Scalable Assembly of Crystalline Binary Nanocrystal Superparticles and Their Enhanced Magnetic and Electrochemical Properties

Bi-magnetic Mn3O4@Ni core-shell binary superparticles: Self-assembly preparation and magnetic behaviors

Binary superparticles formed by self-assembling two different types of nanoparticles may utilize the synergistic interactions and create advanced multifunctional materials. Bi-magnetic superparticles with a core-shell structure have unique properties due to their specific spatial configurations. Herein, we built Mn3O4@Ni core-shell binary superparticles via an emulsion self-assembly technique. The superparticles are generated with a spherical morphology, and have a typical average size of about 240 nm. By altering the ratio of the two magnetic nanoparticles, the thickness of Ni shells can be adjusted. Oleic acid ligands are crucial for the formation of core-shell structure. Magnetic analysis suggests that core-shell superparticles display dual-phase magnetic interactions, contrasting with the single-phase magnetic behaviors of commonly core-shell magnetic nanoparticles. The calculation on the effective magnetic anisotropy constants indicates that the presence of Ni shell layers reduces the dipole interactions among the Mn3O4 core particles. Due to the presence of Ni nanoparticle shells, the blocking temperature of Mn3O4 is reduced, while the Curie temperature of Mn3O4 is independent on Ni content. Tunable magnetic properties can be achieved by modulating the Ni nanoparticle shell thickness. This study offers insights for the development of core-shell superparticles with varied magnetic characteristics.

2D MXene/MBene Superlattice with Narrow Bandgap as Superior Electrocatalyst for High-Performance Lithium-Oxygen Battery

Lithium-oxygen (Li-O2) battery with large theoretical energy density (≈3500 Wh kg-1) is one of the most promising energy storage and conversion systems. However, the slow kinetics of oxygen electrode reactions inhibit the practical application of Li-O2 battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti3C2 MXene/Mo4/3B2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O2 battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti3C2 and Mo4/3B2-x will power the charge transfer at the interface from titanium (Ti) site in Ti3C2 to molybdenum (Mo) site in Mo4/3B2-x. This charge transfer increases the electron density in 4d orbital of Mo site and decreases the d-band center of Mo site, thus optimizing the adsorption of intermediate product LiO2 at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li2O2) improve the contact with electrode and facilitate the decomposition of Li2O2. Based on the above advantages, the Ti3C2 MXene/Mo4/3B2-x MBene superlattice-based Li-O2 battery exhibits large discharge specific capacity (17 167 mAh g-1), low overpotential (1.16 V), and superior cycling performance (475 cycles).

Icosahedral supracrystal assembly from polymer-grafted nanoparticles via interplay of interfacial energy and confinement effect

Self-assembly of nanoparticles (NPs) in drying emulsion droplets paves the way for intricate three-dimensional (3D) superstructures, given the myriad of control parameters for fine-tuning assembly conditions. With their substantial energetic dynamics that are acutely responsive to emulsion confinements, polymeric ligands incorporated into a system can enrich its structural diversity. Here, we demonstrate the assembly of soft polymer-grafted NPs into Mackay icosahedrons beyond spherical body-centered cubic (BCC) packing structures commonly observed for these soft spheres. This behavior is governed by the free energy minimization within emulsions through the interplay of the oil-water interfacial energy and confinement effect as demonstrated by the experimental observations of structural transitions between icosahedrons and BCC crystals and by corresponding free energy calculations. The anisotropic surface of the icosahedral supracrystals provides the capability of guiding the position of a secondary constituent, creating unique hybrid patchy icosahedrons with the potential to develop into multifunctional 3D clusters that combine the benefits of both polymers and conventional colloids.

