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关键词： Forward osmosis (FO)   Graphene oxide quantum dot (GQD)   Outer-selective hollow fiber (OSHF)   Thin-film nanocomposite (TFN)   Interfacial polymerization (IP)  

摘要： We report an ultra-low loading of graphene oxide quantum dots (GQDs) into the polyamide (PA) layer of an outer-selective hollow fiber (OSHF) thin-film composite (TFC) membrane using the vacuum-assisted interfacial polymerization (VAIP) technique to improve the water permeability of OSHF TFC membranes without sacrificing membrane selectivity. Experimental results showed that GQD loading in the PA layer influenced membrane performance. The membrane with a GQD loading of 5 mg L-1 (TFN5) demonstrated an optimal water flux of 30.9 L m- 2 h-1 and a specific reverse solute flux (SRSF) of 0.12 g L-1. To investigate the effect of GQDs on the interfacial polymerization (IP) reaction and membrane performance, molecular dynamics (MD) simulation was employed at the water-hexane and water-PA interfaces. The simulation results showed that GQDs decreased the reaction rate during the IP process by reducing the diffusivities of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). Additionally, GQDs reduced water permeability by acting as barriers to water molecules when present at a high concentration near the PA layer surface. At a very high loading, GQDs aggregated at the waterhexane interface and reduced the membrane selectivity by forming non-selective voids at the interface between the PA layer and GQDs. Together with the experimental findings, the MD simulation results delivered a good insight into the GQDs' effect on the TFC membrane's surface and transport properties at both macroscopic and microscopic levels.

关键词： Quantum dots   Absorption   Catalysts   Quantum mechanics   Electrical conductivity  

摘要： The photophysical properties of Cu-deficient Cu01.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV-vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping subbandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe-2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV-vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.

关键词： Quaternionic analysis   Vector field theory   Fractals  

摘要： We consider the behavior of generalized Laplacian vector fields on a Jordan domain of R-3 with fractal boundary. Our approach is based on properties of the Teodorescu transform and suitable extension of the vector fields. Specifically, the present article addresses the decomposition problem of a Holder continuous vector field on the boundary (also called reconstruction problem) into the sum of two generalized Laplacian vector fields in the domain and in the complement of its closure, respectively. In addition, conditions on a Hiilder continuous vector field on the boundary to be the trace of a generalized Laplacian vector field in the domain are also established. (C) 2021 Elsevier Inc. All rights reserved.

关键词： Nuclear magnetic resonance spectroscopy  

摘要： Previously, we scrutinized the dielectric spectra of a binary glass former made by a low-molecular high-T-g component 2-(m-tertbutylphenyl)-2'-tertbutyl-9,9'-spirobi[9H]fluorene (m-TPTS;T-g = 350 K) and low-T-g tripropyl phosphate (TPP;T-g = 134 K) [Korber et al., Phys. Chem. Chem. Phys. 23, 7200 (2021)]. Here, we analyze nuclear magnetic resonance (NMR) spectra and stimulated echo decays of deuterated m-TPTS-d(4) (H-2) and TPP (P-31) and attempt to understand the dielectric spectra in terms of component specific dynamics. The high-T-g component (alpha(1)) shows relaxation similar to that of neat systems, yet with some broadening upon mixing. This correlates with high-frequency broadening of the dielectric spectra. The low-T-g component (alpha(2)) exhibits highly stretched relaxations and strong dynamic heterogeneities indicated by "two-phase" spectra, reflecting varying fractions of fast and slow liquid-like reorienting molecules. Missing for the high-T-g component, such two-phase spectra are identified down to w(TPP) = 0.04, indicating that isotropic reorientation prevails in the rigid high-T-g matrix stretching from close to T-g(TPP) to T-g1(w(TPP)). This correlates with low-frequency broadening of the dielectric spectra. Two T-g values are defined: T-g1(w(TPP)) displays a plasticizer effect, whereas T-g2(w(TPP)) passes through a maximum, signaling extreme separation of the component dynamics at low w(TPP). We suggest understanding the latter counter-intuitive feature by referring to a crossover from "single glass" to "double glass" scenario revealed by recent MD simulations. Analyses reveal that a second population of TPP molecules exists, which is associated with the dynamics of the high-T-g component. However, the fractions are lower than suggested by the dielectric spectra. We discuss this discrepancy considering the role of collective dynamics probed by dielectric but not by NMR spectroscopy. Published under an exclusive license by AIP Publishing.

关键词： Molecular dynamics  

摘要： Nonadiabatic molecular dynamics occur in a wide range of chemical reactions and femtochemistry experiments involving electronically excited states. These dynamics are hard to treat numerically as the system's complexity increases, and it is thus desirable to have accurate yet affordable methods for their simulation. Here, we introduce a linearized semiclassical method, the generalized discrete truncated Wigner approximation (GDTWA), which is well-established in the context of quantum spin lattice systems, into the arena of chemical nonadiabatic systems. In contrast to traditional continuous mapping approaches, e.g., the Meyer-Miller-Stock-Thoss and the spin mappings, GDTWA samples the electron degrees of freedom in a discrete phase space and thus forbids an unphysical unbounded growth of electronic state populations. The discrete sampling also accounts for an effective reduced but non-vanishing zero-point energy without an explicit parameter, which makes it possible to treat the identity operator and other operators on an equal footing. As numerical benchmarks on two linear vibronic coupling models and Tully's models show, GDTWA has a satisfactory accuracy in a wide parameter regime, independent of whether the dynamics is dominated by relaxation or by coherent interactions. Our results suggest that the method can be very adequate to treat challenging nonadiabatic dynamics problems in chemistry and related fields. Published under an exclusive license by AIP Publishing.

摘要： Selection of residues and other molecular fragments for inclusion in the quantum mechanics (QM) region for QM/ molecular mechanics (MM) simulations is an important step for these calculations. Here, we present an approach that combines protein sequence/structure evolution and electron localization function (ELF) analyses. The combination of these two analyses allows the determination of whether a residue needs to be included in the QM subsystem or can be represented by the MM environment. We have applied this approach on two systems previously investigated by QM/MM simulations, 4-oxalocrotonate tautomerase (4OT) and ten-eleven translocation-2 (TET2), that provide examples where fragments may or may not need to be included in the QM subsystem. Subsequently, we present the use of this approach to determine the appropriate QM subsystem to calculate the minimum energy path (MEP) for the reaction catalyzed by human DNA polymerase lambda (Pol lambda) with a third cation in the active site. Our results suggest that the combination of protein evolutionary and ELF analyses provides insights into residue/ molecular fragment selection for QM/MM simulations.

关键词： Open quantum systems   Open quantum systems & decoherence   Quantum computation   Quantum control   Quantum simulation   Superconducting qubits  

摘要： Digital quantum simulators provide a diversified tool for solving the evolution of quantum systems with complicated Hamiltonians and hold great potential for a wide range of applications. Although much attention is paid to the unitary evolution of closed quantum systems, dissipation and noise are vital in understanding the dynamics of practical quantum systems. In this work, we experimentally demonstrate a digital simulation of an open quantum system in a controllable Markovian environment with the assistance of a single ancillary qubit. By Trotterizing the quantum Liouvillians, the continuous evolution of an open quantum system is effectively realized, and its application in error mitigation is demonstrated by adjusting the simulated noise intensities. High-order Trotter for open quantum dynamics is also experimentally investigated and shows higher accuracy. Our results represent a significant step toward hardware-efficient simulation of open quantum systems and error mitigation in quantum algorithms in noisy intermediate-scale quantum systems.

关键词： lithium-sulfur batteries   VN quantum dots   holey graphene   shuttle effects   polysulfide conversion  

摘要： Lithium-sulfur batteries (LSBs) have been considered as potential next-generation energy storage systems due to their high specific energy of 2600 Wh kg(-1) and 2800 Wh L-1. Nevertheless, the practical application of LSBs still faces several hazards, including the shuttle effect of soluble lithium polysulfides, low electrical conductivities of solid sulfur and lithium sulfides, and large volume expansion during charge/discharge cycles. To address this critical challenge, we innovatively proposed facile synthesis of nanostructured VN quantum dots (VNQD)/holey graphene matrix for stabilizing the sulfur cathode by simultaneously promoting the trapping, anchoring, and catalyzing efficiencies of both LiPSs and Li2S. Benefiting from abundant edge catalytic sites of VNQD, in-plane nanopores of graphene, and high electrical conductivity, the sulfur host not only provides high adsorption capability toward soluble polysulfides, strong binding ability for anchoring solid Li2S, and their rapid conversion kinetics but also contributes abundant sulfur storage sites and efficient transport pathways for lithium ions (Li+) and electrons. Consequently, the sulfur cathode exhibits high initial capacities of 1320 mAh g(-1), high rate capability (850 mAh g(-1) @ 4 mA cm(-2)), and high capacity retention of 99.95% per cycle after 500 cycles, providing a feasible solution for the practical utilization of shuttle-free Li-S batteries.

关键词： Carrier dynamics   Edge states   Quantum transport   Thermoelectric effects   Topological insulators   Boltzmann theory   Semiclassical methods  

摘要： We study quantum quenches of helical liquids with spin-flip inelastic scattering. Counterpropagating charge packets in helical edges can be created by an ultrashort electric pulse applied across a 2D topological insulator. Localized “hot spots” that form due to scattering enable two types of strongly nonlinear wave dynamics. First, propagating packets develop self-focusing shock fronts. Second, colliding packets with opposite charge can exhibit near-perfect retroreflection, despite strong dissipation. This leads to frequency doubling that could be detected experimentally from emitted terahertz radiation.