ACS Materials Letters最新文献

Under concentrated sunlight with a high operation temperature (>100 °C), the enthalpy reduction performance of interfacial materials still remains largely unexplored, which is crucial for future large-scale industrial seawater desalination. Here, an interfacial material that can reduce the evaporation enthalpy under high solar concentration was developed by chemically grafting cyclodextrin (CD) onto porous MnO₂ (β-CD-MnO₂). Experiments demonstrate a 31.5% reduction in the evaporation enthalpy in the β-CD-MnO₂ system, which has an evaporation rate of 1.76 kg·m^–2·h^–1. Our molecular dynamic simulations reveal that the enthalpy reduction arrives from the existence of water-cluster evaporation promoted by the intermediate water. The large existence of intermediate water content in β-CD-MnO₂, which was observed in REMAN measurements, is attributed to the heterostructures, the silane linker, and the ring structure of cyclodextrin in β-CD-MnO₂. Both outdoor experiments and concentrated solar experiments (13 suns) demonstrate that the β-CD-MnO₂ evaporator could realize highly efficient interfacial evaporation with stable enthalpy reduction characteristics.

The growing demand for high-speed communication and highly integrated electronic devices has emphasized the importance of low-dielectric insulator materials. Herein, we present a facile molecular design strategy for poly(aryl ether ketone)s that simultaneously reduces the dielectric constant (D_k) and loss (D_f). The incorporation of bulky cyclohexane side groups increased the intrinsic free volume while limiting additional relaxation. Selective methyl substitution further modulated dielectric properties; methyl groups on cyclohexane groups increased the free volume, whereas those on aromatic rings restricted the chain mobility. Dispersion-corrected density functional theory single-point calculations revealed a high torsional barrier for aromatic methyl groups, consistent with the restricted rotational motion. Consequently, the resulting polymer exhibited low D_k and D_f values (2.65 and 0.0021, respectively) at 28 GHz. These dielectric property improvements were achieved by preserving the mechanical and thermal stabilities of the films, indicating the effectiveness of precise molecular design for next-generation low-k polymers.

Interfacial solar-driven evaporation offers a sustainable solution to freshwater scarcity. Although two-dimensional (2D) evaporators feature a simple architecture and facile fabrication, their efficiency is limited by high evaporation enthalpy. Here, we report a scalable, one-step solution-blending approach to fabricate a 2D ethylene–vinyl alcohol copolymer (EVOH)–cellulose nanofiber (CNF) substrate functionalized with polydopamine-coated Ti₃C₂T_x MXene (PDA-M/CE). EVOH’s low thermal conductivity and ambient-drying film formation with tunable thickness (150 μm – 2 mm), combined with CNF reinforcement and catechol-modified MXene’s photothermal efficiency, yield pronounced interfacial heat localization and a molecular-level hydrophilic–hydrophobic balance. Density functional theory (DFT) and Raman analysis confirm hydrogen-bond disruption and intermediate water formation, reducing the evaporation enthalpy to 788 kJ·kg^–1. Under one sun illumination, PDA-M/CE achieves an evaporation rate of 3.39 kg·m^–2·h^–1 in 3.5 wt % NaCl brine, with an outdoor freshwater yield of 10.47 kg·m^–2 in 8 h. This work provides a robust and cost-effective platform for solar desalination and wastewater treatment.

Processing halide perovskites from solution is central to their development in optoelectronic devices, yet their solubility has traditionally been limited to a narrow set of solvents. Here, we demonstrate that primary alkylamine (RNH₂) additives can greatly expand the solvent space. By screening 24 unconventional solvent systems, including nitriles, sulfites, carbonates, and others, we identify 13 that dissolve perovskite precursors (MAI and PbI₂) in the presence of amine additives. Using acetonitrile (ACN) as a model system, we show that amines promote dissolution through Pb-coordination, while excess amine induces the deprotonation of methylammonium (MA) cations, directing the formation of 2D Ruddlesden–Popper (RP) perovskite phases. Robot-assisted precipitation and thin-film deposition experiments validate our theoretical predictions, revealing a systematic shift toward lower-n RP phases with an increasing amine amount. This work presents alternative solvent systems and provides mechanistic insights into amine-assisted perovskite processing, offering opportunities for sustainable device fabrication.

