Single Atomic Species Research Articles

Precision Engineering of Nanorobots: Toward Single Atom Decoration and Defect Control for Enhanced Microplastic Capture

AbstractNanorobots are being received with a great attention for their move‐sense‐and‐act capabilities that often originate from catalytic decomposition of fuels. In the past decade, single‐atom engineering has demonstrated exceptional efficiency in catalysis, energy‐related technologies, and medicine. Here, a novel approach involving point defect engineering and the incorporation of platinum (Pt) single atoms and atomic level species onto the surface of titanium dioxide nanotubes (TiO2‐NT)‐based nanorobots is presented and its impact on the propulsion capabilities of the resulting nanorobots is investigated. The achievement of point defect engineering is realized through the annealing of TiO2‐NT in a hydrogen atmosphere yielding to the point‐defect decorated nanotube (TiO2‐HNT) nanorobots. Subsequently, the atomic level Pt species decorated TiO2 nanotube (TiO2‐SA‐NT) nanorobots are achieved through a wet‐chemical deposition process. Whereas TiO2‐SA‐NT nanorobots showed the highest negative photogravitaxis when irradiated with ultraviolet (UV) light, TiO2‐HNT nanorobots reached the highest velocity calculated in 2D. Both TiO2‐HNT and TiO2‐SA‐NT nanorobots demonstrated a pronounced affinity for microplastics, exhibiting the capability to irreversibly capture them. This pioneering approach utilizing point‐defect and atomic level Pt species nanorobotics is anticipated to pave the way for highly efficient solutions in the remediation of nano‐ and microplastics and related environmental technologies.

Imparting selective polysulfide conversion via geminal-atom moieties in lithium-sulfur batteries

Electrocatalysis in lithium-sulfur (Li–S) chemistry has readily stimulated extensive interests because of its irreplaceable role in realizing high-performance batteries. In this sense, achieving accelerated catalytic conversion of polysulfides is essential for the shuttle inhibition and kinetics promotion. Nonetheless, selective catalysis of sulfur reduction/evolution reaction via precise control over electrocatalytic mediators is still in its infancy. Moreover, specific catalytic role of the active metal center in dual-atom catalyst sites remains relatively unexplored. Herein, we utilize a salt-confined strategy to fabricate FeCo geminal-atom moieties dispersed on N-doped carbon support (FeCo-NC) for Li–S batteries throughout leveraging Fe and Co single-atom species with selective catalysis. The enhanced bidirectional conversion kinetics of polysulfide with the incorporation of Fe and Co atoms are uncovered throughout theoretical simulation and electrokinetic analysis. As a result, the FeCo-NC endows a rechargeable Li–S battery with excellent capacity retention rate of 98.6% after 100 cycles at 0.2 C and cycling stability with a decay rate of 0.033% per cycle over 2000 cycles at 3.0 C. More encouragingly, the assembled Li–S cell at a sulfur loading of 6.7 mg cm−2 can harvest an areal capacity of 7.13 mAh cm−2, signifying the rational design of geminal-atom mediators to dictate selective catalysis behaviors toward practical Li–S batteries.

High-efficient Ag(I) ion binding, Ag(0) nanoparticle loading, and iodine trapping in ultrastable benzimidazole-linked polymers

Interest in functional silver has rapidly grown over the years due to significant advances in separation, sensing, catalysis, and biomedical applications. Here we developed a new strategy to load single atomic silver species in the rigid and open unit of the fully conjugated benzimidazole-linked polymers (BILPs). Due to the well-defined chelating units of N-heterocycles, the Ag+ ion species can be coordinated by N ligands and stabilized in the atomic level without aggregating into nanoscale Ag clusters and nanoparticles. The obtained Ag+-BILP-101 exhibits a selective binding property of Ag+ ions from solutions. The ultrastable structure and the property of taking up metal species, endow BILPs with the advantages of functionalizing metal species. After the reduction by NaBH4, the Ag+ ions were transferred into Ag nanoparticles. The substantial and intrinsic porosity of BILPs also gives excellent accessibility to Ag species loaded in the frameworks. The plentiful N-heterocycles and loaded Ag species show a synergistic/coadsorption effect for iodine vapor, and the charge transfer from frameworks promotes the formation of iodide ions. The iodine capture capacities of Ag+-BILP-101 and Ag0-BILP-101 reach 3.3 g/g and 3.7 g/g at 80 ℃, and still maintain 3.2 g/g and 3.5 g/g at 150 ℃, respectively. After ethanol elution, the residual iodine/Ag molar ratios in Ag+/Ag0-BILP-101 samples are still more than one (about 1.5), suggesting their strong affinity toward iodine. This work highlights the excellent selective Ag+ ion binding and Ag species supporting properties of BILPs, which can extend to other porous organic framework platforms for various applications based on silver species-skeleton interactions.

