Chemistry of Materials最新文献

Materials exhibiting negative thermal expansion (NTE),characterizedby anomalous lattice contractions upon heating, have attracted considerableattention because of the unique attendant changes in crystal structure.A wide variety of compounds, including metal oxides, fluorides, andcyanides, show this phenomenon as a consequence of open-frameworkstructures. However, compounds containing linear, triatomic dumbbell-likecarbodiimide anion NCN^2– have received less attention.Herein, we report that ZnNCN exhibits uniaxial NTE along the c-axis with a coefficient of −5.34(1) × 10^–6 K^–1 together with a coefficientof 4.12(3) × 10^–6 K^–1 alongthe a-axis at 300 K. Structural refinement usingneutron diffraction data acquired at different temperatures indicatesa contraction of the averaged N–N separation along the c-axis. Pair distribution functions (PDFs) generated fromneutron total scattering data reveal that the ∠NCN angle decreasesfrom 175° at 30 K to 160.5° at 673 K. Ab initio moleculardynamics calculations examining the local structure indicate an increasedproportion of dynamical transverse bending of NCN^2– anions, consistent with the PDF analysis. At higher temperatures,enhanced intramolecular bending of the anions is suggested to induceNTE along the c-axis in ZnNCN. Dynamical bendingof molecular anions provides a design strategy for NTE materials,thereby expanding the scope of molecular-anion-based compounds.

The slow kineticsof the oxygen evolution (OER) and reduction(ORR)reactions, combined with the high costs of noble metals, remain majorbarriers to a sustainable hydrogen economy. Earth-abundant brownmillerite-typeoxides (A₂B₂O₅) offer a promisingalternative, yet their catalytic mechanism is frequently misunderstood.Because the highest activities emerge following electrochemical surfaceamorphization (OER) or order–disorder transitions (ORR), thepristine vacancy-ordered framework is rarely the static active phase.Herein, we reframe brownmillerites as highly specific, compositionallyaddressable precatalysts whose initial crystal chemistry acts as astructural template that governs the depth, composition, and stabilityof the operando-reconstructed active phase. Despite their potential,existing literature often treats them as perovskite subsets, neglectingthe mechanistic impact of their vacancy-ordered structure and operandosurface reconstruction. This review provides a unified framework linkingbrownmillerite defect chemistry to electrocatalytic performance. Byevaluating synthesis, structural, and anionic modifications alongwith a comprehensive benchmarking table for this material class, weestablish the mechanistic depth and structure–property correlationsnecessary for designing next-generation, noble-metal-free catalysts.

Two-dimensional organic–inorganicperovskitescan attainlower congruent melting temperatures (T_m) through compositional design, including, for example,by incorporating nonprimary ammonium cations, enabling solvent-freemelt processing and glass formation. Although Pb- and Sn-based systemshave been explored, the structural and mechanistic origins of theirdistinct thermal behaviors remain poorly understood. Here, startingfrom the model (MC3I)₂PbI₄ (MC3I = N-methyliodopropylammonium), we demonstrate that replacing Pb withSn lowers T_m to 86.0°C (359.2 K) and markedly modulates glass-forming ability. Temperature-dependentsingle-crystal X-ray diffraction, pair distribution function, andfirst-principles electron localization functions provide continuousstructural insights from 100 K to the molten state, enabling directcomparison across the melting transition and correlation with thermalbehavior. We demonstrate that Sn substitution yields larger structuraldistortions (e.g., associated with increased lone-pair stereoactivity),selectively elongated and more ionic Sn–I bonds, reduced tolerancefor atomic thermal vibrations, and more accessible atomic arrangementsin the melt, resulting in a higher melting entropy (ΔS_m) and lower T_m. Both Pb and Sn compounds exhibit robustmelt stability over 50 crystal-melt-glass cycles without discernibledecomposition, while showing increased glass-forming propensity. Prolongedmelt dwelling effectively promotes vitrification in the Sn compound,despite its relatively lower glass-forming ability relative to thePb-based system.

