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1.
J Phys Chem Lett ; : 5728-5733, 2020 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-32598149

RESUMO

Hybrid organic-inorganic perovskites have emerged as promising thermoelectric materials due to their attractive figure of merits. To further reduce their thermal conductances (G) and improve the thermoelectric efficiencies, fabrication of phononic crystals (PnCs) could be an effective approach. In this work, CH3NH3PbI3-based PnCs were developed and their thermal transports were engineered by optimizing the configurations of both basal bodies and scatterers. Our cross-scale simulations demonstrate that low relative G can be achieved in CH3NH3PbI3 PnCs with large scatterers but low-symmetric PnC lattices, basal bodies, and scatterers. Moreover, we discovered the increased disorder of CH3NH3+ cations from tetragonal to cubic transition significantly increases the phonon velocities and reverses the phonon transport from diffusive to quasi-ballistic, leading to an abnormal reduction of relative G. This work provides a new pathway for engineering thermal conductivity of hybrid perovskites and improving the performance of corresponding devices.

2.
Inorg Chem ; 2020 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-32526144

RESUMO

In spite of the attractive potential application of the dynamic behavior and defect of metal-organic framework (MOF), the achievement of these features is a challenging goal in the MOF research field. Herein, we report a Co(II) MOF, namely, [Co3(L)2(4-PTZ)2(H2O)2]n·solvent (H2L = 5-(isonicotinamido)isophthalic acid, 4-PTZ = 5-(4-pyridyl)-1H-tetrazole), that features dynamic structural transformation behaviors. By varying the coordination configuration of metal center through the removal of coordinated water molecules, the porous compound could undergo structural transformation to give a new crystalline phase with larger pore dimension. Moreover, the new phase features a mesoporous structure originating from the spatial defect that formed with the transformation process, which indicates that the modulation of dynamic behavior of the MOF could be a potential method for the engineering of a spatial defect. In addition, the gas sorption investigation results reveal that the new phase has enhanced selectivity for CO2/N2, CO2/CH4, and C2H2/C2H4 systems compared with that of the pristine phase, suggesting the potential of spatial defect engineering for the tuning of MOF gas sorption properties.

3.
Chem Soc Rev ; 49(8): 2378-2407, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32154522

RESUMO

The design and development of crystalline porous materials (CPMs), including metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), have been subjects of extensive study due to their regular crystalline lattices and well-defined pore structures. In recent times, an enormous amount of research effort has gone into using CPMs as sacrificial templates to fabricate electrochemically functional materials. The inherently electrochemically active sites inside CPMs are notably abundant and being explored with respect to electrochemical reactions. In this review, electrochemically active sites and the space around them (metal ions, ligands, crystal structures, pores, and morphologies) inside CPMs are the focus and recent progress in the fields of metal-ion batteries, metal-air batteries, water splitting, and other related electrochemical devices has been summarized. Overall, this review provides guidance on the preparation of electroactive CPMs via rational design and modulation of active sites such as redox-active metal clusters and organic ligands, and the space around the electrochemically active sites, and their applications in electrochemical energy storage and conversion systems.

4.
Small ; : e1906432, 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-32105388

RESUMO

The Keggin-type polyoxometalates (POMs) are effective catalysts for oxidative desulfurization (ODS) and confining these POMs in metal-organic frameworks (MOFs) is a promising strategy to improve their performances. Herein, postsynthetic modification of POMs confined in MOFs by adding thiourea creates more unsaturated metal sites as defects, promoting ODS catalytic activity. Additional modification by confining 1-butyl-3-methyl imidazolium POMs in MOFs is performed to obtain higher ODS activity, owing to the affinity between electron-rich thiophene-based compounds and electrophilic imidazolium compounds. The ODS catalytic activities of four Zr-MOF-based composites (bottle around ship) including phosphomolybdate acid (PMA)/UiO-66, [Bmim]3 PMo12 O40 /UiO-66, PMA/Thiourea/UiO-66, and [Bmim]3 PMo12 O40 /Thiourea/UiO-66 are therefore investigated in detail. In order to explore the catalytic mechanism of these MOF composites, their microstructures and electronic structures are probed by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, Raman, scanning electron microscope, transmission electron microscope, BET, X-ray photoelectron spectroscopy, EPR, UV-vis, NMR spectra, and H2 -temperature-programmed reduction. The results reveal that phosphomolybdate blues and imidazolium phosphomolybdate blues with different Mo5+ /Mo6+ ratios with the Keggin structure are confined in defected UiO-66 for all four composites. This approach can be applied to design and synthesize other POMs/MOFs composites as efficient catalysts.

