have to show long-term stability under the conditions imposed by the application. Here, we demonstrate the structural stability of MFM-300(Al) to the presence of a series of industrially-relevant toxic and corrosive gases, including SO2, NO2 and NH3, over four years using long duration synchrotron X-ray powder diffraction. Full structural analysis of gas-loaded MFM-300(Al) confirms the retention of these toxic gas molecules within the porous framework for up to 200 weeks, and cycling adsorption experiments verified the reusability of MFM-300(Al) for the capture of these toxic air pollutants.
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Aug 2020
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I11-High Resolution Powder Diffraction
|
Chao
Xu
,
Katharina
Märker
,
Juhan
Lee
,
Amoghavarsha
Mahadevegowda
,
Philip J.
Reeves
,
Sarah J.
Day
,
Matthias F.
Groh
,
Steffen P.
Emge
,
Caterina
Ducati
,
B. Layla
Mehdi
,
Chiu C.
Tang
,
Clare P.
Grey
Diamond Proposal Number(s):
[16733, 25186]
Abstract: Ni-rich layered cathode materials are among the most promising candidates for high-energy-density Li-ion batteries, yet their degradation mechanisms are still poorly understood. We report a structure-driven degradation mechanism for NMC811 (LiNi0.8Mn0.1Co0.1O2), in which a proportion of the material exhibits a lowered accessible state of charge at the end of charging after repetitive cycling and becomes fatigued. Operando synchrotron long-duration X-ray diffraction enabled by a laser-thinned coin cell shows the emergence and growth in the concentration of this fatigued phase with cycle number. This degradation is structure driven and is not solely due to kinetic limitations or intergranular cracking: no bulk phase transformations, no increase in Li/Ni antisite mixing and no notable changes in the local structure or Li-ion mobility of the bulk are seen in aged NMCs. Instead, we propose that this degradation stems from the high interfacial lattice strain between the reconstructed surface and the bulk layered structure that develops when the latter is at states of charge above a distinct threshold of approximately 75%. This mechanism is expected to be universal in Ni-rich layered cathodes. Our findings provide fundamental insights into strategies to help mitigate this degradation process.
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Aug 2020
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I11-High Resolution Powder Diffraction
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Mark A.
Levenstein
,
Yi-Yeoun
Kim
,
Liam
Hunter
,
Clara
Anduix-Canto
,
Carlos
Gonzalez Nino
,
Sarah J.
Day
,
Shunbo
Li
,
William J.
Marchant
,
Phillip A.
Lee
,
Chiu C.
Tang
,
Manfred
Burghammer
,
Fiona C.
Meldrum
,
Nikil
Kapur
Diamond Proposal Number(s):
[10425, 12352]
Open Access
Abstract: The clean and reproducible conditions provided by microfluidic devices are ideal sample environments for in situ analyses of chemical and biochemical reactions and assembly processes. However, the small size of microchannels makes investigating the crystallization of poorly soluble materials on-chip challenging due to crystal nucleation and growth that result in channel fouling and blockage. Here, we demonstrate a reusable insert-based microfluidic platform for serial X-ray diffraction analysis and examine scale formation in response to continuous and segmented flow configurations across a range of temperatures. Under continuous flow, scale formation on the reactor walls begins almost immediately on mixing of the crystallizing species, which over time results in occlusion of the channel. Depletion of ions at the start of the channel results in reduced crystallization towards the end of the channel. Conversely, segmented flow can control crystallization, so it occurs entirely within the droplet. Consequently, the spatial location within the channel represents a temporal point in the crystallization process. Whilst each method can provide useful crystallographic information, time-resolved information is lost when reactor fouling occurs and changes the solution conditions with time. The flow within a single device can be manipulated to give a broad range of information addressing surface interaction or solution crystallization.
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Jul 2020
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