Highly effective H2/D2 separation in a stable Cu-based metal-organic framework

A three-dimensional copper metal-organic framework with the rare chabazite(CHA)topology namely FJI-Y11 has been constructed with flexibly carboxylic ligand 5,5'-[(1,4-phenylenebis(methylene))bis(oxy)]diisophthalic acid(H₄L).FJI-Y11 exhibits high water stability with the pH range from 2 to 12 at temperature as high as 373 K.Importantly,FJI-Y11 also shows high efficiency of hydrogen isotope separation using dynamic column breakthrough experiments under atmospheric pressure at 77 K.Attributed to its excellent structural stability,FJI-Y11 possesses good regenerated performance and maintains high separation efficiency after three cycles of breakthrough experiments.     

Layer-by-layer assembled dual-ligand conductive MOF nano-films with modulated chemiresistive sensitivity and selectivity

In this paper,a dual-ligand design strategy is demonstrated to modulate the performance of the electronically conductive metalorganic frameworks(EC-MOFs)thin film with a spray layer-by-layer assembly method.The thin film not only can be precisely prepared in nanometer scale(20-70 nm),but also shows the pin-hole-free smooth surface.The high quality nano-film of 2,3,6,7,10,11-hexaiminotriphenylene(HITP)doped Cu-HHTP enables the precise modulation of the chemiresistive sensitivity and selectivity.Selectivity improvement over 220%were realized for benzene vs.NH3>as well as enhanced response and recovery properties.In addition,the selectivity of the EC-MOF thin film sensors toward other gases(e.g.triethylamine,methane,ethylbenzene,hydrogen,butanone,and acetone)vs.NH3 at room temperature is also discussed.     

Elucidating the electro-catalytic oxidation of hydrazine over carbon nanotube-based transition metal single atom catalysts

Elucidating the reaction mechanism of hydrazine oxidation reaction (HzOR) over carbon-based catalysts is highly propitious for the rational design of novel electrocatalysts for HzOR. In present work, isolated first-row transition metal atoms have been coordinated with N atoms on the graphite layers of carbon nanotubes via a M-N₄-C configuration (MSA/CNT, M=Fe, Co and Ni). The HzOR over the three single atom catalysts follows a predominant 4-electron reaction pathway to emit N₂ and a negligible 1-electron pathway to emit trace of NH₃, while their electrocatalytic activity for HzOR is dominated by the absorption energy of N₂H₄ on them. Furthermore, FeSA/CNT reverses the passivation effect on Fe/C and shows superior performance than CoSA/CNT and NiSA/CNT with a recorded high mass activity for HzOR due to the higher electronic charge of Fe over Co and Ni in the M-N₄-C configuration and the lowest absorption energy of N₂H₄ on FeSA/CNT among the three MSA/CNT catalysts.

     

High proton conductivity in metalloring-cluster based metal-organic nanotubes

Two novel anionic single-walled metal-organic nanotubes(MONTs),[(CH₃)₂NH₂][ln(cdc)(thb)].2DMF.9.5H₂O(FJU-105)and[(CH₃)₂NH₂][ln(cdc)(H-btc)]-2DMA·11H₂O(FJU-106)(H₂cdc=9H-carbazole-3,6-dicarboxylic acid,H₂thb=2,5-thiophene dicarboxylic acid,H3btc=1,3,5-benzene tricarboxylic acid),are achieved by employing[ln₆(cdc)₆]⁶⁺metalloring cluster with largest diameter as the secondary building blocks(SBUs).The inner surface of FJU-106 is functionalized by uncoordinated-COOH groups of the H-btc linkers,leading to a higher proton conduction than FJU-105.At 70℃,FJU-106 displays the proton conduction performances among MONTs,up to 1.80×10^-2S·cm(^-1).And FJU-105 and FJU-106 are the first examples of MONT proton conductors operating at subzero temperature.     

Structural revolution of atomically dispersed Mn sites dictates oxygen reduction performance

An efficient preparation and local coordination environment regulation of isolated single-atom sites catalysts (ISASC) for improved activity is still challenging. Herein, we develop a solid phase thermal diffusion strategy to synthesize Mn ISASC on highly uniform nitrogen-doped carbon nanotubes by employing MnO₂ nanowires@ZIF-8 core-shell structure. Under high-temperature, the Mn species break free from core-MnO₂ lattice, which will be trapped by carbon defects derived from shell-ZIF-8 carbonization, and immobilized within carbon substrate. Furthermore, the poly-dispersed Mn sites with two nitrogen-coordinated centers can be controllably renovated into four-nitrogen-coordinated Mn sites using NH₃ treatment technology. Both experimental and computational investigations indicate that the symmetric coordinated Mn sites manifest outstanding oxygen reduction activity and superior stability in alkaline and acidic solutions. This work not only provides efficient way to regulate the coordination structure of ISASC to improve catalytic performance but also paves the way to reveal its significant promise for commercial application.

