The Sub-Nanometer Scale as a New Focus in Nanoscience

Ultra-Stable Ti Vacancies-Pt Atomic Clusters Structure on Titanium Oxycarbide Supports for High Current Density Hydrogen Evolution Reaction

Electrocatalysts with low Pt loading mass to achieve high current density (≥1 A cm-2) for hydrogen evolution reaction (HER) are still extremely challenging due to the limited intrinsic activity and weak stability of catalytic sites. The modulation of the electronic microenvironment of the support-Pt structure is crucial to enhance the intrinsic activity and stability of catalytic sites. Herein, an innovative titanium oxycarbide (TiVCO) solid solution with Ti vacancies (TiV) is proposed as support to anchor sub-nanoscale Pt atomic clusters (Pt ACs) and a stable "TiV-Pt ACs" structure is carefully designed. The electronic microenvironment of "TiV-Pt ACs" is indirectly optimized by an unsaturated C/O site near TiV. Thanks to this, novel "TiV-Pt ACs" structure (Pt@TiVCO) with low Pt loading mass (2.44 wt.%) exhibits excellent HER activity in acidic solution and the mass activity is more than ten times that of commercial 20% Pt/C at the overpotentials of 50 and 100 mV. Particularly, Pt@TiVCO shows amazing stability at high and fluctuating current density of 1-2 A cm-2 for 120 h. This work provides a novel and promising method to develop stable and low-loading Pt-based catalysts adapting to high current density.

Polymer nanocomposite dielectrics for capacitive energy storage

Owing to their excellent discharged energy density over a broad temperature range, polymer nanocomposites offer immense potential as dielectric materials in advanced electrical and electronic systems, such as intelligent electric vehicles, smart grids and renewable energy generation. In recent years, various nanoscale approaches have been developed to induce appreciable enhancement in discharged energy density. In this Review, we discuss the state-of-the-art polymer nanocomposites with improved energy density from three key aspects: dipole activity, breakdown resistance and heat tolerance. We also describe the physical properties of polymer nanocomposite interfaces, showing how the electrical, mechanical and thermal characteristics impact energy storage performances and how they are interrelated. Further, we discuss multi-level nanotechnologies including monomer design, crosslinking, polymer blending, nanofiller incorporation and multilayer fabrication. We conclude by presenting the current challenges and future opportunities in this field.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Reversible chirality inversion of an AuAgx-cysteine coordination polymer by pH change

Responsive chiral systems have attracted considerable attention, given their potential for diverse applications in biology, optoelectronics, photonics, and related fields. Here we show the reversible chirality inversion of an AuAgx-cysteine (AuAgx-cys) coordination polymer (CP) by pH changes. The polymer can be obtained by mixing HAuCl4 and AgNO3 with L-cysteine (or D-cysteine) in appropriate proportions in H2O (or other surfactant solutions). Circular dichroism (CD) spectrum is used to record the strong optical activity of the AuAg0.06-L-cys enantiomer (denoted as L0.06), which can be switched to that of the corresponding D0.06 enantiomer by alkalization (final dispersion pH > 13) and can be switched back after neutralization (final dispersion pH <8). Multiple structural changes at different pH values (≈9.6, ≈13) are observed through UV-Vis and CD spectral measurements, as well as other controlled experiments. Exploration of the CP synthesis kinetics suggests that the covalent bond formation is rapid and then the conformation of the CP materials would continuously evolve. The reaction stoichiometry investigation shows that the formation of CP materials with chirality inversion behavior requires the balancing between different coordination and polymerization processes. This study provides insights into the potential of inorganic stereochemistry in developing promising functional materials.

Subnanometric Bismuth Clusters Confined in Pyrochlore-Bi2 Sn2 O7 Enable Remarkable CO2 Photoreduction

The development of highly efficient photocatalysts for conversion of carbon dioxide (CO2 ) with water (H2 O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore-Bi2 Sn2 O7 frameworks, leading to the remarkable improvements of photocatalytic performances for CO2 reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 μmol g-1  h-1 has been achieved, more than 20-fold improvement compared with the pristine Bi2 Sn2 O7 (5.7 μmol g-1  h-1 ). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge-separation/electron-enrichment and adsorption/activation of CO2 molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO2 conversion into solar fuels.