6.
Adv Mater ; 32(3): e1806736, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30883987

RESUMO

Halide perovskites provide an ideal platform for engineering highly promising semiconductor materials for a wide range of applications in optoelectronic devices, such as photovoltaics, light-emitting diodes, photodetectors, and lasers. More recently, increasing research efforts have been directed toward the nonlinear optical properties of halide perovskites because of their unique chemical and electronic properties, which are of crucial importance for advancing their applications in next-generation photonic devices. Here, the current state of the art in the field of nonlinear optics (NLO) in halide perovskite materials is reviewed. Halide perovskites are categorized into hybrid organic/inorganic and pure inorganic ones, and their second-, third-, and higher-order NLO properties are summarized. The performance of halide perovskite materials in NLO devices such as upconversion lasers and ultrafast laser modulators is analyzed. Several potential perspectives and research directions of these promising materials for nonlinear optics are presented.

7.
Adv Mater ; 32(3): e1806445, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31106907

RESUMO

The separation and purification of light hydrocarbons (LHs) mixtures is one of the most significantly important but energy demanding processes in the petrochemical industry. As an alternative technology to energy intensive traditional separation methods, such as distillation, absorption, extraction, etc., adsorptive separation using selective solid adsorbents could potentially not only lower energy cost but also offer higher efficiency. The need to develop solid materials for the efficiently selective adsorption of LHs molecules, under mild conditions, is therefore of paramount importance and urgency. Metal-organic frameworks (MOFs), emerging as a relatively new class of porous organic-inorganic hybrid materials, have shown promise for addressing this challenging task due to their unparalleled features. Herein, recent advances of using MOFs as separating agents for the separation and purification of LHs, including the purification of CH4 , and the separations of alkynes/alkenes, alkanes/alkenes, C5 -C6 -C7 normal/isoalkanes, and C8 alkylaromatics, are summarized. The relationships among the structural and compositional features of the newly synthesized MOF materials and their separation properties and mechanisms are highlighted. Finally, the existing challenges and possible research directions related to the further exploration of porous MOFs in this very active field are also discussed.

8.
Top Curr Chem (Cham) ; 378(1): 5, 2019 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-31823121

RESUMO

Over the past two decades, metal-organic frameworks (MOFs) with flexible structures or dynamic behavior have shown great potential as functional materials in many fields. This paper presents a review of these dynamic and functional MOFs, which can undergo controllable and reversible transformation, with regard to their application as smart switches. Trigger conditions, which include physical/chemical stimuli (e.g., guest molecules, light, temperature, pressure), are also discussed. Research methods for investigating the dynamic processes and mechanisms involving experimental characterization and computational modeling are briefly mentioned as well. The emphasis is on the aspects of the design and functionalization of dynamic MOFs. The pre-design of metal nodes, organic linkers, and topology, as well as post-modification of components, increases the possibility of obtaining functionalized dynamic materials. Recent advances with regard to potential applications for dynamic frameworks as smart switches for adsorption and sensing are also reviewed.


Assuntos
Estruturas Metalorgânicas/química , Adsorção , Aminas/análise , Gases/análise , Luz , Estruturas Metalorgânicas/efeitos da radiação , Pressão , Solventes/química , Temperatura
9.
Chem Sci ; 10(38): 8850-8854, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31803459

RESUMO

Solid-liquid separation of similarly sized organic molecules utilizing sorbents offers the potential for new energy-efficient approaches to a number of important industrial separations such as xylenes (C8) separations. Research on selective C8 sorption has tended to focus upon rigid porous materials such as zeolites and MOFs but has revealed generally weak selectivity that is inconsistent across the range of C8 molecules. Nevertheless, there are a few recent examples of non-porous molecular materials that exhibit relatively high selectivity for p-xylene (pX) from pX/oX, approaching that of the current benchmark pX sorbent, the zeolite H/ZSM-5. Herein, we report that a L-shaped Ag(i) complex, AgLClO4 (M), which crystallizes as a non-porous molecular solid material, offering exceptional performance for pX selectivity across the range of C8 isomers with liquid extraction selectivity values of 24.0, 10.4 and 6.2 vs. oX, eB and mX, respectively. The pX selectivities over oX and eB are among the highest yet reported. Moreover, M also exhibits strong vapor extraction selectivity and can be regenerated by exposure to vacuum drying.