     

Solid-state phase transformations toward a metal-organic framework of 7-connected Zn4O secondary building units

In the development of metal-organic frameworks (MOFs), secondary building units (SBUs) have been utilized as molecular modules for the construction of nanoporous materials with robust structures. Under solvothermal synthetic conditions, dynamic changes in the metal coordination environments and ligand coordination modes of SBUs determine the resultant product structures. Alternatively, MOF phases with new topologies can also be achieved by post-synthetic treatment of as-synthesized MOFs via the introduction of acidic or basic moieties that cause the simultaneous cleavage/reformation of coordination bonds in the solid state. In this sense, we studied the solid-state transformation of two ndc-based Zn-MOFs (ndc = 1,4-naphthalene dicarboxylate) with different SBUs but the same pcu topology to another MOF with sev topology. One of the chosen MOFs with pcu nets is [Zn₂(ndc)₂(bpy)]_n (bpy = 4,4′-bipyridine), (6C_bpy-MOF) consisting of a 6-connected pillared-paddlewheel SBU, and the other is IRMOF-7 composed of 6-connected Zn₄O(COO)₆ SBUs and ndc. Upon post-structural modification, these pcu MOFs were converted into the same MOF with sev topology constructed from the uncommon 7-connected Zn₄O(COO)₇ SBU (7C-MOF). The appropriate post-synthetic conditions for the transformation of each SBUs were systematically examined. In addition, the effect of the pillar molecules in the pillared-paddlewheel MOFs on the topology conversion was studied in terms of the linker basicity, which determines the inertness during the solid-state phase transformation. This post-synthetic modification approach is expected to expand the available methods for designing and synthesizing MOFs with controlled topologies.

     

Robust enhanced hydrogen production at acidic conditions over molybdenum oxides-stabilized ultrafine palladium electrocatalysts

Electrochemical water splitting is quite seductive for eco-friendly hydrogen fuel energy production,however,the attainment of highly efficient,durable,and cheap catalysts for the hydrogen evolution reaction(HER)remains challenging.In this study,molybdenum oxides stabilized palladium nanoparticle catalysts(MoO_x-Pd)are in situ prepared on commercial carbon cloth(CC)by the facile two-step method of dip-coating and electrochemical reduction.As a self-supported Pd-based catalyst electrode,the MoO_x-Pd/CC presents a competitive Tafel slope of 45.75 mV·dec^-1,an ultralow overpotential of 25 mV,and extremely long cycling durability(one week)in 0.5M H₂S0₄electrolyte,superior to unmodified Pd catalysts and comparable to commercial Pt mesh electrode.On the one hand,the introduction of MoO_xcan inhibit the growth of Pd particles to obtain ultrafine Pd nanoparticles,thus exposing more available active sites.On the other hand,density functional theory(DFT)calculation revealed that MoO_xon the surface of Pd metal can regulate the electronic structure of Pd metal and enhance its intrinsic catalytic activity of HER.This work suggests that transitional metal nanoparticles stabilized by molybdenum oxides are hopeful approaches for obtaining fruitful hydrogen-producing electrocatalysts.     

Light-responsive color switching of self-doped TiO2-x/WO3·0.33H2O hetero-nanoparticles for highly efficient rewritable paper

Smart materials that reversibly change color upon light illumination are widely explored for diverse appealing applications.However,light-responsive color switching materials are mainly limited to organic molecules.The synthesis of inorganic counterparts has remained a significant challenge because of their slow light response and poor reversibility.Here,we report a seeded growth strategy for the synthesis of TiO_2-x/WO₃·0.33H₂Ohetero-nanoparticles(HNPs)with networked wire-like structure of?10 nm in diameters that enable the highly reversible light-responsive color switching properties.For the TiO_2-x/WO₃·0.33H₂OHNPs,T P species self-doped in TiO_2-xnanoparticles(NPs)act as efficient sacrificial electron donors(SEDs)and Ti-O-W linkages formed between TiO2-x and WO30.33H2O NPs ensure the nanoscale interfacial contact,endowing the HNPs enhanced photoreductive activity and efficient interfacial charge transfer upon ultraviolet(UV)illumination to achieve highly efficient color switching.The TiO_2-x/WO₃·0.33H₂OHNPs exhibits rapid light response(<15 s)and long reversible color switching cycles(>180 times).We further demonstrate the applications of TiO_2-x/WO₃·0.33H₂O HNPs in ink-free,light-printable rewritable paper that can be written on freehand or printed on through a photomask using UV light.This work opens an avenue for designing inorganic light-responsive color switching nanomaterials and their smart applications.     

