Bismuth Telluride Supported Sub-1 nm Polyoxometalate Cluster for High-Efficiency Thermoelectric Energy Conversion.

Size plays a crucial role in chemistry and material science. Subnanometer polyoxometalate (POM) clusters have gained attention in various fields, but their use in thermoelectrics is still limited. To address this issue, we propose the POM clusters as an effective second phase to enhance the thermoelectric properties of Bi0.4Sb1.6Te3. Thanks to their subnanometer size, POM clusters improve electrical transport behavior through the superposition of atomic orbitals and the interfacial scattering effect. Furthermore, their ultrasmall size strongly reduces thermal conductivity. Consequently, the introduction of a mere 0.1 mol % of POM into the Bi0.4Sb1.6Te3 matrix realizes a state-of-the-art zT value of 1.46 at 348 K, a 45% enhancement over Bi0.4Sb1.6Te3 (1.01), along with a maximum thermoelectric-conversion efficiency of the integrated module of 6.0%. The enhancement of carrier mobility and the suppression of thermal conduction achieved by introducing the subnanometer clusters hold promise for various applications, such as electronic devices and thermal management.

Electron-Delocalization Across High Surface Entropy Sub-1 nm Nanobelts Toward Enhanced Electrocatalytic Urea Oxidation.

Integration of inherently incompatible elements into a single sublattice, resulting in the formation of monophasic metal oxide, holds great scientific promise; it unveils that the overlooked surface entropy in subnanometer materials can thermodynamically facilitate the formation of homogeneous single-phase structures. Here a facile approach is proposed for synthesizing multimetallic oxide subnanometer nanobelts (MMO-PMA SNBs) by harnessing the potential of phosphomolybdic acid (PMA) clusters to capture inorganic nuclei and inhibiting their subsequent growth in solvothermal reactions. Experimental and theoretical analyses show that PMA in MMO-PMA SNBs not only aids subnanometer structure formation but also induces in situ modifications to catalytic sites. The electron transfer from PMA, coupled with the loss of elemental identity of transition metals, leads to electron delocalization, jointly activating the reaction sites. The unique structure makes pentametallic oxide (PMO-PMA SNBs) achieve a current density of 10 mA cm-2 at a low potential of 1.34 V and remain stable for 24 h at 10 mA cm-2 on urea oxidation reaction (UOR). The exceptional UOR catalytic activity suggests a potential for utilizing multimetallic subnanometer nanostructures in energy conversion and environmental remediation.

Fast Water Transport through Subnanometer Diameter Vertically Aligned Carbon Nanotube Membranes.

Small-diameter carbon nanotubes (CNTs) have outstanding mass-transport properties, especially enhanced water flow. Here, we report on water transport through the first macroscopic membranes with vertically oriented, subnanometer (0.8 nm) CNT pores, made by a scalable, solution-based method with electric-field alignment of bulk-grown single-wall CNTs (SWCNTs). After plasma etching to open pores, vertically aligned CNTs served as the primary pathway for liquid-water transport. The CNT membranes showed fast pressure-driven water transport, with up to 105-fold enhancement compared to no-slip Hagen-Poiseuille flow. Comparing 0.8 and 3 nm CNTs, we found that the hydrodynamic slip lengths increased with decreasing nanotube diameter, reaching 8.5 µm for the smaller-diameter CNTs. The results suggest that pressure-driven water transport in small-diameter CNTs is increasingly dominated by entrance resistance, thus becoming independent of nanotube length. Scalably fabricated membranes incorporating vertically aligned subnanometer CNT pores could have applications in water filtration, desalination, and energy harvesting.

Unraveling the Unique Strong Metal-Support Interaction in Titanium Dioxide Supported Platinum Clusters for the Hydrogen Evolution Reaction.

