Non-Markovian models of stochastic biochemical kinetics often incorporate explicit time delays to effectively model large numbers of intermediate biochemical processes. Analysis and simulation of ...these models, as well as the inference of their parameters from data, are fraught with difficulties because the dynamics depends on the system's history. Here we use an artificial neural network to approximate the time-dependent distributions of non-Markovian models by the solutions of much simpler time-inhomogeneous Markovian models; the approximation does not increase the dimensionality of the model and simultaneously leads to inference of the kinetic parameters. The training of the neural network uses a relatively small set of noisy measurements generated by experimental data or stochastic simulations of the non-Markovian model. We show using a variety of models, where the delays stem from transcriptional processes and feedback control, that the Markovian models learnt by the neural network accurately reflect the stochastic dynamics across parameter space.
Molecularly soft organic-inorganic hybrid perovskites are susceptible to dynamic instabilities of the lattice called octahedral tilt, which directly impacts their carrier transport and exciton-phonon ...coupling. Although the structural phase transitions associated with octahedral tilt has been extensively studied in 3D hybrid halide perovskites, its impact in hybrid 2D perovskites is not well understood. Here, we used scanning tunneling microscopy (STM) to directly visualize surface octahedral tilt in freshly exfoliated 2D Ruddlesden-Popper perovskites (RPPs) across the homologous series, whereby the steric hindrance imposed by long organic cations is unlocked by exfoliation. The experimentally determined octahedral tilts from n = 1 to n = 4 RPPs from STM images are found to agree very well with out-of-plane surface octahedral tilts predicted by density functional theory calculations. The surface-enhanced octahedral tilt is correlated to excitonic redshift observed in photoluminescence (PL), and it enhances inversion asymmetry normal to the direction of quantum well and promotes Rashba spin splitting for n > 1.
Although polymers have been studied for well over a century, there are few examples of covalently linked polymer crystals synthesised directly from solution. One-dimensional (1D) covalent polymers ...that are packed into a framework structure can be viewed as a 1D covalent organic framework (COF), but making a single crystal of this has been elusive. Herein, by combining labile metal coordination and dynamic covalent chemistry, we discover a strategy to synthesise single-crystal metallo-COFs under solvothermal conditions. The single-crystal structure is rigorously solved using single-crystal electron diffraction technique. The non-centrosymmetric metallo-COF allows second harmonic generation. Due to the presence of syntactic pendant amine groups along the polymer chains, the metallopolymer crystal can be further cross-linked into a crystalline woven network.
Dion–Jacobson (DJ) phase organic–inorganic hybrid perovskites (OIHPs) have emerged as promising alternatives to Ruddlesden–Poppers perovskites because of their chemical stability and ferroelectric ...phase. Here we fabricate a ferroelectricity-modulated photodetector based on the n = 2 homologue of the ferroelectric two-dimensional DJ-OIHP (AMP)(MA)Pb2I7 (DJP n =2 , AMP = 4-(aminomethyl)piperidinium; MA = methylammonium), which shows an out-of-plane polarization and a saturated polarization (P s) value of 3.7 μC/cm2. The coercive field of DJP n =2 (0.34 kV/cm) is lower than that for the n = 1 homologue (AMP)PbI4 (DJP n =1 ,0.4 kV/cm). DJP n =2 has a much longer carrier lifetime and absorption edge (580 nm, 2.13 eV) in comparison to DJP n =1 (523 nm, 2.37 eV); thus, DJP n =2 can be used for efficient photodetection in the visible range, in which a responsivity of 0.16 mA/W was achieved at 532 nm. The influence of remnant polarization on the direction and magnitude of the photocurrent was also demonstrated.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
Covalent organic frameworks (COF), with rigid, highly ordered and tunable structures, can actively manipulate the synergy of entropic selectivity and enthalpic selectivity, holding great ...potential as next-generation membrane materials for ion separations. Here, we demonstrated the efficient separation of monovalent cations by COF membrane. The channels of COF membrane are decorated with three different kinds of acid groups. A concept of confined cascade separation was proposed to elucidate the separation process. The channels of COF membrane comprised two kinds of domains, acid-domains and acid-free-domains. The acid-domains serve as confined stages, rendering high selectivity, while the acid-free-domains preserve the pristine channel size, rendering high permeation flux. A set of descriptors of stage properties were designed to elucidate their effect on selective ion transport behavior. The resulting COF membrane acquired high ion separation performances, with an actual selectivity of 4.2–4.7 for K
+
/Li
+
binary mixtures and an ideal selectivity of ~13.7 for K
+
/Li
+
.