A Computational Exploration of Exohedrally Transition Metal Doped Si94- Superatom Based Magnetic MSi9M' Clusters (M, M' = Sc(II) to Cu(II))

Nanosized clusters are drawing immense attention of the scientific community due to their size and composition dependent tunability of physical and chemical properties. Silicon nanoclusters are especially important because of their abundance and ample utility in the domains of electronics and semiconductor industry. Zintl phases of Si offer an excellent opportunity in the domain of nanocluster research owing to their superior stability and multifarious possibilities of tunability of electronic properties through doping with other elements. Doping silicon clusters with transition elements is a prevalent strategy to induce magnetic properties in such clusters. Although doping silicon clusters with single transition metal atoms can induce significant magnetism in nanoclusters, the dominant covalent interaction between silicon and the transition metal causes the magnetic moment to quench. The rational strategy of inducing a sustainable magnetic moment can be to introduce ferromagnetic interaction between two sites carrying nonvanishing magnetic moments. In the present work, such a possibility is explored in terms of the stability of the clusters and corresponding magnetic exchange coupling in them. The Si94-superatomic cluster is doped with two transition metal atoms exohedrally and the neutral clusters designed thereby are investigated computationally if they reduce or reinforce the high stability of the superatom and substantiate the possibility of obtaining nanosized magnetic units as building blocks of tunable materials for various applications.

One-pot synthesis of 3D surface-wrinkled PdAu nanospheres for robust alcohols electrocatalysis

Three dimensional (3D) noble-metal nanomaterials with special surface structures have been regarded as high-performance catalysts for alcohol oxidation on account of their superior thermal stability, electrical conductivity and large specific surface area. Although extensive efforts have been devoted to the preparation of 3D Pd-based catalysts with superior activity and stability, designing a simple, effective and eco-friendly method remains a challenge. Herein, we developed a facile one-step coreduction strategy to synthesize a series of 3D surface-wrinkled PdAu nanospheres (NSs) with tunable Pd/Au atomic ratios and found a universal method to prepare surface-wrinkled PdM (M = Au, Pt, Cu and Pb) NSs. Benefiting from the function of the surfactant cetyltrimethylammonium chloride (CTAC), the synthesized PdAu NSs with different composition possess abundant surface wrinkles, which is beneficial for exposing more electroactive centers. Attributed to the unique geometric morphology and optimized atomic ratio, the PdAu-2 NSs exhibited an optimal mass activity (MA) of 8103 mA mg-1 and 5113 mA mg-1 for the ethylene glycol oxidation reaction (EGOR) and ethanol oxidation reaction (EOR), which was 6.1 and 4.1 times that of commercial Pd/C, respectively. Moreover, the PdAu-2 NSs exhibited superb stability after long-term current-time (i-t) and cyclic voltammetry (CV) tests of the EGOR and EOR. This work not only provides new avenues to engineer PdAu NSs with enhanced electrocatalytic performance but also offers guidance for extending to more 3D PdM (M = other metals) NSs with novel morphology applied to fuel cell fields.

Hybrid Sub-1 nm Nanosheets of Co-assembled MnZnCuOx and Polyoxometalate Clusters as Anodes for Li-ion Batteries

Transition metal oxide (TMO) anode materials in lithium-ion batteries (LIBs) usually suffer from serious volume expansion leading to the pulverization of structures, further giving rise to lower specific capacity and worse cycling stability. Herein, by introducing polyoxometalate (POM) clusters into TMOs and precisely controlling the amount of POMs, the MnZnCuOx -phosphomolybdic acid hybrid sub-1 nm nanosheets (MZC-PMA HSNSs) anode is successfully fabricated, where the special electron rich structure of POMs is conducive to accelerating the migration of lithium ions on the anode to obtain higher specific capacity, and the non-covalent interactions between POMs and TMOs make the HSNSs possess excellent structural and chemical stability, thus exhibiting outstanding electrochemical performance in LIBs, achieving a high reversible capacity (1157 mAh g-1 at 100 mA g-1 ) and an admirable long-term cycling stability at low and high current densities.

Local Built-In Field at the Sub-nanometric Heterointerface Mediates Cascade Electrochemical Conversion of Lithium-sulfur Batteries

Heterogeneous catalytic mediators have been proposed to play a vital role in enhancing the multiorder reaction and nucleation kinetics in multielectron sulfur electrochemistry. However, the predictive design of heterogeneous catalysts is still challenging, owing to the lack of in-depth understanding of interfacial electronic states and electron transfer on cascade reaction in Li-S batteries. Here, a heterogeneous catalytic mediator based on monodispersed titanium carbide sub-nanoclusters embedded in titanium dioxide nanobelts is reported. The tunable catalytic and anchoring effects of the resulting catalyst are achieved by the redistribution of localized electrons caused by the abundant built-in fields in heterointerfaces. Subsequently, the resulting sulfur cathodes deliver an areal capacity of 5.6 mAh cm-2 and excellent stability at 1 C under sulfur loading of 8.0 mg cm-2 . The catalytic mechanism especially on enhancing the multiorder reaction kinetic of polysulfides is further demonstrated via operando time-resolved Raman spectroscopy during the reduction process in conjunction with theoretical analysis.