Strong metal-support interaction (SMSI) is crucial to modulating the nature of metal species, yet the SMSI behaviors of sub-nanometer metal clusters remain unknown due to the difficulties in constructing SMSI at cluster scale. Herein, we achieve the successful construction of the SMSI between Pt clusters and amorphous TiO2 nanosheets by vacuum annealing, which requires a relatively low temperature that avoids the aggregation of small clusters. In situ scanning transmission electron microscopy observation is employed to explore the SMSI behaviors, and the results reveal the dynamic rearrangement of Pt atoms upon annealing for the first time. The originally disordered Pt atoms become ordered as the crystallizing of the amorphous TiO2 support, forming an epitaxial interface between Pt and TiO2. Such a SMSI state can remain stable in oxidation environment even at 400 °C. Further investigations prove that the electron transfer from TiO2 to Pt occupies the Pt 5d orbitals, which is responsible for the disappeared CO adsorption ability of Pt/TiO2 after forming SMSI. This work not only opens a new avenue for constructing SMSI at cluster scale but also provides in-depth understanding on the unique SMSI behavior, which would stimulate the development of supported metal clusters for catalysis applications.

Regulating Li-Ion Transport through Ultrathin Molecular Membrane to Enable High-Performance All-Solid-State-Battery.

Solid-state lithium metal batteries with garnet-type electrolyte provide several advantages over conventional lithium-ion batteries, especially for safety and energy density. However, a few grand challenges such as the propagation of Li dendrites, poor interfacial contact between the solid electrolyte and the electrodes, and formation of lithium carbonate during ambient exposure over the solid-state electrolyte prevent the viability of such batteries. Herein, an ultrathin sub-nanometer porous carbon nanomembrane (CNM) is employed on the surface of solid-state electrolyte (SSE) that increases the adhesion of SSE with electrodes, prevents lithium carbonate formation over the surface, regulates the flow of Li-ions, and blocks any electronic leakage. The sub-nanometer scale pores in CNM allow rapid permeation of Li-ions across the electrode-electrolyte interface without the presence of any liquid medium. Additionally, CNM suppresses the propagation of Li dendrites by over sevenfold up to a current density of 0.7 mA cm-2 and enables the cycling of all-solid-state batteries at low stack pressure of 2 MPa using LiFePO4 cathode and Li metal anode. The CNM provides chemical stability to the solid electrolyte for over 4 weeks of ambient exposure with less than a 4% increase in surface impurities.

Self-Assembly of Polyoxometalate-Based Sub-1†nm Polyhedral Building Blocks into Rhombic Dodecahedral Superstructures.

Self-assembly of subnanometer (sub-1 nm) scale polyhedral building blocks can yield some superstructures with novel and interesting morphology as well as potential functionalities. However, achieving the self-assembly of sub-1 nm polyhedral building blocks is still a great challenge. Herein, through encapsulating the titanium-substituted polyoxometalate (POM, K7 PTi2 W10 O40 ) with tetrabutylammonium cations (TBA+ ), we first synthesized a sub-1 nm rhombic dodecahedral building block by further tailoring the spatial distribution of TBA+ on the POM. Molecular dynamics (MD) simulations demonstrated the eight TBA+ cations interacted with the POM cluster and formed the sub-1 nm rhombic dodecahedron. As a result of anisotropy, the sub-1 nm building blocks have self-assembled into rhombic dodecahedral POM (RD-POM) assemblies at the microscale. Benefiting from the regular structure, Br- ions, and abundant active sites, the obtained RD-POM assemblies exhibit excellent catalytic performance in the cycloaddition of CO2 with epoxides without co-catalysts. This work provides a promising approach to tailor the symmetry and structure of sub-1 nm building blocks by tuning the spatial distribution of ligands, which may shed light on the fabrication of superstructures with novel properties by self-assembly.

Precise Assembly of Polyoxometalates at Single-cluster Levels.

Polyoxometalate (POM) clusters with atomic precision structures are promising candidates construct functional nanomaterials via self-assembly. Non-covalent interactions at molecular levels can govern the self-assembly of POM clusters, for which the precise control of POM-based assemblies can be realized at single-cluster levels. This mini-review focuses on the synthesis and properties of POM-based nanostructures, including amphiphilic POM assemblies and co-assemblies of POM clusters and other subnanometer building blocks. Several synthetic strategies have been developed for rational control of POM-based assemblies in terms of morphologies, compositions and properties. 1D subnanometer POM assemblies demonstrate remarkable enhanced mechanical properties due to the topological interactions between nanowires and surroundings. The in-depth understanding of POM-based assemblies may help in the design of functional nanomaterials in fundamental perspectives and applications.

