Reversible Structural Changes Research Articles

Efficient paddle-wheel copper cluster-based metal-organic framework for catalytic conversion of CO2 to oxazolidinones under mild conditions

Efficient utilization of CO2 and its conversion into high-value-added products contribute to mitigating environmental issues such as the greenhouse effect. Among these methods, the carboxylation cyclization of CO2 with propargylic amine represents a green and atom-economical approach. Developing cost-effective catalyst that can promote this reaction under mild condition is desirable but challenging. Herein, a unique two-dimensional (2D) metal–organic framework (MOF) {[Cu(QCA)2]∙0.5DMF∙0.5H2O}n (1) (QCA =6-quinolinecarboxylic acid, DMF = N,N-dimethylformamide) have been synthesized and thoroughly characterized. Compound 1 was constructed from paddle-wheel dinuclear copper clusters [Cu2(COO)4] and carboxylate ligands, presenting a two-dimensional framework with new topology. Stability tests indicate that compound 1 undergoes reversible structural changes in different solvents and exhibits good thermal stability. 1 as heterogeneous catalyst enabled the transformation of CO2 and propargylic amine into oxazolidinones under mild conditions with broad substrate generality. In addition, 1 could maintain its catalytic performance with five continuous reactions. This work presents an infrequent example of a 2D noble metal free MOF-based catalyst that shows high catalytic efficiency under mild conditions.

Dual surface-bulk aluminum modification in a-Al2O3@Na3VAl(PO4)3 sodium-ion batteries cathode to boost high voltage utilization and electrolyte protection

Amorphous alumina (a-Al2O3)-coated Na3VAl(PO4)3 samples are prepared by a low-cost, easily scalable, and environmentally friendly sol-gel process. X-ray diffraction reveals no significant structural changes after deposition. The presence of the amorphous carbon conductive and a-Al2O3 phases will be respectively confirmed in the light of Raman and NMR spectroscopies. Electron microscopy evidences the presence of alumina particles deposited on the substrate. Ex-situ XRD shows the reversible structural changes while sodium is inserted. Ex-situ XPS reveals the effective participation of V5+/V4+/V3+ species during the electrochemical reaction, while the formation of aluminum oxyfluorides justifies the efficient HF removal that prevents electrode degradation.Electrochemical tests will validate this proposal. Thus, rate capability essays indicate that 1–3 % a-Al2O3 coating enhances capacity at high rates, with coated samples exhibiting a fast sodium migration and lower cell resistance at both the beginning and conclusion of cycling tests. It is supported by evaluating the kinetic response showing their high capacitive contributions and diffusion coefficients, especially in the 2 % a-Al2O3 coated sample. Eventually, these findings are corroborated by the good capacity retention of the 2 % coated sample during prolonged cycling at both room and low temperatures.

Zinc hexacyanoferrate with open framework for efficient aqueous cobalt ions storage

In this work, we report a high-performance aqueous Co-ion battery with zinc hexacyanoferrate as Co2+ storage material. Owing to the open framework, zinc hexacyanoferrate exhibits excellent electrochemical performance. The reversible capacity of zinc hexacyanoferrate is up to 62.4 mAh g−1 at 5C with ultralow capacity decay (0.0084 % per cycle) within 500 cycles. Even cycled at a higher rate of 10C, zinc hexacyanoferrate still can remain a high capacity retention of 98.8 % after 700 cycles. The excellent electrochemical performance is attributed to the rapid kinetics behavior of Co2+ in the open and stable framework structure. Besides, a joint analysis of in-situ X-ray diffraction, ex-situ Fourier transform infrared spectroscopy and ex-situ X-ray photoelectron spectroscopy verifies the highly reversible structural change of zinc hexacyanoferrate during charge/discharge process. All these evidences suggest that zinc hexacyanoferrate may be a promising host material for Co2+ storage in aqueous rechargeable batteries.