Synergy of Pt Single Atom and Clusters toward Selective Glycerol Oxidation

AbstractSelective oxidation of excess glycerol to glyceric acid is a significant reaction but the reaction is inhibited by the C−H activation that has a high energy barrier. Here, we introduced Pt single atom species (Pt−O−Ce) into Pt/CeO2, which gave a high glycerol conversion of 90.9% with a high glyceric acid selectivity of 83.2% under the mild reaction conditions (T=100 °C, O2 flow of 5 mL min−1, and non‐alkaline). The C−H bond can be easily adsorbed and activated over Pt−O−Ce, which facilitated the selective oxidation of primary C−OH with a bidentate adsorption on Ptcluster, verified by the CO‐DRIFT, XPS, HRTEM, and in situ IR adsorption experiments. This synergy provided a way to design stable and active catalyst in biomass conversion.

Controlled-Release Mechanism Regulates Rhodium Migration and Size Redistribution Boosting Catalytic Methane Conversion

The migration of Rh atoms under a gas/reactive environment has a great impact on the dynamic restructuring and size redistribution of Rh catalysts in a variety of structure-sensitive catalytic reactions. To date, regulating the size distribution of active Rh species via controlled atomic migration remains challenging. Here, we show a controlled-release mechanism to regulate Rh atom migration through two-dimensional (2D) zeolite nanosheets, enabling quasi-continuous size redistribution of active Rh species from a single atom to nanoparticles with reversibility. Utilizing state-of-the-art in situ characterizations, a reversible aggregation/redispersion of Rh catalysts in/out of the 2D zeolite was directly observed under H2 or CO environment. The interplay between gas environment and support confinement was disclosed that substantially restrained the dynamic migration of Rh species and enabled a quasi-continuous control of Rh size distribution over a wide temperature window and size range. The catalytic testing for mild oxidation of methane demonstrated a volcano correlation of methanol activity with increasing particle size. The sub-nanometer Rh clusters with an average diameter of 0.9 nm exhibited the highest methanol activity of 39.7 molCH3OOH·molRh–1·h–1 with remarkable selectivity as high as 73.2%, far beyond that of single atom species and larger particles. Density functional theory calculations and electron paramagnetic resonance spectroscopy further revealed that this size dependency is related to the preferential formation of •OH radicals on Rh clusters with different sizes, which acts as a key initiator for methane activation. Our results thus provide a practical approach to synthesize size-specific metal catalysts via controlled atomic migration.

Light-Induced Defect Formation and Pt Single Atoms Synergistically Boost Photocatalytic H2 Production in 2D TiO2-Bronze Nanosheets

Ultrathin two-dimensional (2D) semiconductor nanosheets decorated with single atomic species (SAs) have recently attracted increasing attention due to their abundant surface-exposed reactive sites and maximum SAs binding capabilities thus lowering the catalyst cost, without sacrificing high performance for photocatalytic hydrogen (H2) production from water. Here, we present a strategy to prepare titanium dioxide-bronze nanosheets (TiO2-BNS) and H2-reduced TiO2 nanosheets (TiO2-HRNS) synthesized, characterized, and applied for photocatalytic H2 production. Surprisingly, black TiO2-HRNS show complete photo inactivity, while the TiO2-BNS-Pt0.05 nanohybrid shows excellent H2 production rate with a very low loading of 0.05 wt % Pt. TiO2-BNS-Pt0.05 presents around 10 and 99 times higher photocatalytic rate than pristine TiO2-BNS under solar and 365 nm UV-LED light irradiation, respectively. Due to the 2D morphology and the presence of abundant coordinating sites, the successful formation of widely dispersed Pt SAs was achieved. Most excitingly, the in situ formation of surface-exposed defect sites (Ti3+) was observed for TiO2-BNS under light illumination, suggesting their significant role in enhancing the H2 production rate. This self-activation and amplification behavior of TiO2-BNS can be extended to other 2D systems and applied to other photocatalytic reactions, thus providing a facile approach for fully utilizing noble metal catalysts via the successful formation of SAs.

A Progress Report on Laser Resonance Chromatography

Research on superheavy elements enables probing the limits of nuclear existence and provides a fertile ground to advance our understanding of the atom’s structure. However, experimental access to these atomic species is very challenging and often requires the development of new technologies and experimental techniques optimized for the study of a single atomic species. The Laser Resonance Chromatography (LRC) technique was recently conceived to enable atomic structure investigations in the region of the superheavy elements. Here, we give an update on the experimental progress and simulation results.

DFT insights into the electronic structure of Rh single-atom catalysts stabilized on the CeO2(1 1 1) surface

The insights into an Rh single-atom catalyst (SAC) stabilized on CeO2(111) surface is studied by employing DFT + U calculations on various structural models and comparing with the experimental spectral data from the literature. The possible models investigated include (Rh)ads, (RhOH)ads, (RhO2H2)ads, (RhO)ads, (RhO2)ads, (Rh)subCe, and (Rh)subO species. For a comparison with single Rh atom species, Rh4 cluster deposited on CeO2(111) surface is also investigated. Based on the calculated results of CO adsorption properties and the comparison with experimental data , we can figure out that single-atom Rh species stably reside on CeO2(111) surface as (Rh)ads, (RhOH)ads, (RhO)ads structures.

DFT insight into the high stability of single Pt atoms on the CeO2(111) surface

Introduction: Single Pt atom catalysts supported on CeO2(111) surfaces have attracted considerable attention in recent years due to their high reactivity and selectivity in important reactions, such as water–gas shift reactions for hydrogen production and CO oxidation. However, the geometrical and electronic structure of Pt/CeO2(111) at the atomic level is still not clearly understood. In this study, we aim to gain insight into the geometrical and electronic structure of a single Pt atom on the CeO2(111) surface. Methodology: Various single Pt atom species, including (Pt)ads, (PtOH)ads, (PtO)ads, (PtO2H2)ads, (PtO2)ads, (Pt)subCe, and (Pt)subO, deposited on the CeO2(111) surface were investigated by the DFT+U method with dispersion corrections. Furthermore, the CO molecule was adopted to evaluate the electronic structures of these single Pt atoms. In addition, the supported Pt3 cluster was applied as a metallic model to distinguish it from single Pt atom models. Results: By comparing the CO adsorption properties of single Pt atom models and Pt3 cluster models to those of experimental observations in the literature, the stretching frequency of CO on (PtO2)ads species agrees well with the experimental results, while the frequencies of CO on other single Pt atom structures and on Pt3 clusters largely differ from the experimental results. Conclusion: Based on the DFT calculated results, we conclude that the activity and high stability of single Pt atom species that were observed from the experiment are formed via the interaction between Pt and two extra O atoms on the CeO2(111) surface.

Quantifying the Amount of Single Atom Species in Supported Pt Catalysts Via Xrd

Quantifying the Amount of Single Atom Species in Supported Pt Catalysts Via Xrd

Accurate measurement of atomic magnetic moments by minimizing the tip magnetic field in STM-based electron paramagnetic resonance

Electron paramagnetic resonance (EPR) performed with a scanning tunneling microscope (STM) allows for probing the spin excitation of single atomic species with MHz energy resolution. One of the basic applications of conventional EPR is the precise determination of magnetic moments. However, in an STM, the local magnetic fields of the spin-polarized tip can introduce systematic errors in the measurement of the magnetic moments by EPR. We propose to solve this issue by finding tip-sample distances at which the EPR resonance shift caused by the magnetic field of the tip is minimized. To this end, we measure the dependence of the resonance field on the tip-sample distance at different radiofrequencies and identify specific distances for which the true magnetic moment is found. Additionally, we show that the tip's influence can be averaged out by using magnetically bistable tips, which provides a complementary method to accurately measure the magnetic moment of surface atoms using EPR STM.

Hydrophobic-to-hydrophilic affinity change of sub-monolayer water molecules at water–graphene interfaces

Investigating the interfacial properties between water and graphene is important, as the water–carbon interface influences various applications. Graphene is the fundamental unit of various carbon allotropes and composed of a single atomic species, although slight oxygen groups are normally attached on it. Therefore, adsorption properties on graphene is inevitable to advance fundamental understating on surface sciences. However, the detection of water adsorption on graphene is considerably hard, because amount of water is tiny and mass production of graphene to a detectable level using a standard adsorption apparatus is extremely difficult. We succeeded to detect water vapor adsorption on several layer graphene using lab-made adsorption apparatus with a quartz crystal microbalance technique. This study derives the properties of water on single-, triple-, and six-layer graphene from the contact angles of water droplets and the water vapor adsorption isotherms. The surface hydrophobicity evaluated from the contact angles and water vapor adsorption isotherms decreased in the following order: single-layer graphene > triple-layer graphene > six-layer graphene. At a relative pressure of 0.4 and water surface densities of 0.5–1.5 mg m −2 (corresponding to 2–5 water layers), the water stability was 1.0 kJ mol −1 smaller on single-layer graphene than on triple- and six-layer graphene. The weak interaction between water molecules and single-layer graphene induced slight water adsorption on graphene. As the water amount increased, the water–graphene interaction energy increased with steps of 0.17–0.18 mg m −2 (corresponding to nearly 50% of a water monolayer), and the water structure correspondingly transformed from cluster to layer. The structure transformation of adsorbed water induced the affinity change from hydrophobic to hydrophilic on graphene interfaces. The mechanism of water–graphene interfaces can be exploited in applications of graphene-based carbon nanomaterials. • Water contact angles of graphene were 57–80°, indicating hydrophobic interfaces. • Water vapor on single-layer graphene was rarely adsorbed below P/P 0 = 0.4. • Water-adsorbed structure was changed from cluster to layer form at 0.5 water layer. • Cluster-to-layer transformation triggers affinity change of water on graphene.

Autoheterodyne Characterization of Narrow-Band Photon Pairs.

We describe a technique to measure photon pair joint spectra by detecting the time-correlation beat note when nondegenerate photon pairs interfere at a beam splitter. The technique implements a temporal analog of the Ghosh-Mandel effect with one photon counter and a time-resolved Hong-Ou-Mandel interference with two. It is well suited to characterize pairs of photons, each of which can interact with a single atomic species, as required to study recently predicted photon-photon interaction in subwavelength atomic arrays. With this technique, we characterize photon pairs from cavity-enhanced parametric down-conversion with a bandwidth ≈ 5 MHz and frequency separation of ∼200 MHz near the D_{1} line of atomic Rb.

Revealing the Chemical Bonding in Adatom Arrays via Machine Learning of Hyperspectral Scanning Tunneling Spectroscopy Data.

The adatom arrays on surfaces offer an ideal playground to explore the mechanisms of chemical bonding via changes in the local electronic tunneling spectra. While this information is readily available in hyperspectral scanning tunneling spectroscopy data, its analysis has been considerably impeded by a lack of suitable analytical tools. Here we develop a machine learning based workflow combining supervised feature identification in the spatial domain and unsupervised clustering in the energy domain to reveal the details of structure-dependent changes of the electronic structure in adatom arrays on the Co3Sn2S2 cleaved surface. This approach, in combination with first-principles calculations, provides insight for using artificial neural networks to detect adatoms and classifies each based on their local neighborhood comprised of other adatoms. These structurally classified adatoms are further spectrally deconvolved. The unexpected inhomogeneity of electronic structures among adatoms in similar configurations is unveiled using this method, suggesting there is not a single atomic species of adatoms, but rather multiple types of adatoms on the Co3Sn2S2 surface. This is further supported by a slight contrast difference in the images (or slight size variation) of the topography of the adatoms.

Single atomic Co coordinated with N in microporous carbon for oxygen reduction reaction obtained from Co/2-methylimidazole anchored to Y zeolite as a template

Zeolite-templated carbons (ZTCs) composed of curved and single-layer graphene frameworks have uniform micropores (ca. 1.2 nm) and high surface areas (~4,000 m2/g). Owing to their outstanding properties originating from the porous structures, ZTCs have been used in many applications. In this work, we synthesized Co/N-doped ZTC (Co/N-ZTC) by complexing Co ion with 2-methylimidazole in Y zeolite to expand further utilization of ZTCs. The obtained Co/N-ZTC has a high surface area (ca. 2,000 m2/g) and single atomic Co species in CoNx moieties, which actually contributes to its excellent catalytic performance on oxygen reduction reaction. This synthetic concept is beneficial to fabricate single atomic transition metals coordinated with heteroatoms in ZTCs, which contributes to the progress of material design of single atomic catalyst–supported porous materials.

Origin of the Activity of Co–N–C Catalysts for Chemoselective Hydrogenation of Nitroarenes

The production of functionalized anilines by chemoselective hydrogenation of nitroarenes occupies an important position in the chemical industries. Recently, cobalt and nitrogen codoped carbon (Co–N–C) catalysts have been reported to show outstanding catalytic performance in this process, whereas the nature of their active sites is still at the center of intense debate. In this paper, based on the well-controlled experiments on four types of typical Co–N–C materials derived from different methodologies, several unusual generalities in the hydrogenation of nitroarenes are clearly revealed, including protic-solvent dependence, antipoisoning, acid resistance, and reversible deactivation. Further investigations indicate that the single-atom species Co–Nx are the main active sites of the Co–N–C catalysts in this chemoselective hydrogenation process. The present work sheds light on the mechanism study on the metal–N–C catalysts and further contributes to the rational design of the high-performance single-atom catalysts.