A chemically stable nanoporous coordination polymer with fixed and free Cu2+ ions for boosted C2H2/CO2 separation

Safely and highly selective acetylene(C₂H₂)capture is a great challenge,because of its highly explosive nature,as well as its nearly similar molecule size and boiling point toward the main impurity of carbon dioxide(CO₂).Adsorption separation has shown a promising future.Herein,a new nanoporous coordination polymer(PCP)adsorbent with fixed and free Cu ions(termed NTU-66-Cu)was prepared through post-synthetic approach via cation exchanging from the pristine NTU-66,an anionic framework with new 3,4,6-c topology and two kinds of cages.The NTU-66-Cu shows significantly improved C₂H₂/CO₂selectivity from 6 to 32(v/v:1/1)or 4 to 4₂(v/v:1/4)at low pressure under 298 K,along with enhanced C₂H₂capacity(from 89.22to 111.53 cm³·g^-1).More importantly,this observation was further validated by density functional theory(DFT)calculations and breakthrough experiments under continuous and dynamic conditions.Further,the excellent chemical stability enables this adsorbent to achieve recycle C₂H₂/CO₂separation without loss of C₂H₂capacity.     

Nickel phosphonate MOF as efficient water splitting photocatalyst

A novel microporous two-dimensional(2D)Ni-based phosphonate metal-organic framework(MOF;denoted as IEF-13)has been successfully synthesized by a simple and green hydrothermal method and fully characterized using a combination of experimental and computational techniques.Structure resolution by single-crystal X-ray diffraction reveals that IEF-13 crystallizes in the triclinic space group Pi having bi-octahedra nickel nodes and a photo/electroactive tritopic phosphonate ligand.Remarkably,this material exhibits coordinatively unsaturated nickel(II)sites,free-P0₃H₂and-P0₃H acidic groups,a C0₂accessible microporosity,and an exceptional thermal and chemical stability.Further,its in-deep optoelectronic characterization evidences a photoresponse suitable for photocatalysis.In this sense,the photocatalytic activity for challenging H₂generation and overall water splitting in absence of any co-catalyst using UV-Vis irradiation and simulated sunlight has been evaluated,constituting the first report for a phosphonate-MOF photocatalyst.IEF-13 is able to produce up to 2,200 fimol of H₂per gram using methanol as sacrificial agent,exhibiting stability,maintaining its crystal structure and allowing its recycling.Even more,170μmol of H₂per gram were produced using IEF-13 as photocatalyst in the absence of any co-catalyst for the overall water splitting,being this reaction limited by the 0₂reduction.The present work opens new avenues for further optimization of the photocatalytic activity in this type of multifunctional materials.     

Layered CuNi-Cu2O/NiAlOx nanocatalyst for rapid conversion of p-nitrophenol to p-aminophenol

In order to well arrange active sites and avoid byproducts, the reasonable structured carrier nanocatalyst plays a crucial role in high catalytic performance, but still remains a challenge. Herein, the layered CuNi-Cu₂O/NiAlO_x nanosheets have been constructed through hydrothermal synthesis followed by calcination and H₂ reduction treatment process. The in-situ formed CuNi nanoalloys (NAs) and nano-Cu₂O were evenly distributed on the bilateral surface of layered NiAlO_x nanosheets. Based on the planar structure of nanosheet, the synergy between catalytic active CuNi NAs and photocatalytic active nano-Cu₂O endows CuNi-Cu₂O/NiAlO_x nanosheets with rapid conversion efficiency for catalyzing p-nitrophenol (p-NP, 14 mg·L⁻¹) to p-aminophenol (p-AP) in 32 s with the reaction rate constant k up to 0.1779 s⁻¹, and no obvious performance decay can be observed even over 27 cycles. Moreover, high concentration of p-NP at 10 and 20 g·L⁻¹ could be reduced to p-AP within 14 and 20 min, respectively. Such designed nanoalloy/bimetal-oxide heterostructure can provide a solution for rapid conversion of aminoaromatics from nitroaromatics wastewater even at a large concentration range.

     

Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m²·g⁻¹), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.

     

Effects of connecting sequences of building blocks on reticular synthesis of covalent organic frameworks

The principle of reticular chemistry has been widely used to guide the design of crystalline porous materials such as metal organic frameworks(MOFs)and covalent organic frameworks(COFs).While in the early strategies only the symmetries of the building blocks were considered for reticular synthesis of COFs,recently a few researches on COFs with hierarchical porosities indicate that connecting sequence of building blocks also plays a crucial role in determining crystalline structures of COFs.However,this important phenomenon has not been systematically investigated yet.In this article,a model system has been established to demonstrate how different connecting sequences of two C_2v-symmetric building blocks lead to the formation of four two-dimensional(2D)COFs with distinct framework structures.To verify this concept,target synthesis was conducted to produce three COFs,whose structures were confirmed by powder X-ray diffraction and pore size distribution analysis.     

Highly efficient multi-metal catalysts for carbon dioxide reduction prepared from atomically sequenced metal organic frameworks

The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks(MOFs)endowed by reticular chemistry,allows the obtaining of materials with compositions that are programmed for achieving enhanced reactivity.The present work illustrates how through the transformation of MOFs with desired arrangements of metal cations,multi-metal spinel oxides with precise compositions can be obtained,and used as catalyst precursor for the reverse water-gas shift reaction.The differences in the spinel initial composition and structure,determined by neutron powder diffraction,influence the overall catalytic activity with changes in the process of in s itu formation of active,metal-oxide supported metal nanoparticles,which have been monitored and characterized with in situ X-ray diffraction and photoelectron spectroscopy studies.     

Oxygen vacancy engineering of calcium cobaltate: A nitrogen fixation electrocatalyst at ambient condition in neutral electrolyte

In order to sustainably transform N2 to ammonia(NRR)using electrocatalysts under mild ambient condition,it is urgent to design and develop non-nobel metal nanocatalysts that are inexpensive and suitable for mass-production.Herein,a calcium metalate catalyst CaCoO_xwith oxygen vacancies was synthesized and used as an electrocatalyst for NRR for the first time,whose morphology can be controlled by the calcination temperature and the heating rate.Under the optimal conditions,the CaCoO_xcatalyst achieved the yield of nitrogen conversion to ammonia of 16.25μg·h^-1·mg_cat.^-1at the potential of-0.3 V relative to the reversible hydrogen electrode(RHE)with a Faraday efficiency of 20.51%.The electrocatalyst showed good stability even after 12 times recyclability under environmental conditions and neutral electrolyte.Later,the electrocatalytic nitrogen reduction performance of CaFeO_x,CaNiO_x,CaCuO_xwas investigated.These earth-rich transition metals also exhibited certain NRR electrocatalytic capabilities,which provided a door for further development of inexpensive and easily available transition metal as nitrogen reduction electrocatalysts.     

Highly active multivalent multielement catalysts derived from hierarchical porous TiNb2O7 nanospheres for the reversible hydrogen storage of MgH2

Critical limitations in applying MgH₂ as a hydrogen-storage medium include the high H₂ desorption temperature and slow reaction kinetics.In this study,we synthesized hierarchical porous TiNb₂O₇ spheres in micrometer scale built with 20-50 nm nanospheres,which showed stable activity to catalyze hydrogen storage in MgH₂ as precursors.The addition of 7 wt.%TiNb₂O₇ in MgH₂ reduced the dehydrogenation onset temperature from 300 to 177℃.At 250℃,approximately 5.5 wt.%H₂ was rapidly released in 10 min.Hydrogen uptake was detected even at room temperature under 50 bar hydrogen;4.5 wt.%H₂ was absorbed in 3 min at 150℃,exhibiting a superior low-temperature hydrogenation performance.Moreover,nearly constant capacity was observed from the second cycle onward,demonstrating stable cyclability.During the ball milling and initial de/hydrogenation process,the high-valent Ti and Nb of TiNb₂O₇ were reduced to the lower-valent species or even zero-valent metal,which in situ created multivalent multielement catalytic surroundings.A strong synergistic effect was obtained for hybrid oxides of Nb and Ti by density functional theory(DFT)calculations,which largely weakens the Mg-H bonding and results in a large reduction in kinetic barriers for hydrogen storage reactions of MgH₂.Our findings may guide the further design and development of high-performance complex catalysts for the reversible hydrogen storage of hydrides.     

