Anisotropic Transfer Research Articles

(Invited) Photocatalysis of Mg-Doped SrTiO3 for Conversion of CO2 with H2O

Photocatalysis has been highly attracting the world-wide attentions among many approaches to convert CO2 into value-added products such as CO, HCOOH, CH3OH and CH4, because photocatalytic conversion of CO2 can be a solution for global warming in terms of its renewability, harmlessness, relatively low cost, and stability. Large number of photocatalysts reported in the research field of the photocatalytic conversion of CO2 require the photoirradiation with deep UV light < 300 nm. Recently, our research group found that Al-doped SrTiO3 photocatalyst (Al-STO), which has been previously reported as a superior photocatalyst for overall water splitting[1], also showed the photocatalytic activity for the conversion of CO2 into CO[2]. In this study, the effect of metal dopant in SrTiO3 on the photocatalytic conversion of CO2 was investigated, and it was found that Mg-doped SrTiO3 showed excellent photocatalytic activity for the conversion of CO2 into CO in the presence of AgCo dual cocatalyst[3].Mg-doped SrTiO3 (Mg-STO) was synthesized by a flux method; the mixture of SrTiO3, MgO, and SrCl2 flux was calcined at 1418 K for 15 h. Ag and Co dual cocatalyst was loaded by a chemical reduction method. An aqueous solution of NaH2PO2 reductant was added to the suspension containing Mg-STO, AgNO3, and Co(NO3)2, and it was kept at 353 K for 90 min with vigorous stirring. Photocatalytic conversion of CO2 with H2O was carried out using an external-irradiation-type reaction vessel. AgCo/Mg-STO was dispersed in an aqueous solution of 0.1 M NaHCO3, and high purity CO2 gas was bubbled into the suspension at a flow rate of 30 mL min−1. The monochromatic UV LED lamp (365 nm) was used as a light source. The gaseous products were analyzed by TCD-GC (H2, O2) and FID-GC equipped with a methanizer (CO).AgCo/Mg-STO exhibited much higher photocatalytic activity for the conversion of CO2 into CO than AgCo/STO and AgCo/Al-STO, which were previously reported. CO was produced at a formation rate of 20 μmol h−1, which was 2.3 times larger than that for Al-STO, and the selectivity toward CO evolution was almost 100 %. H2 formation was completely suppressed in this case. Moreover, the stoichiometric amount of O2 was evolved, indicating that H2O should contribute to the photocatalytic conversion of CO2 as an electron donor. The isotope-labeling experiments using 13CO2 gas as a substrate revealed that the carbon source of CO evolved in this photocatalytic reaction CO2 gas bubbled into the suspension. Therefore, we concluded that CO2 surely split into CO and O2 by the photocatalysis of AgCo/Mg-STO. According to SEM images of undoped STO and Mg-STO, particle shape was obviously changed by Mg doping from pure cubes to irregular edge-shaved cubes. {110} facets were observed in Mg-STO accompanied with {100} facets. Moreover, Ag and Co species were selectively located on the {100} facets and the {110} edge-shaved facets, respectively, after the photoirradiation. The photogenerated electrons and holes were considered to be transferred to {100} and {110} facets separately, and the anisotropic charge transfer should result in the high photocatalytic activity of Mg-STO for the conversion of CO2 with H2O.[1] T. Takata et al., Nature, 2020, 581, 411-414.[2] S. Wang et al., Chem. Sci., 2021, 12, 4940-4948.[3] T. Nakamoto et al., Catal. Sci. Technol., 2023, 13, 4534-4541.

