Materials Chemistry Frontiers最新文献

Maghemite (γ-Fe₂O₃) is an important magnetic material for wide utilization; however, it tends to transform into hematite (α-Fe₂O₃) under high temperature and humidity (HT and H) conditions. Here, we report that this phase transition can be completely suppressed by a reduced graphene oxide (rGO) hydrogel. Experiments demonstrate that γ-Fe₂O₃ first dissolves in water and then recrystallizes into α-Fe₂O₃ in a hydrothermal autoclave at 180 °C (an HT and H environment). In contrast, after adding γ-Fe₂O₃ to graphene oxide (GO) solution, its transformation into α-Fe₂O₃ is completely prevented during hydrothermal treatment up to 240 °C. The possible mechanism for this phase transition suppression is that the rGO hydrogel formed through hydrothermal reduction of GO fully encapsulates γ-Fe₂O₃ to prevent its contact with water and subsequent dissolution. This work highlights the stabilizing role of the rGO hydrogel in improving the stability of metastable metal oxides under HT and H conditions.

Improving thermoelectric performance of flexible thermoelectric materials is critical for practical implementation of thermoelectric technology in wearable electronic devices and sensors. In this work, Se/Ag₂Se, Ag₂Se, and Ag/Ag₂Se nanoparticles were synthesized via a convenient one-step solution method, and flexible Ag₂Se-based thermoelectric films were fabricated using a vacuum-assisted filtration process. The Ag/Ag₂Se composite nanoparticles were sintered after cold pressing combined with annealing treatment in the Ag/Ag₂Se composite films, leading to the reduction of interfaces and the formation of conductive pathways in the films; simultaneously, the crystallization of Ag and Ag₂Se components was enhanced, and the preferred orientation of Ag₂Se was regulated toward the (013) direction. Consequently, the electrical transport performance of the Ag/Ag₂Se composite films was significantly improved, and the highest power factor of 2139.27 µW m⁻¹ K⁻² was achieved for the films at 360 K. The electrical conductivity of Ag/Ag₂Se composite films remains at 94.2% after bending for 1000 cycles at a radius of 4 mm, revealing the prime flexibility of the sample. A flexible 4-arm thermoelectric generator assembled with Ag/Ag₂Se composite films can generate an open-circuit voltage of 3.99 mV at a temperature difference of ∼11.5 K. Moreover, the Ag/Ag₂Se thermoelectric generator had the ability to respond to external temperature fluctuations, demonstrating its positive temperature sensing capability. This study presents a viable strategy for fabricating flexible high-performance Ag₂Se-based thermoelectric films, and the as-prepared Ag/Ag₂Se composite films show great potential for use in powering wearable electronics and as flexible temperature sensors.

Novel and functional organic building blocks are essential resources for developing materials with unique structures and outstanding properties. Here, we designed ultracycles that contain oxacalix[2]arene[2]triazine as subunits and pentaethylene glycol chains as linkers. These ultracycles were synthesized through a one-pot reaction between rigid and flexible macrocyclic precursors and diphenol derivatives. Featuring multitopic binding sites in close proximity, the ultracycles extracted various ion pairs from solids into organic solvent under ¹H NMR monitoring, and the ion pair binding was confirmed quantitatively in solution. The crystal structures of [UC1-2CaBr₂] and [UC2-2LiClO₄] complexes indicate that cations are dominantly chelated by glycol chains through ion–dipole interactions, while anions are stabilized by cation–anion electrostatic attraction or anion–π interactions. The large size of the ultracycles and their unique ion-pair binding modes afford crystals with a hierarchical framework with a porous architecture, namely ion pair organic frameworks (IPOFs). This includes the largest central cavities of the ultracycles, the intrinsic cavities of the constituent sub-macrocycles, and the interspaces arising from molecular packing. These IPOFs, serving as sorbents, demonstrated highly efficient iodine vapor capture at room temperature and atmospheric pressure, with a maximum uptake amount of 1.81 mg mg⁻¹.

