ACS Materials Letters最新文献

Many thermoplastic polymers are ductile by combining strength and large deformations. These deformations are irreversible ─ known as plastic deformation. Elastomers can deform reversibly but have low strength. To this end, we developed glassy and ductile polyamide networks capable of large plastic deformation (>200% strain) and high strength (∼50 MPa tensile strength and ∼1500 MPa Young’s modulus), similar to those of polyolefins and Nylon-66. We discovered that hydrogen bonding between meta-phthalamide groups was essential to the ductility. Since these polyamide networks are covalently bonded, we demonstrated their unique durability by repeatable elastic recovery at elevated temperatures, exhibiting indifferent tensile properties in each cycle. Furthermore, when we fixed the strain during the elastic recovery, these polyamide networks actuated stresses of 9–18 MPa, among the highest reported in shape-memory polymer actuators. We envision these ductile, glassy polymer networks as promising alternatives to ductile thermoplastics, given the combined benefit of ductility and durability.

Metal-free or purely organic phosphorescent materials (phosphors) with ultralong emission lifetimes have emerged as an important class of multifunctional materials with a wide array of applications. However, the mechanistic understanding of phosphorescence in purely organic emitters apparently lags behind practical accomplishments, and the existing knowledge has not been summarized properly. For example, despite the impurity effect on phosphorescence from metal-free organic emitters having been well-recognized for over a century, recent studies have rediscovered the critical role of impurities in the phosphorescence. Hence, this review aims at bridging the apparent knowledge gap by integrating prior understanding with the latest findings on the role of impurities in phosphorescence. In addition, purification methods of phosphors, methodologies to test for impurity-induced emission, and mechanistic considerations for impurity-induced phosphorescence are highlighted.

Electrochemical water-splitting processes are a safe, sustainable, and ecofriendly method to generate pure hydrogen, with minimal carbon emission. Typically, water reduction (hydrogen evolution) and oxidation (oxygen evolution) occur simultaneously, although such coupled processes lead to several limitations such as gas crossover, electrocatalyst degradation by reactive oxygen species, and more. This review presents several strategies to design decoupled water splitting devices, separating the two half-reactions spatially and temporally, to address several of these issues. The designs change according to the electrode materials, electrolyte, and decoupling strategy employed (redox mediator). The review describes how the decoupling mechanisms adopted affect different properties and lead to designs with optimal efficiency. It also focuses on their integration with renewable energy, which can be used to power each half-reaction independently. Lastly, the merits and constraints of the decoupled systems in addressing global environmental issues are discussed along with potential questions to further advance this technology-based strategy.

Like all conductive materials, electrically conductive metal–organic frameworks glean their properties from their defects. Owing to the synthesis conditions required to form the peak-performing triphenylene-based conductors, adatomic H atoms are likely the most prevalent defect and may occur in the charge state of −1, 0, and +1. However, some forms of these defects necessitate unpaired electrons, and the interplay between the ligand-centered unpaired electron and spin-polarized metals remains unknown. Here, we report the formation energies of hydrogenic defects in Cu₃(HITP)₂ (HITP ≡ 2,3,6,7,10,11-hexaiminotriphenylene), the Cu²⁺ analogue of Ni₃(HITP)₂, and show that they are comparable to the Ni²⁺ system. d⁹ Cu²⁺ does not appreciably affect the electronic band properties of the defective framework.

The second near-infrared window (NIR-II, 1000–3000 nm) presents an attractive platform for phototheranostics due to improved tissue penetration. However, developing efficient phototheranostic agents for this range presents a significant challenge. Herein, we report an NIR-II organic theranostic agent, CNTIC-4F, based on a fused-ring acceptor structure, which features efficient absorption extending beyond 1200 nm and fluorescence emission reaching up to 1800 nm. The incorporation of a proaromatic π-bridge, thieno[3,4-b]pyrazine (TP), enhances the quinoidal character of CNTIC-4F, reducing the optical bandgap and enhancing intermolecular interactions. In vivo fluorescence imaging of mouse vasculature with CNTIC-4F nanoparticles shows high-contrast imaging beyond 1500 nm under 1064 nm excitation. Furthermore, CNTIC-4F nanoparticles also exhibit a high photothermal conversion efficiency of 82% under 1064 nm excitation, enabling effective NIR-II imaging-guided photothermal therapy of 4T1 tumors in mice. This study illustrates the potential of quinoidal structures in developing advanced organic agents for high-contrast and deep-penetrating NIR-II phototheranostics.

