Showing papers in "Chemistry of Materials in 2022"

Adhesive Ionohydrogels Based on Ionic Liquid/Water Binary Solvents with Freezing Tolerance for Flexible Ionotronic Devices

Abstract: Ionic hydrogels hold substantial promise as soft materials for achieving versatile wearable ionotronics due to the integrated merits of appropriate mechanical properties, excellent conductivity, and good conformability. However, overcoming freezing at subzero temperatures and hindering the evaporation of water are still huge challenges for ionic hydrogels. Herein, a dual-cross-linked ionohydrogel was designed using Al3+ to cross-link with the polymer network through dynamic metal coordination bonds in the water and ionic liquid (IL) binary solvent system, allowing for excellent mechanical properties (∼1 MPa, ∼600%), transparency (>90%), high ionic conductivity (∼12.40 mS cm–1), and robust adhesion, along with the advantages of superior antifreezing and long-term antidehydration properties. These exceptional characteristics inspired us to fabricate dual-responsive sensors, which could simultaneously detect human motion signals and a wide range change of temperatures (from −30 to 40 °C) with an impressive temperature coefficient of resistance (TCR) value (from −0.035 to −0.44 °C–1). More promisingly, benefiting from the superior interfacial adhesion between the poly(dimethylsiloxane) (PDMS) and the ionohydrogels, a triboelectric nanogenerator was assembled with a single-electrode mode that was capable of providing sustainable energy for wearable ionotronic devices even at subzero temperatures. This work opens up an effective strategy to design a multifunctional ionohydrogel, enabling various applications integrated into the single device.

Constructing Synergistic Triazine and Acetylene Cores in Fully Conjugated Covalent Organic Frameworks for Cascade Photocatalytic H₂O₂ Production

Abstract: Covalent organic frameworks (COFs) are an ideal template for photocatalytic H2O2 synthesis because of the tunable chemical structures and semiconductor properties. However, the photoactivity for COFs is still under-improved due to the inefficient intrinsic charge generation, fast recombination of photogenerated charges, and limited electron transport along the frameworks. Herein, spatially separated and synergistic triazine and acetylene units are first integrated into COFs (EBA-COF and BTEA-COF) for photocatalytic H2O2 production. The spatial separation of triazine and acetylene cores leads to efficient charge separation and suppressed charge recombination, and C═C linkage facilitates electrons transport over the skeletons. Both experimental and computational results suggested that triazine and acetylene units synergistically promote H2O2 synthesis in a two-electron pathway. The EBA-COF showed an attractive activity with a H2O2 production rate of 1830 μmol h–1 gcat–1, superior to that of most other COF-based catalysts. This study provides a method for designing photocatalysts with synergistic photocatalytic active sites based on vinylene-linked COFs.

Dopant and Compositional Modulation Triggered Broadband and Tunable Near-Infrared Emission in Cs2Ag1–xNaxInCl6:Cr3+ Nanocrystals

Abstract: Lead-free halide perovskite nanocrystals (NCs) have attracted more attention and demonstrated versatile potential in optoelectronic applications. However, achieving broadband near-infrared (NIR) emission in such materials remains a challenge. Herein, we successfully obtained Cr3+-doped Cs2AgInCl6 NCs via hot-injection synthesis, which exhibits a NIR emission with a large full width at half-maximum of 193 nm. Furthermore, tunable emission from 998 to 958 nm along with an enhanced photoluminescence quantum yield of 19.7% is realized by gradually substituting Ag+ with Na+, and the blue shift luminescence behavior is attributed to a strengthened crystal field around Cr3+. The excellent chemical and moisture stability together with the as-fabricated Cs2NaInCl6:Cr3+ NC film made by screen printing showcases its application potential in high-resolution images and NIR fluorescent signs. This work proves the possibility of realizing tunable broadband NIR emission in lead-free perovskite NCs and provides guidance for expanding their application in the NIR region.

High-Entropy Laminate Metal Carbide (MAX Phase) and Its Two-Dimensional Derivative MXene

Abstract: High-entropy (HE) ceramics, by analogy with HE metallic alloys, are an emerging family of multielemental solid solutions. These materials offer a large compositional space, with a corresponding large range of properties. Here, we report the experimental realization of a 3D HE MAX phase, Ti1.0V0.7Cr0.05Nb1.0Ta1.0AlC3, and a corresponding 2D HE MXene in the form of freestanding flakes of average composition Ti1.1V0.7CrxNb1.0Ta0.6C3Tz (Tz = −F, −O, −OH), as produced by selective removal of Al from the HE MAX phase in aqueous hydrofluoric acid (HF). Initial tests on HE MXene “paper” electrodes show their high potential as electrode materials in supercapacitors through volumetric and gravimetric capacitances of 1688 F/cm3 and 490 F/g, respectively, originating from a combination of diffusion- and surface-controlled charge storage processes. The introduction of the HE concept into the field of 2D materials suggests a wealth of future 2D materials and applications.

Injectable Adhesive Self-Healing Multiple-Dynamic-Bond Crosslinked Hydrogel with Photothermal Antibacterial Activity for Infected Wound Healing

Abstract: The development of multifunctional injectable adhesive hydrogels with self-healing capacity, shape adaptability, on-demand removability, and excellent photothermal antibacterial activity to promote bacteria-infected wound healing is highly recommended in practical applications. In this work, an injectable adhesive self-healing multiple-dynamic-bond crosslinked hydrogel was formed by a multiple-dynamic-bond crosslinked network of dynamic borate/didiol interactions, hydrogen bonding, and Schiff base bond. The introduction of Mussel-inspired catechol groups into the hydrogels could endow tissues with adhesive properties, and the hydrogel could adhere well to the skin under water with good shape adaptability under bent and twisted states. The mechanical and adhesive properties improved through the introduction of borate/didiol interactions into the catechol-modified hydrogel with dynamic Schiff base crosslinking at low cost and easy preparation, and the adhesive hydrogel could be removed without second damage to the wound. Moreover, polydopamine nanoparticles (PDA NPs) were introduced into the hydrogels through Schiff base reactions between the quinone group on PDA NPs and the primary amine in glycol chitosan (GC), resulting in an efficient photothermal antibacterial activity with uniformly dispersed PDA NPs in the hydrogel. And the hydrogels illustrated good cytocompatibility and hemocompatibility. Finally, they could be injected to fully fill irregular wounds and significantly promote bacteria-infected wound healing by reducing the inflammatory response, accelerating collagen deposition, and promoting blood vessel reconstruction. Therefore, this demonstrated their superiority in serving as multifunctional dressings for treating a bacteria-infected wound.

Enhanced Second-Harmonic-Generation Efficiency and Birefringence in Melillite Oxychalcogenides Sr2MGe2OS6 (M = Mn, Zn, and Cd)

Abstract: Simultaneous regulation and control of non-linear second-harmonic-generation (SHG) coefficients (deff) and linear birefringence (Δn) of non-centrosymmetric (NCS) crystals is a crucial aspect of improving the non-linear optical (NLO) performance, yet it remains a huge challenge in modern laser techniques and science. Herein, a series of melilite-type oxide-derived NCS oxychalcogenides, Sr2MGe2OS6 (M = Mn, Zn, and Cd), are successfully designed and synthesized through a facile partial isovalent chemical substitution strategy. These isostructural compounds crystallize in the tetragonal NCS space group P4̅21m (no. 113) and feature unique two-dimensional Cairo pentagonal tiling layers composed of heteroligand [GeOS3] and tetrahedral [MS4] asymmetric building units (ABUs). Compared to the parent melilite-type oxides, the derived title compounds not only successfully realize the phase matchability transformation [i.e., from non-phase-matching (NPM) to phase-matching (PM)] but also greatly improve the IR-NLO performance (especially, simultaneously boosting deff and Δn). Sr2CdGe2OS6 exhibits the best comprehensive performance among oxychalcogenides, including a wide PM cutoff edge (>525 nm), a strong deff (0.8 × AgGaS2), a giant laser-induced damage threshold (19.2 × AgGaS2), a large band gap (3.62 eV), as well as a broad transmission cutoff region (0.28–12.0 μm). Furthermore, highly distorted [GeOS3] ABU in this melilite-type structure is proved to be the profitable bifunctional NLO-active unit, which can contribute to the search and design of novel IR-NLO crystals with a large Δn and a strong deff based on the experimental results and theoretical calculations. This work demonstrates the first examples of PM melilite-type oxychalcogenides and offers new perspectives on the phase matchability transformation through the partial isovalent chemical substitution approach, which will play a constructive role in the future design of high-performance IR-NLO heteroanionic materials.

