ACS Publications最新文献

Charge transfer at solid–liquid interfaces is pivotal in biochemical processes, catalysis, and electrochemical devices. However, understanding the charge transfer mechanism at the nanoscale solid–liquid interface remains highly challenging. Here, we conduct ab initio molecular dynamics simulations to investigate interfacial charge transfer between water and the two most common two-dimensional materials: graphene with nonpolar C–C bonds and hexagonal boron nitride (hBN) with polar B–N bonds. It is counterintuitive to find that the charge transfer between water and hBN is approximately 1 order of magnitude higher than that between water and graphene despite the fact that graphene is semiconducting and hBN is insulating. Our further analyses attribute this phenomenon to a higher tendency of water molecules to point a hydrogen atom toward the hBN surface compared to the graphene surface, although they have similar crystallographic structures. This single hydrogen-down water configuration on the hBN surface prompts electron delocalization from hBN and facilitates electron migration to water. Moreover, the polar B–N bonds in hBN result in a strong orbital overlap between nitrogen atoms and hydrogen atoms of water. A similar charge transfer enhancement is also observed between water and two-dimensional gallium nitride (GaN) and aluminum nitride (AlN), which also own polar bonds, and a positive correlation between the charge transfer and the bond polarity is demonstrated. Further simulations indicate that the friction coefficient of water on graphene and hBN surfaces positively correlates with the amount of charge transfer. These findings suggest that materials with polar bonds like hBN can serve as promising materials for biochemical sensors and energy conversion devices.

Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor that is promising as a host material for solid-state quantum technologies through defect engineering. It has been shown that boron atoms can be removed from the lattice upon irradiation by electrons or light ions, creating boron vacancies and boron interstitials. While the optical properties of boron-vacancy-derived defects have been studied extensively, little is known about the optical properties of boron-interstitial-derived defects. In this work, we use state-of-the-art first-principles calculations to predict the electronic and optical properties of boron interstitials (B_int) and defect complexes comprising B_int and substitutional carbon impurities at boron and nitrogen sites (C_B and C_N). These carbon impurities can be present in as-grown hBN and can also be introduced intentionally. We demonstrate that these complexes are expected to be stable at room temperature. Our GW-Bethe–Salpeter equation (BSE) calculations show that B_int–C_B and B_int–C_N have low-energy optical transitions that are isolated in energy, making them suitable as single-photon emitters. Together with constrained density functional theory calculations to capture the red shift due to emission, we predict that B_int–C_B and B_int–C_N have zero phonon lines at ∼2.0 eV and ∼2.6 eV, respectively. Defects involving B_int are likely to be the source of blue emitters recently observed in regions several microns away from ion-irradiated parts of hBN. Our work sheds light on these recent experiments and introduces a fresh perspective to the field of quantum emitters in hBN─we show that defects related to B_int are potential single-photon emitters that can be intentionally created in hBN.

NVMEERKIK, a peptide derived from ovalbumin, exhibited remarkable immunomodulatory activity. This study investigated the effect of simulated gastrointestinal digestion on its structure and bioactivity. NVMEERKIK was found to be unstable against gastrointestinal enzymes and completely degraded into NVME, NVMEE, KIK, K, and R. Among these, NVME, which constituted 90.90% of the digest, was synthesized and demonstrated a superior immune-enhancing activity than NVMEERKIK. Specifically, NVME improved phagocytosis, NO production, and TNF-α content in RAW264.7 cells by 1.31–15.86%, 17.17–122.08%, and 0.36–16.76%, respectively. TLR4 inhibition and immunofluorescence assays revealed the strong TLR4 activation and recognition capacities of both peptides. Furthermore, the Western blot results showed that NVMEERKIK and NVME activated the MAPK/NF-κB pathway by upregulating ERK, JNK, p38, and p65, leading to enhanced activation of RAW264.7 cells. The improved immune-enhancing activity of NVMEERKIK after digestion highlighted its potential as an immunomodulatory peptide for functional food applications.

