ACS Materials Letters最新文献

Due to the enhanced carrier–carrier interaction, carrier multiplication (CM) in graphitic materials is efficient and exhibits strong wavelength dependence. However, there is still a lack of direct evidence for excitation photon energy-dependent impact ionization, the origin of CM. In this work, time- and angle-resolved photoelectron spectroscopy has been used to measure the electron dynamics in graphite. We find the unusual preceding growth of electron signal in 0–0.35 eV compared with that in 0.35–0.70 eV and 0.70–1.05 eV during the absorption of UV (3.10 eV) pulses, unambiguously suggesting the occurrence of impact ionization. Such phenomena are much less significant under IR (1.55 eV) excitation. Taking into account the electron–phonon scatterings during the electron thermalization, the CM value is calculated to be 2.0 and 1.4 under UV and IR excitation, respectively. This work provides direct evidence for excitation photon energy-dependent impact ionization, which will benefit the potential applications of graphitic materials.

An elemental mapping method using electron microscopy with energy dispersive X-ray spectroscopy has proved to be a versatile tool to track the crystallization of zeolites. We have observed that disparities in local concentration of inorganic structure-directing agent (e.g., alkali metal) is an effective indicator of the degree of crystallization in zeolites. In this study, we demonstrate this approach for zeolite ZSM-22 (TON) with very small crystal sizes (<1 μm), where the high spatial resolution of elemental mapping in combination with scanning transmission electron microscopy allows one to obtain a high sensitivity for the detection of early-stage crystals. The crystallization of TON proceeds through a primary alkali rich amorphous phase that evolves to a secondary poorly crystalline phase which already possesses the composition of the final zeolite crystals. This fact gives us the possibility to determine the onset of disorder-to-order transitions in individual crystals of materials, that are amorphous by X-ray diffraction.

Gas sensing is vital for ecological protection in agriculture, early disease diagnosis in biomedicine, and safety in industrial production. Covalent organic frameworks (COFs), a new class of porous polymer materials, can be customized through specific ligand selection to tailor pore sizes and active sites, enabling them to selectively enrich and interact with targeted gas molecules, making them promising candidates for gas sensing. To advance their use in this field, it is essential to investigate the mechanisms of the complex interactions between COFs and target molecules as well as to improve COF film fabrication methods. This review outlines design strategies for COF films across multiscale: molecular interaction mechanisms, macroscopic interfacial synthesis methods, and microscale/nanoscale approaches such as double-layer films for filtration and micro/nanostructured films for improved gas transfer. Finally, several key research directions are proposed to improve the suitability of COF-based materials for gas sensing in complex environments.

Flame-retardant surface treatments effectively reduce the fire hazard of polymeric foams but are plagued by high coating thickness and deterioration of inherent thermal insulation. Constructing a nanostructure can significantly enhance the thermal insulation of coatings, but current methods usually rely on toxic solvents and harsh conditions. Herein, we present a facile and eco-friendly strategy employing a Cu²⁺-assisted aqueous phase separation (APS) strategy for the assembly of nanostructured polyelectrolyte coatings in situ. Exploiting the multiple cross-linking interactions between Cu²⁺ and the polyelectrolyte complex (PEC), the unique nanosheet (∼200 nm) structure was assembled in the PEC coating. When coated on rigid polyurethane foam (RPUF), the thermal conductivity was reduced to 28.1 from 30.0 mW/m·K. Moreover, the coated RPUF manifests a limiting oxygen index of 36% and reduces heat/smoke release (>60%). This work provides a facile and eco-friendly strategy to cast flame-retardant nanostructured coatings for materials with excellent integrated performances.

The choice of ionic-liquid-like monomers (ILM) for single-ion conducting polyelectrolytes (SICPs) is crucial for the performance of all-solid-state lithium batteries. In the current study, we propose a novel approach for development of SICPs via design and synthesis of a new ILM with long poly(ethylene oxide) spacer between methacrylic group and (trifluoromethane)sulfonylimide anion. Its homopolymer shows an ionic conductivity that is ∼5 orders of magnitude higher (9.2 × 10^–8 S cm^–1 at 25 °C), in comparison with previously reported analogues, while the conductivity of its random copolymer with poly(ethylene glycol)methyl ethermethacrylate reaches the levels of 10^–6 and 10^–5 S cm^–1 at 25 and 70 °C, respectively. The copolymer provides excellent thermal (T_onset ≈ 200 °C) and electrochemical (4.5 V vs Li⁺/Li) stabilities, good compatibility with Li metal, and effective suppression of dendrite growth. Li/SICP/LiFePO₄ cells are capable of reversibly operating at different C rates, demonstrating excellent Coulombic efficiency and retaining specific capacity upon prolonged charge/discharge cycling at a relatively high current rate (C/5) at 70 °C.