Crafting boron (B)-free, purely organic narrowband ultraviolet (UV) emitters for organic light-emitting diodes (OLEDs) remains a significant challenge. Herein, a simple regioisomeric engineering strategy by integrating the rigid indolo[3,2,1-jk]carbazole into carbazole at different positions were unveiled. Conjugation isolation and steric effects enabled tunable emission from deep-blue to UV and ultra-narrow FWHM. The C3-isomer (3CzICz) exhibited broad blue emission, while C1- and C4-isomers (1CzICz, 4CzICz) delivered UV-emission (λ_em ≤ 385 nm) with ultra-narrow FWHM ≤ 17 nm. These materials function as both emitters and hosts owing to their wide bandgap and high triplet energies. Notably, 4CzICz as an emitter demonstrated outstanding performance with a EQE of 4.2% and UV-emission (CIEy ≈ 0.028). As a host for green phosphorescent organic light-emitting diodes (PHOLEDs), it exhibited a high EQE of 25.0% with minimal efficiency roll-off (5.0%). This study provides key insights for designing efficient B-free, narrowband organic luminophores for next-generation OLEDs.

This review investigates the application of machine learning (ML) techniques in predicting the tribological characteristics of bearing steel, a crucial element in determining the efficiency and lifespan of mechanical systems. Traditional methods, which rely on empirical equations and physical models, often fall short in handling complex material behaviors and variable operating conditions. ML, particularly deep learning, has become a highly effective instrument for capturing nonlinear relationships and providing accurate predictions. This paper outlines key factors influencing bearing steel friction, including material composition, microstructure, and surface treatment, and discusses the application of a range of ML algorithms, including Artificial Neural Networks (ANN), Support Vector Machines (SVM), and Regression Trees (RT). We compare their performance across various data sets and highlight key issues such as data acquisition, model generalization, and real-time prediction. Recommendations for future research are proposed to enhance the application of ML in this field.

Interstitial carbide ceramics are sought-after materials for their extreme hardness and temperature resistance. However, current processing techniques are time-intensive and geometry-restricted. Hydrogel infusion additive manufacturing is an alternative route to forming and synthesizing carbide ceramics compared with traditional ceramic processing methods. Using a purely polymeric 3D printed preform, metal atoms are infused into the polymer gel by soaking the object in an aqueous or organic solution. Pyrolysis in an inert atmosphere converts the polymer matrix into a reactive carbon source leading to carbothermal reduction at higher temperatures. Ceramic lattice structures of TiC, MoC-Mo₂C, and WC are created from a single polymer precursor. These infused gels are efficient for carbothermal reduction, with minimal oxide phases present after heating at 1500 °C for 2 h. The flexibility and simplicity in preparing various carbides from the single polymer precursor reported here can streamline the production process for these materials.

Direct electrosynthesis of hydrogen peroxide (H₂O₂) via the oxygen reduction reaction (ORR) is a green and safe alternative to the conventional anthraquinone process. Here, we report a functionalized two-dimensional redox-active cationic porphyrin-based covalent organic polymer (cpCOP) used directly as a low-cost, pyrolysis-free ORR electrocatalyst for H₂O₂ production. Its performance was further enhanced by coordinating cobalt ions to the porphyrin pyrrole nitrogen (Co-cpCOP), leading to an improved ORR activity and selectivity. Co-cpCOP exhibits an onset potential of 0.76 V vs RHE with 98% H₂O₂ selectivity, outperforming metal-free cpCOP (0.65 V vs RHE, 77%). When employed as a cathode catalyst in electrolyzers, Co-cpCOP achieved high H₂O₂ production rates of 233.4–983.4 mmol h^–1 g^–1 at 0.35–0.65 V vs RHE. The generated H₂O₂ was successfully applied for the degradation of the textile dye Congo red.

Low-valent metal–organic frameworks (LVMOFs) are an emerging subclass of materials that utilize low oxidation state metal ions for their secondary building units (SBUs). Herein, four LVMOFs and one coordination polymer have been synthesized by combining polytopic phosphine ligands with AgI. In previous examples of LVMOFs, the SBUs are mononuclear metal centers or, in rarer cases, derived from preformed metal clusters. The LVMOFs described here were synthesized from AgI and phosphine ligands resulting in formation of Ag₄I₄ or Ag₂I₂ SBUs. These LVMOFs display one-, two-, or three-dimensional structures and are among the only examples of LVMOFs with polynuclear metal-cluster SBUs that form during LVMOF synthesis. In this regard, these LVMOFs form polynuclear SBUs in the same manner as found in more conventional MOFs. Importantly, one LVMOF formed a rare, 3-dimensional, 4-connected topology with only one prior occurrence among MOFs, demonstrating that LVMOFs can generate distinct opportunities in MOF chemistry.