Mn-Incorporation-Induced Phase Transition in Bottom-Up Synthesized Colloidal Sub-1-nm Ni(OH)2 Nanosheets for Enhanced Oxygen Evolution Catalysis

Sub-1-nm structures are attractive for diverse applications owing to their unique properties compared to those of conventional nanomaterials. Transition-metal hydroxides are promising catalysts for oxygen evolution reaction (OER), yet there remains difficulty in directly fabricating these materials within the sub-1-nm regime, and the realization of their composition and phase tuning is even more challenging. Here we define a binary-soft-template-mediated colloidal synthesis of phase-selective Ni(OH)₂ ultrathin nanosheets (UNSs) with 0.9 nm thickness induced by Mn incorporation. The synergistic interplay between binary components of the soft template is crucial to their formation. The unsaturated coordination environment and favorable electronic structures of these UNSs, together with in situ phase transition and active site evolution confined by the ultrathin framework, enable efficient and robust OER electrocatalysis. They exhibit a low overpotential of 309 mV at 100 mA cm^-2 as well as remarkable long-term stability, representing one of the most high-performance noble-metal-free catalysts.

Gold nanoclusters with enhanced near-infrared emission and its application as sensors for biological molecules

Ultrasmall gold nanoclusters (NCs) have been engineered as a new kind of functional material due to their excellent photoluminescence properties. However, the synthesis of highly luminescent water-soluble nanoclusters with near-infrared (NIR) emission remains limited. Herein, we developed a pH-regulated strategy to facilitate the construction of self-assemblies with enhanced luminescence based on aggregation-induced emission (AIE) strategy. Using 2-mercaptobenzoic acid (MBA) as reductant and stabilizer, the original weakly luminescent AuNCs exhibited intense emission by adjusting pH controllably. The formation of compact organized nanostructures could effectively restrict the rotation and vibration of capping ligands by non-covalent interactions, which reduced the nonradiative relaxation from excited states and finally improved the emission properties of AuNCs. Moreover, the assemblies possess many intriguing features including bright NIR luminescence and excellent biocompatibility, which could be used as luminous probes in biological molecules sensing (tyrosinase (TYR) and dopamine (DA)) and promising candidates for cell imaging. This study provides a simple and feasible strategy for developing metal NCs-based smart optical materials in the field of bioscience.

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.

Freestanding Block Copolymer Membranes with Tunable Pore Sizes Promoted by Subnanometer Nanowires

Block copolymers (BCPs) have enduring appeal for its intriguing assembly behaviors. Nevertheless, the unsatisfactory mechanical properties of BCPs make it a problem to fabricate freestanding membranes and hindered practical applications. Herein, a freestanding membrane with tunable pore size is prepared simply by co-assembly of BCPs and subnanometer nanowires (SNWs), combining the abundant function of BCPs and prominent mechanical properties of SNWs. Benefited from synergy of the components and the hierarchical structure, the tensile strength of composite membrane is promoted by two orders of magnitude compared to that of BCPs. With the columnar pores aligning vertically to surfaces and the pore size regulated by processing conditions, the membranes exhibit precise size-selected effect in ultrafiltration of Au nanoparticles (Au NPs) and can distinct NPs with diameter difference as tiny as 5 nm, demonstrating the promising prospect in separation technology and even widespread fields.

Synergistic Mechanism of Sub-Nanometric Ru Clusters Anchored on Tungsten Oxide Nanowires for High-Efficient Bifunctional Hydrogen Electrocatalysis

The construction of strong interactions and synergistic effects between small metal clusters and supports offers a great opportunity to achieve high-performance and cost-effective heterogeneous catalysis, however, studies on its applications in electrocatalysis are still insufficient. Herein, it is reported that W₁₈ O₄₉ nanowires supported sub-nanometric Ru clusters (denoted as Ru SNC/W₁₈ O₄₉ NWs) constitute an efficient bifunctional electrocatalyst for hydrogen evolution/oxidation reactions (HER and HOR) under acidic condition. Microstructural analyses, X-ray absorption spectroscopy, and density functional theory (DFT) calculations reveal that the Ru SNCs with an average RuRu coordination number of 4.9 are anchored to the W₁₈ O₄₉ NWs via RuOW bonds at the interface. The strong metal-support interaction leads to the electron-deficient state of Ru SNCs, which enables a modulated RuH strength. Furthermore, the unique proton transport capability of the W₁₈ O₄₉ also provides a potential migration channel for the reaction intermediates. These components collectively enable the remarkable performance of Ru SNC/W₁₈ O₄₉ NWs for hydrogen electrocatalysis with 2.5 times of exchange current density than that of carbon-supported Ru nanoparticles, and even rival the state-of-the-art Pt catalyst. This work provides a new prospect for the development of supported sub-nanometric metal clusters for efficient electrocatalysis.

Regulating the Mechanical and Optical Properties of Polymer-based Nanocomposites by Sub-Nanowires

Sub-nanowires (SNWs) exhibit great potential applications in nanocomposites owing to their high specific surface area, high flexibility, and similarity to polymer chains in dimension, which are a good entry point to bridge inorganic materials and polymer materials. Herein, we synthesized hydroxyapatite sub-nanowires (HAP SNWs) and engineered hydroxyapatite sub-nanowires/polyimide (HSP) gels and films by simple mixing of HAP SNWs and polyimide (PI). Benefiting from the interactions between HAP SNWs and PI, these nanocomposites were a continuous hybrid network. As the increase of HAP SNWs contents, the viscosity and modulus of HSP gels were greatly improved by one or two orders of magnitude compared with PI gel. HSP films not only maintained high transparency but also gained high haze, as well as exhibited enhanced Young's modulus. Thus, both HSP gels and films developed in this work are promising for various applications in coatings and high-performance films.

How a Facet of a Nanocrystal Is Formed: The Concept of the Symmetry Based Kinematic Theory

Conventional nanocrystal (NC) growth mechanisms have overwhelmingly focused on the final exposed facets to explain shape evolution. However, how the final facets are formed from the initial nuclei or seeds, has not been specifically interrogated. In this concept paper, we would like to concentrate on this specific topic, and introduce the symmetry based kinematic theory (SBKT) to explain the formation and evolution of crystal facets. It is a crystallographic theory based on the classical crystal growth concepts developed to illustrate the shape evolution during the NC growth. The most important principles connecting the basic NC growth processes and morphology evolution are the preferential growth directions and the properties of kinematic waves. On the contrary, the final facets are just indications of how the crystal growth terminates, and their formation and evolution rely on the NC growth processes: surface nucleation and layer advancement. Accordingly, the SBKT could even be applied to situations where non-faceted NCs such as spheres are formed.

Alloying at a Subnanoscale Maximizes the Synergistic Effect on the Electrocatalytic Hydrogen Evolution

Bonding dissimilar elements to provide synergistic effects is an effective way to improve the performance of metal catalysts. However, as the properties become more dissimilar, achieving synergistic effects effectively becomes more difficult due to phase separation. Here we describe a comprehensive study on how subnanoscale alloying is always effective for inter-elemental synergy. Thirty-six combinations of both bimetallic subnanoparticles (SNPs) and nanoparticles (NPs) were studied systematically using atomic-resolution imaging and catalyst benchmarking based on the hydrogen evolution reaction (HER). Results revealed that SNPs always produce greater synergistic effects than NPs, the greatest synergistic effect was found for the combination of Pt and Zr. The atomic-scale miscibility and the associated modulation of electronic states at the subnanoscale were much different from those at the nanoscale, which was observed by annular-dark-field scanning transmission electron microscopy (ADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively.

A comparison of deep-learning-based inpainting techniques for experimental X-ray scattering

The implementation is proposed of image inpainting techniques for the reconstruction of gaps in experimental X-ray scattering data. The proposed methods use deep learning neural network architectures, such as convolutional autoencoders, tunable U-Nets, partial convolution neural networks and mixed-scale dense networks, to reconstruct the missing information in experimental scattering images. In particular, the recovered pixel intensities are evaluated against their corresponding ground-truth values using the mean absolute error and the correlation coefficient metrics. The results demonstrate that the proposed methods achieve better performance than traditional inpainting algorithms such as biharmonic functions. Overall, tunable U-Net and mixed-scale dense network architectures achieved the best reconstruction performance among all the tested algorithms, with correlation coefficient scores greater than 0.9980.

Topological Interaction among Molecular Cluster Assemblies Affords Tunable Viscoelasticity

In the assemblies of subnanoscale polyhedral oligomeric silsesquioxane, topological interaction makes the dominant contribution to their viscoelasticity with broad tunability. The assembly molecules are designed with dumbbell, triangular, and tetrahedral shapes, and they demonstrate an intrinsic glassy feature with neither long-range ordering nor supramolecular assembly formation in their bulk. Their viscoelasticity can be broadly tuned through the tailoring of molecular topologies, while the trimer and tetramer assemblies afford elastic moduli comparable to those of rubbers (∼0.5 MPa) even 80 K above their glass transition temperatures. Molecular dynamics studies reveal the topological constraints resulting from the topology-disrupted cooperative dynamics among the cluster assemblies, and this finally leads to the typical caging dynamics of the structural units and the elasticity of the bulk materials. Further broadband dielectric spectroscopy studies uncover the unique hierarchical relaxation dynamics, inspiring the strategy for the decoupling of mechanical strengths and toughness for the design of impact resistant materials.

Subnanometric Cu clusters on atomically Fe-doped MoO2 for furfural upgrading to aviation biofuels

Single cluster catalysts (SCCs) are considered as versatile boosters in heterogeneous catalysis due to their modifiable single cluster sites and supports. In this work, we report subnanometric Cu clusters dispersed on Fe-doped MoO₂ support for biomass-derived furfural upgrading. Systematical characterizations suggest uniform Cu clusters (composing four Cu atoms in average) are homogeneously immobilized on the atomically Fe-doped ultrafine MoO₂ nanocrystals (Cu₄/Fe_0.3Mo_0.7O₂@C). The atomic doping of Fe into MoO₂ leads to significantly modified electronic structure and consequently charge redistribution inside the supported Cu clusters. The as-prepared Cu₄/Fe_0.3Mo_0.7O₂@C shows superior catalytic performance in the oxidative coupling of furfural with C₃~C₁₀ primary/secondary alcohols to produce C₈~C₁₅ aldehydes/ketones (aviation biofuel intermediates), outperforming the conventionally prepared counterparts. DFT calculations and control experiments are further carried out to interpret the structural and compositional merits of Cu₄/Fe_0.3Mo_0.7O₂@C in the oxidative coupling reaction, and elucidate the reaction pathway and related intermediates.

Single Molecular Layer of Chitin Sub-Nanometric Nanoribbons: One-Pot Self-Exfoliation and Crystalline Assembly into Robust, Sustainable, and Moldable Structural Materials

Sub-nanometric materials (SNMs) represent a series of unprecedented size-/morphology-related properties applicable in theoretical research and diverse cutting-edge applications. However, in-depth investigation and wide utilization of organic SNMs are frequently hindered, owing to the complex synthesis procedures, insufficient colloidal stability, poor processability, and high cost. In this work, a low-cost, energy-efficient, convenient, effective, and scalable method is demonstrated for directly exfoliating chitin SNMs from their natural sources through a one-pot "tandem molecular intercalation" process. The resultant solution-like sample, which exhibits ribbon-like feature and contains more than 85% of the single molecular layer (thickness <0.6 nm), is capable of being solution-processed to different types of materials. Thanks to the sub-nanometric size and rich surface functional groups, chitin SNMs reveal versatile intriguing properties that rarely observe in their nano-counterparts (nanofibrils), e.g., crystallization-like assembly in the colloidal state and alcoplasticity/self-adhesiveness in the bulk aggregate state. The finding in this work not only opens a new avenue for the high value-added utilization of chitin, but also provides a new platform for both the theoretical study and practical applications of organic SNMs.

Copper and palladium bimetallic sub-nanoparticles were stabilized on modified polyaniline materials as an efficient catalyst to promote C-C coupling reactions in aqueous solution

Modified polyaniline self-stabilizing Cu/Pd bimetallic sub-nanocluster composite materials (Cu/Pd@Mod-PANI-3OH) are obtained through the three steps of oxidative polymerization, structural modification, and metal self-trapping. Palladium and copper are confined and coordinated in the composite material by participating in the reaction and are highly uniformly dispersed in the carrier in the form of sub-nano clusters. The Cu/Pd@Mod-PANI-3OH micro-nano reactor catalyst formed by the self-assembly of copper, palladium and polyaniline has excellent electronic effects, including a tunable microenvironment, metal-carrier and metal-metal synergy, and the stabilizing effect of metal by polyaniline materials. It can efficiently catalyse C-C coupling (Sonogashira and Suzuki) reactions in aqueous solution with high catalytic activity and a wide range of applications (40 substrates). The characterization test results show that the Cu/Pd@Mod-PANI-3OH composite material obtained by self-trapping metal is a kind of prefabricated catalyst. During the reaction process, the high-valent metals in the pre-catalyst are in situ converted into active zero-valent metals. The catalyst's pre-fabrication strategy well protects the catalytic active centre, largely prevents agglomeration of the metal particles (can be recycled 8 times) and exhibits excellent interfacial domain-limited catalysis. The research strategy of modulation of catalytic active sites to improve the properties of materials at the molecular and atomic level reported in this article will open a new door in the research of polyaniline materials.

Curvature and self-assembly of semi-conducting nanoplatelets

Semi-conducting nanoplatelets are two-dimensional nanoparticles whose thickness is in the nanometer range and controlled at the atomic level. They have come up as a new category of nanomaterial with promising optical properties due to the efficient confinement of the exciton in the thickness direction. In this perspective, we first describe the various conformations of these 2D nanoparticles which display a variety of bent and curved geometries and present experimental evidences linking their curvature to the ligand-induced surface stress. We then focus on the assembly of nanoplatelets into superlattices to harness the particularly efficient energy transfer between them, and discuss different approaches that allow for directional control and positioning in large scale assemblies. We emphasize on the fundamental aspects of the assembly at the colloidal scale in which ligand-induced forces and kinetic effects play a dominant role. Finally, we highlight the collective properties that can be studied when a fine control over the assembly of nanoplatelets is achieved.

Cadmium removal by FeOOH nanoparticles accommodated in biochar: Effect of the negatively charged functional groups in host

Metallic oxide nanoparticles (NPs) anchored in biochar provide a promising measure forward into the scaled-up application of these NPs in water treatment, and reducing the size of the dwelled NPs is expected to boost the adsorption performance of biochar-based composites because of the size and surface effect. Nevertheless, it is still of great challenge to regulate the size of the impregnated NPs due to their intrinsic self-agglomeration caused by high surface energy. In this study, we fabricated the charged biochar (C-BC) bearing high-density negatively charged groups (i.e., carboxyl and hydroxyl groups) via HNO₃ oxidization to load the model metal oxide FeOOH NPs. The average sizes of anchored FeOOH NPs were ultrasmall, ranging from 19.9 ± 1.5 to 3.1 ± 0.5 nm, and decreased with the increased amount of carboxyl and hydroxyl groups in C-BC. Whether in batch adsorption or fixed-bed column setting, adsorption of Cd(II) onto the as-made composites was greatly enhanced by carboxyl and hydroxyl groups in carrier. The normalized adsorption capacities of Cd(II) by ferric mass of the loaded FeOOH were 499.9-724.9 mg/g-Fe, approximately 18.6-27.1 and 2.51-3.64 folds over the bulky FeOOH and FeOOH-impregnated biochar. Our study results should provide a significant reference on how to acquire highly efficient biochar-based composites for water decontamination.

Recent Progress of Sub-Nanometric Materials in Photothermal Energy Conversion

Sub-nanometric materials (SNMs) are an attractive scope in recent years due to their atomic-level size and unique properties. Among various performances of SNMs, photothermal energy conversion is one of the most important ones because it can efficiently utilize the light energy. Herein, the SNMs with photothermal energy conversion behaviors and their applications are reviewed. First, a hydrothermal/solvothermal method for the synthesis of SNMs is systematically discussed, including the LaMer pathway and the cluster-nuclei coassembly pathway. Based on this synthetic strategy, many kinds of SNMs with different morphologies are successfully prepared, such as nanorings, nanowires, nanosheets, and nanobelts. These SNMs exhibit excellent photothermal performance under the laser or solar irradiation according to their different light absorption ranges. These enhanced absorption performances of SNMs are induced by the mechanism of plasmonic localized heating or nonradiative relaxation. Finally, the applications of the photothermal SNMs are illustrated. The SNMs with photothermal behaviors can be widely applied in the fields of solar vapor generation, biomedicine, and light-responsive composites construction. It is hoped that this review can provide new viewpoints and profound understanding to the SNMs in photothermal energy conversion.

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.

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 T_x , 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.

Chiral Conformation of Subnanometric Materials

Subnanometric materials (SNMs) refer to nanomaterials with sizes comparable to the diameter of common linear polymers or confined at the level of a single unit cell in at least one dimension, usually <1 nm. Conventional inorganic nanoparticles are usually deemed to be rigid, lacking self-adjustable conformation. In contrast, the size at subnanometric scale endows SNMs with flexibility analogous to polymers, resulting in their abundant self-adjustable conformation. It is noteworthy that some highly flexible SNMs can adjust their shape automatically to form chiral conformation, which is rare in conventional inorganic nanoparticles. Herein, we summarize the chiral conformation of SNMs and clarify the driving force behind their formation, in an attempt to establish a better understanding for the origin of flexibility and chirality at subnanometric scale. In addition, the general strategies for controlling the conformation of SNMs are elaborated, which might shed light on the efficient fabrications of chiral inorganic materials. Finally, the challenges facing this area as well as some unexplored topics are discussed.

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.

Polymer Topology Reinforced Synergistic Interactions among Nanoscale Molecular Clusters for Impact Resistance with Facile Processability and Recoverability

The intrinsic conflicts between mechanical performances and processability are main challenges to develop cost-effective impact-resistant materials from polymers and their composites. Herein, polyhedral oligomeric silsesquioxanes (POSSs) are integrated as side chains to the polymer backbones. The one-dimension (1D) rigid topology imposes strong space confinements to realize synergistic interactions among POSS units, reinforcing the correlations among polymer chains. The afforded composites demonstrate unprecedented mechanical properties with ultra-stretchability, high rate-dependent strength, superior impact-resistant capacity as well as feasible processability/recoverability. The hierarchical structures of the hybrid polymers enable the co-existence of multiple dynamic relaxations that are responsible for fast energy dissipation and high mechanical strengths. The effective synergistic correlation strategy paves a new pathway for the design of advanced cluster-based materials.

Solvent-Mediated Shell Dimension Reconstruction of Core@Shell PdAu@Pd Nanocrystals for Robust C1 and C2 Alcohol Electrocatalysis

The core@shell structure dimension of the Pd-based nanocrystals deeply impacts their catalytic properties for C1 and C2 alcohol oxidation reactions. However, the precise simultaneous control on the synthesis of core@shell nanocrystals with different shell dimensions is difficult, and most synthesis on Pd-based core@shell nanocatalysts involves the surfactants participation by multiple steps, thus leads to limited catalytic properties. Herein, for the first time, a facile one-step surfactant-free strategy is developed for shell dimension reconstruction of PdAu@Pd core@shell nanocrystals by altering volume ratios of mixed solvents. The Pd-based sunflower-like (SL) and coral grass-like (CGL) nanocrystals are obtained with different 2D hexagonal nanosheet assembles and 3D network shells, respectively. Benefitting from the clean surface shell of 2D ultrathin nanosheets structure, high atom utilization efficiency, and robust electronic effect. The PdAu@Pd SL achieves the ascendant methanol/ethanol/ethylene glycol oxidation reaction (MOR/EOR/EGOR) activities, much higher than Pd/C catalysts, as well as the improved antipoisoning ability. Notably, this one-step construction shell dimension of PdAu@Pd core@shell catalysts not only provide a significant reference for the improvement of surfactant-free synthetic routes, but also shed light on the advanced engineering on shell dimensions in core@shell nanostructures for electrocatalysis and so forth.

Single-Crystal Inorganic Helical Architectures Induced by Asymmetrical Defects in Sub-Nanometric Wires

Constructing single-crystal inorganic helical structures is a fascinating subject for a large variety of research fields. However, the driving force of self-coiling, particularly in helical architectures, still remains a major challenge. Here, using MoO_3-x sub-nanometric wires (SNWs) as an example, we identified that spontaneous helical architecture with different dimensional features is closely related with their surface asymmetrical defects. Specifically, the surface defects of SNWs are critical to produce the self-coiling process, thereby achieving the ordered helical conformations. Theoretical calculations further suggest that the formation of in-plane and out-of-plane coiling structures is determined by the asymmetrical distribution of the surface defects, and the inhomogeneous charge separation with strong Coulomb attraction dominates the different structural configurations. The resulting MoO_3-x SNW exhibits excellent photothermal behaviors in both aqueous solutions and hydrogel matrixes. Our study provides a novel protocol to achieve helical structure design for their future applications.

Superatomic solid solutions

In atomic solids, substitutional doping of atoms into the lattice of a material to form solid solutions is one of the most powerful approaches to modulating its properties and has led to the discovery of various metal alloys and semiconductors. Herein we have prepared solid solutions in hierarchical solids that are built from atomically precise clusters. Two geometrically similar metal chalcogenide clusters, Co₆Se₈(PEt₃)₆ and Cr₆Te₈(PEt₃)₆, were combined as random substitutional mixture, in three different ratios, in a crystal lattice together with fullerenes. This does not alter the underlying crystalline structure of the [cluster][C₆₀]₂ material, but it influences its electronic and magnetic properties. All three solid solutions showed increased electrical conductivities compared with either the Co- or Cr-based parent material, substantially so for two of the Co:Cr ratios (up to 100-fold), and lowered activation barriers for electron transport. We attribute this to the existence of additional energy states arising from the materials' structural heterogeneity, which effectively narrow transport gaps.

In Situ Anchoring Polymetallic Phosphide Nanoparticles within Porous Prussian Blue Analogue Nanocages for Boosting Oxygen Evolution Catalysis

The controllable synthesis of metal-based nanoclusters for heterogeneous catalytic reactions has received considerable attention. Nevertheless, manufacturing these architectures, while avoiding aggregation and retaining surface activity, remains challenging. Herein, for the first time we designed NiCoFe-Prussian blue analogue (PBA) nanocages as a support for in situ dispersion and anchoring of polymetallic phosphide nanoparticles (pMP-NPs). Benefiting from the porous surfaces and the synergistic effects between pMP-NPs and the cyano groups in PBA, the NiCoFe-P-NP@NiCoFe-PBA nanocages exhibit a significantly enhanced catalytic activity for oxygen evolution reaction (OER) with an overpotential of 223 mV at 10 mA cm^-2 and a Tafel slope of 78 mV dec^-1, outperforming the NiCoFe-PBA nanocubes, NiCoFe-P nanocages, NiFe-P-NP@NiFe-PBA nanocubes, and CoFe-P-NP@CoFe-PBA nanoboxes. This work not only offers the synthesis strategy of in situ anchoring pMP-NPs on PBA nanocages but also provides a new insight into optimized Gibbs free energy of OER by regulating electron transfer from metallic phosphides to PBA substrate.

Iron-Based Catalytically Active Complexes in Preparation of Functional Materials

Iron complexes are particularly interesting as catalyst systems over the other transition metals (including noble metals) due to iron’s high natural abundance and mediation in important biological processes, therefore making them non-toxic, cost-effective, and biocompatible. Both homogeneous and heterogeneous catalysis mediated by iron as a transition metal have found applications in many industries, including oxidation, C-C bond formation, hydrocarboxylation and dehydration, hydrogenation and reduction reactions of low molecular weight molecules. These processes provided substrates for industrial-scale use, e.g., switchable materials, sustainable and scalable energy storage technologies, drugs for the treatment of cancer, and high molecular weight polymer materials with a predetermined structure through controlled radical polymerization techniques. This review provides a detailed statement of the utilization of homogeneous and heterogeneous iron-based catalysts for the synthesis of both low and high molecular weight molecules with versatile use, focusing on receiving functional materials with high potential for industrial application.

Sub-nanoscaled Metal Oxide Cluster-Integrated Polymer Network for Quasi-Homogeneous Catalysis

The simultaneous improvement of catalytic activity and recyclability of metal oxides is exciting, however challenging, due to the paradox for particle size requirements. Herein, we report the design of polymer nanocomposites (PNCs) by covalently integrating a sub-nanoscaled metal oxide cluster (∼0.7 nm) into a polymer network with superelasticity. Due to the ultrasmall sizes of loaded clusters and the high swelling ratios (SRs) of PNCs, the swelled organogels from PNCs claim similar catalytic efficiencies to homogeneous catalysts, while their recyclability can be simply achieved after the catalytic reactions. Thanks to their robust mechanical properties, the PNCs can be processed into microgel particles for column reactors, enabling large-scale and continuous-flow catalysis.

Organic-Inorganic Hybrid Nanomaterials for Electrocatalytic CO2 Reduction

Electrochemical CO₂ reduction (ECR) to value-added chemicals and fuels is regarded as an effective strategy to mitigate climate change caused by CO₂ from excess consumption of fossil fuels. To achieve CO₂ conversion with high faradaic efficiency, low overpotential, and excellent product selectivity, rational design and synthesis of efficient electrocatalysts is of significant importance, which dominates the development of ECR field. Individual organic molecules or inorganic catalysts have encountered a bottleneck in performance improvement owing to their intrinsic shortcomings. Very recently, organic-inorganic hybrid nanomaterials as electrocatalysts have exhibited high performance and interesting reaction processes for ECR due to the integration of the advantages of both heterogeneous and homogeneous catalytic processes, attracting widespread interest. In this work, the recent advances in designing various organic-inorganic hybrid nanomaterials at the atomic and molecular level for ECR are systematically summarized. Particularly, the reaction mechanism and structure-performance relationship of organic-inorganic hybrid nanomaterials toward ECR are discussed in detail. Finally, the challenges and opportunities toward controlled synthesis of advanced electrocatalysts are proposed for paving the development of the ECR field.

Tiny Ir doping of sub-one-nanometer PtMn nanowires: highly active and stable catalysts for alcohol electrooxidation

One-dimensional (1D) Pt-based nanowires (NWs) materials serve as efficient catalysts for alcohol electrocatalysis. However, precisely tailoring their size towards sub-one-nanometer scale has been verified as an effective method for enhancing electrocatalytic properties, which is rarely studied. In this work, we developed a one-pot simple yet efficient method for synthesizing a kind of sub-one-nanometer tiny Ir-doped PtMn NWs. The prepared PtMnIr NWs have an ultrathin structure with a mean diameter of around only 0.97 nm (about 3-5 atomic thickness), which display large surface areas and promote superficial Pt atom utilization. With the robust tiny Ir incorporation, the composition-optimized Pt74Mn21Ir5 NWs showed enhanced mass activity, which was 1.51 and 1.53 times higher than those of non-Ir-doped Pt79Mn21 NWs for acidic ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). Moreover, benefiting from the atom-level ultrathin size and well-tuned ligand effect from Ir to PtMn, the EOR/MOR mass activities of sub-nanometric Pt74Mn21Ir5 NWs were 3.99- and 3.98-fold higher than those of Pt/C catalysts. More importantly, after successive EOR and MOR CV tests, the Ir-doped PtMn NWs still maintained 85.6% and 73.4% of the initial mass activity, which were much better than those of Pt79Mn21 NWs, Pt NWs, and Pt/C catalysts. This work could be extended to engineering other advanced materials with super sub-one-nanometer structure, which is beneficial for largely improving the catalytic performance.