Unlocking the charge efficiency of γ’-V2O5 for Na-ion battery through a solution synthesis technique

In this study, the γ’-V2O5 cathode material was prepared through a solution synthesis technique leading to homogeneous, fine and porous particles 100–200 nm in size. This successful preparation allows to overcome the huge drawback of the microsized material in terms of charge efficiency and to take benefit of the attractive Na insertion properties of γ’-V2O5, i. e. a significant available capacity of 145 mAh g- 1, a high working potential of about 3.25 V vs. Na+/Na, an excellent charge efficiency, a high-rate capability and good cycle life. A detailed structural study upon Na insertion/extraction shows that the proposed nanosizing approach promotes a homogeneous Na solubility and solid solution behavior in a wider composition range (0.4 < x ≤ 1 in γ-NaxV2O5) compared to the results previously reported for solid-state synthesized γ’-V2O5. Furthermore, highly reversible structural changes are evidenced. Key kinetic parameters governing the Na insertion-extraction reaction are discussed thanks to an impedance spectroscopy study revealing a faster Na diffusivity in the one-phase region. The obtained results allow a comprehensive understanding of the enhanced performance exhibited by the present sub-micronic γ’-V2O5 material.

Separation of the cis- and trans-isomers 1,4-cyclohexanedicarboxylic acid by a dynamic MOF

Achieving an efficient method to separate cis–trans isomers of trans-1,4-cyclohexanedicarboxylic acid remains a formidable challenge within the chemical industry. Here, we have synthesized a Co(II)-based dynamic metal–organic framework material involving the coordination of 1,4-cyclohexanedicarboxylic acid. Single-crystal X-ray diffraction and high-performance liquid chromatography (HPLC) analysis confirmed that only pure trans-1,4-cyclohexanedicarboxylic acid was present in all synthesized crystals, a characteristic that can be utilized for the separation of the cis- and trans-isomers of 1,4-cyclohexanedicarboxylic acid. Moreover, the MOF crystals displayed reversible structural changes and were capable of releasing the pure trans-isomer through ion exchange with a salt solution, underscoring their potential for applications in molecular separation.

Mn-Based Transition Metal Oxide Positive Electrode for K-Ion Battery Using an FSA-based Ionic Liquid Electrolyte

Layered Mn-based transition metal oxides have gained interest as positive electrode materials for K-ion batteries due to their high capacity, excellent structural stability, and abundant resources. However, their practical utility is significantly hindered by insufficient electrochemical performances during operations. This study reports the successful synthesis of P3-K0.46MnO2 via the solid-state method and investigates its charge–discharge behavior as a positive electrode working in an FSA-based (FSA= bis(fluorosulfonyl)amide) ionic liquid electrolyte at 298 K. The K0.46MnO2 electrode demonstrates superior performance compared to previously reported K x MnO2 counterparts, delivering a reversible discharge capacity of about 100 mAh g−1 at a current density of 20 mA g−1 and a capacity retention of 68.3% over 400 cycles at 100 mA g−1. Ex situ X-ray diffraction analyses confirm the occurrence of reversible structural changes during the charge–discharge process. Further, we explore potassium storage mechanisms through ex situ synchrotron soft X-ray absorption spectroscopy. Spectra obtained in Mn L-edge region suggest that Mn is reversibly oxidized and reduced during K+ deintercalation and intercalation processes. Remarkably, discharging the electrode below 2.3 V induces reversible formation of Mn2+ from Mn3+/4+ on the electrode surface. The study demonstrates superior electrochemical performance of K0.46MnO2 positive electrode for K-ion battery using ionic liquid electrolyte.

High-energy bimetallic substituted Na3V2(PO4)3 cathode for advanced sodium-ion batteries

NASICON-type cathodes have attracted great attention due to their open three-dimensional (3D) frame structure and excellent ion transport properties. Accordingly, how to improve the stability and energy density of materials is a hot topic of research. In this study, the significant effects of aluminum-zirconium bimetallic substitution on electrode kinetics and structural stability are reported. The designed Na2.9V1.8Al0.1Zr0.1(PO4)3 cathode exhibits a highly reversible capacity of 107 mAh g-1 at 1C and decent cyclic stability (75 mAh g-1 capacity after 2000 cycles at 20C). These excellent electrochemical properties can be attributed to expanding the lattice structure and activating part of V4+, which facilitates the migration of Na+ and increases the reversible capacity. The cyclic voltammetry, electrochemical impedance spectra and galvanostatic intermittent titration technique tests analyze the diffusion kinetics of sodium ions and confirm the desired sodium ion diffusion coefficients (DNa+). In situ X-ray diffraction reveals reversible structural changes during the electrochemical reaction, which confirms that the bimetallic doping strategy slows down material volume change. This work provides a new perspective for the construction of high-performance NASICON cathode materials.

