Metal-organic frameworks derived transition metal phosphides for electrocatalytic water splitting

It is critical to synthesize high-efficiency electrocatalysts to boost the performance of water splitting to meet the requirements of industrial applications. Metal-organic frameworks(MOFs) can function as ideal molecular platforms for the design of highly reactive transition metal phosphides(TMPs), a kind of candidates for high-efficiently electrocatalytic water splitting. The intrinsic activity of the electrocatalysts can be greatly improved via modulating the electronic structure of the catalytic center through the MOF precursors/templates. Moreover, the carbon layer converted in-situ by the organic ligands can not only protect the TMPs from being degraded in the harsh electrochemical environments, but also avoid agglomeration of the catalysts, thereby promoting their activities and stabilities. Furthermore,heteroatom-containing ligands can incorporate N, S or P, etc. atoms into the carbon matrixes after conversion, regulating the coordination microenvironments of the active centers as well as their electronic structures. In this review, we first summarized the latest developments in MOF-derived TMPs by the unique advantages in metal, organic ligand, and morphology regulations for electrocatalytic water splitting. Secondly, we concluded the critical scientific issues currently facing for designing state-of-the-art TMP-based electrocatalysts. Finally, we presented an outlook on this research area, encompassing electrocatalyst construction, catalytic mechanism research, etc.

Disclosing the active integration structure and robustness of a pseudo-tri-component electrocatalyst toward alkaline hydrogen evolution

Designing multicomponent integration catalysts(MICs)has been a promising strategy for improving electrocatalytic hydrogen evolution reaction(HER)due to the highly active interfaces as well as electronic synergy.Nevertheless,many fundamental questions such as their actual active species and the influence on long-term stability remain to be answered.Herein,we present the structural evolution from a pseudotri-component electrocatalyst of nitrogen-doped carbon supported nickel/vanadium nitride/vanadium oxide(Ni-VN-V_(2)O_(3)/NC)nanorods to the heterostructural nickel/vanadium nitride(Ni-VN/NC)nanosheets during chemical or electrochemical processes.The self-reconstructed Ni-VN/NC exhibits a robust stability under alkaline conditions,while maintaining initial efficient HER activity with a low overpotential of 76 mV at the current density of 10 mA cm^(-2).Theoretical calculations and quasi-in-situ spectroscopic technology unveil the redistribution of electrons on the synergistic active interface,which synchronously optimizes the affinities for hydrogen,hydroxide,and water molecules,thereby remarkably accelerating the HER kinetics by reducing the barrier of Volmer step.

Non-3d metal modulated zinc imidazolate frameworks for CO_(2) cycloaddition in simulated flue gas under ambient condition

Cycloaddition of CO_(2) and epoxide into cyclic carbonate is one of the most efficient ways for CO_(2) conversion with 100% atom-utilization. Metal–organic frameworks are a kind of potential heterogeneous catalysts, however, high temperature, high pressure, and high-purity CO_(2) are still required for the reaction.Here, we report two new Zn(Ⅱ) imidazolate frameworks incoporating MoO_(4)^(2–)or WO_(4)^(2–)units, which can catalyse cycloaddition of CO_(2) and epichlorohydrin at room temperature and atomospheric pressure, giving 95% yield after 24 h in pure CO_(2) and 98% yield after 48 h in simulated flue gas(15% CO_(2)+ 85% N_(2)),respectively. For comparison, the analogic Zn(Ⅱ) imidazolate framework MAF-6 without non-3d metal oxide units showed 71% and 33% yields under the same conditions, respectively. The insightful modulation mechanisms of the MoO_(4)^(2–)unit in optimizing the electronic structure of Zn(Ⅱ) centre, facilitating the rate-determined ring opening process, and minimizing the reaction activation energy, were revealed by X-ray photoelectron spectroscopy, temperature programmed desorption and computational calculations.

分子钙钛矿含能材料(英文)

设计合成兼具良好爆轰性能、高稳定性和低成本的含能化合物是发展实用含能材料的关键.本文报道了一类新型分子钙钛矿含能化合物,它们可以通过使用低成本原料经简单一锅反应制备.作为氧化组分的高氯酸根阴离子和作为燃料组分的还原性有机阳离子交替紧密堆积于钙钛矿结构中,使该类化合物不仅有比目前军用含能炸药(例如RDX和HMX)更优异的爆炸性能,而且有更高的稳定性;其中无金属组分的分子钙钛矿含能化合物具有与CL-20相当的爆炸性能以及更高的比冲(约344秒).这种将低成本有机燃料组分和氧化剂组分组装在高对称性三元晶体结构的分子组装策略为设计有实用前景的含能材料提供了新思路.

Thermal-induced reversible ferroelastic phase transition in a new bromethyl-substituted molecular rotor

A new bromethyl-substituted molecular rotor, [Cu(dabco CH2Br)(H2O)Br3](dabco CH2Br+=1-(2-bromethyl)-1,4-diazoniabicyclo[2.2.2]octane cation), which belongs to a family of halomethyl-substituted molecular rotors, was synthesized and structurally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder transformation of the rotator part(dabco moiety) causes ferroelastic phase transition with an Aizu notation of mmm F2/m from hightemperature orthorhombic phase(Pbnm) to low-temperature monoclinic phase(P21/n). More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors were discussed in detail for this family of halomethyl-substituted molecular rotors.

Flexibility of Metal-Organic Framework Tunable by Crystal Size at the Micrometer to Submillimeter Scale for Efficient Xylene Isomer Separation

Understanding,controlling,and utilizing the flexibility of adsorbents are of great importance and difficulty.Analogous with conventional solid materials,downsizing to the nanoscale is emerging as a possible strategy for controlling the flexibility of porous coordination polymers(or metal-organic frameworks).We report a unique flexibility controllable by crystal size at the micrometer to submillimeter scale.Template removal transforms[Cu_(2)(pypz)_(2)]·0.5p-xylene(MAF-36,Hpypz=4-(1H-pyrazol-4-yl)pyridine)with one-dimensional channels toα-[Cu_(2)(pypz)_(2)]with discrete small cavities,and further heating gives a nonporous isomerβ-[Cu_(2)(pypz)_(2)].Both isomers can adsorb p-xylene to give[Cu_(2)(pypz)_(2)]·0.5p-xylene,meaning the coexistence of guest-driven flexibility and shape-memory behavior.The phase transition temperature fromα-[Cu_(2)(pypz)_(2)]toβ-[Cu_(2)(pypz)_(2)]decreased from~270℃ to~150℃ by increasing the crystal size from the micrometer to the submillimeter scale,ca.2-3 orders larger than those of other size-dependent behaviors.Single-crystal X-ray diffraction showed coordination bond reconstitution and chirality inversion mechanisms for the phase transition,which provides a sufficiently high energy barrier to stabilize the metastable phase without the need of downsizing to the nanoscale.By virtue of the crystalline molecular imprinting and gate-opening effects,α-[Cu_(2)(pypz)_(2)]andβ-[Cu_(2)(pypz)_(2)]show unprecedentedly high p-xylene selectivities of 16 and 51,respectively,as well as ultrafast adsorption kinetics(<2 minutes),for xylene isomers.

Mild metal-organic-gel route for synthesis of stable sub-5-nm metal-organic framework nanocrystals

Nanoscale metal-organic frameworks （NMOFs） have attracted increased attention in recent years for miniaturized and/or biological applications.However,the synthesis of ultrasmall NMOFs with good stability is a great challenge.In this study,sub-5-nm nano-HKUST-1 was prepared for the first time via a mild metalorganic gel route without surfactants or capping agents.Controlling the gelation process via anion-ligand self-assembly is the key to the formation of NMOFs.The Tyndall effect,zeta potential,and liquid adsorption indicated strong stability of the obtained nano-HKUST-1,even in water.Adsorption experiments were performed using different dyes （crystal violet and methylene blue） to demonstrate the size-dependent adsorption thermodynamics and kinetics of this famous MOF.The results of this study provide new insights regarding the synthesis of NMOFs and their efficient applications.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C_(2)H_(2)/CO_(2)Separation

The similarities in molecular size and physical properties of acetylene(C_(2)H_(2))and carbon dioxide(CO_(2))produce a formidable challenge for their separation.Herein,we report two isoreticular fluorinated metal–organic frameworks(MOFs),labeled as JXNU-11(Fe2M)(M=Ni and Co),featuring unique octahedral cages encapsulated by cuboctahedral cages.JXNU-11(Fe_(2)Ni)shows a record high C_(2)H_(2)-capture amount of 4.8mmol g−1 and a long C_(2)H_(2)/CO_(2)breakthrough interval time of 55 min g^(−1)in an actual breakthrough experiment based on the equimolar C_(2)H_(2)/CO_(2)mixture under ambient conditions,indicating a high-performance material for C_(2)H_(2)capture andC_(2)H_(2)/CO_(2)separation.

A novel pillared-layer-type porous coordination polymer featuring three-dimensional pore system and high methane storage capacity

Solvothermal reaction of Zn(NO_3)_2, 4-(1H-pyrazol-4-yl)pyridine(Hpypz) and 1,3,5-benzenetricarboxylic acid(H_3btc) in N,N-dimethylacetamide(DMA) produced a new porous coordination polymer [Zn_5(pypz)_4(btc)_2](1). Single-crystal X-ray diffraction study of 1 showed that deprotonated pypz~– ligands served as 1,2,4-triazolate-like ligands, linking Zn(II) ions to form porous two-dimensional(2-D) sql-a layers {Zn(pypz)}^+, which were further connected by eight-legged pillars {Zn_2(btc)_4(H_2O)_2}^(8–) based on the typical paddlewheel dinuclear Zn_2(RCOO)_4(H_2O)_2 cluster to form a novel type of non-interpenetrated pillared-layer framework with 3-D intersecting pore system and large pore volume. Gas sorption measurements revealed that 1 possesses large BET surface area of 2061 m^2 g^(–1) and very high methane total uptake of 245 cm^3(STP) cm^(–3) at 298 K and 65 bar.

A gating ultramicroporous metal-organic framework showing high adsorption selectivity,capacity and rate for xylene separation

Adsorptive separation of p-xylene(pX)from xylene isomers is a key process in chemical industry,but known adsorbents cannot simultaneously achieve high adsorption selectivity,capacity,and rate.Here,we demonstrate gating ultramicropore as a solution for this challenge.Slight modification of the synthetic condition gives rise to isomeric metal-organic frameworksα-[Zn(pba)](MAF-88,H2pba=4-(1H-pyrazol-4-yl)benzoic acid)andβ-[Zn(pba)](MAF-89)possessing similar pillared-column structures,porosities,and high pX capacities of 2.0 mmol g^(−1),but very different framework/pore topologies,pore sizes,and pX selectivities.For binary and ternary mixtures of liquid xylene isomers,MAF-88 with narrow one-dimensional(1D)channels shows pX selectivity of 11 and 1.6,while MAF-89 with 3D-connected quasi-discrete pores shows pX selectivity up to 221 and 46,respectively.Thermogravimetry,differential scanning calorimetry,and time-dependent separation experiments reveal that the kinetic effects of the gating pores play more important roles than the thermodynamic effects,which is further confirmed by single-crystal X-ray diffraction and computational simulations.

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators

As an extended model of conventional molecular rotors,a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here.The supramolecular self-assembly of 18-crown-6 host and two rotator-containing ion-pair guests affords a three-in-one cocrystal,(2-NH_(3)-iBuOH)(18-crown-6)[ZnBr_(3)(H_(2)O)],in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators.On the basis of the variable-temperature single-crystal X-ray diffraction,variable-temperature/frequency dielectric response,density functional theory calculations,and molecular dynamics simulations,it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature,and more importantly,could be controlled by a reversible polar-to-polar structural phase transition,i.e.,from a“single-(polar rotator)”state at low-temperature phase to a“mixed-dual-(polar rotator)”state in the vicinity of transition,and to an unusual“synchronized-dual-(polar rotator)”state at high-temperature phase.