10.
Small ; 15(51): e1906086, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31762172

RESUMO

Controlled growth of metal-organic frameworks (MOFs) nanocrystals on requisite surfaces is highly desired for myriad applications related to catalysis, energy, and electronics. Here, this challenge is addressed by overlaying arbitrary surfaces with a thermally evaporated metal layer to enable the well-aligned growth of ultralong quasi-2D MOF nanoarrays comprising cobalt ions and thiophenedicarboxylate acids. This interfacial engineering approach allows preferred chelation of carboxyl groups in the ligands with the metal interlayers, thereby making possible the fabrication and patterning of MOF nanoarrays on substrates of any materials or morphologies. The MOF nanoarrays grown on porous metal scaffolds demonstrate high electrocatalytic capability for water oxidation, exhibiting a small overpotential of 270 mV at 10 mA cm-2 , or 317 mV at 50 mA cm-2 as well as negligible decay of performance within 30 h. The enhanced performance stems from the improved electron and ion transport in the hierarchical porous nanoarrays consisting of in situ formed oxyhydroxide nanosheets in the electrochemical processes. This approach for mediating the growth of MOF nanoarrays can serve as a promising platform for diverse applications.

11.
Adv Mater ; 31(48): e1904771, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31588636

RESUMO

Bismuth has emerged as a promising anode material for sodium-ion batteries (SIBs), owing to its high capacity and suitable operating potential. However, large volume changes during alloying/dealloying processes lead to poor cycling performance. Herein, bismuth nanoparticle@carbon (Bi@C) composite is prepared via a facile annealing method using a commercial coordination compound precursor of bismuth citrate. The composite has a uniform structure with Bi nanoparticles embedded within a carbon framework. The nanosized structure ensures a fast kinetics and efficient alleviation of stress/strain caused by the volume change, and the resilient and conductive carbon matrix provides an interconnected electron transportation pathway. The Bi@C composite delivers outstanding sodium-storage performance with an ultralong cycle life of 30 000 cycles at a high current density of 8 A g-1 and an excellent rate capability of 71% capacity retention at an ultrahigh current rate of 60 A g-1 . Even at a high mass loading of 11.5 mg cm-2 , a stable reversible capacity of 280 mA h g-1 can be obtained after 200 cycles. More importantly, full SIBs by pairing with a Na3 V2 (PO4 )3 cathode demonstrates superior performance. Combining the facile synthesis and the commercial precursor, the exceptional performance makes the Bi@C composite very promising for practical large-scale applications.

12.
J Am Chem Soc ; 141(44): 17703-17712, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31603672

RESUMO

Physical adsorption of gas molecules in microporous materials is an exothermic process, with desorption entropy driving a decrease in uptake with temperature. Enhanced gas sorption with increasing temperature is rare in porous materials and is indicative of sorbate initiated structural change. Here, sorption of C2H6, C3H6, and C3H8 in a flexible microporous metal-organic framework (MOF) {Cu(FPBDC)]·DMF}n (NKU-FlexMOF-1) (H2FPBDC = 5-(5-fluoropyridin-3-yl)-1,3-benzenedicarboxylic acid) that increases with rising temperature over a practically useful temperature and pressure range is reported along with other small molecule and hydrocarbon sorption isotherms. Single X-ray diffraction studies, temperature-dependent gas sorption isotherms, in situ and variable temperature powder X-ray diffraction experiments, and electronic structure calculations were performed to characterize the conformation-dependent sorption behavior in NKU-FlexMOF-1. In total, the data supports that the atypical sorption behavior is a result of loading-dependent structural changes in the flexible framework of NKU-FlexMOF-1 induced by sorbate-specific guest-framework interactions. The sorbates cause subtle adaptations of the framework distinct to each sorbate providing an induced-fit separation mechanism to resolve chemically similar hydrocarbons through highly specific sorbate-sorbent interactions. The relevant intermolecular contacts are shown to be predominantly repulsion and dispersion interactions. NKU-FlexMOF-1 is also found to be stable in aqueous solutions including toleration of pH changes. These experiments demonstrate the potential of this flexible microporous MOF for cost and energy efficient industrial hydrocarbon separation and purification processes. The efficacy for the separation of C3H6/C3H8 mixtures is explicitly demonstrated using NKU-FlexMOF-1a (i.e., activated NKU-FlexMOF-1) for a particular useful temperature range.

