Nanozyme Metabolism Controls Air Pollution over an Atomic Potassium Cyano Site.

Increasing threats of air pollution prompt the design of air purification systems. As a promising initiative defense strategy, nanocatalysts are integrated to catalyze the detoxification of specific pollutants. However, it remains a grand challenge to tailor versatile nanocatalysts to cope with diverse pollutants in practice. Here, we report a nanozyme metabolism system to realize broad-spectrum protection from air pollution. Atomic K-modified carbon nitride featuring flavin oxidase-like and peroxidase-like activities was synthesized to initiate nanozyme metabolism. In situ experiments and theoretical investigations collectively show that K sites optimize the geometric and electronic structure of cyano sites for both enzyme-like activities. As a proof of concept, the nanozyme metabolism was applied to the mask against volatile organic compounds, persistent organic pollutants, reactive oxygen species, bacteria, and so on. Our finding provides a thought to tackle global air pollution and deepens the understanding of nanozyme metabolism.

Regulating Reactive Oxygen Species over M-N-C Single-Atom Catalysts for Potential-Resolved Electrochemiluminescence.

The development of potential-resolved electrochemiluminescence (ECL) systems with dual emitting signals holds great promise for accurate and reliable determination in complex samples. However, the practical application of such systems is hindered by the inevitable mutual interaction and mismatch between different luminophores or coreactants. In this work, for the first time, by precisely tuning the oxygen reduction performance of M-N-C single-atom catalysts (SACs), we present a dual potential-resolved luminol ECL system employing endogenous dissolved O2 as a coreactant. Using advanced in situ monitoring and theoretical calculations, we elucidate the intricate mechanism involving the selective and efficient activation of dissolved O2 through central metal species modulation. This modulation leads to the controlled generation of hydroxyl radical (·OH) and superoxide radical (O2·-), which subsequently trigger cathodic and anodic luminol ECL emission, respectively. The well-designed Cu-N-C SACs, with their moderate oxophilicity, enable the simultaneous generation of ·OH and O2·-, thereby facilitating dual potential-resolved ECL. As a proof of concept, we employed the principal component analysis statistical method to differentiate antibiotics based on the output of the dual-potential ECL signals. This work establishes a new avenue for constructing a potential-resolved ECL platform based on a single luminophore and coreactant through precise regulation of active intermediates.

Transition in electronic and magnetic properties of transition metal embedded semimetallic B-graphyne.

Spintronics is extremely important in the future development of information technology. Notably, two-dimensional carbon materials with atomically thick and p-electron systems have great potential for application in ultrathin spintronic devices. B-graphyne (B-GY) is a recently proposed two-dimensional carbon allotrope with double Dirac cones. It is a promising nanomaterial for high-speed spintronic devices due to its ultra-high Fermi velocity and thermodynamic stability. We tune the electronic and magnetic properties of B-GY by doping 3d transition metals (TM) (Cr, Mn, Fe, Co, Ni) based on first-principles calculations. After doping, TM forms strong covalent bonds (Fe, Co, Ni) and ionic bonds (Cr, Mn) with adjacent C atoms. The system of TM-doped B-GY (TM@B-GY) is transformed from a semimetal for B-GY to a metal (Cr, Mn, Fe, Co), but Ni@B-GY is still semimetal. Among them, Co@B-GY is approximately a half-metal. Moreover, TM (except Ni) can induce the magnetism of B-GY to undergo spin splitting. The TM d-orbitals are strongly coupled to the C p-orbitals, which play an important role in inducing magnetism. The results show that the tunable electronic and magnetic properties of TM@B-GY are promising as a high-speed spintronic device. Our research helps advance the study of semimetallic carbon allotropes in the field of spintronics.

Engineering the microenvironment of electron transport layers with nickle single-atom sites for boosting photoelectrochemical performance.

Advances in the rational design of semiconductor-electrocatalyst photoelectrodes provide robust driving forces for improving energy conversion and quantitative analysis, while a deep understanding of elementary processes remains underwhelming due to the multistage interfaces involved in semiconductor/electrocatalyst/electrolyte. To address this bottleneck, we have constructed carbon-supported nickel single atoms (Ni SA@C) as an original electron transport layer with catalytic sites of Ni-N4 and Ni-N2O2. This approach illustrates the combined effect of photogenerated electron extraction and the surface electron escape ability of the electrocatalyst layer in the photocathode system. Theoretical and experimental studies reveal that Ni-N4@C, with excellent oxygen reduction reaction catalytic activity, is more beneficial for alleviating surface charge accumulation and facilitating electrode-electrolyte interfacial electron-injection efficiency under a similar built-in electric field. This instructive method enables us to engineer the microenvironment of the charge transport layer for steering the interfacial charge extract and reaction kinetics, providing a great prospect for atomic scale materials to enhance photoelectrochemical performance.