Viscoelastic polymer materials exhibiting high dampingcapacitywithin a specified frequency–temperature range effectivelydissipate mechanical energy as heat, thereby mitigating damage inducedby vibrations and impact loads. However, developing a convenient methodfor precisely designing damping materials with tunable energy dissipationproperties across a desired frequency–temperature range remainschallenging. Herein, we present a strategy for fabricating high-dampingpolyborosiloxane (PBS) elastomers (PBSEs) with tunable damping performanceacross a specified frequency–temperature range. This is achievedby precisely modulating the PBS relaxation behavior─specifically,through systematic variation of both the B–O bond content andthe molecular weight of the PDMS diol precursors. We found that theresultant PBSEs exhibit controllable high-damping performance acrossan ultrawide frequency range (tan δ > 0.3,10^–3 to 10² Hz) and temperature range(tan δ = 0.5–0.6, −20 to 150°C). Moreover, PBSEs exhibit excellent impact-protective performancecompared with commercial materials and attenuate impact force by morethan 95%. This unique design concept will provide a convenient approachto developing advanced damping materials.

As our technology advances, the demand for more functionalsemiconductormaterials has grown. In layered hybrid perovskites, an enhanced functionalitycan be achieved by introducing molecular switches as spacers. Thesespacers permit the reversible modulation of the semiconductor properties,which can, for example, induce distinct photoresponses. In particular,negative and positive photocurrents (NPC, PPC) hold much potentialfor multistate photosensing. However, NPC in a single-layered hybridperovskite material remains currently unknown. Here, we report onNPC and PPC in layered Dion-Jacobson-like and Ruddlesden–Popperhybrid perovskites induced by a switchable ferrocene-based spacer.Electronic communication in the form of charge transfer between theferrocene moiety and the perovskite framework was confirmed via transientabsorption spectroscopy. Under an external electric field, the ferrocene-inducedcharge carriers are rearranged into space charge zones, which quenchesthe conductivity, resulting in the NPC. This charge carrier arrangementis prohibited in Ruddlesden–Popper phases due to the presenceof a van der Waals gap, leading to the PPC. Furthermore, NPC can alsobe realized for hybrid perovskites with different band gaps by adjustingbromide and iodide contents, highlighting the potential of spacer-inducedphotocurrents as the semiconductor properties can be tuned as needed.

Various framework materials offer potential platformsfor developingnext-generation electro-responsive functional and smart materialsbecause they are electro-active or polarizable by either ions in channelsor electrons in frameworks. However, the present framework materialsstill face challenges in achieving high electro-response while maintaininglow charge leakage or electrode polarization. In this study, we developeda kind of bipolar carbonaceous framework (CF) materials codoped withpyridinic nitrogen and graphitic nitrogen, which can simultaneouslyprovide local electrons and holes, via an ionothermal polymerizationof task-specific ionic liquid at target temperature. The structureof CF was characterized by thermogravimetric analysis, Fourier transforminfrared spectra, solid-state nuclear magnetic resonance spectra,wide-angle X-ray scattering spectra, and X-ray photoelectron spectra,and the bipolar charge characteristic was analyzed by Mott–Schottkycurves and photocurrent measurements. Dielectric spectra of the CFparticles in suspensions were measured and showed enhanced interfacialpolarization but very weak electrode polarization and leakage conductiondue to the coupled movement of electrons and holes. Consequently,the bipolar CF suspensions show significantly higher electro-responsiveelectrorheological effect (τ_s =12 kPa@3 kV/mm) and lower current density (j = 46μA/cm²@3 kV/mm) compared to single electron-dominated,single ion-dominated, and even mixed ionic-electronic systems. So,this bipolar CF provides a preferred platform for the design of high-performancecarbonaceous-based electro-responsive functional and smart materials.