Reaction Pathways toward Sustainable Photosynthesis of Hydrogen Peroxide by Polymer Photocatalysts

Abstract: Harnessing solar energy to generate hydrogen peroxide (H2O2) from H2O and O2 via artificial photosynthesis is an attractive route, as this approach only uses sunlight as the energy input. Organic polymers have emerged as a promising class of materials for solar-driven H2O2 production, owing to their virtually unlimited molecular building blocks and rich bond-forming reactions. This distinctive feature leads to the existence of different reaction pathways characterized by different electron transfer numbers. For the overall photosynthesis of H2O2, the O2 reduction reaction and the H2O oxidation reaction must occur concurrently. Thus, in-depth insights into these reaction pathways are crucial for solar-driven H2O2 production, with the eventual aim of steering these pathways to optimize efficiency. In this perspective, we primarily focus on the state-of-the-art progress in developing polymer photocatalysts for the overall photosynthesis of H2O2 via coupling different O2 reduction and H2O oxidation reactions. We also present key challenges and opportunities in developing polymer photocatalysts for H2O2 production in the future. Organic polymers offer an ample molecular-level design space. They have now found extensive applications in solar-driven photochemical reactions. Therefore, this perspective serves as a guideline for designing polymer photocatalysts toward sustainable photosynthesis of H2O2 and has significant implications for the future development of polymer materials in the broad area of solar-to-chemical energy conversion research.

The Emerging Role of Halogen Bonding in Hybrid Perovskite Photovoltaics

Abstract: The ongoing effort toward stabilizing hybrid perovskite solar cells and enhancing their performance has stimulated the community to pursue a number of strategies. Over the recent years, these efforts have focused on perovskite materials design, which increasingly relies on molecular modulators that engage in halogen bonding, a uniquely directional noncovalent (supramolecular) interaction. Halogen bonding in hybrid perovskites is reported to drive perovskite assembly, increase its stability against moisture and ion migration, passivate defects, and tune interfacial energetics. The resulting perovskites are shown to exhibit superior mechanical properties, and devices incorporating these materials have seen drastic improvements in their performance, all of which have been ascribed to halogen bonding. While most of these developments have so far relied on the incorporation of off-the-shelf molecular modulators that interact with the perovskite surface to effect interfacial properties, further advancements will require careful consideration of the nature of halogen bonding and rigorous structural assessments in order to aid development of next-generation materials. Here, we provide a critical overview of the recent developments in the use of halogen bonding agents in hybrid perovskite photovoltaics with a perspective on their utility in the future.

Driving Nonlinear Optical Activity with Dipolar 2-Aminopyrimidinium Cations in (C4H6N3)+(H2PO3)−

Abstract: Organic–inorganic hybrid nonlinear optical (NLO) crystals have been attracting increasing attention because of their unique ability to combine the structural diversity of the organic moiety and the high stability of the inorganic moiety. However, organic NLO genes are rare. Herein, a new organic NLO material gene, the 2-aminopyrimidinium cation (C4H6N3)+ ((2AP)+), is reported, which constructs a novel organic–inorganic hybrid (C4H6N3)+(H2PO3)− (2APP) that exhibits excellent NLO properties and thermal stability, e.g., strong second-harmonic generation (SHG) intensity (2 × KDP), large birefringence (0.225 at 589.3 nm), high laser-induced-damage threshold (1.7 × KDP), and one of the highest thermal stabilities among the metal-free-(2AP)+-containing compounds. Our first-principles theoretical studies confirm the dominant contribution of (2AP)+ to optical properties. The inorganic phosphite anions well separate the (2AP)+ cations to successfully eliminate the unwanted centrosymmetric trap that is induced by the dipole–dipole interactions between (2AP)+ cations. Furthermore, the unique layered structure decorated by the uniformly oriented individual (2AP)+ chromophores, dramatically enhances the quantum yield of purple fluorescence (Φ = 30.6%), which is 3 orders of magnitude higher than that of pure 2AP and its derivatives.