Non-planar Nest-like [Fe2 S2 ] Cluster Sites for Efficient Oxygen Reduction Catalysis.

Metal-nitrogen-carbon catalysts, as promising alternative to platinum-based catalysts for oxygen reduction reaction (ORR), are still highly expected to achieve better performance by modulating the composition and spatial structure of active site. Herein, we constructed the non-planar nest-like [Fe2 S2 ] cluster sites in N-doped carbon plane. Adjacent double Fe atoms effectively weaken the O-O bond by forming a peroxide bridge-like adsorption configuration, and the introduction of S atoms breaks the planar coordination of Fe resulting in greater structural deformation tension, lower spin state, and downward shifted Fe d-band center, which together facilitate the release of OH* intermediate. Hence, the non-planar [Fe2 S2 ] cluster catalyst, with a half-wave potential of 0.92 V, displays superior ORR activity than that of planar [FeN4 ] or [Fe2 N6 ]. This work provides insights into the co-regulation of atomic composition and spatial configuration for efficient oxygen reduction catalysis.

Cluster-Nuclei Coassembled One-Dimensional Subnanometer Heteronanostructures.

The cluster-nuclei coassembled strategy provides an impressive way to obtain 1D subnanometer heteronanostructures, including subnanometer nanowires and subnanometer nanobelts. These nanomaterials have diameters and thicknesses close to the size of a unit cell and exhibit excellent performance originating from multicomponent synergy. This Mini Review summarizes the recent progress of these novel functional nanomaterials, including their properties and applications in catalysis, energy conversion, and other fields. On the basis of previous studies, the development direction of cluster-nuclei coassembled 1D subnanometer materials is pointed out.

Oriented UiO-67 Metal-Organic Framework Membrane with Fast and Selective Lithium-Ion Transport.

Metal-organic frameworks (MOFs) membranes with high pore density and tunable pore size down to the subnanoscale exhibit great potential in ion separation when appropriately designed and prepared. By a washing-assisted secondary growing method, a well intergrown UiO-67 membrane with preferential growth along the [022] direction was synthesized on a polyvinylpyrrolidone (PVP)-modified AAO substrate. Because of the oriented growth of UiO-67 nanocrystals, highly interconnected ion-transporting channels are created throughout the UiO-67/AAO membrane capable of achieving an ultrahigh Li+ permeance of 27.01 mol m-2 h-1 as well as very decent Li+ /Mg2+ selectivity of up to 159.4. Molecular dynamics simulations reveal that the high selectivity is associated with the large disparity of the transport energy barrier between Li+ and Mg2+ , which is caused by different extents of ion dehydration in unique bimodal and oriented membrane channels.

Sub-Nanometer Confined Ions and Solvent Molecules Intercalation Capacitance in Microslits of 2D Materials.

The ion intercalation behavior in 2D materials is widely applied in energy storage, electrocatalysis, and desalination. However, the detailed effect of ions on the performance, combining the influence of interlayer force and the change of solvent shell, is far less well understood. Here the solvated alkali metal ions with different sizes are intercalated into the lattice of 2D materials with different spacings (Ti3 C2 Tx , δ-MnO2 , and reduced graphene oxide) to construct the intercalation model related with sub-nanometer confined ions and solvent molecules to further understand the intercalation capacitance. Based on electrochemical methods and density functional theory calculation, the ions lose the electrostatic shielding solvent shell or shorten the distance between the layers, resulting in a significant increase in capacitance. It is found that the intercalation capacitance arises from the diffusion of solvated ions and is controlled by quantum and electrochemical capacitance for desolvated ions. This effect of solvation structure on performance can be applied in a variety of electrochemical interface studies and provides a new research view for energy storage mechanisms.