A metal selenide resulting from a mixed-site Fe/Cu solidsolutionwas synthesized, Ba₆Cu_24-xFe_xSe₂₇, in the compositionrange between Ba₆Cu₁₁Fe₁₃Se₂₇ (x = 13; 1) to Ba₆Cu₆Fe₁₈Se₂₇ (x = 18; 2). Its structure is derived from a parent mineral, i.e.,naturally occurring bartonite K₆Fe_24-xS₂₆(S,Cl), with the bartonite structuretype in the I4/mmm space group andthe general formula Ba₆M₂₄Se₂₇ (M = Fe, Cu). In contrast to known low-dimensional ironselenides consisting of FeSe₄ tetrahedra arranged in chainsor layers, its structure is composed of a three-dimensional (3D) anionicframework of ³_∞[M₂₄Se₂₆]^10–. This3D framework is constructed from fluorite-type clusters that linkvia shared-vertices. Open channels are filled by charge-compensatingBa(II) cations and isolated Se^2– anions in all crystallographicdirections. At the compositional end limits of the solid solutionsynthesized here, the Fe cations possess an average oxidation statebetween +2.32 in 1 and +2 in 2. Magneticmeasurements reveal that 2 exhibits ferrimagnetic orderat least up to 350 K, with a secondary magnetic transition at ∼170K. In summary, these results demonstrate the utilization of a mixedCu/Fe solid solution to stabilize a 3D metal–selenide framework,hence opening the door to wider investigations of their intriguingmagnetic properties.

A simpleone-step route for designing three covalentlybonded porousorganosilica polymers via tandem condensation, bearing an adjustabletriazine moiety and N–Si cooperative microenvironments, hasbeen reported for the first time. In contrast to the traditional methodsthat rely on prefabricated supports or postsynthetic triazine integration,our strategy allows triazine moieties to be covalently embedded insitu inside the silica backbone, providing uniform distribution andimproved structural integrity. The produced silica-based porous organicpolymers (POPs) have high thermal stability (up to 250 °C) alongwith high specific surface areas (200–600 m²g^–1). The presence of hierarchical porosity (meso- andmicroporosity) guarantees quick diffusion of the reactant and intermediatesduring catalytic reactions in addition to facilitating efficient CO₂ adsorption at the pore surfaces. Using this structural advantage,a two-step CO₂-valorization method was investigated: first,CO₂ was converted to cyclic carbonates, and then it wasreduced to methanol. Due to high porosity and easily accessible activesites, these hybrid materials catalyze the transformation of the carbonateto methanol, facilitating effective hydride transfer and intermediateconversion. Among the three silica-incorporated POPs, SL-1-Silica-POPproduced the highest methanol yield of 20.5 mmol g^–1 in the hydrogenation of epichlorohydrin carbonate by using phenylsilaneas the hydride source.

Decoupling supportand ligand contributions in supportedmetalnanoparticle (NP) catalysts remains an open challenge, and the challengeis synthetic: what makes a support interface inert is also what limitsits ability to bind and disperse NPs, requiring ligands that are themselvesactive participants in the catalytic cycle. Here, we address thischallenge using melamine cyanurate (MCA), whose supramolecular constructionexposes coordinatively saturated terminations of melamine and cyanuricacid (CA) subunits that are interfacially inert yet accessible forfunctionalization using molecular recognition. Under mild aqueousconditions, a Au-bound thiol-functionalized CA derivative uniformlydisperses onto the edges of MCA sheets via complementary hydrogen-bonddonor–acceptor pairs, as shown by X-ray photoelectron spectroscopy(XPS), transmission electron microscopy (TEM), and density functionaltheory (DFT). Thermal treatment yields 2.5 ± 0.5 nm, monodisperse(dispersity index = 1.1), ligand-free Au⁰ NPs. MCA’sinertness at both NP-support and reactant-pool-support interfacesis established by XPS and the Au-catalyzed aerobic oxidative dehydrogenationof N-methyl-4-piperidinone, respectively, and benchmarkedagainst conventional supports (graphite, silica, P25 TiO₂), with and without capping ligands. The interfacial inertness ofMCA, together with the bare, uniform NPs afforded by the recognition-basedsynthesis, enables quantitative decoupling of support and ligand contributionsto reactivity, revealing that carbonaceous deposit formation and overoxidationare direct consequences of support functionality, rather than intrinsicto the Au⁰ active site. Free of both contributions, AuNPs on MCA achieve 100% selectivity to the target enaminone and 90%yield, versus <70% on conventional supported catalysts. More broadly,by resolving the usual trade-off between support inertness and ligand-freeNP functionalization, this strategy, rooted in supramolecular principles,expands the design space of noninterfering supports for metal NP catalysts.