Accelerated Oxygen Evolution Kinetics by Engineering Heterojunction Coupling of Amorphous NiFe Hydr(oxy)oxide Nanosheet Arrays on Self-Supporting Ni-MOFs.

Designing definite transition metal heterointerfaces is considered an effective strategy for the construction of efficient and robust oxygen evolution reaction (OER) electrocatalysts, but rather challenging. Herein, amorphous NiFe hydr(oxy)oxide nanosheet arrays (A-NiFe HNSAs) are grown in situ on the surface of a self-supporting Ni metal-organic frameworks (SNMs) electrode via a combination strategy of ion exchange and hydrolytic co-deposition for efficient and stable large-current-density water oxidation. The existence of the abundant metal-oxygen bonds on the heterointerfaces can not only be of great significance to alter the electronic structure and accelerate the reaction kinetics, but also enable the redistribution of Ni/Fe charge density to effectively control the adsorption behavior of important intermediates with a close to the optimal d-band center, dramatically narrowing the energy barriers of the OER rate-limiting steps. By optimizing the electrode structure, the A-NiFe HNSAs/SNMs-NF exhibits outstanding OER performance with small overpotentials of 223 and 251 mV at 100 and 500 mA cm-2 , a low Tafel slope of 36.3 mV dec-1 , and excellent durability during 120 h at 10 mA cm-2 . This work significantly provides an avenue to understand and realize rationally designed heterointerface structures toward effective oxygen evolution in water-splitting applications.

Photothermal-Switched Single-Atom Nanozyme Specificity for Pretreatment and Sensing.

Various applications lead to the requirement of nanozymes with either specific activity or multiple enzyme-like activities. To this end, intelligent nanozymes with freely switching specificity abilities hold great promise to adapt to complicated and changeable practical conditions. Herein, a nitrogen-doped carbon-supported copper single-atom nanozyme (named Cu SA/NC) with switchable specificity is reported. Atomically dispersed active sites endow Cu SA/NC with specific peroxidase-like activity at room temperature. Furthermore, the intrinsic photothermal conversion ability of Cu SA/NC enables the specificity switch by additional laser irradiation, where photothermal-induced temperature elevation triggers the expression of oxidase-like and catalase-like activity of Cu SA/NC. For further applications in practice, a pretreatment-and-sensing integration kit (PSIK) is constructed, where Cu SA/NC can successively achieve sample pretreatment and sensitive detection by switching from multi-activity mode to specific-activity mode. This study sets the foundation for nanozymes with switchable specificity and broadens the application scope in point-of-care testing.

Deep potential for a face-centered cubic Cu system at finite temperatures.

The state-of-the-art method generating potential functions used in molecular dynamics is based on machine learning with neural networks, which is critical for molecular dynamics simulation. This method provides an efficient way for fitting multi-variable nonlinear functions, attracting extensive attention in recent years. Generally, the quality of potentials fitted by neural networks is heavily affected by training datasets and the training process and could be ensured by comprehensively verificating the model accuracy. In this study, we obtained the neural network potential of face-centered cubic (FCC) Cu with the most accurate and adequate training datasets from first-principle calculations and the training process performed by Deep Potential Molecular Dynamics (DeePMD). This potential could not only succeed in reproductions of the variety of properties of Cu at 0 K, but also have a good performance at finite temperatures, such as predicting elastic constants and the melting point. Moreover, our potential has a better generalization capacity to predict the grain boundary energy without including extra datasets about grain boundary structures. These results support the applicability of the method under more practical conditions.

Peroxymonosulfate Activation on Synergistically Enhanced Single-Atom Co/Co@C for Boosted Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative.

Tris(bipyridine) ruthenium(II)-based luminophores have been well developed in the area of electrochemiluminescence, while their applications in chemiluminescence (CL) are rarely studied due to the poor luminous efficiency and complicated CL reaction. Herein, a novel tris(bipyridine) ruthenium(II)-based ternary CL system is proposed by introducing cobalt single atoms integrated with graphene-encapsulated cobalt nanoparticles (Co SAs/Co@C) and peroxymonosulfate (PMS) as advanced coreaction accelerator and promising coreactant, respectively. On the basis of the experimental results and density functional theory calculations, it is concluded that Co@C can synergistically modulate the adsorption behavior of PMS on Co SAs and then efficiently activate PMS to produce massive singlet oxygen for remarkable CL emission. Under the optimum conditions, the as-prepared CL biosensor exhibits a good linear range, excellent sensitivity, and selectivity, holding great potential for the practical detection of prostate-specific antigen in human serum.