Molecular beam scattering from flat jets of liquid dodecane and water

AbstractMolecular beam experiments in which gas molecules are scattered from liquids provide detailed, microscopic perspectives on the gas–liquid interface. Extending these methods to volatile liquids while maintaining the ability to measure product energy and angular distributions presents a significant challenge. The incorporation of flat liquid jets into molecular beam scattering experiments in our laboratory has allowed us to demonstrate their utility in uncovering dynamics in this complex chemical environment. Here, we summarize recent work on the evaporation and scattering of Ne, CD4, ND3, and D2O from a dodecane flat liquid jet and present first results on the evaporation and scattering of Ar from a cold salty water jet. In the evaporation experiments, Maxwell–Boltzmann flux distributions with a cosθ angular distribution are observed. Scattering experiments reveal both impulsive scattering (IS) and trapping followed by thermal desorption (TD). Super‐specular scattering is observed for all four species scattered from dodecane and is attributed to anisotropic momentum transfer to the liquid surface. In the IS channel, rotational excitation of the polyatomic scatterers is a significant energy sink, and these species accommodate more readily on the dodecane surface compared to Ne. Our preliminary results on cold salty water jets suggest that Ar atoms undergo some vapor‐phase collisions when evaporating from the liquid surface. Initial scattering experiments characterize the mechanisms of Ar interacting with an aqueous jet, allowing for comparison to dodecane systems.Key Points Molecular beam scattering from flat liquid jets is a powerful technique to elucidate mechanistic detail at the gas–liquid interface. Previous dodecane scattering experiments have uncovered angularly‐resolved thermal desorption fractions and energy transfer at the interface for several small molecule scatterers. Preliminary results on scattering from cold salty water reveal mechanisms of interaction between argon and an aqueous jet.

Brain tumor X-ray images enhancement and classification using anisotropic diffusion filter and transfer learning models

Brain tumor X-ray images enhancement and classification using anisotropic diffusion filter and transfer learning models

Ice templated honeycomb-like porous copper foam to improve the anisotropic thermal transfer property of phase change composites

This study explores the use of copper foam (CF) as a thermally conductive scaffold for phase change materials (PCMs), enhancing shape stability. Employing the ice template method (ITM), we fabricate a CF with a low-density, honeycomb structure and anisotropy from flake copper powders. The resulting phase change composites (PCCs), infused with paraffin wax (PW), showcase high thermal conductivity and shape retention compared to pure PW, with anisotropic heat flow due to directional channels in the CF. With a 34.4 wt% filling ratio, the PCCs achieve axial and lateral thermal conductivities of 2.85 W m−1 K−1 and 1.51 W m−1 K−1, respectively, and a thermal storage enthalpy of 158.18 J g−1. This work presents a novel method for advanced thermal energy storage and management, indicating the promise of ITM-derived CF in high-performance PCCs for diverse applications.

Ferroelectric Polarization Modulated Facet-selective Charge Separation in Bi4 NbO8 Cl Single Crystal for Boosting Visible-light Driven Bifunctional Water Splitting.

Developing bifunctional water-splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific-facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well-built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi4 NbO8 Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in-plane polarization from octahedral off-centering of Nb5+ and out-of-plane polarization from lone pair electron effect of anisotropic Bi3+ , both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built-in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet-selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity-optimized Bi4 NbO8 Cl shows an excellent H2 and O2 evolution rate of 54.21 and 36.08 μmol ⋅ h-1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet-selective charge transfer process of photocatalysts.

Ferroelectric Polarization Modulated Facet‐selective Charge Separation in Bi4NbO8Cl Single Crystal for Boosting Visible‐light Driven Bifunctional Water Splitting

AbstractDeveloping bifunctional water‐splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific‐facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well‐built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi4NbO8Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in‐plane polarization from octahedral off‐centering of Nb5+ and out‐of‐plane polarization from lone pair electron effect of anisotropic Bi3+, both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built‐in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet‐selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity‐optimized Bi4NbO8Cl shows an excellent H2 and O2 evolution rate of 54.21 and 36.08 μmol ⋅ h−1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet‐selective charge transfer process of photocatalysts.

Creating Biomimetic Central-Radial Skeletons with Efficient Mass Adsorption and Transport.

Porous skeletons play a crucial role in various applications. Their fundamental significance stems from their remarkable surface area and capacity to enhance mass adsorption and transport. Freeze-casting is a commonly utilized methodology for the production of porous skeletons featuring vertically aligned channels. Nevertheless, the resultant single-oriented skeleton displays anisotropic mass transfer characteristics and suboptimal mechanical properties. Our investigation was motivated by the intricate microstructures observed in botanical organisms, leading us to devise an advanced freeze-casting methodology. A novel central-radial skeleton with significantly enhanced capabilities has been successfully engineered. The central-radial architecture demonstrates superior refinement and uniformity in its pore structure, featuring an axial mass transfer axis and meticulously arranged radial channels. This microstructure endows the porous skeleton with a higher compression resilience, superior adsorption rate, and structural maintenance capacity. Through a rigorous examination of the thermal conductivity of skeleton-filled composites coupled with comprehensive COMSOL simulations, the exceptional characteristics of this unique structural arrangement have been definitively ascertained. Furthermore, the efficacy of implementing this skeleton in chip cooling and photothermal conversion has been convincingly substantiated. Our pioneering method of microstructure preparation, employing freeze-casting, holds immense potential in expanding its applicability and inspiring innovative concepts for the advancement of novel structures.

Hexaazatriphenylene‐Based Two‐Dimensional Conductive Covalent Organic Framework with Anisotropic Charge Transfer

AbstractThe development of covalent organic frameworks (COFs) with efficient charge transport is of immense interest for applications in optoelectronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor‐made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD‐COF. With the support of theoretical calculations, we found that the HAT units in the HD‐COF induce strong, eclipsed π–π stacking. The unique stacking of HAT units and the weak in‐plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD‐COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD‐COF films showed an electrical conductivity as high as 1.25 S cm−1 after doping with tris(4‐bromophenyl)ammoniumyl hexachloroantimonate.

Hexaazatriphenylene-based two-dimensional conductive covalent organic framework with anisotropic charge transfer.

The development of covalent organic frameworks (COFs) with efficient charge transport is of high immense interest for application in opto-electronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor-made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD-COF. With the support of theoretical calculations, we found that the HAT units in the HD-COF induce strong, eclipsed π-π stacking. The unique stacking of HAT units and the weak in-plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD-COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD-COF films showed an electrical conductivity as high as 1.25 S cm-1 after doping with tris(4-bromophenyl)ammoniumyl hexachloroantimonate.

Anisotropic energy transfer near multi-layer black phosphorus

Energy transfer (ET) between quantum emitters is a key process for many scientific domains and technological applications, and can be influenced by strategic placement of appropriate materials in the vicinity. However, all explored conventional isotropic materials lacks directional control over this process. Here, we show that multilayered black phosphorus (bP), a novel anisotropic two-dimensional material, can simultaneously dramatically boost and directionally control ET rates in the near-field regime. We find that bP exhibits a critical thickness above which the ET rates increase by several orders of magnitude compared to vacuum. Moreover, we demonstrate that bP can manipulate the ET in specific in-plane directions due to its strong in-plane anisotropy. Our results build the framework and provide fundamental insights into the mechanisms of ET near anisotropic materials, and open up new possibilities for designing and optimizing ET-based devices, systems and applications.

Blocking Accretion Enables Dimension Reduction of Metal-Organic Framework for Photocatalytic Performance.

The evolution and formation process of two-dimensional metal-organic frameworks (MOFs) primarily arise from the anisotropic growth of crystals, leading to variations in photocatalytic performance. It is crucial to achieve a synergistic combination of anisotropic electron transfer direction and dimension reduction strategies. In this study, a novel approach that effectively blocks crystal growth accretion through the coordination of solvent molecules is presented, achieving the successful synthesis of impurity-free two-dimensional nanosheet Zn-PTC with exceptional hydrogen evolution reaction (HER) performance (15.4mmolg-1 h-1 ). The structural and photophysical characterizations validate the successful prevention of crystal accretion, while establishing correlation between structural anisotropy and intrinsic charge transfer mode through transient spectroscopy. These findings unequivocally demonstrate that electron transfer along the [001] direction plays a pivotal role in the redox performance of nano-Zn-PTC. Subsequently, by coupling the photocatalytic performance and density functional theory (DFT) simulation calculations, the carrier diffusion kinetics is explored, revealing that effective dimension reduction along the ligand-to-metal charge transfer (LMCT) direction is the key to achieving superior photocatalytic performance.

Evaporation and scattering of neon, methane, and water from a dodecane flat liquid jet.

The evaporation and scattering of Ne, CD4, and D2O from a dodecane flat liquid jet are investigated in a molecular beam apparatus. The experiment yields translational energy distributions as a function of scattering angle by means of a rotatable mass spectrometer. In the evaporation experiments, one observes a Maxwell-Boltzmann distribution with a cos θ angular distribution superimposed on a weak, isotropic background. The scattering experiments show contributions from impulsive scattering and thermal desorption. At select incident angles for the three systems, angular distributions show super-specular scattering for the impulsive scattering channel, an effect attributed to anisotropic momentum transfer to the liquid surface. The impulsive scattering channel is analyzed with a soft-sphere model to explore energy transfer between the scatterer and liquid as a function of deflection angle. Compared to Ne scattering, the polyatomic gases exhibit more thermal desorption and, in the impulsive scattering channel, a higher degree of internal excitation.

Anisotropic Transport of Dielectric Particles by a Uniform Electric Field in an Inhomogeneously Heated Viscous Fluid

The anisotropic transfer of dielectric particles by a uniform electric field in a nonuniformly heated fluid is modeled. The transport anisotropy is determined by the mechanism of interaction between particles whose permittivity depends on temperature. The temperature distribution in the particles and in the fluid is determined by their thermal diffusivity and does not depend on the motion of the fluid, thus corresponding to small Peclet numbers. The fluid flow is considered in the approximation of small Reynolds numbers. The transfer of particles is due to the action of an anisotropic force exerted by applied uniform electric field and friction forces exerted by the fluid. The interaction of particles is taken into account. Numerical modeling of anisotropic transport dynamics of two dielectric particles is carried out. The process mentioned depends on the mutual orientation of electric field vector, temperature gradient, and initial orientation of the vector connecting the particle centers. For the case of a large number of particles, an anisotropic equilibrium distribution of the particle concentration in an external electric field is found taking into account the mechanisms of their diffusion and interaction.

In Situ Constructed Perovskite-Chalcogenide Heterojunction for Photocatalytic CO2 Reduction.

Perovskite nanocrystals (PNCs) are promising candidates for solar-to-fuel conversions yet exhibit low photocatalytic activities mainly due to serious recombination of photogenerated charge carriers. Constructing heterojunction is regarded as an effective method to promote the separation of charge carriers in PNCs. However, the low interfacial quality and non-directional charge transfer in heterojunction lead to low charge transfer efficiency. Herein, a CsPbBr3 -CdZnS heterojunction is designed and prepared via an in situ hot-injection method for photocatalytic CO2 reduction. It is found that the high-quality interface in heterojunction and anisotropic charge transfer of CdZnS nanorods (NRs) enable efficient spatial separation of charge carriers in CsPbBr3 -CdZnS heterojunction. The CsPbBr3 -CdZnS heterojunction achieves a higher CO yield (55.8µmolg-1 h-1 ) than that of the pristine CsPbBr3 NCs (13.9µmolg-1 h-1 ). Furthermore, spectroscopic experiments and density functional theory (DFT) simulations further confirm that the suppressed recombination of charge carriers and lowered energy barrier for CO2 reduction contribute to the improved photocatalytic activity of the CsPbBr3 -CdZnS heterojunction. This work demonstrates a valid method to construct high-quality heterojunction with directional charge transfer for photocatalytic CO2 reduction. This study is expected to pave a new avenue to design perovskite-chalcogenide heterojunction.

In-Situ Measurement of Magnetoelectric Coupling and Strain Transfer in Multiferroic Nanocomposites of CoFe2O4 and Hf0.5Zr0.5O2 with Residual Porosity

With increasing applications for voltage-controlled magnetism, the need to more fully understand magnetoelectric coupling and strain transfer in nanostructured multiferroic composites has also increased. Here, multiferroic nanocomposites were synthesized using block copolymer templating to create mesoporous cobalt ferrite (CFO), followed by partly filling the pores with ferroelectric zirconium-substituted hafnia (HZO) using atomic layer deposition (ALD) to produce a porous multiferroic composite with enhanced mechanical flexibility. Upon electrical poling of the nanocomposite, we observed large changes in the magnetization. These changes partly relaxed upon removing the electric field, suggesting a strain-mediated mechanism. Both the anisotropic strain transfer from HZO to CFO and the strain relaxation after the field was removed were confirmed using high-resolution X-ray diffraction measurements collected during in-situ poling. The in-situ observation of both anisotropic strain transfer and large magnetization changes allows us to directly characterize the strong multiferroic coupling that can occur in flexible, nanostructured composites.

Efficient Exciton Dissociation through the Edge Interfacial State in Metal Halide Perovskite-Based Photocatalysts

Metal halide perovskites (MHPs) with superior optoelectronic properties have recently been actively pursued as catalysts in heterogeneous photocatalysis. Dissociating excitons into charge carriers holds the key to enhancing the photocatalytic performance of MHP-based photocatalysts, especially for those with strong quantum-confinement effects. However, attaining efficient exciton dissociation has been rather challenging. Herein, we propose a novel concept that the edge interfacial state can trigger anisotropic electron transfer to promote exciton dissociation. By taking Cs4PbBr6/TiO2 mesocrystal heterojunction as a proof-of-concept, we demonstrate that the unique interfacial state at the edge of the system is generated by the defect-mediated chemical interaction and acts as a trap state, which brings on a directionally favored electron transfer from the center to edge regions, thereby significantly enhancing the desired exciton dissociation. Consequently, such a system achieves an excellent performance in photocatalytic CO2 reduction. This paradigmatic work sheds light on the excitonic aspects for rational design of advanced photocatalysts toward high performance.

Gap opening mechanism for correlated Dirac electrons in organic compounds α−(BEDT−TTF)2I3 and α−(BEDT−TSeF)2I3

To determine how electron correlations open a gap in two-dimensional massless Dirac electrons in the organic compounds $\alpha$-(BEDT-TTF)$_2$I$_3$ [$\alpha$-(ET)$_2$I$_3$] and $\alpha$-(BEDT-TSeF)$_2$I$_3$ [$\alpha$-(BETS)$_2$I$_3$], we derive and analyze $ab$ $initio$ low-energy effective Hamiltonians for these two compounds. We find that the horizontal stripe charge ordering opens a gap in the massless Dirac electrons in $\alpha$-(ET)$_2$I$_3$, while an insulating phase without explicit symmetry breaking appears in $\alpha$-(BETS)$_2$I$_3$. We clarify that the combination of the anisotropic transfer integrals and the electron correlations induces a dimensional reduction in the spin correlations, i.e., one-dimensional spin correlations develop in $\alpha$-(BETS)$_2$I$_3$. We show that the one-dimensional spin correlations open a gap in the massless Dirac electrons. Our finding paves the way for opening gaps for massless Dirac electrons using strong electronic correlations.

Spatial Data Augmentation: Improving the Generalization of Neural Networks for Pansharpening

Deep learning (DL) methods have achieved impressive performance for pansharpening in recent years. However, because of poor generalization, most DL methods achieve unsatisfactory performance for data acquired by sensors not considered during the training phase and decreased performance for samples at full resolution. To solve this issue, we propose a data augmentation framework for pansharpening neural networks. Specifically, we introduce first a random spatial degradation based on anisotropic Gaussian-shaped modulation transfer functions (MTFs) to increase the generalization with respect to different spatial models and sensors. Then, considering that various sensors have different ground sampling distances (GSDs), we randomly rescale the GSD of the training samples to improve the generalization with respect to spatial resolution. Thanks to this module, the generalization to tests from different sensors and samples at full resolution can easily be achieved. Experimental results demonstrate the effectiveness of the proposed approach with better performance when data for training are decoupled with the ones for testing and comparable performance when training and testing are coupled (i.e., data acquired by the same sensor are considered in the two phases). Besides, performance at full resolution for pansharpening neural networks is improved by the proposed approach. The proposed approach has been integrated into existing pansharpening neural networks showing satisfactory performance for widely used sensors, including, GaoFen-1, QuickBird, WorldView-2, WorldView-3, IKONOS, Spot-7, GeoEye, and PHR1A.

Light Harvesting Antenna Properties of Framework Solids

ConspectusEnergy transport within organic solids typically takes place via the movement of localized excitation or excitons, i.e., tightly bound electron–hole pairs. Exciton diffusion dynamics are crucial to applications like solar fuels production through photocatalysis and organic optoelectronics. Covalent organic frameworks (COFs) and metal–organic frameworks (MOFs) are classes of framework solids that integrate ordered assemblies of chromophores. These materials possess properties desirable for the aforementioned applications. Their absorption cross sections across the ultraviolet–visible spectrum can be tuned via linker design. They are often crystalline and provide control over the framework topology in terms of spatial separation and relative orientation of chromophores. These properties allow for detailed understanding and tuning of structure–activity relationships.In this Account, we highlight our recent studies on photophysics and photonics of MOFs and COFs. Three materials are discussed with the focus on structural factors that govern the exciton properties in terms of diffusion, delocalization, and transport. The first is COF-5, a layered, two-dimensional COF with boronate ester linkages. We show that the molecular excitons in COF-5 are delocalized over multiple constituent building blocks with optical signatures of mixed (e.g., H- and J-type) excitonic interactions. The exciton of the S1 state decays and evolves into an excimer trap state in a few picoseconds. The excitons in COF-5 possess a diffusivity of about 0.02 cm2/s and a diffusion radius of about 5 nm based on exciton–exciton annihilation studies. To investigate the range of exciton diffusion, parallel exciton dynamics measurements were performed on COF-5 colloids with varying crystallite size, revealing that exciton diffusion is limited by crystallite size. The second system studied is an imine-linked two-dimensional COF with a hexagonal structure, the TAPB-DiOMe COF. To understand the photophysics of this material, we extended the study toward isomeric materials with a lower dimensionality: cofacially stacked nanotubes and free macrocycles assembled from the same primary building blocks. In-plane exciton delocalization and movement cannot occur in these lower dimensional species. We find that the exciton lifetime is prolonged significantly in the π-stacked nanotubes where the macrocycles undergo planarization that restricts atomic movements of the imine bonds in the peripheral groups, which may reduce the rate of internal conversion. In addition, orientation-dependent anisotropic energy transfer through the nanotubes was detected via optical transient absorption anisotropy. The third system discussed is the MOF NDC-NU-1000 decorated with single-atom metal-oxy (i.e., mix of oxo, hydroxo, and/or aqua) TiIV, CoIII, and NiII species mimicking single-atom catalysts (SACs). These composite materials display photoinduced charge separation. We show the formation of charge-separated states in these M-oxy decorated MOF samples upon photoexcitation with an electron transferred from the MOF linker to the M-oxy moiety. We compare and rationalize the differences in photoinduced charge separation kinetics among these M-oxy decorated MOFs and hope to identify energetic and structural factors that make the material an effective light harvesting platform and facilitate formation of the charge-separated state. Finally, we review our progress in context of the research published previously in the field and provide our perspective on the future of crystalline porous assemblies serving as light-harvesting antennae.

Transfers of energy and helicity in helical rotating turbulence

Helical rotating turbulence is a chiral and anisotropic flow. The energy and helicity transfers of helical rotating turbulence are studied in this paper. First, we discuss the antisymmetry and conservation of energy and helicity transfers. There are three expressions for helicity transfers due to the commutability of differential operators. The first expression is derived here. The second expression violates antisymmetry, and the third one introduces non-physical effects. The relations of these expressions are discussed in detail, including those about the sum of all triads and partial triads, as well as those about helical wave decomposition. Through direct numerical simulations, we find that helicity can reduce inverse energy cascades. The inhibition is mainly associated with transhelical energy fluxes and the interactions of two-dimensional modes. The inverse cascades of decomposed energy fluxes are related to the two-dimensionalization. For helicity, rotation does not affect the total helicity flux but generally suppresses the decomposed helicity fluxes. Positive homochiral and negative heterochiral helicity fluxes are associated with corresponding positive anisotropic transfers. Notably, the transhelical helicity fluxes increase the amplitudes of both positive and negative helicity, which is related to the chirality polarization.