Multifunctionalized Gold Sub-Nanometer Particles for Sensitizing Radiotherapy against Glioblastoma.

Glioblastoma is the most common lethal malignant intracranial tumor with a low 5-year survival rate. Currently, the maximal safe surgical resection, followed by high-dose radiotherapy (RT), is a standard treatment for glioblastoma. However, high-dose radiation to the brain is associated with brain injury and results in a high fatality rate. Here, integrated pharmaceutics (named D-iGSNPs) composed of gold sub-nanometer particles (GSNPs), blood-brain barrier (BBB) penetration peptide iRGD, and cell cycle regulator α-difluoromethylornithine is designed. In both simulated BBB and orthotopic murine GL261 glioblastoma models, D-iGSNPs are proved to have a beneficial effect on the BBB penetration and tumor targeting. Meanwhile, data from cell and animal experiments reveal that D-iGSNPs are able to sensitize RT. More importantly, the synergy of D-iGSNPs with low-dose RT can exhibit an almost equal therapeutic effect with that of high-dose RT. This study demonstrates the therapeutic advantages of D-iGSNPs in boosting RT, and may provide a facile approach to update the current treatment of glioblastoma.

Facile Size-Selective Defect Sealing in Large-Area Atomically Thin Graphene Membranes for Sub-Nanometer Scale Separations.

Atomically thin graphene with a high-density of precise subnanometer pores represents the ideal membrane for ionic and molecular separations. However, a single large-nanopore can severely compromise membrane performance and differential etching between pre-existing defects/grain boundaries in graphene and pristine regions presents fundamental limitations. Here, we show for the first time that size-selective interfacial polymerization after high-density nanopore formation in graphene not only seals larger defects (>0.5 nm) and macroscopic tears but also successfully preserves the smaller subnanometer pores. Low-temperature growth followed by mild UV/ozone oxidation allows for facile and scalable formation of high-density (4-5.5 × 1012 cm-2) useful subnanometer pores in the graphene lattice. We demonstrate scalable synthesis of fully functional centimeter-scale nanoporous atomically thin membranes (NATMs) with water (∼0.28 nm) permeance ∼23× higher than commercially available membranes and excellent rejection to salt ions (∼0.66 nm, >97% rejection) as well as small organic molecules (∼0.7-1.5 nm, ∼100% rejection) under forward osmosis.

Sub-Nanometer Thick Wafer-Size NiO Films with Room-Temperature Ferromagnetic Behavior.

Adding ferromagnetism into semiconductors attracts much attentions due to its potential usage of magnetic spins in novel devices, such as spin field-effect transistors. However, it remains challenging to stabilize their ferromagnetism above room temperature. Here we introduce an atomic chemical-solution strategy to grow wafer-size NiO thin films with controllable thickness down to sub-nanometer scale (0.92 nm) for the first time. Surface lattice defects break the magnetic symmetry of NiO and produce surface ferromagnetic behaviors. Our sub-nanometric NiO thin film exhibits the highest reported room-temperature ferromagnetic behavior with a saturation magnetization of 157 emu/cc and coercivity of 418 Oe. Attributed to wafer size, the easily-transferred NiO thin film is further verified in a magnetoresistance device. Our work provides a sub-nanometric platform to produce wafer-size ferromagnetic NiO thin films as atomic layer magnetic units in future transparent magnetoelectric devices.

Subnanometer Gold Clusters Adhere to Lipid A for Protection against Endotoxin-Induced Sepsis.