13.
Small ; 15(45): e1903410, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31517439

RESUMO

Benefiting from metal-organic frameworks (MOFs) unique structural characteristics, their versatility in composition and structure has been well explored in electrochemical oxygen evolution reaction (OER) processes. Here, a ligand/ionic exchange phenomenon of MOFs is reported in alkaline solution due to their poor stability, and the active species and reaction mechanism of MOFs are revealed in the OER process. A series of mixed Ni-MOFs and Fe-MOFs are synthesized by straightforward sonication and then directly used as catalyst candidates for OER in alkaline electrolyte. It can be confirmed via ex situ transmission electron microscopic images and X-ray diffraction patterns analysis, that the bimetallic hydroxide (NiFe-LDH) is generated in 1.0 m KOH in situ and acts as protagonist for oxygen evolution. The optimized catalyst (FN-2) exhibits a lower overpotential (275 mV at a current density of 10 mA cm-2 ) and excellent long-term stability (strong current density for 100 h without fading). The revelation of the real active species of MOF materials may contribute to better understanding of the reaction mechanism.

14.
Angew Chem Int Ed Engl ; 58(39): 13890-13896, 2019 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-31231920

RESUMO

Photonic materials use photons as information carriers and offer the potential for unprecedented applications in optical and optoelectronic devices. In this study, we introduce a new strategy for photonic materials using metal-organic frameworks (MOFs) as the host for the rational construction of donor-acceptor (D-A) heterostructure crystals. We have engineered a rich library of heterostructure crystals using the MOF NKU-111 as a host. NKU-111 is based upon an electron-deficient tridentate ligand (acceptor) that can bind to various electron-rich guests (donors). The resulting heterocrystals exhibit spatially segregated multi-color emission resulting from the guest-dependent charge-transfer (CT) emission. Spatially effective mono-directional energy transfer results from tuning the energy gradient between adjacent domains through the selection of donor guest molecules, which suggests potential applications in integrated optical circuit devices, for example, photonic diodes, on-chip signal processing, optical logic gates.

15.
J Am Chem Soc ; 141(23): 9134-9139, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31131600

RESUMO

The flexible organic amine cations on the interfaces of two-dimensional (2D) hybrid organic-inorganic perovskite nanosheets could form relaxed structures, which would lead to exotic optoelectronic properties but are hard to understand. Here, the unusual interfacial relaxation of nanosheets exfoliated from an orthorhombic 2D lead halide perovskite, [(C6H5CH2NH3)2]PbCl4, is interrogated via ultrafast second-harmonic generation (SHG) spectroscopy. The in-plane SHG intensity anisotropy of these nanosheets is found to decrease with reducing layer thickness. Combined first-principles calculations and Monte Carlo simulations reveal that the induced second-order polarization arises primarily from the (C6H5CH2NH3)+ cations; and these organic amine cations form significantly reorganized conformations with decreasing nanosheet thickness due to weakened van der Waals interactions. Because the orientations of organic components at the interface determine their electric properties and specifically the dipolar susceptibility, the resulting structure leads to striking changes in the SHG properties.

16.
ACS Appl Mater Interfaces ; 11(23): 20995-21003, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31117453

RESUMO

The synergy of a stretchy ligand and highly variable π-π interaction has been proposed as a rational strategy for the construction of breathing metal-organic frameworks (MOFs). Based on this strategy, a breathing MOF, {[Cd2(AzDC)2(TPT)2](DMF)3} n, was successfully constructed with stretchy 4,4'-diazene-1,2-diyldibenzoate acid (H2AzDC) and 2,4,6-tris(4-pyridyl)triazine (TPT) as a source of the π-π interaction. The MOF features structure transformation upon stimulation with solvent guests and varied temperatures, which is straightforwardly characterized by single-crystal structures. Moreover, the solvent-free framework shows breathing behaviors in response to light hydrocarbon (C2H4, C2H6, C3H6, and C3H8) sorption, which was verified by stepwise sorption isotherms and in situ powder X-ray diffraction. Additional investigation of the sorption selectivity of C3/C2 systems indicated that the selectivity can be regulated by the modulation of the dynamic breathing behaviors, which can be used for the selective separation of C3/C2 light hydrocarbons.