The need for the reversible and on-demand reconfiguration of local surface plasmon resonances (LSPR) has driven the emerging field of active plasmonics. The overwhelming majority of electrochromic-polymer-mediated active plasmonic nanostructures consist of lithographically fabricated nanoarrays or colloidal nanoparticles embedded in conductive polymers, such as polyaniline (PANI). Herein, we introduce the semiconducting polymer poly(3-methylthiophene) (P3MT) as a novel tunable dielectric medium for active plasmon control. Likewise, we employ thermally dewetted gold nanoislands (AuNIs) as scalable, cost-effective, and robust plasmonic nanostructures. To date, active plasmonic devices based on P3MT or thermally dewetted nanostructures have yet to be explored. Active plasmonic devices consisting of AuNIs coated with ultrathin 12–15 nm P3MT shells were fabricated and tested. Modulation between reduced and oxidized P3MT resulted in a reversible average LSPR modulation of 22 nm, which compares to or even outperforms other electrochromic polymers at similar shell thicknesses. The plasmochromic performance of P3MT-coated Au nanoislands with various LSPRs and size distributions was evaluated in terms of modulation depth, response time, reversibility, chromaticity, and stability. Cyclic stability measurements reveal that plasmonic shifts can still be observed after 1000 cycles of repeated modulation. This work not only expands the current roster of tunable dielectric media and plasmonic nanostructures for use in active plasmonics but also lays the foundation for next-generation active plasmonic technologies such as tunable organic photovoltaics (OPVs), organic photodiodes (OPDs), and plasmonic field-effect transistors (FETs).

Light-induced polarization change has attracted significant attention due to its rapid response and nondestructive nature, positioning it as a promising candidate for next-generation molecular storage devices and energy harvesting. However, achieving substantial photoconversion that results in giant polarization changes via a hidden phase under near-infrared light irradiation remains a formidable challenge. In this study, we successfully synthesized a novel [CrCo] complex with an enantiopure ligand. Unlike previously reported Co valence tautomeric (VT) complexes, this complex exhibits light-induced VT (LIVT) with nearly complete photoconversion ratio upon irradiation with a 1340 nm laser. Additionally, the molecules pack in the P2₁ polar space group with an optimized arrangement, leading to a giant NIR-induced polarization change (1.71 μC cm^–2), which surpasses that of other nonferroelectric crystals. Importantly, electric measurements and single-crystal X-ray analysis after irradiation revealed that the induced polarization change is related to not only the directional electron transfer but also the displacement of anions, which render a distinct hidden metastable phase compared to the thermally approachable one. Moreover, pyroelectric measurement was first used to characterize relaxation kinetics after light irradiation.

Potential-induced electrode charging is a prerequisite to initiate electrochemical reactions at the electrode–electrolyte interface. The ‘interface space charge’ could dramatically alter the reaction environment and the charge density of the active site, both of which potentially affect the electrochemical activity. However, our understanding of the electrocatalytic role of space charge has been limited. Here, we separately modulate the amount of space charge (characterized by the areal density, σ) with maintaining the electrochemical potential for the oxygen reduction reaction (ORR) at the same level, by exploiting the unique structural feature of MeNC. We reveal that changes in σ control the ORR activity, which is computationally explained by the inductive polarization of the charge density at the active sites, affecting their turnover rates. To guide catalyst design including the space charge effect, we develop a new descriptor, explaining the activity trend in various metal centers and pH conditions using a single volcano. These findings offer fresh insights into the role of space charge in electrocatalysis, providing a new framework for optimizing catalyst design and performance.