Modeling Interactions between Graphene and Heterogeneous Molecules

The Lennard–Jones potential and a continuum approach can be used to successfully model interactions between various regular shaped molecules and nanostructures. For single atomic species molecules, the interaction can be approximated by assuming a uniform distribution of atoms over surfaces or volumes, which gives rise to a constant atomic density either over or throughout the molecule. However, for heterogeneous molecules, which comprise more than one type of atoms, the situation is more complicated. Thus far, two extended modeling approaches have been considered for heterogeneous molecules, namely a multi-surface semi-continuous model and a fully continuous model with average smearing of atomic contribution. In this paper, we propose yet another modeling approach using a single continuous surface, but replacing the atomic density and attractive and repulsive constants in the Lennard–Jones potential with functions, which depend on the heterogeneity across the molecules, and the new model is applied to study the adsorption of coronene onto a graphene sheet. Comparison of results is made between the new model and two other existing approaches as well as molecular dynamics simulations performed using the LAMMPS molecular dynamics simulator. We find that the new approach is superior to the other continuum models and provides excellent agreement with molecular dynamics simulations.

Visualizing strange metallic correlations in the two-dimensional Fermi-Hubbard model with artificial intelligence

Strongly correlated phases of matter are often described in terms of straightforward electronic patterns. This has so far been the basis for studying the Fermi-Hubbard model realized with ultracold atoms. Here, we show that artificial intelligence (AI) can provide an unbiased alternative to this paradigm for phases with subtle, or even unknown, patterns. Long- and short-range spin correlations spontaneously emerge in filters of a convolutional neural network trained on snapshots of single atomic species. In the less well-understood strange metallic phase of the model, we find that a more complex network trained on snapshots of local moments produces an effective order parameter for the non-Fermi-liquid behavior. Our technique can be employed to characterize correlations unique to other phases with no obvious order parameters or signatures in projective measurements, and has implications for science discovery through AI beyond strongly correlated systems.

Rare-earth-platinum alloy nanoparticles in mesoporous zeolite for catalysis.

Platinum is a much used catalyst that, in petrochemical processes, is often alloyed with other metals to improve catalytic activity, selectivity and longevity1-5. Such catalysts are usually prepared in the form of metallic nanoparticles supported on porous solids, and their production involves reducing metal precursor compounds under a H2 flow at high temperatures6. The method works well when using easily reducible late transition metals, but Pt alloy formation with rare-earth elements through the H2 reduction route is almost impossible owing to the low chemical potential of rare-earth element oxides6. Here we use as support a mesoporous zeolite that has pore walls with surface framework defects (called 'silanol nests') and show that the zeolite enables alloy formation between Pt and rare-earth elements. We find that the silanol nests enable the rare-earth elements to exist as single atomic species with a substantially higher chemical potential compared with that of the bulk oxide, making it possible for them to diffuse onto Pt. High-resolution transmission electron microscopy and hydrogen chemisorption measurements indicate that the resultant bimetallic nanoparticles supported on the mesoporous zeolite are intermetallic compounds, which we find to be stable, highly active and selective catalysts for the propane dehydrogenation reaction. When used with late transition metals, the same preparation strategy produces Pt alloy catalysts that incorporate an unusually large amount of the second metal and, in the case of the PtCo alloy, show high catalytic activity and selectivity in the preferential oxidation of carbon monoxide in H2.

Carbon-based materials with tunable morphology confined Ni (0) and Ni-Nx active sites: Highly efficient selective hydrogenation catalysts

A key challenge faced by the chemical industry is to develop some inexpensive and efficient catalysts with defined sites for selective hydrogenation. Herein, carbon-based materials with specific morphology (Bulks, Nanotubes and Nanosheets, respectively) confined Ni (0) and Ni-Nx active sites have been synthesized by using one Nickel-organic framework (Ni-MOF) as the precursor in high-temperature treatments under argon atmosphere (designated as Ni (0)/Ni-N-CBK, Ni (0)/Ni–N-CNT and Ni (0)/Ni–N–CNS, respectively). Interestingly, the key to obtaining a specific morphology of the carbon-based materials is altering the amount of additional nitrogen source (dicyandiamide, DCDA). The catalytic performance towards α, β-unsaturated aldehyde hydrogenolysis demonstrates that the Ni (0)/Ni–N-CNT and Ni (0)/Ni–N–CNS possess superior selective hydrogenation activity and stability, which could be put down to the synergy effect of Ni (0) and single atomic Ni-Nx species.