The effect of charged defects on the stability of implanted helium and yttrium in cubic ZrO2: a first-principles study.

The effect of charged defects on the stability of implanted He and Y atoms has been fully investigated to gain insight into the occupation mechanism of defects in cubic ZrO2 using first-principles calculations. For the intrinsic point defects in ZrO2, the configurations of VO2+, IO2-, VZr4-, and IZr4+ are dominant, which have the lowest formation energy over the widest Fermi level range, respectively. He atoms at neutral Zr vacancies have the lowest incorporation energy (0.438 eV), illustrating that the VZr0 is probably the most stable trapping site for He atoms. For the Y atoms implanted in ZrO2, the most stable configuration of YZr1- is obtained over the widest Fermi level range. In the Y-doped ZrO2, the incorporation energy of He at the site of Oct2 interstitial is the lowest (1.058 eV). For He atoms trapped at vacancies, He-VZr0 has the lowest incorporation energy of 0.631 eV. These results indicate that He atoms preferentially occupy the sites of VZr0. The state of electric charge plays a significant role in the formation of defects in the ionic compound. The present simulation results provide a theoretical foundation for the effect of charged defects on the stability of He atoms, which contributes to the understanding of the microscopic solution behaviour of He atoms in perfect ZrO2 and Y-doped ZrO2.

First-principles investigation of oxygen interaction with hydrogen/helium/vacancy irradiation defects in Ti3AlC2.

First-principles calculations have been performed to investigate the interaction between solute impurity O and H/He/vacancy irradiation defects in Ti3AlC2. The formation energy and occupation of O atoms within different defects as well as the trapping progress of O/H clusters are discussed. It is found that the O atom preferentially occupies the hexahedral interstitial site (Ihex-1) in bulk Ti3AlC2, whereas it prefers to occupy the neighbouring tetrahedral interstitial site (Itetr-2) within pre-exisiting Al monovacancy (VAl), Al divacancy (2VAl-Al) and the 2VAl-C divacancy composed of Al and C vacancies. The appearance of C vacancy could greatly reduce the oxygen formation energy and make an O atom more inclined to occupy the center of C vacancy. Vacancy could capture more O atoms than H/He atoms, where VAl and 2VAl-Al could hold up to fifteen and eighteen O atoms, respectively. Meanwhile, the O could also promote the formation of Al vacancy. On the other hand, O atoms tend to occupy the interstitial sites near the Al atomic layer and have attraction to Al atoms, which is likely to enable the O atoms to combine with the Al atoms to form a Al2O3 protective layer, thus effectively inhibiting further oxidation inside the Ti3AlC2. In addition, the H-O exhibits repulsion interaction, but strong attraction occurs in the He-O interaction. Therefore, the O atom has an inhibitory effect on the formation of the H cluster, while it could bind more He atoms to form a large number of He bubbles. Besides, the O impurity greatly reduces the trapping ability of vacancy to H atoms, and O and He have a synergistic interaction for inhibiting the aggregation of H clusters. The present results are expected to provide a new insight into the behaviour of Ti3AlC2 under irradiation and oxidation conditions so that structural materials could be better designed.

Aggregation of retained helium and hydrogen in titanium beryllide Be12Ti: a first-principles study.

Titanium beryllide, Be12Ti, has been proposed as a prospective neutron multiplier in fusion reactors. First-principles calculations have been performed to investigate the nucleation mechanism of a He bubble in bulk Be12Ti. Meanwhile, the influence of the presence of H atoms on the nucleation of the He bubble, i.e., the synergistic effect of He and H atoms, has also been investigated. It has been found that the He bubble will initially nucleate around a monovacancy (VBe2). When more He atoms have been implanted, two newly induced vacancies (VBe1 and VBe3) could be successively observed. The nucleation of the He bubble will occur around the divacancy of VBe2VBe1 and the trivacancy of VBe2VBe1VBe3. Dumbbell structures in the He bubble evolve with the number of implanted He atoms and finally disappear. The presence of H atoms will significantly influence the nucleation of the He bubble. It is interesting that some tetrahedral and octahedral structures have also been observed. The maximal number of H atoms trapped by a He bubble has been obtained. These phenomena could be further explained by the continuous shrinking of the isosurface of charge density. The present results provide a microscopic physical foundation to understand the mechanism of He and H atoms retention in neutron multiplier materials. This investigation could be helpful for the design and fabrication of more promising beryllides which could withstand a severe external environment.

New insight into the interaction between divacancy and H/He impurity in Ti3AlC2 using first-principles studies.

First-principles calculations have been conducted to investigate the interaction between vacancy defects and H/He impurity in Ti3AlC2. The formation energies of monovacancy and divacancy have been calculated. It is found that Al monovacancy (VAl), Al divacancy (2VAl-Al), and the divacancy composed of Al and C atoms (2VAl-C) are most easily formed in all vacancies. In addition, the interactions between multiple vacancies are weak. The formation of vacancy is relatively independent and not affected by other vacancies. The configurations and energies of H-mV (m = 0, 1, 2) complexes have been studied to assess the energetically favorable sites for H atoms. Within pre-existing VAl or 2VAl-Al, the most favorable site for H atoms is the Itetr-2 site, but the H atom tends to occupy the Ioct-4 site within 2VAl-C. The formation energies of the secondary vacancy defect nearest to an Al vacancy or C vacancy are significantly influenced by H impurity content. H clusters trapped in a primary Al vacancy can promote the formation of vacancy and prefer to form platelet-like bubbles parallel to the Al plane, while H clusters trapped in a primary C vacancy have higher probability to form spherical ones. The 2VAl-Al and 2VAl-C divacancies exhibit stronger H trapping ability than monovacancy. The 2VAl-Al divacancy could capture up to seven H atoms, and 2VAl-C could capture six H atoms. Meanwhile, the He-2VAl-Al complex could only capture four H atoms to form H-He hybridized bubbles, and He impurities effectively suppress further aggregation of H atoms. The present results provide microstructural images of nH-mV and nH-He-mV complexes as well as the evolution progress of H bubbles in Ti3AlC2, which is especially helpful for us to understand the behavior of H/He in Ti3AlC2 under irradiation.

Room temperature ferromagnetism in D-D neutron irradiated rutile TiO2 single crystals.

Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO2 single crystals prepared by the floating zone method due to oxygen vacancy (VO) defects. D-D neutrons mainly collide elastically with TiO2, producing VO, titanium vacancies (VTi) and other point defects; the density and kind of defect is related to the neutron irradiation fluence. D-D neutron irradiation is used to regulate the concentration and type of defect, avoiding impurity elements. As the irradiation fluence increases, the saturation magnetization (Ms) first increases, then decreases and then increases. To verify the origin of RTFM, the CASTEP module was used to calculate the magnetic and structural properties of point defects in TiO2. VO induces a 2.39 µ B magnetic moment, Ti3+ and F+ induce 1.28 µ B and 1.70 µ B magnetic moments, respectively, while VTi induces a magnetic moment of ∼4 µ B. Combining experimental and theoretical results, increases in VO concentration lead to Ms increases; more VO combine with electrons to form F+, inducing a smaller magnetic moment. VO and VTi play a key role and Ms changes accordingly with larger fluence. VO, F+ and VTi are the most likely origins of RTFM.

Synergetic effect of H and He impurities in Ti3AlC2: first principles calculations.

First principles calculations have been performed to investigate the synergetic effect of H and He impurities with vacancies in Ti3AlC2. The configurations and energetics of Hn-He-VAl complexes (n ≤ 4) and He-He/He-H/H-H interactions have been studied. It is found that the impurity H atom prefers to occupy the tetrahedral interstitial site (Itetr-3), but the He atom prefers to occupy the octahedral interstitial site (Ioct-4) in perfect Ti3AlC2. Within a pre-existing Al vacancy, the most favorable site for a He atom is close to tetr-site, meanwhile the H atom preferentially deviates from the vacancy center with the separation 1.3 Å along the 001 direction. He-H and He-He show a weakly attractive interaction, but weak repulsion occurs in the H-H interaction, which is different from the case of Ti3SiC2. The He-VAl complex plays an important role in the trapping of H atoms. The He-VAl cluster can trap up to three H atoms in the absence of H2 molecules, which leads to the formation of a H-He hybridized bubble. Thus, the He atom can subsequently suppress further aggregation of H atoms and block hydrogen embrittlement and volume swelling.

Retention and diffusion of transmutation H and He atoms in Be12Ti: first-principles calculations.

The beryllide Be12Ti is considered to be the most promising candidate material for advanced plasma facing materials in future fusion reactors because of its excellent performance. In this work, first-principles calculations were conducted to gain insight into the retention and diffusion behavior of transmutation H and He atoms in Be12Ti. The solution energy and migration energy of single impurity H/He atoms were computed to study the behavior of their retention and diffusion. Among seven stable interstitial sites, H atoms preferentially occupy the octahedral interstitial site, I oct, whereas He atoms preferentially occupy the dodecahedral interstitial site, I dode. The solubility of H is much higher than that of He in Be12Ti. When monovacancy is generated, H atoms preferentially stay in the vicinity of Be1 vacancies, while He atoms tend to reside in the center of Ti vacancies. The migration energy barrier of a single He atom between first near-neighbor I dode sites is 0.35 eV. For H atoms, the migration energy barrier from I dode to I tetra2 is 0.45 eV. The barrier along the paths I tri1-I dode-I tri1 is 0.38 eV. When a Be3 vacancy is introduced as the neighbour of I tri1, the migration energy barrier increases to 0.77 eV. These results indicate that vacancies can trap impurity atoms and may act as seeds for bubble formation.

Friction phenomena in the overdamped three-layer model.

An overdamped three-layer model consisting of two harmonic chains of interacting particles, representing the upper and the middle layers, which move over the substrate potential, is studied in the present paper. A dc+ac force is applied only on the upper harmonic chain, and dynamics of both layers are investigated. The results show that the dynamical mode locking and Shapiro steps appear not only in the upper layer but also in the middle one. It is noted that the motion of particles in the upper layer corresponds to the standard Frenkel-Kontorova model. The dependence of the Shapiro steps of the middle layer on the system parameters are determined. It is shown that the height of the first Shapiro step of the upper layer is unrelated to the interaction parameters of the particles of both the upper and the middle layers, while the height of the first Shapiro step of the middle layer depend only on the interaction parameters of the particles of the middle layers. Two critical forces which transfer from locked state to the sliding one of both the upper and the middle layers are also studied. They depend on the amplitude and the frequency of the external ac driving force.

Ratchet effect and amplitude dependence of phase locking in a two-dimensional Frenkel-Kontorova model.

We demonstrate the ratchet and phase locking effects in a two-dimensional overdamped Frenkel-Kontorova model with a square symmetric periodic substrate when both a longitudinal dc drive and a circular ac drive are applied. Besides the harmonic steps, the large half integer steps can also clearly be seen in the longitudinal (x) direction. These half integer steps are directly correlated to the appearance of positive and negative ratchet effects in the transverse (y) direction due to the symmetry breaking in the combination of the dc and ac drives. The angle between the net displacement and the longitudinal direction is analytically obtained in a single period of the ac drive. In the examination of the amplitude dependence of the ac drive, the maxima decrease monotonically with the amplitude, while the anomalies occur for the critical depinning force and the harmonic steps due to the spatial symmetry breaking of orbits in the presence of the ac drive.

Existence and stability of the resonant phenomena in the dc- and ac-driven overdamped Frenkel-Kontorova model with the incommensurate structure.

Dynamical mode-locking phenomena in the incommensurate structures of the dc- and ac-driven overdamped Frenkel-Kontorova model are studied by molecular-dynamics simulations. The obtained results have shown that Shapiro steps exhibit significantly different amplitude and frequency dependence from the one observed in the commensurate structures. Due to the incommensurability of the system the special symmetry of the motion of particles is broken, and in the amplitude dependence of Shapiro steps, this will result in the appearance of anomalies and deviation from the well-known Bessel-like behavior. In the frequency or period dependence, oscillations have been observed in the high-amplitude limit; however, they exhibit strong anomalies compared with those in the commensurate structures. The oscillatory behavior and the anomalies have been also be revealed in the (F(ac),F) and the (ν(0),F) phase diagrams where several phases are defined.

Friction phenomena and phase transition in the underdamped two-dimensional Frenkel-Kontorova model.

Locked-to-sliding phase transition has been studied in the driven two-dimensional Frenkel-Kontorova model with the square symmetric substrate potential. It is found that as the driving force increases, the system transfers from the locked state to the sliding state where the motion of particles is in the direction different from that of driving force. With the further increase in driving force, at some critical value, the particles start to move in the direction of driving force. These two critical forces, the static friction or depinning force, and the kinetic friction force for which particles move in the direction of driving force have been analyzed for different system parameters. Different scenarios of phase transitions have been examined and dynamical phases are classified. In the case of zero misfit angle, the analytical expressions for static and kinetic friction force have been obtained.