Nanocrystal Assemblies: Current Advances and Open Problems

We explore the potential of nanocrystals (a term used equivalently to nanoparticles) as building blocks for nanomaterials, and the current advances and open challenges for fundamental science developments and applications. Nanocrystal assemblies are inherently multiscale, and the generation of revolutionary material properties requires a precise understanding of the relationship between structure and function, the former being determined by classical effects and the latter often by quantum effects. With an emphasis on theory and computation, we discuss challenges that hamper current assembly strategies and to what extent nanocrystal assemblies represent thermodynamic equilibrium or kinetically trapped metastable states. We also examine dynamic effects and optimization of assembly protocols. Finally, we discuss promising material functions and examples of their realization with nanocrystal assemblies.

Self-Assembled Preparation of Porous Nickel Phosphide Superparticles with Tunable Phase and Porosity for Efficient Hydrogen Evolution

Self-assembly of colloidal nanoparticles enables the easy building of assembly units into higher-order structures and the bottom-up preparation of functional materials. Nickel phosphides represent an important group of catalysts for hydrogen evolution reaction (HER) from water splitting. In this paper, the preparation of porous nickel phosphide superparticles and their HER efficiencies are reported. Ni and Ni2P nanoparticles are self-assembled into binary superparticles via an oil-in-water emulsion method. After annealing and acid etching, the as-prepared Ni-Ni2P binary superparticles change into porous nickel phosphide superparticles. The porosity and crystalline phase of the superparticles can be tuned by adjusting the ratio of Ni and Ni2P nanoparticles. The resulting porous superparticles are effective in driving HER under acidic conditions, and the modulation of porosity and phase further optimize the electrochemical performance. The prepared Ni3P porous superparticles not only possess a significantly enhanced specific surface area compared to solid Ni-Ni2P superparticles but also exhibit an excellent HER efficiency. The calculations based on the density functional theories show that the (110) crystal facet exhibits a relatively lower Gibbs free energy of hydrogen adsorption. This work provides a self-assembly approach for the construction of porous metal phosphide nanomaterials with tunable crystalline phase and porosity.

Controllable synthesis of star-shaped FeCoMnOx nanocrystals and their self-assembly into superlattices with low-packing densities

We present a novel method for synthesizing monodisperse, star-shaped FeCoMnOx nanocrystals with tunable concavity. Through liquid-air interfacial assembly, these colloidal nanostars can form two-dimensional superlattices, which are characterized by low packing densities. Notably, the ability to adjust the degree of concavity of nanostars allows for the tuning of the packing symmetry of the assembled superlattices.

High-Precision Calculation of Nanoparticle (Nanocrystal) Potentials of Mean Force and Internal Energies

Thermodynamic stability assessment of nanocrystal systems requires precise free energy calculations. This study highlights the importance of meticulous control over various factors, including the thermostat, time step, potential cutoff, initial configuration, sampling method, and overall simulation duration. Free energy computations in dry (solvent-free) systems are on the order of several hundred kBT but can be obtained with consistent accuracy. However, calculation of internal energies becomes challenging, as they are typically much larger in magnitude than free energies and exhibit significant noise and reduced reliability. To address this limitation, we propose a new internal energy estimate that drastically reduces the noise. We also present formulas that enable the optimization of the parameters of the harmonic bias potential for optimal convergence. Finally, we discuss the implications of these findings for the computation of free energies in nanocrystal clusters and superlattices.

On-Demand Assembly of Nanocrystals into a Superstructure Library in Co(OH)2 Single-Walled Nanotubes

The hierarchical self-assembly of colloidal particles facilitates the bottom-up manufacturing of metamaterials with synergistically integrated functionalities. Here, we define a modular assembly methodology that enables multinary co-assembly of nanoparticles in one-dimensional confined space. A series of isotropic and anisotropic nanocrystals such as plasmonic, metallic, visible, and near-infrared responsive nanoparticles as well as transition-metal phosphides can be selectively assembled within the single-walled Co(OH)2 nanotubes to achieve various increasingly sophisticated assembly systems, including unary, binary, ternary, and quaternary superstructures. Moreover, the selective assembly of distinct functional nanoparticles produces different integrated functional superstructures. This generalizable methodology provides predictable pathways to complex architectures with structural programming and customization that are otherwise inaccessible.

Entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres

Integrating binary mixtures of nanoparticles (NPs) into well-defined superstructures gives rise to novel collective properties depending on the shapes and individual properties of both species. In this paper, we studied the entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres. The results indicated that the conformational entropy of the polymer chains and the mixing entropy of the nanorods and nanospheres are two parameters that determine the formation of binary superlattices.

Polyhedral Colloidal Clusters Assembled from Amphiphilic Nanoparticles in Deformable Droplets

Polyhedral colloidal clusters assembled from functional inorganic nanoparticles have attracted great interest in both scientific research and applications. However, the spontaneous assembly of colloidal nanoparticles into polyhedral clusters with regular shape and tunable structures remains a grand challenges. Here, we successfully construct Mackay icosahedral and regular tetrahedral colloidal clusters assembled from gold nanoparticles grafted with a mixture of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) homopolymers by precisely tuning the interfacial interaction between the nanoparticles and the oil/water interface. By increasing the proportion of hydrophilic P2VP ligands on the surface of gold nanoparticles, the Mackay icosahedral clusters can transform into regular tetrahedral clusters in order to maximize the surface area of the polyhedral assembly. Furthermore, we reveal the formation mechanism of these regular polyhedral colloidal clusters. The formation of polyhedral colloidal clusters is not only dependent on the entropy but also determined by the interfacial free energy. This finding demonstrates an effective approach to organize nanoparticles into polyhedral colloidal clusters with potential applications in various fields.

Entropically Driven Fabrication of Binary Superlattices Assembled from Polymer-Tethered Nanocubes and Nanospheres

The spontaneous organization of two types of nanoparticles (NPs) with different shapes or properties into binary nanoparticle superlattices (BNSLs) with different configurations has recently attracted significant attention due to the coupling or synergistic effect of the two types of NPs, providing an efficient and general route for designing new functional materials and devices. Here, this work reports the co-assembly of polystyrene (PS) tethered anisotropic gold nanocubes (AuNCs@PS) and isotropic gold NPs (AuNPs@PS) via an emulsion-interface self-assembly strategy. The distributions and arrangements of the AuNCs and spherical AuNPs in the BNSLs can be precisely controlled by adjusting the effective size ratio (λ_eff ) of the effective diameter (d_eff ) of the embedded spherical AuNPs to the polymer gap size (L) between the neighboring AuNCs. λ_eff determines not only the change of the conformational entropy of the grafted polymer chains (∆S_con ) but also the mixing entropy (∆S_mix ) of the two types of NPs. During the co-assembly process, ∆S_mix tends to be as high as possible, and the -∆S_con tends to be as low as possible, leading to free energy minimization. As a result, well-defined BNSLs with controllable distributions of spherical and cubic NPs can be obtained by tuning λ_eff . This strategy can also be applied for other NPs with different shapes and atomic properties, thus largely enriching the BNSL library and enabling the fabrication of multifunctional BNSLs, which have potential applications in photothermal therapy, surface-enhanced Raman scattering, and catalysis.

Interlayer Sodium Plating/Stripping in Van der Waals-Layered Quantum Dot Superstructure