Endotoxicity originating from a dangerous debris (i.e., lipopolysaccharide, LPS) of Gram-negative bacteria is a challenging clinical problem, but no drugs or therapeutic strategies that can successfully address this issue have been identified yet. In this study, we report a subnanometer gold cluster that can efficiently block endotoxin activity to protect against sepsis. The endotoxin blocker consists of a gold nanocluster that serves as a flakelike substrate and a coating of short alkyl motifs that act as an adhesive to dock with LPS by compacting the intramolecular hydrocarbon chain-chain distance ( d-spacing) of lipid A, an endotoxicity active site that can cause overwhelming cytokine induction resulting in sepsis progression. Direct evidence showed the d-spacing values of lipid A to be decreased from 4.19 Å to either 3.85 or 3.54 Å, indicating more dense packing densities in the presence of subnanometer gold clusters. In terms of biological relevance, the concentrations of key pro-inflammatory NF-κB-dependent cytokines, including plasma TNF-α, IL-6, and IL-1ß, and CXC chemokines, in LPS-challenged mice showed a noticeable decrease. More importantly, we demonstrated that the treatment of antiendotoxin gold nanoclusters significantly prolonged the survival time in LPS-induced septic mice. The ultrasmall gold nanoclusters could target lipid A of LPS to deactivate endotoxicity by compacting its packing density, which might constitute a potential therapeutic strategy for the early prevention of sepsis caused by Gram-negative bacterial infection.

Synthesis of Highly Active Sub-Nanometer Pt@Rh Core-Shell Nanocatalyst via a Photochemical Route: Porous Titania Nanoplates as a Superior Photoactive Support.

Sub-nanometer Pt@Rh nanoparticles highly dispersed on MIL-125-derived porous TiO2 nanoplates are successfully prepared for the first time by a photochemical route, where the porous TiO2 nanoplates with a relatively high specific surface area play a dual role as both effective photoreductant and catalyst support. The resulting Pt@Rh/p-TiO2 can be utilized as a highly active catalyst.

Thermally Stable and Regenerable Platinum-Tin Clusters for Propane Dehydrogenation Prepared by Atom Trapping on Ceria.

Ceria (CeO2 ) supports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single-atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The single-atom Pt/CeO2 catalysts are stable during propane dehydrogenation, but are not selective for propylene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when tin (Sn) is added to CeO2 , the single-atom Pt catalyst undergoes an activation phase where it transforms into Pt-Sn clusters under reaction conditions. Formation of small Pt-Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO2 -supported Pt-Sn clusters are very stable, even during extended reaction at 680 °C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore, upon oxidation the Pt-Sn clusters readily revert to the atomically dispersed species on CeO2 , making Pt-Sn/CeO2 a fully regenerable catalyst.

Sub-1 nm Nickel Molybdate Nanowires as Building Blocks of Flexible Paper and Electrochemical Catalyst for Water Oxidation.

Sub-1 nm, extremely long nickel molybdate nanowires are synthesized based on a good/poor solvent system. The ultrathin nanowires can be hierarchically assembled into flexible, free-standing films with good mechanical properties. Compared with the large-size counterpart, nickel molybdate ultrathin nanowires display promising oxygen evolution reaction catalytic performance derived from the ultrathin feature.

Using the thickness of graphene to template lateral subnanometer gaps between gold nanostructures.

This work demonstrates the use of single-layer graphene as a template for the formation of subnanometer plasmonic gaps using a scalable fabrication process called "nanoskiving." These gaps are formed between parallel gold nanowires in a process that first produces three-layer thin films with the architecture gold/single-layer graphene/gold, and then sections the composite films with an ultramicrotome. The structures produced can be treated as two gold nanowires separated along their entire lengths by an atomically thin graphene nanoribbon. Oxygen plasma etches the sandwiched graphene to a finite depth; this action produces a subnanometer gap near the top surface of the junction between the wires that is capable of supporting highly confined optical fields. The confinement of light is confirmed by surface-enhanced Raman spectroscopy measurements, which indicate that the enhancement of the electric field arises from the junction between the gold nanowires. These experiments demonstrate nanoskiving as a unique and easy-to-implement fabrication technique that is capable of forming subnanometer plasmonic gaps between parallel metallic nanostructures over long, macroscopic distances. These structures could be valuable for fundamental investigations as well as applications in plasmonics and molecular electronics.

Identification of Subnanometric Ag Species, Their Interaction with Supports and Role in Catalytic CO Oxidation.

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO2, Ag/Mg/TiO2 and Ag/Ce/TiO2 catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals.