Self-driven carbon atom implantation into fullerene embedding metal-carbon cluster.

Hundreds of members have been synthesized and versatile applications have been promised for endofullerenes (EFs) in the past 30 y. However, the formation mechanism of EFs is still a long-standing puzzle to chemists, especially the mechanism of embedding clusters into charged carbon cages. Here, based on synthesis and structures of two representative vanadium-scandium-carbido/carbide EFs, VSc2C@Ih (7)-C80 and VSc2C2@Ih (7)-C80, a reasonable mechanism-C1 implantation (a carbon atom is implanted into carbon cage)-is proposed to interpret the evolution from VSc2C carbido to VSc2C2 carbide cluster. Supported by theoretical calculations together with crystallographic characterization, the single electron on vanadium (V) in VSc2C@Ih (7)-C80 is proved to facilitate the C1 implantation. While the V=C double bond is identified for VSc2C@Ih (7)-C80, after C1 implantation the distance between V and C atoms in VSc2C2@Ih (7)-C80 falls into the range of single bond lengths as previously shown in typical V-based organometallic complexes. This work exemplifies in situ self-driven implantation of an outer carbon atom into a charged carbon cage, which is different from previous heterogeneous implantation of nonmetal atoms (Group-V or -VIII atoms) driven by high-energy ion bombardment or high-pressure offline, and the proposed C1 implantation mechanism represents a heretofore unknown metal-carbon cluster encapsulation mechanism and can be the fundamental basis for EF family genesis.

Construction of an Electron Capture and Transfer Center for Highly Efficient and Selective Solar-Light-Driven CO2 Conversion.

Exploring high-efficiency photocatalysts for selective CO2 reduction is still challenging because of the limited charge separation and surface reactions. In this study, a noble-metal-free metallic VSe2 nanosheet was incorporated on g-C3N4 to serve as an electron capture and transfer center, activating surface active sites for highly efficient and selective CO2 photoreduction. Quasi in situ X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and femtosecond transient absorption spectroscopy (fs-TAS) unveiled that VSe2 could capture electrons, which are further transferred to the surface for activating active sites. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations revealed a kinetically feasible process for the formation of a key intermediate and confirmed the favorable production of CO on the VSe2/PCN (protonated C3N4) photocatalyst. As an outcome, the optimized VSe2/PCN composite achieved 97% selectivity for solar-light-driven CO2 conversion to CO with a high rate of 16.3 µmol·g-1·h-1, without any sacrificial reagent or photosensitizer. This work offers new insights into the photocatalyst design toward highly efficient and selective CO2 conversion.

Gate-Tunable Spin Seebeck Effect and Pure Spin Current Generation in Molecular Junctions Based on Bipolar Magnetic Molecules.

Generating pure spin currents is very desirable in spintronics, as it provides a promising way to substantially reduce Joule heating and achieve ultrahigh integration density. However, to date, most spintronic devices exhibit spin currents that are accompanied by charge currents. The generation of pure spin currents on the nanoscale, particularly at the single-molecule level, remains challenging. Here, we propose that by exploiting our recently reported bipolar magnetic molecules (BMMs) as the core component of single-molecule devices, where the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) come from different spin channels, the generation of pure spin currents can be easily realized via the spin Seebeck effect (SSE) with applied temperature gradient. Moreover, the spin Seebeck coefficient can be modulated over a wide range by applying an external gate voltage. The proposal is verified through first-principles calculations on two BMM-based molecular junctions.

Tailoring Catalysis of Encapsulated Pt Nanoparticles by Pore Wall Engineering of Covalent Organic Frameworks.

While supported metal nanoparticles (NPs) have shown significant promise in heterogeneous catalysis, precise control over their interaction with the support, which profoundly impacts their catalytic performance, remains a significant challenge. In this study, Pt NPs are incorporated into thioether-functionalized covalent organic frameworks (denoted COF-Sx), enabling precise control over the size and electronic state of Pt NPs by adjusting the thioether density dangling on the COF pore walls. Notably, the resulting Pt@COF-Sx demonstrate exceptional selectivity (>99%) in catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline, in sharp contrast to the poor selectivity of Pt NPs embedded in thioether-free COFs. Furthermore, the conversion over Pt@COF-Sx exhibits a volcano-type curve as the thioether density increases, due to the corresponding change of accessible Pt sites. This work provides an effective approach to regulating the catalysis of metal NPs via their microenvironment modulation, with the aid of rational design and precise tailoring of support structure.

Self-Limited Embedding Alternating 585-Ringed Divacancies and Metal Atoms into Graphene Nanoribbons.

Because of their theoretically predicted intriguing properties, it is interesting to embed periodic 585-ringed divacancies into graphene nanoribbons (GNRs), but it remains a great challenge. Here, we develop an on-surface cascade reaction from periodic hydrogenated divacancies to alternating 585-ringed divacancies and Ag atoms via intramolecular cyclodehydrogenation in a seven-carbon-wide armchair GNR on the Ag(111) surface. Combining scanning tunneling microscopy/spectroscopy and noncontact atomic force microscopy combined with first-principles calculations, we in-situ-monitor the evolution of the distinct structural and electronic properties in the reaction intermediates. The observation of embedded Ag atoms and further nudged elastic band calculations provide unambiguous evidence for Ag adatom-mediated C-H activation in the intramolecular cyclodehydrogenation pathway, where the strain-induced self-limiting effect contributes to the formation of the GNR superlattice with alternating 585-ringed divacancies and Ag atoms, which shows a band gap of about 1.4 eV. Our findings open an avenue to introducing periodic impurities of single metal atoms and nonhexagonal rings in on-surface synthesis, which may provide a novel route for multifunctional graphene nanostructures.

Dual Microenvironment Modulation of Pd Nanoparticles in Covalent Organic Frameworks for Semihydrogenation of Alkynes.

The chemical microenvironment modulation of metal nanoparticles (NPs) holds promise for tackling the long-lasting challenge of the trade-off effect between activity and selectivity in catalysis. Herein, ultrafine PdCu2 NPs incorporated into covalent organic frameworks (COFs) with diverse groups on their pore walls have been fabricated for the semihydrogenation of alkynes. The Cu species, as the primary microenvironment of Pd active sites, greatly improves the selectivity. The functional groups as the secondary microenvironment around PdCu2 NPs effectively regulate the activity, in which PdCu2 NPs encapsulated in the COF bearing -CH3 groups exhibit the highest activity with >99 % conversion and 97 % selectivity. Both experimental and calculation results suggest that the functional group affects the electron-donating ability of the COFs, which successively impacts the charge transfer between COFs and Pd sites, giving rise to a modulated Pd electronic state and excellent catalytic performance.

Exclusive Co-N4 Sites Confined in Two-dimensional Metal-Organic Layers Enabling Highly Selective CO2 Electroreduction at Industrial-Level Current.

Metal-organic framework catalysts bring new opportunities for CO2 electrocatalysis. Herein, we first conduct density-functional theory calculations and predict that Co-based porphyrin porous organic layers (Co-PPOLs) exhibit good activity for CO2 conversion because of the low *CO adsorption energy at Co-N4 sites, which facilitates *CO desorption and CO formation. Then, we prepare two-dimensional Co-PPOLs with exclusive Co-N4 sites through a facile surfactant-assisted bottom-up method. The ultrathin feature ensures the exposure of catalytic centers. Together with large specific area, high electrical conductivity and CO2 adsorption capability, Co-PPOLs achieve a peak faradaic efficiency for CO production (FECO =94.2 %) at a moderate potential in CO2 electroreduction, accompanied with good stability. Moreover, Co-PPOLs reach an industrial-level current above 200 mA in a membrane electrode assembly reactor, and maintain near-unity CO selectivity (FECO >90 %) over 20 h in CO2 electrolysis.

Step-Assisted On-Surface Synthesis of Graphene Nanoribbons Embedded with Periodic Divacancies.

The bottom-up approach through on-surface synthesis of porous graphene nanoribbons (GNRs) presents a controllable manner for implanting periodic nanostructures to tune the electronic properties of GNRs in addition to bandgap engineering by width and edge configurations. However, owing to the existing steric hindrance in small pores like divacancies, it is still difficult to embed periodic divacancies with a nonplanar configuration into GNRs. Here, we demonstrate the on-surface synthesis of atomically precise eight-carbon-wide armchair GNRs embedded with periodic divacancies (DV8-aGNRs) by utilizing the monatomic step edges on the Au(111) surface. From a single molecular precursor correspondingly following a trans- and cis-coupling, the DV8-aGNR and another porous nanographene are respectively formed at step edges and on terraces at 720 and 570 K. Combining scanning tunneling microscopy/spectroscopy, atomic force microscopy, and first-principles calculations, we determine the out-of-plane conformation, wide bandgap (∼3.36 eV), and wiggly shaped frontier orbitals of the DV8-aGNR. Nudged elastic band calculations further quantitatively reveal that the additional steric hindrance effect in the cyclodehydrogenative reactions has a higher barrier of 1.3 eV than that in the planar porous nanographene, which also unveils the important role played by the monatomic Au step and adatoms in reducing the energy barriers and enhancing the thermodynamic preference of the oxidative cyclodehydrogenation. Our results provide the first case of GNRs containing periodic pores as small as divacancies with a nonplanar configuration and demonstrate the strategy by utilizing the chemical heterogeneity of a substrate to promote the formation of novel carbon nanomaterials.

Bipolar Magnetic Molecules for Spin-Polarized Electric Current in Molecular Junctions.

Electrical control of spin transport at single molecule level is highly desired for molecular nanospintronics. By exploiting magnetic bistability of spin crossover complexes, the magnitude of spin polarization can be modulated. However, efficiently controlling the direction of spin polarization at single molecule level is still challenging. Here, we propose a general method to flip the transport electron spin simply by electrical gating in single molecule devices based on bipolar magnetic molecules (BMMs), of which the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) come from different spin channels. Thus, when the device's Fermi level is reversibly adjusted approaching either HOMO or LUMO by changing the polarity of the applied voltage gate, a 100 % spin polarized current with switchable spin direction is achievable. The proposed method is verified by the calculated electronic and transport properties of 9 potential transition metal coordination BMMs.

Non-Collinear Orbital-induced Planar Quantum Anomalous Hall Effect.

Based on the 2D star lattice with noncollinear orbital, we present an intriguing six-band tight-binding model for planar quantum anomalous Hall effect (PQAHE) with in-plane magnetization. Depending on the orientation of the noncollinear orbital, the characterized Dirac-, Kagome-, and Four-band are all realizable. Moreover, including the intrinsic spin-orbital coupling, a topological phase diagram versus angle of both in-plane magnetization and noncollinear orbital is mapped out, showing a tunable PQAHE with Chern number of either +1 or -1. Most remarkably, using first-principles calculations, this exact model of PQAHE is identified in an experimentally synthesized 2D metal-organic framework (MOF) of Pr2(C6O4Cl2)3. These notable results not only demonstrate the significance of noncollinear orbital for designing PQAHE but also provide a MOF platform for its realization, greatly enriching the fundamental topological physics and extending the candidate topological materials.

Tuning the Doping Types in Graphene Sheets by N Monoelement.

The doping types of graphene sheets are generally tuned by different dopants with either three or five valence electrons. As a five-valence-electrons element, however, nitrogen dopants in graphene sheets have several substitutional geometries. So far, their distinct effects on electronic properties predicted by theoretical calculations have not been well identified. Here, we demonstrate that the doping types of graphene can be tuned by N monoelement under proper growth conditions using chemical vapor deposition (CVD), characterized by combining scanning tunneling microscopy/spectroscopy, X-ray/ultraviolet photoelectron spectroscopy, Hall effect measurement, Raman spectroscopy, and density functional theory calculations. We find that a relatively low partial pressure of CH4 (mixing with NH3) can lead to the growth of dominant pyridinic N substitutions in graphene, in contrast with the growth of dominant graphitic N substitutions under a higher partial pressure of CH4. Our results unambiguously confirm that the pyridinic N leads to the p-type doping, and the graphitic N leads to the n-type doping. Interestingly, we also find that the pyridinic N and the graphitic N are preferentially separated in different domains. Our findings shed light on continuously tuning the doping level of graphene monolayers by using N monoelement, which can be very convenient for growth of functional structures in graphene sheets.

Spin-Transport Tuning of Individual Magnetic Mn-Salophen Molecule via Chemical Adsorption.

Control over spin states at the single molecule level is a key issue in the emerging field of molecular spintronics. Here, we explore the chemical adsorption effect on the magnetic and spin-transport properties of individual magnetic molecule by performing extensive density functional theory calculations in combining with non-equilibrium Green's function method. Theoretical results clearly reveal that the molecular magnetic moment of Mn-salophen can be effectively tuned by adsorbing F and CO on the central Mn cation, while the adsorbed NO molecule quenches the molecular magnetic moment. Without chemical adsorption, the currents through Mn-salophen molecular junction just show a little distinction for two spin channels, which agrees well with previous investigation. Remarkably, the conductive channel can be switched from the spin-up electrons to the spin-down electrons via adsorbing F and CO, respectively, and the corresponding two Mn-salophen molecular junctions with chemical modifications display nearly perfect spin-filtering effect. The observed spin switch and the predicted spin-filtering effect via chemical adsorption indicates that Mn-salophen holds potential applications in molecular spintronic devices.

Interfacial coupling induced direct Z-scheme water splitting in metal-free photocatalyst: C3N/g-C3N4 heterojunctions.

Mimicking the natural photosynthesis in green plants, artificial Z-scheme photocatalysis enables more efficient utilization of solar energy for photocatalytic water splitting. Most currently designed g-C3N4-based Z-scheme heterojunctions are usually based on metal-containing semiconductor photocatalysts, thus exploiting metal-free photocatalysts for Z-scheme water splitting is of huge interest. Herein, we propose two metal-free C3N/g-C3N4 heterojunctions with the C3N monolayer covering g-C3N4 sheet (monolayer or bilayer) and systematically explore their electronic structures, charge distributions and photocatalytic properties by performing extensive hybrid density functional calculations. We clearly reveal that the relative strong built-in electric fields around their respective interface regions, caused by the charge transfer from C3N monolayer to g-C3N4 monolayer or bilayer, result in the bands bending, renders the transfer of photogenerated carriers in these two heterojunctions following the Z-scheme instead of the type-II pathway. Moreover, the photogenerated electrons and holes in these two C3N/g-C3N4 heterojunctions can not only be efficiently separated, but also have strong redox abilities for water oxidation and reduction. Compared with the isolated g-C3N4 sheets, the light absorption in visible to near-infrared region are significantly enhanced in these proposed heterojunctions. These theoretical findings suggest that these proposed metal-free C3N/g-C3N4 heterojunctions are promising direct Z-scheme photocatalysts for solar water splitting.

Blending Non-Group-3 Transition Metal and Rare-Earth Metal into a C80 Fullerene Cage with D5h Symmetry.

Rare-earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non-Group-3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an Ih -C80 cage. Non-Group-3 transition-metal-containing endohedral fullerenes based on a C80 cage with D5h symmetry, Vx Sc3-x N@D5h -C80 (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc2 N@D5h -C80 was unambiguously determined by X-ray crystallography. According to a comparative study with the reported Ti- and V-containing clusterfullerenes based on a Ih -C80 cage and the analogous D5h -C80 -based metal nitride clusterfullerenes containing rare-earth metals only, the decisive role of the non-Group-3 transition metal on the formation of the corresponding D5h -C80 -based clusterfullerenes is unraveled.

Tin Oxide Crystals Exposed by Low-Energy {110} Facets for Enhanced Electrochemical Heavy Metal Ions Sensing: X-ray Absorption Fine Structure Experimental Combined with Density-Functional Theory Evidence.

Herein, we revealed that the electrochemical behaviors on the detection of heavy metal ions (HMIs) would largely rely on the exposed facets of SnO2 nanoparticles. Compared to the high-energy {221} facet, the low-energy {110} facet of SnO2 possessed better electrochemical performance. The adsorption/desorption tests, density-functional theory (DFT) calculations, and X-ray absorption fine structure (XAFS) studies showed that the lower barrier energy of surface diffusion on {110} facet was critical for the superior electrochemical property, which was favorable for the ions diffusion on the electrode, and further leading the enhanced electrochemical performance. Through the combination of experiments and theoretical calculations, a reliable interpretation of the mechanism for electroanalysis of HMIs with nanomaterials exposed by different crystal facets has been provided. Furthermore, it provides a deep insight into understanding the key factor to improve the electrochemical performance for HMIs detection, so as to design high-performance electrochemical sensors.

Accurate Determination of the Quasiparticle and Scaling Properties Surrounding the Quantum Critical Point of Disordered Three-Dimensional Dirac Semimetals.

Exploiting the enabling power of the Lanczos method in momentum space, we determine accurately the quasiparticle and scaling properties of disordered three-dimensional Dirac semimetals surrounding the quantum critical point separating the semimetal and diffusive metal regimes. We unveil that the imaginary part of the quasiparticle self-energy obeys a common power law before, at, and after the quantum phase transition, but the power law is nonuniversal, whose exponent is dependent on the disorder strength. More intriguingly, whereas a common power law is also found for the real part of the self-energy before and after the phase transition, a distinctly different behavior is identified at the critical point, characterized by the existence of a nonanalytic logarithmic singularity. This nonanalytical correction serves as the very basis for the unusual power-law behaviors of the quasiparticles and many other physical properties surrounding the quantum critical point. Our approach also allows the ready and reliable determination of the scaling properties of the correlation length and dynamical exponents. We further show that the central findings are valid for both uncorrelated and correlated disorder distributions and should be directly comparable with future experimental observations.

Entrapping a Group-VB Transition Metal, Vanadium, within an Endohedral Metallofullerene: V(x)Sc(3-x)N@I(h)-C80 (x = 1, 2).

So far the entrapped metals for the isolated endohedral metallofullerenes (EMFs) are primarily limited to rare earth metals, whereas except group-IVB metals, whether it is possible to entrap other d-block transition metals remains unclear. Herein we report the successful entrapment of the group-VB transition metal vanadium(V) into fullerene cage, affording the heretofore unknown V-containing EMFs. Two novel V-containing EMFs--V(x)Sc(3-x)N@C80 (x = 1, 2)--were isolated, and their molecular structures were unambiguously determined by X-ray crystallography to be I(h)(7)-C80 cage entrapping the planar VSc2N/V2ScN clusters. V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) were further characterized by UV-vis-NIR and ESR spectroscopies and electrochemistry, revealing that the electronic and magnetic properties of V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) are tunable upon varying the number of entrapped V atoms (i.e., x value). The molecular structures and electronic properties of V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) were further compared with those of the reported analogous EMFs based on lanthanide metals and the adjacent group-IVB transition metal Ti, revealing the peculiarity of the group-VB transition metal V-based EMFs.

Carbon Tetragons as Definitive Spin Switches in Narrow Zigzag Graphene Nanoribbons.

Precise spatial control of the spin propagation channels is of fundamental and practical importance in future graphene-based spintronic devices. Here we use first-principles calculations to show that when narrow zigzag graphene nanoribbons are connected to form junctions or superlattices, properly placed square-shaped carbon tetragons not only serve as effective bundles of the two incoming spin edge channels, but also act as definitive topological spin switches for the two outgoing channels. The nanoribbon segments are largely drawn from different acene molecules. We further show that such spin switches can lift the degeneracy between the two spin propagation channels, which enables tunability of different magnetic states upon charge doping. Preliminary experimental supports for the realization of such tetragons connecting nanoribbon segments are also presented.

Singly Bonded Monoadduct rather than Methanofullerene: Manipulating the Addition Pattern of Trimetallic Nitride Clusterfullerene through One Endohedral Metal Atom Substitution.

Bingel-Hirsch reactions of trimetallic nitride clusterfullerenes (NCFs) generally yield methanofullerene (cyclopropane) adducts instead of singly bonded derivatives, which have been reported for monometallofullerenes. Herein, we report the synthesis and characterization of the Bingel-Hirsch derivative of a mixed metal nitride clusterfullerene (MMNCF) TiY2 N@Ih -C80 . Surprisingly, in contrast to the reported Bingel-Hirsch cyclopropane adducts of the analogous NCF Y3 N@Ih -C80 , the Bingel-Hirsch derivative of TiY2 N@Ih -C80 is the first singly bonded monoadduct (labeled as TiY2 N@C80 -Mono) to be reported, which was determined unambiguously by single-crystal X-ray crystallography. Besides, the reactivity of TiY2 N@Ih -C80 was found to be significantly improved relative to that of Y3 N@Ih -C80 . Upon substituting one endohedral yttrium (Y) atom of Y3 N@Ih -C80 with titanium (Ti), the Bingel-Hirsch derivative changes from the cyclopropane to the singly bonded monoadduct, revealing that not only the reactivity but also the addition pattern of NCFs can be manipulated simultaneously through one endohedral metal atom substitution.

Single-layer cadmium chalcogenides: promising visible-light driven photocatalysts for water splitting.

Recently, various single-layer materials have been explored as desirable photocatalyts for water splitting. In this work, based on extensive density functional theory calculations, we examine the geometric, electronic, optical, and potential photocatalytic properties of single-layer cadmium chalcogenides (CdX sheets, X = S, Se, and Te), which are cleaved from the (001) plane of the bulk wurtzite structure. The predicted formation energies have relatively low values and a suitable substrate (i.e. graphene) that can effectively stabilize CdX sheets, which imply that the fabrication and application of CdX sheets are highly possible in experiments. The calculated band gaps, band edge positions and optical absorptions clearly reveal that CdSe and CdTe sheets are promising photocatalysts for water splitting driven by visible light. Moreover, the band gaps and band edge positions of three CdX sheets can be effectively tuned by applying biaxial strain, which then can enhance their photocatalytic performance. These theoretical findings imply that CdX sheets are promising candidates for photocatalytic water splitting.