The choice of ionic-liquid-like monomers (ILM) for single-ion conducting polyelectrolytes (SICPs) is crucial for the performance of all-solid-state lithium batteries. In the current study, we propose a novel approach for development of SICPs via design and synthesis of a new ILM with long poly(ethylene oxide) spacer between methacrylic group and (trifluoromethane)sulfonylimide anion. Its homopolymer shows an ionic conductivity that is ∼5 orders of magnitude higher (9.2 × 10^-8 S cm^-1 at 25 °C), in comparison with previously reported analogues, while the conductivity of its random copolymer with poly(ethylene glycol)methyl ethermethacrylate reaches the levels of 10^-6 and 10^-5 S cm^-1 at 25 and 70 °C, respectively. The copolymer provides excellent thermal (T _onset ≈ 200 °C) and electrochemical (4.5 V vs Li⁺/Li) stabilities, good compatibility with Li metal, and effective suppression of dendrite growth. Li/SICP/LiFePO₄ cells are capable of reversibly operating at different C rates, demonstrating excellent Coulombic efficiency and retaining specific capacity upon prolonged charge/discharge cycling at a relatively high current rate (C/5) at 70 °C.

Spinal cord injury (SCI) remains a serious problem, owing to its severe consequences and therapeutic limitations. It leads to irreversible impairment of both motor and sensory functions, posing a challenge to recovery and imposing an immense socioeconomic burden on patients. Existing treatment strategies for SCI primarily focus on secondary injury, particularly the modulation of the immune microenvironment after SCI. Infiltrating macrophages play a crucial role in regulating inflammation around the injury site. Macrophages alter their functional phenotypes in response to various stimuli. Classically activated macrophages (M1) exacerbate SCI owing to their pro-inflammatory function, whereas alternatively activated macrophages (M2) inhibit the inflammatory response. Therefore, regulating macrophage polarization represents a promising therapeutic strategy for SCI. Several biomaterial-based strategies for repairing SCI have been developed and are constantly being updated with technological advancements owing to their ability to alleviate neuroinflammation and promote neuroregeneration. In this Review, we focus on the role of macrophages in SCI and discuss the recent research progress of biomaterials targeting macrophage-mediated inflammation for repair and regeneration following SCI. Altogether, this Review provides novel insights into the treatment of SCI.

Sulfide-based solid-state electrolytes (SSEs) are promising materials with superior Li-ion conductivity; however, their poor atmospheric stability limits commercial manufacturing at scale. Here, we investigate the impact of ultrathin metal oxide layers deposited via atomic layer deposition (ALD) on the stability of Li₆PS₅Cl (LPSCl). Al₂O₃ layers grown directly on LPSCl particles significantly stabilize the surface chemistry and Li-ion transport properties relative to uncoated material upon exposure to both an ambient atmosphere (22% relative humidity, RH) and humidified O₂ (100% RH). Detailed investigations indicate that coatings impede the surface and bulk degradation kinetics of exposed materials, even for coatings as thin as ∼1 Å. This suggests that stabilization is due to more than just a physical barrier. Shifts in valence band edge positions of coated LPSCl indicate that ALD coatings alter the surface electronic structure and resulting oxidation tendency of underlying LPSCl, suggesting new avenues to improving the environmental stability of sulfide SSEs.

Overcoming the cathodic limits of water-in-salt electrolyte (WiSE) and developing new active materials are crucial to producing aqueous Li-ion batteries (ALIBs) with higher voltage and energy. Stabilizing the solid-electrolyte interphase (SEI) in a WiSE is expected to improve battery performance. Here, a polymer is designed with pH-responsive properties under alkaline conditions and remains soluble in WiSE, which expands the electrochemical stability window of ALIBs. The polymer prevents water reduction and coprecipitates with the LiTFSI salt in alkaline conditions, resulting in the formation of a stable SEI layer. Moreover, this polymer promotes the crystallization of LiTFSI, leading to a change in the morphology of the SEI as observed by X-ray photoelectron spectroscopy and transmission electron microscopy. Finally, the addition of the polymer in Mo₆S₈//LiFePO₄ full cells during charge/discharge cycling tests significantly improves cycling stability, achieving 87% discharge capacity after 100 cycles at 0.5 C.

The development of activatable immunomodulators for cancer treatment in a controlled and effective manner has been extensively pursued. However, the creation of a spatiotemporally controllable and cascade-activatable tumor-specific photoimmunotherapy platform for precise immunotherapy remains a challenge. Herein, cascade-activatable tumor-specific immunomodulators (CAI) are reported for cancer photoimmunotherapy. Under 808 nm irradiation, the CAI not only mediates phototherapy effect to achieve tumor eradication and immunogenic cell death but also triggers in situ release of caged toll-like receptor 7/8 R848-QPA. Additionally, the intracellular NQO1 activates R848-QPA, leading to the cleavage of trimethyl lock and release of active R848 agonist, enhancing the antitumor immune response. Such a cascade-activatable nanoimmunomodulator can effectively inhibit bilateral tumor growth and enhances systemic immune activation, resulting in improved infiltration of cytotoxic T lymphocytes and helper T cell. Therefore, this modular-designed engineered paradigm provides a generic strategy for developing immunomodulators for precise cascade-activatable immunotherapy.