ACS Materials Letters最新文献

We report a water induced phase transformation in a flexible MOF, [Zn₃(OH)₂(btca)₂] (Hbtca = 1H-benzotriazole-5-carboxylic acid), that exhibits a two-step water vapor sorption isotherm associated with water-induced phase transformations. Variable temperature X-ray diffraction studies revealed that the dehydrated phase, LP-β, is almost isostructural with the previously reported solvated phase, LP-α. LP-β reversibly transformed to a partially hydrated phase, NP, at 5% RH, and a fully hydrated phase, LP-γ, at 47% RH. Structural studies reveal that host-guest and guest-guest interactions are involved in the NP, LP-α, and LP-γ phases. The LP-β phase, however, is atypical; molecular modeling studies indicating that it is indeed energetically favorable as a LP structure. To our knowledge, [Zn₃(OH)₂(btca)₂] is only the second sorbent that exhibits water induced LP-NP-LP transformations (after MIL-53) and represents the first regeneration optimized sorbent (ROS) with two steps at RH ranges relevant for both atmospheric water harvesting and dehumidification.

We report a water induced phase transformation in a flexible MOF, [Zn₃(OH)₂(btca)₂] (Hbtca = 1H-benzotriazole-5-carboxylic acid), that exhibits a two-step water vapor sorption isotherm associated with water-induced phase transformations. Variable temperature X-ray diffraction studies revealed that the dehydrated phase, LP-β, is almost isostructural with the previously reported solvated phase, LP-α. LP-β reversibly transformed to a partially hydrated phase, NP, at 5% RH, and a fully hydrated phase, LP-γ, at 47% RH. Structural studies reveal that host–guest and guest–guest interactions are involved in the NP, LP-α, and LP-γ phases. The LP-β phase, however, is atypical; molecular modeling studies indicating that it is indeed energetically favorable as a LP structure. To our knowledge, [Zn₃(OH)₂(btca)₂] is only the second sorbent that exhibits water induced LP-NP-LP transformations (after MIL-53) and represents the first regeneration optimized sorbent (ROS) with two steps at RH ranges relevant for both atmospheric water harvesting and dehumidification.

Here, we report the solvent-induced polymorphism in [Cu₁₅(PET)₁₃(TPP)₆][BF₄]₂(Cu₁₅) (TPP = triphenylphosphine, PET = 2-phenylethanthiol), and double-helical assembly of the [Cu₁₈H(PET)₁₄(TPP)₆Cl₃] (Cu₁₈) nanocluster (NC) from reaction intermediates. Both copper NCs have an intrinsically chiral triple-stranded helicate metal core, unlike traditional copper NCs with a polyhedral-based kernel. The chiral structure of Cu₁₅ resembles an enantiomeric pair in the unit cell. Moreover, Cu₁₈ has a three-layered 3D chirality of a sandwich constructed of sulfur-bridged copper NCs aligned in a top-middle-down configuration. Furthermore, the Cu₁₈ NC self-hierarchically assembles into a complex double-stranded helix secondary structure sustained by noncovalent interactions. Electrospray ionization mass spectrometry (ESI-MS), density functional theory (DFT), and X-ray photoelectron spectroscopy (XPS) were utilized to validate the single-crystal X-ray diffraction (SCXRD) data. Overall, this study provides an interesting example of polymorphism, chirality, and hierarchical double-helical assembly of NCs, allowing for extensive understanding of complicated structures at the atomic level.

The problems of high volatile organic compound (VOC) emission and low efficiency of silane coupling agents (SCAs) used in the rubber/silica composites for “green tires” have been troubling the rubber industry. A unique silane (MFSi) integrating hydroxyls, tertiary nitrogen, and norbornenyl were prepared by a solvent-free/catalyst-free one-pot method. MFSi can graft onto the rubber chain through a highly efficient norbornenyl/sulfur reaction, while the dangling hydroxyls in MFSi can improve its affinity with silica and tertiary nitrogen has a significant internal catalytic effect on the silanization of silica. As a result, MFSi shows a significantly higher coupling efficiency of silica-filled composites compared to the most widely used SCAs. Consequently, MFSi-modified composites exhibit excellent environmental friendliness, including significantly reduced heat buildup (∼55%) and abrasion loss (∼53%) and VOC emissions (∼42%). We envision that the design of the multifunctional mediator will provide valuable insights into the development of high-performance “green tires” in a more environmentally friendly manner.

Metal–organic frameworks (MOFs) with long afterglow luminescence (LAL) have gained attention for applications in light-emitting devices and anticounterfeiting. However, developing cost-effective and high-performance dynamic multicolor LAL MOFs remains challenging. Here, the rigid organic ligand 5-fluoronicotinic acid (FL), which incorporates a F atom to form molecular interlocking and inhibit nonradiative transitions, was chosen to self-assemble with MCl₂ (M = Zn and Cd) to fabricate long-lived phosphorescent MOFs. The synthesized MOFs, namely, FLCd, FLZn, and FLCd-DMF, exhibit excitation-dependent luminescence, ranging from blue/cyan to green, with cold white light emissions under specific excitations. Furthermore, all MOFs achieve dynamic color-tuning LAL based on excitation wavelength and temperature. Photoluminescence properties and theoretical calculations indicate that the multicolor LAL arises from the emissions of FL and its aggregation state, while enhanced phosphorescence can be assigned to heavy-atom and interlocking effects, coordination, and noncovalent interactions. Additionally, by leveraging their LAL behavior, these MOFs are applied for encrypting/decrypting information.

Enzymatic cascades are critical for energy conversion and chemical transformations in living organisms. Their ecofriendly nature and high selectivity in catalysis make them promising candidates for improving chemical transformations in cell-free systems. However, their applications have been limited by their poor stability. Immobilized cascades, which can enhance activity, remain underexplored due to challenges such as ambiguous support structures and difficulties in controlling enzyme distribution. In this work, we employed NU-1510, a novel metal–organic framework (MOF) with a crystalline hierarchical pore structure, to stabilize an enzyme cascade that oxidizes ethanol to acetaldehyde and subsequently to acetic acid. The impact of enzyme spatial organization on the cascade kinetics was further investigated thanks to the crystalline hierarchical pore structure of the MOF host. These findings pave the way for the design of advanced biocatalytic systems with improved efficiency and durability, potentially transforming applications in sustainable chemical manufacturing and energy conversion.

We report the fabrication of topographically structured surfaces with reversibly switchable topography by using melt electrowriting (MEW). In particular, MEW was used to produce continuous high aspect ratio lamellae of semicrystalline polyester urethane with a poly(1,10-decylene adipate) soft segment. The switching of topography is achieved by the expansion and contraction of the polymer caused by the melting and crystallization of the soft segment that results in the buckling of lamellae. In the molten stage, lamellae can be buckled in a certain direction by capillary forces caused by water droplets between two lamellae. In addition, the interlamellar distance between neighbors’ lamellae can be managed by water droplets. Finally, we have demonstrated the possibility of creating electrically conductive surfaces with switchable conductivity achieved by the reversible buckling of the lamellae.

The intrinsic structural advantages and tunability of covalent organic frameworks (COFs) have made them promising photocatalysts for various photocatalytic reactions. However, it remains a great challenge to systematically tune the linker lengths and to build a linker-length-dependent structure-performance relationship of COFs-based photocatalysts. Herein, five isoreticular COFs with sql underlying nets have been successfully synthesized using benzothiadiazole-based ditopic aldehydes with varied linker lengths and 1,3,6,8-tetrakis(4-aminophenyl)pyrene as organic building units. The five obtained COFs exhibit significantly different activities toward photocatalytic aerobic oxidation. Remarkably, the COF-containing vinyl group, HIAM-0020, exhibited the best photocatalytic performance with near-unity conversion and selectivity for photocatalytic oxidative benzylamine coupling within 2 h. The experimental and theoretical investigations indicate that HIAM-0020 exhibits faster charge separation ability and lower charge migration resistance compared with the other four COFs. This work represents promising guidance for the rational design and synthesis of COF-based photocatalysts to achieve efficient organic transformation.

Existing shape memory polymer based dry adhesives lack the ability to be reprocessed and thus to form multiple permanent shapes, limiting their adaptability to various arbitrary surfaces. Here, we present a shape memory vitrimer (SMV) based reversible dry adhesive that is reprocessable, relying on transesterification. The SMV possesses a glass transition temperature (T_g) of ∼50 °C and a topology freezing transition temperature (T_v) of ∼100 °C and exhibits a significant drop in storage modulus across T_g and stress relaxation above T_v. Combined with surface microstructuring, these characteristics provide our SMV dry adhesive with excellent adhesion strength (∼1.75 MPa) and reversibility (∼1000) due to the shape memory effect. Such an outstanding adhesive capability is further highlighted by reprocessing the SMV dry adhesive, thus reforming its permanent shape to adapt to an arbitrary adherend shape. Moreover, the SMV can self-weld above T_v, enabling easy repairs and enhancing its versatility for dry adhesive applications.

Bilayer organic solar cells, composed of a donor and acceptor layer, provide independent optimization of each layer to enhance the photovoltaic performance. However, the power conversion efficiency remains lower than that of bulk heterojunction cells. Herein, we focus on suppressing nongeminate charge recombination by tuning the acceptor layer’s morphology with fullerene derivatives to improve the performance of bilayer organic solar cells. We use the PM6/Y6 derivatives as model systems and incorporate fullerenes such as PC₇₁BM into the acceptor layer to enhance aggregation, improve crystallinity, increase electron mobility, and reduce trap density. Consequently, bilayer devices based on PM6/BTP-eC9 and PM6/L8-BO achieved efficiencies of 18.0% and 19.5%, respectively, approaching the performance of bulk heterojunction cells. The improved fill factor results from reduced bimolecular recombination and suppressed trap-assisted recombination, offering insights into optimizing the active layer morphology and designing high-mobility acceptor materials for efficient bilayer organic solar cells.