Twisted bilayer graphene (tBLG) near the magic angle is a unique platform where the combination of topology and strong correlations gives rise to exotic electronic phases. These phases are gate-tunable and related to the presence of flat electronic bands, isolated by single-particle band gaps. This enables gate-controlled charge confinements, essential for the operation of single-electron transistors (SETs), and allows one to explore the interplay of confinement, electron interactions, band renormalization, and the moiré superlattice, potentially revealing key paradigms of strong correlations. Here, we present gate-defined SETs in tBLG with well-tunable Coulomb blockade resonances. These SETs allow us to study magnetic field-induced quantum oscillations in the density of states of the source-drain reservoirs, providing insight into gate-tunable Fermi surfaces of tBLG. Comparison with tight-binding calculations highlights the importance of displacement-field-induced band renormalization crucial for future advanced gate-tunable quantum devices and circuits in tBLG including, e.g., quantum dots and Josephson junction arrays.

This study utilized a synthetic gas test bench (SGB) and two engine test benches (ETBs) to evaluate the periodic operation of an industrially relevant three-way catalyst formulation. The goal was to bridge the gap between laboratory-scale testing and real-world applications, ensuring the reliability of catalysts in engine environments under periodic conditions. SGB testing showed significant increases in NO, CO, and hydrocarbon conversion and N₂ selectivity under dynamic operation compared to stoichiometric steady-state conditions. Despite differences in ETB testing due to the realistic conditions, notable improvements in pollutant conversion were achieved. Challenges included inaccurate control of the mean air–fuel equivalence ratio (AFR) by the engine control unit and the AFR sensor. The findings underscore the importance of harmonizing engine operation with formulation-governed catalyst properties to minimize tailpipe emissions. Periodic operation emerges as a promising technique for enhancing catalyst efficiency in varying engine conditions.

Halide vacancies on the surfaces of cesium lead halide perovskite (CsPbX₃, X = Cl, Br, or I) nanocrystals (NCs) play a crucial role in their photoluminescence quantum yield (PLQY) and photostability. However, effectively passivating these vacancies remains a challenge. Here, 2-bromohexadecanoic acid (BHA) is introduced as a bidentate auxiliary ligand for CsPbX₃ NCs. The CsPbBr₃ and CsPbBr_1.5I_1.5 NCs, comodified with BHA, oleic acid (OA), and oleylamine (OLA) with 20% of OA substituted by BHA, are synthesized using a hot-injection technique and are designated as BHA-CsPbBr₃ and BHA-CsPbBr_1.5I_1.5 NCs. The BHA-CsPbBr₃ NCs exhibit a PLQY of 97% and retain 42.19% of their original intensity after 48 h of continuous ultraviolet light exposure. The photoluminescence (PL) properties, stability, and PL recombination mechanism of the BHA-CsPbBr₃ NCs are investigated in detail. It is believed that the carboxyl oxygen and ortho-bromine atoms enhance the binding strength of BHA to the surface of CsPbX₃. Additionally, the Br^– ions produced from the biomolecular nucleophilic substitution reaction between BHA and OLA partially occupy the anionic vacancies on the surface of CsPbX₃. These interactions reduce the halide vacancies and enhance the PL performance of CsPbX₃.

Ferroelectric oxides are generally prone to brittle deformation, which impedes their applicability in flexible devices. Using a damage-free peel-off process, we successfully synthesized wrinkled 10 nm thick membranes of zirconium-doped hafnium oxide Hf_0.5Zr_0.5O₂ (HZO). We studied their self-restoration dynamics via in situ scanning probe microscopy. Substantial deformations were induced as the tip descended by applying and sustaining a predefined static force at the crest of the wrinkled membrane. The membrane was fully restored to its original wrinkled state within a specific force range, with no observed damage after force removal. The membrane demonstrated self-restoration even after forces exceeding 100 nN, which completely collapsed the wrinkles, highlighting the exceptional flexibility of these freestanding HZO membranes─an uncommon property among functional oxides. Combining phase-field simulations, we observed the emergence of a region exhibiting continuous variation in polarization intensity within the strained area. The formation of this specific domain structure plays a pivotal role in the self-restoration behavior of the freestanding ferroelectric membranes. This self-restoration capability is essential for the long-term stability of flexible electronic devices, such as sensors, energy harvesters, and electronic skins.