17.
J Am Chem Soc ; 141(23): 9408-9414, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31117669

RESUMO

Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest for gas storage/separation applications. However, the design and synthesis of SPCs is challenging. Herein, we report a new type of SPC based on a [2 + 3] imide-based organic cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior. Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a "closed" nonporous phase (α) to two porous "open" phases (ß and γ). The net effect is gate-opening behavior induced by CO2 and C3 hydrocarbons. Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane under ambient conditions. Thus, NKPOC-1-α has the potential to separate binary and ternary C3 hydrocarbon mixtures, and the performance was subsequently verified by fixed bed column breakthrough experiments. In addition, molecular dynamics calculations and in situ X-ray diffraction experiments indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption energies from molecular dynamics simulations aid are consistent with the experimentally observed selective adsorption phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for applications in gas separation/storage because SPCs do not inherently suffer from the recyclability problems often encountered with rigid materials.

18.
Angew Chem Int Ed Engl ; 58(30): 10184-10188, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31090998

RESUMO

Although great achievements have been made in the synthesis of giant lanthanide clusters, novel structural models are still scarce. Herein, we report a giant lanthanide cluster Dy76 , constructed from [Dy3 (µ3 -OH)4 ] and [Dy5 (µ4 -O)(µ3 -OH)8 ] building blocks. As the largest known Dy cluster, the structure of Dy76 can be seen as arising from the fusion of two Dy48 clusters; these clusters can be isolated under various synthetic conditions and were characterized by single-crystal X-ray diffraction. This new, fused structural model of the pillar motif has not been found in Ln clusters. Furthermore, the successful conversion of Dy76 back into Dy48 in a retrosynthetic manner supports the proposed fusion formation mechanism of Dy76 . Electrospray ionization mass spectrometry (ESI-MS) analysis suggests that the metal cluster skeleton of Dy76 shows good stability in various solvents. This work not only reveals a new structural type of Ln clusters but also provides insight into the novel fusion assembly process.

19.
Small ; 15(22): e1900426, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30977961

RESUMO

Metal-organic frameworks (MOFs) can be fine-tuned to boost sorbent-sorbate interactions in order to improve gas sorption and separation performance, but the design of MOFs with ideal structural features for gas separation applications remains a challenge. Herein it is reported that unsaturated alkali metal sites can be immobilized in MOFs through a tetrazole based motif and that gas affinity can thereby be boosted. In the prototypal MOF of this type-NKU-521 (NKU denotes Nankai University), K+ cations are effectively embedded in a trinuclear Co2+ -tetrazole coordination motif. The embedded K+ sites are exposed to the pores of NKU-521 through water removal, and the isosteric heat (Qst ) for CO2 is boosted to 41 kJ mol-1 . The nature of the binding site is validated by molecular simulations and structural characterization. The K+ cations in effect serve as gas traps and boost the CO2 -framework affinity, as measured by the Qst , by 24%. In addition, the impact of unsaturated alkali metal sites upon the separation of hydrocarbons is evaluated for the first time in MOFs using ideal adsorbed solution theory (IAST) calculations and column breakthrough experiments. The results reveal that the presence of exposed K+ sites benefits gas sorption and hydrocarbon separation performances of this MOF.

20.
Angew Chem Int Ed Engl ; 58(17): 5614-5618, 2019 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-30779418

RESUMO

We herein report a new coordination network that deforms in a smooth and reversible manner under either thermal or pressure stimulation. Concomitantly, the organic fluorophores coordinatively bound to the channel in a face-to-face arrangement respond to this structural deformation by finely adapting their conformation and arrangement. As a result, the material exhibits a remarkable dual-stimuli-responsive luminescence shift across almost the entire visible region: The emission color of the crystal gradually changes from cyan to green upon heating and then to red upon pressure compression. Furthermore, each stage exhibits a linear dependence of both the emission maximum and intensity on the stimulus and is fully reversible.

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