Structural evolution in desalting Merluccius hubbsi fillets: comparative analysis of varied salting techniques

SummaryThis study investigates the reversible and irreversible structural changes in proteins induced by different salting methods (brining, mixed salting, and dry salting) during the desalting process of Merluccius hubbsi fillets. We focused on mass changes, water content, and NaCl content, employing mathematical models for kinetic analysis and sorption isotherms. Image analysis was utilised to examine tissue microstructure and texture profile analysis assessed the mechanical properties. Our results indicate that salting methods significantly influence mass changes and yield during desalting. Specifically, brining led to the highest weight gain due to controlled salt absorption and enhanced water retention. The Peleg model accurately described NaCl and water content dynamics during desalting. Microscopic analysis revealed substantial structural alterations, while mechanical properties showed significant differences; dry and mixed salting methods caused notable tissue damage and protein denaturation. These findings provide valuable insights for enhancing salting processes and improving the quality of desalted seafood products.

Structural Characterization of Mixed Metal Cathodes via in Operando X-Ray Diffraction

Complex metal oxides used in lithium-based energy storage technologies undergo distinct crystallographic changes based on chemical composition, specific voltage and current states, degree of lithiation, and more. Crystallographic studies via X-ray diffraction (XRD) are a critical part of understanding structure-property relationships and engineering devices to meet specific performance requirements. For the raw electrode materials, XRD provides information about exact crystal structure (e.g. symmetry, unit cell parameters, atomic site mixing) as well as the presence of impurity phases that might arise from a poor sintering process or non-stoichiometric starting reagents. For formed devices such as button- or pouch-cells, XRD can be used in operando to measure changes in phase composition, phase quantification, and crystal lattice expansion/contraction as a function of charge state. This can provide useful information such as the level of reversibility of a device or the onset of impurity phases during aging and long cycling.In this presentation, we will review diffraction data for case studies based on NMC electrodes and highlight key insights into reversible structural changes during device cycling. The figure attached to this abstract shows diffraction data as a function of charge state during a single charge/discharge cycle. The observed peaks show modifications to the crystalline lattice (expansion in one direction, contraction in another orthogonal direction). Figure 1

Induced Anion Redox before Full Oxidation of Ru4+/Ru5+ through Local Configuration Modulation in P2-Na0.67[Mg0.33Ru0.67]O2

The study of anionic redox in layered-oxide cathodes for Na-ion batteries (NIBs) has been extensive, aiming to attain high-energy density. The involvement of Mn4+ or Ru5+ oxidation states is known to be crucial for the anionic O2 −/O− reaction during Na+ de/intercalation. Nevertheless, our findings indicate that anionic redox can activate in Ru-based layered-oxide cathodes prior to complete Ru4+/Ru5+ oxidation. By employing first-principles calculation and experimental techniques, we disclose that additional Na+ deintercalation from P2-Na0.33[Mg0.33Ru0.67]O2 relies on anionic oxidation after extracting 0.33 mol Na+ from P2-Na0.67[Mg0.33Ru0.67]O2, concomitant with cationic oxidation of Ru4+/Ru4.5+. Specifically, only the oxygen adjacent to 2Mg/1Ru is implicated in anionic redox during Na+ de/intercalation, indicating that the Na–O–Mg arrangement in the P2-Na0.33[Mg0.33Ru0.67]O2 structure significantly reduces the thermodynamic stability of anionic redox compared to cationic redox. Through O anionic and Ru cationic reactions, P2-Na0.67[Mg0.33Ru0.67]O2 demonstrates a substantial specific capacity of ∼172 mA h g− 1 and exceptional power capability, facilitated by facile Na+ diffusion and reversible structural changes during charge/discharge. These findings propose an innovative strategy to enhance anionic redox activity by modifying the local oxygen environment, paving the way for high-energy-density cathode materials in NIBs.

Enhancing Stability of SAPO-37 Molecular Sieve through Aluminum Phosphate Utilization: Synthesis, Stability Mechanism, and Catalytic Performance.

SAPO-37 molecular sieve, characterized by its three-dimensional 12-membered-ring FAU structure, has drawn wide attention due to its unique properties and catalytic potential. However, its susceptibility to framework collapse under low-temperature and humid conditions hinders practical applications, affecting both the reaction performance and sample storage. To tackle this, we utilized aluminum phosphate as a precursor for synthesizing SAPO-37, aiming to modify Si incorporation mechanisms and improve P and Al environments. Solid NMR spectroscopy combined with other techniques proves that the resulting SAPO-37-AP has enriched silicon islands, leading to reduced water adsorption, more reversible structural change, and significantly enhanced stability after low-temperature vapor treatment compared to conventional SAPO-37. Remarkably, SAPO-37-AP, after water vapor treatment, still exhibits superior performance in the liquid-phase Beckmann rearrangement reaction. This approach enhances stability, reduces templating agent amounts, and improves the solid product yield, offering promising practical applications.

Cooperative dual single atom Ni/Cu catalyst for highly selective CO2-to-ethanol reduction

The electrochemical CO2-to-ethanol conversion bargains a promising approach to lowering CO2 emission while yielding valuable chemical products. Here, we report the NiCu-SACs/N-C catalysts with cooperative dual heteroactive sites that achieve by far the highest catalytic activity for yielding ethanol with the unprecedented Faradaic efficiency of 92.2 % at the potential of −0.6 V versus RHE. The catalyst exhibits the lowest onset potential of −0.4 V versus RHE to catalyze CO2-to-ethanol conversion. In-operando X-ray absorption spectroscopy provides an interesting observation of restructuring behavior of dynamically generated Cu clusters from atomically distributed Cu single-atoms and reversible structural changes or oxidation states of Cu sites while Ni sites remain unchanged during the catalytic reactions. Our experimental analysis and DFT computation suggest that CO produced on Cu-N4/Ni-N3 cooperative single atom sites undergoes C-C coupling, which is further reduced into ethanol. This strategy provides a new route to design selective and efficient catalysts for CO2-to-ethanol conversion.

K-Doping Suppresses Oxygen Redox in P2-Na0.67Ni0.11Cu0.22Mn0.67O2 Cathode Materials for Sodium-Ion Batteries.

In P2-type layered oxide cathodes, Na site-regulation strategies are proposed to modulate the Na+ distribution and structural stability. However, their impact on the oxygen redox reactions remains poorly understood. Herein, the incorporation of K+ in the Na layer of Na0.67Ni0.11Cu0.22Mn0.67O2 is successfully applied. The effects of partial substitution of Na+ with K+ on electrochemical properties, structural stability, and oxygen redox reactions have been extensively studied. Improved Na+ diffusion kinetics of the cathode is observed from galvanostatic intermittent titration technique (GITT) and rate performance. The valence states and local structural environment of the transition metals (TMs) are elucidated via operando synchrotron X-ray absorption spectroscopy (XAS). It is revealed that the TMO2 slabs tend to be strengthened by K-doping, which efficiently facilitates reversible local structural change. Operando X-ray diffraction (XRD) further confirms more reversible phase changes during the charge/discharge for the cathode after K-doping. Density functional theory (DFT) calculations suggest that oxygen redox reaction in Na0.62K0.03Ni0.11Cu0.22Mn0.67O2 cathode has been remarkably suppressed as the nonbonding O 2p states shift down in the energy. This is further corroborated experimentally by resonant inelastic X-ray scattering (RIXS) spectroscopy, ultimately proving the role of K+ incorporated in the Na layer.

Responsive Acrylamide-Based Hydrogels: Advances in Interpenetrating Polymer Structures.