Efficient fully blade-coated perovskite solar cells in air with nanometer-thick bathocuproine buffer layer

Fully printed perovskite solar cells(PSCs)were fabricated in air with all constituent layers,except for electrodes,deposited by the blade coating technique.The PSCs incorporated,for the first time,a nanometer-thick printed bathocuproine(BCP)hole blocking buffer using blade coating and deposited at relative humidity up to 50%.The PSCs with a p-i-n structure(glass/indium tin oxide(ITO)/poly(3,4-ethylenedioxythiophene)polystyrene sulfonate(PEDOT:PSS)/CH₃NH₃Pbl₃/[6,6]-phenyl-C₆₁-butyric acid methyl ester(PCBM)/BCP/Ag)delivered a maximum power conversion efficiency(PCE)of 14.9%on an active area of 0.5 cm²when measured under standard test conditions.The PSCs with a blade coated BCP delivered performance of 10%and 63%higher(in relative terms)than those incorporating a spin coated BCP or without any BCP film,respectively.The atomic force microscopy(AFM)showed that blade coated films were more homogeneous and acted also as a surface planarizer leading to a reduction of roughness which improved BCP/Ag interface lowering charge recombination.The demonstration of 15%efficient devices with all constituent layers,including nanometer-thick BCP(?10 nm),deposited by blade coating in air,demonstrates a route for industrialization of this technology.     

A robust bifunctional catalyst for rechargeable Zn-air batteries: Ultrathin NiFe-LDH nanowalls vertically anchored on soybean-derived Fe-N-C matrix

ABSTRACT NiFe layered double hydroxide(NiFe-LDH)nanosheets and metal-nitrogen-carbon materials(M-N-C,M=Ni,Fe,Co,etc.)are supreme catalysts in the oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)process,respectively.Nevertheless,the monotonic performance and insufficient stability severely hamper their practical application in rechargeable batteries.Herein,we simultaneously combine ultrathin NiFe-LDH nanowalls with renewable soybean-derived Fe-N-C matrix to obtain a hybrid materials(NiFe-LDH/FeSoy-CNSs-A),which exhibits robust catalytic activities for OER(E_j=10=1.53 V vs.RHE)and ORR(E_1/2=0.91 V vs.RHE),with a top-notch battery parameters and stability in assembled rechargeable Zn-air batteries.Intensive investigations indicate that the vertically dispersed NiFe-LDH nanosheets,Fe-N-C matrix derived from soybean and the strong synergy between them are responsible for the unprecedented OER and ORR performances.The key role of intrinsic N defects involved in the hybrid materials is firstly specified by ultrasoundassisted extraction of soy protein from soybean.The exquisite design can facilitate the utilization of sustainable biomass-derived catalysts,and the mechanism investigations of N defects and oxygenic groups on the structure-activity relationship can stimulate the progress of other functional hybrid electrocatalysts.     

Two-dimensional d-πconjugated metal-organic framework based on hexahydroxytrinaphthylene

The development of new two-dimensional(2D)d-πconjugated metal-organic frameworks(MOFs)holds great promise for the construction of a new generation of porous and semiconductive materials.This paper describes the synthesis,structural characterization,and electronic properties of a new d-πconjugated 2D MOF based on the use of a new ligand 2,3,8,9,14,15-hexahydroxytrinaphthylene.The reticular self-assembly of this largeπ-conjugated organic building block with Cu(II)ions in a mixed solvent system of 1,3-dimethyl-2-imidazolidinone(DMI)and H2 O with the addition of ammonia water or ethylenediamine leads to a highly crystalline MOF Cu3(HHTN)2,which possesses pore aperture of 2.5 nm.Cu3(HHTN)2 MOF shows moderate electrical conductivity of 9.01×10^-8S·cm^-1at 385 K and temperature-dependent band gap ranging from 0.75 to 1.65 eV.After chemical oxidation by l2,the conductivity of Cu3(HHTN)2 can be increased by 360 times.This access to HHTN based MOF adds an important member to previously reported MOF systems with hexagonal lattice,paving the way towards systematic studies of structure-property relationships of semiconductive MOFs.     

Dimethylammonium iodide stabilized bismuth halide perovskite photocatalyst for hydrogen evolution

Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH₃)₂NH₂]₃[Bil₆](DA₃Bil₆)in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^-ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^-ions and with PtCI4 as a co-catalyst(Pt-DA₃Bil₆),photocatalytic H2 evolution with a rate of 5.7μmol·h^-1from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.