Organic ionic plastic crystals (OIPCs) are soft crystalline materials that exhibit plasticity and ionic conductivity, making them promising candidates for use as solid electrolytes. Previously, IPCs based on pyrrolidinium cations derived from the heterocyclic five-membered ring pyrrolidine have been synthesized, and their ionic conductivities have been reported. However, their performance has not yet achieved the required standard. In this study, we focused on tetrahydrothiophene, another five-membered heterocyclic compound, as a novel cationic structure. A series of novel IPCs was synthesized using tetrahydrothiophenium cations in combination with five different anions, yielding 15 compounds. Thermal analysis was conducted to determine the decomposition and phase-transition temperatures. Six of the synthesized compounds were identified as IPCs, and five were classified as ionic liquids. Among them, the compound 1-ethyltetrahydrothiophenium trifluoro(trifluoromethyl)borate ([C₂tht][CF₃BF₃]), consisting of ethyl-substituted tetrahydrothiophenium cation and CF₃BF₃ anion, exhibited an ionic conductivity of 7.19 × 10⁻⁴ S cm⁻¹ at 25 °C. Notably, [C₂tht][CF₃BF₃] demonstrated an approximately one order of magnitude higher ionic conductivity at room temperature than conventional pyrrolidinium-based IPCs.

This study investigates the role of π-electron delocalization in tuning the electronic band structures of two-dimensional metal–organic frameworks (2D MOFs), using 9,10-dicyanoanthracene (DCA) on different metal surfaces. While hydrogen-bonded assemblies form on Ag(111), distinct coordination networks emerge on Cu(111) and Au(111): a Kagome-based 2D framework (DCA₃Cu₂) with flat bands and Dirac cones, and a quasi-one-dimensional chain structure (DCA₃Au₂), respectively. Density functional theory (DFT) calculations reveal a clear correlation between the extent of π-delocalization and the electronic properties. As delocalization evolves from localized (DCA₃Cu₁) to quasi-1D (DCA₃Au₂) character, the bandgap narrows from 0.07 eV to 0.03 eV. Even in localized and quasi-1D systems, weak inter-unit hydrogen-bonding interactions contribute to electronic band formation, indicating the synergy between coordination and non-covalent interactions in shaping band structures. These findings demonstrate that coordination-controlled π-delocalization offers a precise pathway to tailor the electronic properties of 2D MOFs.

Hybrid microgels represent advanced soft colloidal materials engineered by incorporating diverse functional components, such as metal nanoparticles, inorganic non-metals, organics, metal–organic frameworks (MOFs), and biomolecules, within crosslinked polymer networks. By synergistically combining the intrinsic stimuli-responsiveness and dispersibility of pristine microgels with the unique properties of incorporated functional units (e.g., photothermal effects, magnetic responsiveness, and bioactivity), hybrid materials effectively overcome the inherent limitations of conventional microgels, such as insufficient mechanical strength, restricted functionality, and poor stability in complex environments. This review systematically outlines key fabrication strategies (in situ hybridization, seed-mediated growth, and microfluidics), classifies hybrid microgels according to incorporated components (metal-hybrid, inorganic non-metallic hybrid, organic hybrid, MOF-hybrid, biohybrid, and multi-component hybrid), and elucidates their structure–property relationships. Leveraging recent advances in fabrication optimization and property regulation, we highlight emerging applications of hybrid microgels, including catalysis, drug delivery, cell therapy, environmental remediation, sensing, and emulsion stabilization. Furthermore, we discuss persistent challenges in the development of hybrid microgels, emphasizing the need for large-scale production, advanced characterization, biosafety evaluation, and multi-stimuli integration to accelerate the translation of hybrid microgels from fundamental research to practical applications.

Electrochemical CO₂ reduction (ECO2R) offers a promising route to mitigate CO₂ emissions while generating value-added chemicals. Here, we report the synthesis of heteroatom-modified carbon quantum dots (CQDs) via a green hydrothermal method using citric acid, glucosamine, urea, and cysteine as precursors, with copper incorporation. Structural characterization by XPS and Raman spectroscopy confirmed successful Cu, S, and N doping, while water contact angle measurements revealed precursor-dependent surface hydrophilicity. Electrodes prepared with 80 wt% CQDs and 20 wt% anion-exchange ionomer exhibited high electrochemically active surface areas. Among the series, Cu,S,N-CQD-GAH derived from glucosamine, showing lower hydrophilicity, delivered the most effective ECO2R performance. This catalyst selectively produced formate and acetate, as verified by HPLC and ¹H NMR, achieving acetate formation rates up to 1.5 mmol g_cat⁻¹ h⁻¹ at −0.4 V vs. RHE. The half-cell energy efficiency peaked at 52.3% with a faradaic efficiency of 66.8% at −0.2 V vs. RHE. The enhanced activity is attributed to nitrogen functionalities in aminic/pyridinium oxide forms and the presence of Cu(I), which promotes C–C coupling. In contrast, sulfur-free or Cu(II)-rich CQDs exhibited diminished activity. Long-term chronoamperometry confirmed stable current densities after an initial activation period, highlighting the durability of the Cu,S,N-CQD catalysts.