Hydrogels, composed of hydrophilic homopolymer or copolymer networks, have structures similar to natural living tissues, making them ideal for applications in drug delivery, tissue engineering, and biosensors. Since Wichterle and Lim first synthesized hydrogels in 1960, extensive research has led to various types with unique features. Responsive hydrogels, which undergo reversible structural changes when exposed to stimuli like temperature, pH, or specific molecules, are particularly promising. Temperature-sensitive hydrogels, which mimic biological processes, are the most studied, with poly(N-isopropylacrylamide) (PNIPAm) being prominent due to its lower critical solution temperature of around 32 °C. Additionally, pH-responsive hydrogels, composed of polyelectrolytes, change their structure in response to pH variations. Despite their potential, conventional hydrogels often lack mechanical strength. The double-network (DN) hydrogel approach, introduced by Gong in 2003, significantly enhanced mechanical properties, leading to innovations like shape-deformable DN hydrogels, organic/inorganic composites, and flexible display devices. These advancements highlight the potential of hydrogels in diverse fields requiring precise and adaptable material performance. In this review, we focus on advancements in the field of responsive acrylamide-based hydrogels with IPN structures, emphasizing the recent research on DN hydrogels.

In situ thermal conversion strategy derived from metal-organic framework for enhanced cathode performance in aqueous zinc-ion batteries

The development of aqueous zinc-ion batteries as innovative energy storage devices has garnered significant attention due to their low cost, high safety, and environmental friendliness. However, achieving high-performance and excellent cycling reliability remains a challenge for cathode materials. This study introduces an innovative in-situ thermal conversion strategy using MIL-100(Fe) as the sacrificial template to introduce Fe metal ions into vanadium oxide. This strategy promotes the formation of FeVOx with reduced particle size and enhanced active surface area, facilitating the rapid diffusion of Zn2+. As a result, the FeVOx-1/2 cathode delivers a high specific capacity of 325 mAh/g at a current density of 0.05 A/g and maintains a high capacity retention of about 94.8 % after 4000 cycles at 1 A/g. In-situ electrochemical impedance spectroscopy (EIS) was employed to elucidate the changes in the electrode interface during the charge-discharge processes. Additionally, a series of ex-situ characterization methods were utilized to further deepen our understanding of the reversible structural changes in the cathode during charge-discharge processes, as well as the corresponding reversible insertion and extraction mechanism for Zn2+ storage. The introduction of Fe not only enhances electrical conductivity, but also provides further structural stabilization, as supported by theoretical calculation results. This study presents a novel approach to broaden the doping strategies for vanadium oxide cathodes by utilizing metal-organic frameworks as templates.

Photoswitchable Cascades for Allosteric and Bidirectional Control over Covalent Bonds and Assemblies.

Studies of complex systems and emerging properties to mimic biosystems are at the forefront of chemical research. Dynamic multistep cascades, especially those exhibiting allosteric regulation, are challenging. Herein, we demonstrate a versatile platform of photoswitchable covalent cascades toward remote and bidirectional control of reversible covalent bonds and ensuing assemblies. The relay of a photochromic switch, keto-enol equilibrium, and ring-chain equilibrium allows light-mediated reversible allosteric structural changes. The accompanying distinct reactivity further enables photoswitchable dynamic covalent bonding and release of substrates bidirectionally through alternating two wavelengths of light, essentially realizing light-mediated signaling cycles. The downfall of energy by covalent bond formation/scission upon photochemical reactions offers the driving force for the controlled direction of the cascade. To show the molecular diversity, photoswitchable on-demand assembly/disassembly of covalent polymers, including structurally reconfigurable polymers, was realized. This work achieves photoswitchable allosteric regulation of covalent architectures within dynamic multistep cascades, which has rarely been reported before. The results resemble allosteric control within biological signaling networks and should set the stage for many endeavors, such as dynamic assemblies, molecular motors, responsive polymers, and intelligent materials.

Emerging Two–Dimensional Intercalation Pseudocapacitive Electrodes for Supercapacitors

AbstractThe growing need for efficient energy storage has spurred advancements in supercapacitors (SCs), aiming to offer high power and energy density simultaneously. While SCs offer longer cycles and higher power density values, their low energy densities limit practical applications. In response, pseudocapacitive materials have emerged, leveraging reversible Faradaic reactions at or near the surface for enhanced energy storage. This approach surpasses the constraints of the electrical double layer in SCs and the mass transfer constraints of batteries. Progress in asymmetric supercapacitors and high mass loading has improved energy density values, yet maintaining high mass loading without compromising power density remains a hurdle. Advancements in pseudocapacitance through intercalation during charging/discharging processes, especially in layered structures like graphite, graphene, transition metal oxides (TMOs) transition metal dichalcogenides (TMDCs), MXenes, and metal–organic frameworks (MOFs) have proven significant. The intercalated species induce reversible or irreversible structural changes, contributing to the physicochemical characteristics of the electrode materials. Exploring the intercalation mechanism in bulk two‐dimensional (2D) materials reveals distinct differences that enhance our understanding and improve electrochemical properties for superior energy storage. Finally, an in‐depth exploration of the intercalation pseudocapacitance in 2D materials such as TMDCs and MXenes underscores their significance, setting a benchmark for future electrochemical studies in the subsequent advancement of SCs research.

Temporary trade shocks and regional development: evidence from the closure of Abidjan port

Abstract Can temporary trade restrictions reshape regional development? To analyze this, we exploit the Cote d’Ivoire civil war that disrupted access to Abidjan port for neighboring land-locked countries: Mali and Burkina Faso. Estimates from a difference-in-difference design suggest negative effects on economic activity and a reverse structural change in the treatment communes. We find evidence of persistence through irreversible investment in built-up areas and divergence in the growth of nightlights. Treatment communes at the intermediate distance from the nearest city experienced stronger adverse impacts, driven partly by a relocation to the communes close to other ports.

Double‐Helical Carbon Nanotube‐Wrapped Elastomeric Mandrel for Electrical Shortage‐Free, One‐Body Multifunctional Fiber Systems

AbstractSoft and elastic fiber‐based electronic devices exhibiting high electromechanical stability are highly desirable for sustainable and continuous utilization in various applications. However, effectively assembling the cathode and anode in a single body without unwanted interconnections and realizing an intimate contact interface between the electrode and substrate remain challenging. Here, an electrical shortage‐free one‐body fiber system with double‐helix buckle electrodes created by torsion‐ and strain‐mismatch between carbon nanotube (CNT) ribbons and a rubber substrate is reported. The as‐used CNT ribbons serve as the strain‐insensitive electrode, while the rubber mandrel‐core fiber acts as the key matrix in the following three aspects: as an elastic substrate that ensures reversible structural changes during mechanical deformations; as a dielectric layer for capacitive strain sensing; and as an electrothermal expansion element for tensile contraction. Moreover, because of the mismatch‐induced torque‐balance structure, the helically wrapped CNT buckle electrodes can effectively absorb the applied stresses without noticeable delamination and electrical conductance loss. Consequently, the double‐helix buckle fiber system can reliably provide multiple functions, viz. detection of various deformations (e.g., stretching, twisting, and pressing), electrochemical energy storage with excellent strain tolerance, and reversible electrothermal tensile actuation.

Crystal structure analysis of the adduct 1:1 hexamethylenetetramine and succinic acid (HMT−C4) as a function of the temperature

Co−crystals of hexamethylenetetramine [N4(CH2)6, (HMT)] and dicarboxylic acids of general formula HOOC(CH2)n−2COOH with 4 ≤ n ≤ 14 (Cn), called HMT−Cn, exhibits structural properties strongly dependent on the length of the dicarboxylic acid chain, showing a wide variety of thermotropic phase transition sequence. This study focuses on describing the structural features of the HMT−C4 (1:1) adduct, a co-crystal of HMT and succinic acid (C4), exhibiting a reversible first-order phase transition at 222(4)K, as evidenced by differential scanning calorimetry (DSC) experiments. In contrast to a prior investigations , which did not identify this phase transition, our comprehensive temperature-dependent analysis, incorporating single crystal X-ray diffraction and DSC experiments, reveals a reversible structural change in the HMT−C4 (1:1) adduct structure upon cooling and heating. The crystal structures of the different observed phases are discussed in detail, emphasizing the role of O−H···N intermolecular hydrogen bonds in maintaining the connectivity between HMT and C4 molecules. The observed phase transition involves doubling the unit cell volume and significant reorientation of the −COOH groups at the end of the C4 chain at around 222(4)K. Our findings underscore the importance of additional temperature-dependent experiments, such as DSC, in avoiding erroneous structure modeling due to symmetry changes during temperature variations. The preservation of the acidic character of the C4 dicarboxylic chain throughout the temperature range adds additional insights to the understanding of the structural behavior of all the HMT−Cn (1:1) adducts.