Photoresponsive Covalent Organic Frameworks with Diarylethene Switch for Tunable Singlet Oxygen Generation

Abstract: Incorporation of molecular switches with light, heat, and electricity responsibility into artificial solids has been developed as a successful strategy to construct stimuli-responsive functional materials. However, precise manipulation of their molecular geometries and electronic structures to control the properties of macroscopic materials still remains a fundamental challenge. Herein, a photoresponsive covalent organic framework (o-COF) with the square lattice was fabricated from the dynamic covalent chemistry reaction of ring-open dithienylethene–dialdehyde with 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (H2TAPP). UV irradiation of the dithienylethene-based units in o-COF afforded its reversible photoisomer (c-COF) in the ring-closed form. In addition to a range of diffraction, microscopic, and gas physical sorption characterizations, spectroscopic investigations with the help of theoretical simulations revealed different photocatalytic activities toward the evolution of singlet oxygen and corresponding photocatalytic oxidation of amines due to the different energy transfer pathways from the porphyrin unit to BBTP photoisomers in these two COFs. Most interestingly, such different photocatalytic behaviors for two COFs could be easily tuned in a reversible manner by adjusting the ring-closed/open form of dithienylethene units by means of UV and visible light.

Insights into the Ultra-High Volumetric Capacity in a Robust Metal–Organic Framework for Efficient C2H2/CO2 Separation

Abstract: The efficient separation of C2H2/CO2 is a challenging problem due to their similar physical properties. This is in addition to the risk of explosion when pressuring C2H2 over 2.07 bar. Besides, understanding the framework–guest and guest–guest interactions is also critical to achieving an optimal separation. Herein, we report the development of a robust and low-cost adsorbent, MIL-160(Al), with an extremely high acetylene volumetric capacity of 227 cm3(STP)/cm3 and high C2H2/CO2 selectivity of 7.1 under ambient conditions. We combine in situ solid-state nuclear magnetic resonance spectroscopy and in-depth theoretical calculations to unravel the synergistic interactions, driven by the hydrogen bonding of C2H2-MOF, and the electrostatic interactions between C2H2 molecules in the confined ångström-scale pores. This suitable pore confinement is also reflected in the rotation of the MOF ligands and the resultant evolution in the interacting distances between the metal–organic framework (MOF) backbone and C2H2 molecules. Acetylene is adsorbed as a unique dimer in MIL-160(Al), leading to an extremely efficient packing inside the pores. Breakthrough experiments confirm the efficient performance of MIL-160(Al) in real C2H2/CO2 mixtures, showing a C2H2-volumetric breakthrough performance superior to any previous MOF.

Construction of Hydrazone-Linked Macrocycle-Enriched Covalent Organic Frameworks for Highly Efficient Photocatalysis

Abstract: Covalent organic frameworks (COFs) are an emerging class of crystalline porous materials with tailor-made functionalities for improved photocatalytic activity. However, limited choice of building blocks greatly restricts the photochemical performance and application scope of COFs in photocatalysis. Herein, a covalent hybridization approach is reported to address these issues by knitting rigid macrocyclic struts, namely, pillararenes, into the extended network of COFs. Varying different ratios of pillararenes with unique conformations and electron-rich cavities can not only generate a confined molecular space for exciton migration and carrier transport but also create new interfaces to interplay with photogenerated charge carriers, leading to high performance in promoting efficient oxidation of amines to imines. This work paves the way for constructing macrocycle-derived COFs and provides a promising molecular platform for photocatalysis through predesign and functionalization of the pore surface.