A new acceptor–linker–donor–linker–acceptor (A–π–D–π–A) structured porphyrin dimer, F-C19ZnP, was designed and synthesized as a visible-to-near-infrared (Vis-NIR) light-harvesting photosensitizer for photocatalytic hydrogen evolution (PHE). F-C19ZnP features a bimetallic Zn(II)-coordinated fused porphyrin dimer as the donor, a phenylene–ethynylene π-linker, and a 3-ethylrhodanine acceptor. Its photophysical, electrochemical, thermal, and morphological properties, as well as photocurrent response, water contact angle, and PHE performance, were systematically investigated and compared with those of C19ZnP, a structurally similar monometallic porphyrin. Density functional theory calculations provided further insight into the optoelectronic and charge separation characteristics of both porphyrins. F-C19ZnP exhibited markedly broader light absorption (400–1100 nm) and stronger Vis-NIR light-harvesting ability than C19ZnP. F-C19ZnP also exhibits a higher surface area and a larger pore size than C19ZnP, providing more accessible channels for electron transport. It also showed a longer photoexcited electron lifetime (4.9 ns vs. 2.1 ns), enabling more efficient electron transfer to water and resulting in enhanced PHE performance. F-C19ZnP demonstrated a higher photocurrent response, signifying improved charge separation and transport. Its lower water contact angle, attributed to its well-dispersed 300 nm nanosphere morphology, enabled better interfacial interaction with water. Under optimized PHE conditions, F-C19ZnP achieved a PHE rate (ηH₂) of 7.93 mmol g⁻¹ h⁻¹, which is eight times higher than that of C19ZnP (1.01 mmol g⁻¹ h⁻¹), and outperformed C19ZnP at all tested irradiation wavelengths (420, 630, and 810 nm). Furthermore, F-C19ZnP displayed excellent photostability and reusability. As the first Vis-NIR fused porphyrin dimer for efficient PHE, F-C19ZnP paves a promising path for the development of advanced porphyrin-based photosensitizers.

There is an exigent demand for establishing a systematic supramolecular engineering strategy to support the extraordinary tuning of desired emission from functional fluorescent organic materials. Simultaneous emission modulation in solids, aggregates, solvents, and viscous media is highly onerous with several associated photophysical pitfalls. The present research has coined a design concept in which bridged oxo/thioethers are conjugated to a highly twisted molecular core, generating multisite nonplanarity within the molecular system. Moreover, the non-covalent interactions and slip-stack angles can be altered by reducing or expanding the heterocycle. Furthermore, alterations to the present heteroatoms result in various molecular packing patterns, including H, herringbone-H*, X, and charge-transfer (CT)-mediated J-type examples. In addition, the fluorophore's polarizability, electronic conjugation, and conformation can be systematically regulated to tune a wide range of emission, from blue to red. Indeed, we achieved a 118-nm emission tuning in solids, 150-nm emission modulation in aggregates, and 100-nm emission alteration in a viscous medium. Moreover, a 99-nm to 150-nm solvatochromic shift was attained for some fluorophores. Different emissions from aggregates and the viscous medium were also detected, and excimer formation was possible for some fluorophores, particularly in aggregates. Also, a noncytotoxic orange-red-emitting fluorophore was applied in solution-processed yellow OLED (organic light-emitting device) fabrication to realize its further utility.

A new cyano-substituted olefin-linked COF was synthesized and utilized as a support for palladium nanoparticles. The resulting Pd@CN-COF was demonstrated as a versatile heterogeneous catalyst in cross-coupling reactions, cyanation, and allylic substitution with the productivity exceeding the commercial homogeneous precatalyst [Pd(PPh₃)₄]. The catalytic activity of Pd@CN-COF was further evaluated in synthetically valuable transformations towards industrially, agrochemically, and pharmacologically relevant products.