The rapid growth of the global population and industry has increased global warming and energy consumption. Clean, sustainable, and renewable sources of energy must be employed if this critical problem is to be resolved. Hydrogen (H₂) has become one of the most promising fuel sources within the range of alternatives. A noteworthy method of creating hydrogen is by electrochemically splitting water into H₂ and O₂. As a result, the need for inexpensive, accessible catalysts with remarkable catalytic performance for producing environmentally friendly H₂ has become crucial. The newly emerging class of 2-D layered MXenes, which consists of nitrides, transition metal carbides (TMC), and carbonitrides, is an impressive competitor in this race. MXenes offer excellent electrochemical properties, hydrophilicity, and reactivity, making them suitable for water-splitting applications. However, systematic reviews on strategies and mechanical chemistry of electrocatalytic water redox reactions for H₂ productions are rare. This comprehensive review analysis addresses many strategies for boosting MXene catalytic efficiency during oxygen evolution (OER) and hydrogen evolution reactions (HER). These approaches include heteroatom doping, alloying, quantum dot doping, and plasma surface modification. Furthermore, this study highlights the many efforts and prospective paths for increasing the economic viability of MXenes as electrocatalysts for green H₂ generation. As a result, this review opens new avenues for high-performance MXenes in green energy applications, promising a more sustainable energy future.

Swapping the sluggish oxygen evolution reaction (OER) for the thermodynamically advantageous sulfur ion oxidation reaction (SOR) makes it possible to produce low-energy hydrogen. We report here on an electrocatalytic SOR-coupled HER system that allows for the joint production of sulfur and hydrogen. We prepare a CoMoO₄ nanoarray on nickel foam (NF) for anodic SOR and N-doped CoMoO₄/NF, CoMoN/NF, for cathodic HER. The current density of 100 mA cm^–2 was obtained at 0.29 V (vs RHE) in the SOR process. After nitridation, the electrode can achieve a current density of 10 mA cm^–2 in HER at a voltage of only 32 mV (vs RHE). The coupling system (SOR//HER) can run steadily for 150 h. Detailed exploration and discussion were conducted on the pathways of SOR. This work develops an energy-efficient mixed water electrolysis system for H₂, providing a viable option for toxic waste treatment.

High-entropy alloys (HEAs) contain five or more main elements, and each element ranges in content from 5% to 35%. Due to the abundant selectivity of elements, excellent structural stability, and adjustable active centers, HEAs have been widely used in electrocatalysis. Designing HEA catalysts at the atomic scale can deeply describe their structural complexity and accurately reflect the relationship between HEA structure and catalytic performance. In this Review, the atomic design of HEA-based electrocatalysts is introduced and it is evaluated in terms of activity, stability, selectivity, and efficiency. Ingenuity at the atomic level can customize the atomic composition and geometric structure of HEAs, thereby enhancing the intrinsic activity of the catalytic site, creating new active sites, and improving operational stability. The Review provides insights into excellent electrocatalytic properties and guidance for the design and synthesis of advanced HEA electrocatalysts from the viewpoint of atomic fabrication.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) room temperature (RT) gas sensors are of great value for monitoring leaks of hazardous gases under harsh environments. However, the highly sensitive and rapid detection of TMDs in an energy-efficient state is still a formidable obstacle. This work reports the ultrasensitive NO₂ sensor based on rare-earth Nd doped VS₂/carbon nanofibers (CNFs) (abbreviated as x%Nd-VS₂-C), which exhibits a fast response/recovery and intense response at RT. The impact of the Nd doping amount on the NO₂-sensing properties of x%Nd-VS₂-C was systematically explored. The active Nd-doping and abundant S vacancies could activate the inert basal planes of VS₂ efficiently and increase the active sites of the surface, thereby improving the NO₂-sensing performance of the sensor. Additionally, theoretical calculations validate the finding by demonstrating a more negative NO₂ adsorption energy of −3.12 eV on the (001) surface of Nd-VS₂-C compared to −1.26 eV on pure VS₂. The 2% Nd-VS₂-C exhibits optimal RT NO₂-sensing properties, with a thrilling response/recovery rate (∼17 s/20 s), high sensitivity (∼3.03 to 10 ppm of NO₂), favorable selectivity and stability, and low detection limit (18 ppb). The outstanding “‘4S’” features make the 2%Nd-VS₂-C sensor greatly attractive for precise and ultrasensitive NO₂ detection at RT.

The effect of single atom positions and coordination environments on photocatalytic performance is not clear. Herein, Co single atoms with surface coordination or lattice coordination mode in Bi₂₄O₃₁Br₁₀ atomic layers are presented for CO₂ photoreduction. A novel strategy based on metal-based ionic liquids is developed to prepare stable surface single atom tuned catalysts. In contrast to high-coordinated lattice-doped Co single atoms, the low-coordinated Co single atoms loaded on the catalyst surface play a crucial role in decreasing the activation energy and rate-limiting step energy barriers. The surface-modified Co single atoms work as a polarization center to drive photogenerated electron migration, accelerate reaction kinetics, and enhance CO₂ reduction activity. Benefiting from these features, Co_sur-Bi₂₄O₃₁Br₁₀ exhibits a more enhanced CO₂ photoreduction performance than Bi₂₄O₃₁Br₁₀ and Co_lat-Bi₂₄O₃₁Br₁₀. This work provides insight into the effect of positions of single atoms on photocatalytic behavior and offers a strategy to load other low-coordinated surface metal single atoms.