Reversible Triple-Mode Switching in Photoluminescence from 0D Hybrid Antimony Halides

Abstract: Hybrid metal halides are an emerging class of highly efficient photoluminescent (PL) materials. However, very few of them show reversible on–off PL switching under external stimuli and have the potential to perform as next-generation intelligent materials with applications in cutting-edge photoelectric devices. Herein, we report single crystal-to-single crystal (SC–SC) structural and PL transitions among three 0D hybrid antimony halides, namely, nonemissive α-[DHEP]SbCl5 (1), yellow-emissive β-[DHEP]SbCl5·2H2O (2), and red-emissive β-[DHEP]SbCl5 (3), by a dynamic phonon-engineering strategy. The reversible SC–SC transformation between 1 and 2 is triggered by acetone or methanol, affording the reversible PL on–off switching. The transition between yellow-emissive and red-emissive solids is achieved by the reversible SC–SC transformation between 2 and 3 through the process of removal/adsorption of guest water molecules. Meanwhile, the 3 to 1 transition is performed by the introduction of methanol, which is accompanied by the quenching of red emission. Therefore, a triple-mode reversible PL off–onI–onII–off switching is realized in metal halide hybrids for the first time, including the off–onI (yellow), color-tunable onI–onII (yellow-red), and onII–off (red) modes. More importantly, the reversible PL switching in 0D hybrid antimony halides make them suitable for successful applications in the protection and anti-counterfeiting of confidential information as well as in optical logic gates.

Efficient Multicolor and White Photoluminescence in Erbium- and Holmium-Incorporated Cs2NaInCl6:Sb3+ Double Perovskites

Abstract: Inorganic lead-free halide perovskites with a broad-band emission of self-trapped excitons (STEs) have attracted great attention in lighting applications. However, it remains a fundamental challenge to expand the display color gamut because it is difficult to individually tune the emitting proportion at different wavelengths. Herein, we employ a doping route to incorporate Sb3+, Er3+, and Ho3+ ions into the Cs2NaInCl6, which enables multicolor emissions with narrow full width at half-maxima and high photoluminescence quantum yields (PLQYs). The blue emission (445 nm) originates from STEs in the [SbCl6]3– octahedrons, while the narrowband green (550 nm) and red (655 nm) emissions are mainly derived from the Er3+ and Ho3+ ions, respectively. An efficient energy transfer between multiple luminescent centers is the key point to achieve such an efficient and tunable emission. By controlling the lanthanide doping level, the emission color can be systematically modulated, and cold 10401 K (0.278, 0.286) to warm 4608 K (0.347, 0.298) adjustable white-light emission (PLQY of ∼70%) can be achieved successfully. The results provide inspiration for the material design of lead-free perovskites with efficient and tunable light-emitting properties for optoelectronic applications.

High Verdet Constant Materials for Magneto-Optical Faraday Rotation: A Review

Abstract: The Faraday effect is a magneto-optical (MO) phenomenon by which the polarization direction of linearly polarized light is rotated when passing through a transparent material with the application of a magnetic field along the direction of light propagation. The magnitude of the angle by which light is rotated at specific wavelengths, temperatures, and applied magnetic fields is directly proportional to the Verdet constant, which is an intrinsic bulk property of an optically transparent material. A high Verdet constant is desired for MO applications such as optical isolators, sensors, or modulators to reduce the path length required to obtain large optical rotation with modest magnetic fields to enable device miniaturization and overall cost reduction. MO material development has been ongoing for nearly the past two centuries, from which a wide range of materials have emerged. Herein, we review the development of high Verdet constant MO materials across many material classes, with an emphasis on recent developments of higher Verdet constant polymeric and polymer-nanocomposite materials. Inorganic materials have primarily been used for Faraday rotation systems which initially focused on the use of amorphous glasses and has since expanded into MO active crystals, ceramics, ferrofluids, organic small molecules, synthetic polymers, and polymer–nanoparticle nanocomposites. Although the most widely used materials for MO applications, hard matter based on inorganic materials typically possess Verdet constants on the order of 103–104 °/T·m at room temperature when measured in the visible and NIR ranges. More recent work has focused on using soft matter alternatives composed of organic small molecules, polymers, and polymer–nanoparticle nanocomposites which afford higher Verdet constants ranging from 104 to 106 °/T·m at room temperature. The current Review aims to discuss inorganic, organic, and hybrid high Verdet constant materials, which has been previously complicated by nonuniformity in the units and sampling conditions used for these MO measurements.