Abstract
Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high ...charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm
2
V
−1
s
−1
between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.
Two‐dimensional transition metal dichalcogenides (TMDs) play host to a wide range of novel topological states, such as quantum spin Hall insulators, superconductors, and Weyl semimetals. The rich ...polymorphism in TMDs suggests that phase engineering can be used to switch between different charge order states. Intercalation of atoms or molecules into the van der Waals gap of TMDs has emerged as a powerful approach to modify the properties of the material, leading to phase transition or the formation of substoichiometric phases via compositional tuning, thus broadening the electronic and optical landscape of these materials for a wide range of applications. Here, we review the current efforts in the preparation of intercalated TMD. The challenges and opportunities for intercalated TMDs to create a new device paradigm for material science are discussed.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Single-atom catalysts (SACs) offer many advantages, such as atom economy and high chemoselectivity; however, their practical application in liquid-phase heterogeneous catalysis is hampered by the ...productivity bottleneck as well as catalyst leaching. Flow chemistry is a well-established method to increase the conversion rate of catalytic processes, however, SAC-catalysed flow chemistry in packed-bed type flow reactor is disadvantaged by low turnover number and poor stability. In this study, we demonstrate the use of fuel cell-type flow stacks enabled exceptionally high quantitative conversion in single atom-catalyzed reactions, as exemplified by the use of Pt SAC-on-MoS
/graphite felt catalysts incorporated in flow cell. A turnover frequency of approximately 8000 h
that corresponds to an aniline productivity of 5.8 g h
is achieved with a bench-top flow module (nominal reservoir volume of 1 cm
), with a Pt
-MoS
catalyst loading of 1.5 g (3.2 mg of Pt). X-ray absorption fine structure spectroscopy combined with density functional theory calculations provide insights into stability and reactivity of single atom Pt supported in a pyramidal fashion on MoS
. Our study highlights the quantitative conversion bottleneck in SAC-mediated fine chemicals production can be overcome using flow chemistry.
Abstract
Organics separation for purifying and recycling environment-detrimental solvents is essential to sustainable chemical industries. Covalent organic framework (COF) membranes hold great ...promise in affording precise and fast organics separation. Nonetheless, how to well coordinate facile processing—high crystalline structure—high separation performance remains a critical issue and a grand challenge. Herein, we propose a concept of heterocrystalline membrane which comprises high-crystalline regions and low-crystalline regions. The heterocrystalline COF membranes are fabricated by a two-step procedure, i.e., dark reaction for the construction of high-crystalline regions followed by photo reaction for the construction of low-crystalline regions, thus linking the high-crystalline regions tightly and flexibly, blocking the defect in high-crystalline regions. Accordingly, the COF membrane exhibits sharp molecular sieving properties with high organic solvent permeance up to 44-times higher than the state-of-the-art membranes.
Commercialization of the lithium‐sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li2Sx deposition and sluggish kinetics of Li2S activation. ...Herein, we developed a densely stacked redox‐active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m2 g−1 and a very high bulk density of ca. 1.60 g cm−3. Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li2Sx and its transformation chemistry within the bulky polymer host, leading to fast Li2S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mgs cm−2 (200‐μm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm−2 and good cycling stability (200 cycles) at electrolyte–sulfur (E/S) ratio of 5 μL mgs−1. The assembled pouch cell delivers a cell‐level high energy density of 303 Wh kg−1 and 392 Wh L−1.
A dense‐stacking hexaazatrinaphthylene (HATN) porous polymer is reported. The compact polymer/S cathode (ca. 15 mgs cm−2, 200‐μm thickness) presents a low cathode porosity of 41 % and high areal capacity (>10 mAh cm−2) in a lean electrolyte of 5 μL mg−1. The lithiation/delithiation of HATN polymer by Li2Sx facilitates the formation of intimately bound nanostructured Li2S/S on the bulky polymer host, leading to fast Li2S/S kinetics.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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