Assembling quantum dots (QDs) into van der Waals (vdW)-layered superstructure holds great promise for the development of high-energy-density metal anode. However, designing such a superstructure remains to be challenging. Here, a chemical-vapor Oriented Attachment (OA) growth strategy is proposed to achieve the synthesis of vdW-layered carbon/QDs hybrid superlattice nanosheets (Fe₇ S₈ @CNS) with a large vdW gap of 3 nm. The Fe₇ S₈ @CNS superstructure is assembled by carbon-coated Fe₇ S₈ (Fe₇ S₈ @C) QDs as building blocks. Interestingly, the Fe₇ S₈ @CNS exhibits two kinds of edge dislocations similar to traditional atom-layered materials, suggesting that Fe₇ S₈ @C QDs exhibit quasi-atomic growth behavior during the OA process. More interestingly, when used as host materials for sodium metal anodes, the Fe₇ S₈ @CNS shows the interlayer sodium plating/stripping behavior, which well suppresses Na dendrite growth. As a result, the cell with Fe₇ S₈ @CNS anode can keep stable cycling for 1000 h with a high Coulombic efficiency (CE) of ≈99.5% at 3.0 mA cm^-2 and 3.0 mAh cm^-2 . Noticeably, the Na@Fe₇ S₈ @CNS||Na₃ V₂ (PO₄ )₃ full cells can attain a capacity of 88.8 mAh g^-1 with a retention of 97% after 1000 cycles at 1.0 A g^-1 (≈8 C), showing excellent cycle stability for practical applications. This work enriches the vdW-layered QDs superstructure family and their application toward energy storage.

Discovery of two-dimensional binary nanoparticle superlattices using global Monte Carlo optimization

Binary nanoparticle (NP) superlattices exhibit distinct collective plasmonic, magnetic, optical, and electronic properties. Here, we computationally demonstrate how fluid-fluid interfaces could be used to self-assemble binary systems of NPs into 2D superlattices when the NP species exhibit different miscibility with the fluids forming the interface. We develop a basin-hopping Monte Carlo (BHMC) algorithm tailored for interface-trapped structures to rapidly determine the ground-state configuration of NPs, allowing us to explore the repertoire of binary NP architectures formed at the interface. By varying the NP size ratio, interparticle interaction strength, and difference in NP miscibility with the two fluids, we demonstrate the assembly of an array of exquisite 2D periodic architectures, including AB-, AB₂-, and AB₃-type monolayer superlattices as well as AB-, AB₂-, A₃B₅-, and A₄B₆-type bilayer superlattices. Our results suggest that the interfacial assembly approach could be a versatile platform for fabricating 2D colloidal superlattices with tunable structure and properties.

Amphiphilic Self-Assembly of Nanocrystals at Emulsion Interface Renders Fast and Scalable Quasi-Nanosheet Formation

Scalable assembly of nanocrystals (NCs) into two-dimensional (2D) nanosheets has aroused great interest, yet it remains under-explored. This is because current 2D assembly methods rely mainly on the use of solid- or liquid-air interfaces, which are inherently difficult for upscaling and thus lack practicability. Here, with a microemulsion-based amphiphilic assembly technique, we achieve a fast and scalable preparation of free-standing nanosheets comprising few-layer, tightly packed NCs, namely, quasi-nanosheets (quasi-NSs). Acetic acid, acting as both solvent and surface-treatment agent, is used to render the initially hydrophobic NCs amphiphilic, while simultaneously inducing the interfacial instability right after the assembly of NCs at the emulsion interface to afford quasi-NSs. This amphiphilic assembly method is applicable to a variety of NCs, and multicomponent quasi-NSs are also attainable upon coassembly of different types of NCs. In addition, the structural advantages of quasi-NSs in catalysis are showcased by using NiFe2O4 quasi-NSs as electrocatalysts for the oxygen evolution reaction. This work opens a new route for the scalable construction of 2D NC sheets with designated components and functions.

A supraparticle-based biomimetic cascade catalyst for continuous flow reaction

Robust millimeter-sized spherical particles with controlled compositions and microstructures hold promises of important practical applications especially in relation to continuous flow cascade catalysis. However, the efficient fabrication methods for producing such particles remain scare. Here, we demonstrate a liquid marble approach to fabricate robust mm-sized porous supraparticles (SPs) through the bottom-up assembly of silica nanoparticles in the presence of strength additive or surface interactions, without the need for the specific liquid-repellent surfaces used by the existing methods. As the proof of the concept, our method was exemplified by fabricating biomimetic cascade catalysts through assembly of two types of well-defined catalytically active nanoparticles. The obtained SP-based cascade catalysts work well in industrially preferred fixed-bed reactors, exhibiting excellent catalysis efficiency, controlled reaction kinetics, high enantioselectivity (99% ee) and outstanding stability (200~500 h) in the cascades of ketone hydrogenation-kinetic resolution and amine racemization-kinetic resolution. The excellent catalytic performances are attributed to the structural features, reconciling close proximity of different catalytic sites and their sufficient spatial isolation.

Robust millimeter-sized spherical particles with controlled compositions and microstructures hold promises of important practical applications. Here the authors develop a liquid marble method to facilely fabricate robust millimeter-sized supraparticles with controlled microstructures through the bottom-up assembly of silica nanoparticles.

Iron-Based Nanocatalysts for Electrochemical Nitrate Reduction

Nitrate has a high level of stability and persistence in water, endangering human health and aquatic ecosystems. Due to its high reliability and efficiency, the electrochemical nitrate reduction reaction (NO₃ RR) is regarded as the best available option for mitigating excess nitrate in water and wastewater, especially for the removal of trace levels of nitrate. One of the most critical factors in the electrochemical reduction are the catalysts, which directly affect the reaction efficiency of nitrate removal. Iron-based nanocatalysts, which have the advantages of nontoxicity, wide availability, and low cost, have emerged as a promising electrochemical NO₃ RR material in recent years. This review covers major aspects of iron-based nanocatalysts for electrochemical NO₃ RR, including synthetic methods, structural design, performance enhancement, electrocatalytic nitrate reduction test, and reduction mechanism. The recent progress of iron-based nanocatalysts for electrochemical NO₃ RR and the mechanism of functional advantages for modified structures are reviewed from the perspectives of loading, doping, and assembly strategies, in order to realize the conversion from pollutant nitrate to harmless nitrogen or ammonia and other sustainable products. Finally, challenges and future directions for the development of low-cost and highly-efficient iron-based nanocatalysts are explored.

Mismatched ligand density enables ordered assembly of mixed-dimensional, cross-species materials

The ordered coassembly of mixed-dimensional species-such as zero-dimensional (0D) nanocrystals and 2D microscale nanosheets-is commonly deemed impracticable, as phase separation almost invariably occurs. Here, by manipulating the ligand grafting density, we achieve ordered coassembly of 0D nanocrystals and 2D nanosheets under standard solvent evaporation conditions, resulting in macroscopic, freestanding hybrid-dimensional superlattices with both out-of-plane and in-plane order. The key to suppressing the notorious phase separation lies in hydrophobizing nanosheets with molecular ligands identical to those of nanocrystals but having substantially lower grafting density. The mismatched ligand density endows the two mixed-dimensional components with a molecular recognition-like capability, driving the spontaneous organization of densely capped nanocrystals at the interlayers of sparsely grafted nanosheets. Theoretical calculations reveal that the intercalation of nanocrystals can substantially reduce the short-range repulsions of ligand-grafted nanosheets and is therefore energetically favorable, while subsequent ligand-ligand van der Waals attractions induce the in-plane order and kinetically stabilize the laminate superlattice structure.

Nanocrystal Superparticles with Whispering-Gallery Modes Tunable through Chemical and Optical Triggers

Whispering-gallery microresonators have the potential to become the building blocks for optical circuits. However, encoding information in an optical signal requires on-demand tuning of optical resonances. Tuning is achieved by modifying the cavity length or the refractive index of the microresonator. Due to their solid, nondeformable structure, conventional microresonators based on bulk materials are inherently difficult to tune. In this work, we fabricate irreversibly tunable optical microresonators by using semiconductor nanocrystals. These nanocrystals are first assembled into colloidal spherical superparticles featuring whispering-gallery modes. Exposing the superparticles to shorter ligands changes the nanocrystal surface chemistry, decreasing the cavity length of the microresonator by 20% and increasing the refractive index by 8.2%. Illuminating the superparticles with ultraviolet light initiates nanocrystal photo-oxidation, providing an orthogonal channel to decrease the refractive index of the microresonator in a continuous fashion. Through these approaches, we demonstrate optical microresonators tunable by several times their free spectral range.

Structural Diversity in Multicomponent Nanocrystal Superlattices Comprising Lead Halide Perovskite Nanocubes

Nanocrystal (NC) self-assembly is a versatile platform for materials engineering at the mesoscale. The NC shape anisotropy leads to structures not observed with spherical NCs. This work presents a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr₃ NCs (and FAPbBr₃ NCs) coassembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr₃ nanocubes combined with Fe₃O₄ or NaGdF₄ spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB₂, quasi-ternary ABO₃, and ABO₆ types as well as previously known NaCl, AlB₂, and CuAu types. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF₄ nanodisks results in the orthorhombic SL resembling CaC₂ structure with pairs of CsPbBr₃ NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Oil-in-oil templated assembly results in the formation of binary supraparticles. Self-assembly at the liquid-air interface from the drying solution cast over the glyceryl triacetate as subphase yields extended thin films of SLs. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K.

2D FeP Nanoframe Superlattices via Space-Confined Topochemical Transformation

Self-assembled nanocrystal superlattices represent an emergent class of designer materials with potentially programmable functionalities. The ability to construct hierarchically structured nanocrystal superlattices with tailored geometry and porosity is critical for extending their applications. Here, 2D superlattices comprising monolayer FeP nanoframes are synthesized through a space-confined topochemical transformation approach induced by the Kirkendall effect, using carbon-coated Fe₃ O₄ nanocube superlattices as a precursor. The particle shape and the close-packed nature of Fe₃ O₄ nanocubes as well as the interconnected carbon layer network contribute to the topochemical transformation process. The resulting 2D FeP nanoframe superlattices possess several unique and advantageous structural features that are unavailable in conventional 3D nanocrystal superlattices, which make them particularly attractive for catalytic applications. As a proof of concept, such 2D FeP nanoframe superlattices are harnessed as highly efficient and durable electrocatalysts for the hydrogen evolution reaction, the performance of which is superior to that of most FeP-based catalysts reported previously. This topochemical transformation approach is scalable and general, representing a new route of designing hierarchical superlattices with highly open features that cannot be accessible by traditional self-assembly methods.

Highly Stable 3D Supercuboids to 2D ZnSe Nanosheets: Formation for a High-Efficiency Catalysis System

Assembling into desired and higher-ordered superstructures makes nanocrystals superior candidates in a wide range of applications. Herein, we report a facile but robust colloidal chemistry method to obtain three-dimensional (3D) supercuboids from two-dimensional (2D) ZnSe nanosheets. It is well-defined that the formation mechanism of the supercuboids is based on the interaction among ligands on the ZnSe nanosheets. The highly stable supercuboids are composed of nanosheets with thickness of approximately ∼1.4 nm, and the spacing between two nanosheets in the supercuboid is revealed as ∼1.2 nm. Importantly, 2D nanosheets are readily regained by an exfoliation process of 3D supercuboids in a high-temperature solvothermal process. Furthermore, the Au@ZnSe heteronanosheets could be obtained by Au nanoparticles (NPs) decorated on 2D nanosheets. As a proof-of-concept application, the ZnSe nanosheets are applied in the catalysis of the aldol condensation reaction, which shows the high isolated yield of chalcone up to 80%.

Nanoparticle Assembly as a Materials Development Tool

Nanoparticle assembly is a complex and versatile method of generating new materials, capable of using thousands of different combinations of particle size, shape, composition, and ligand chemistry to generate a library of unique structures. Here, a history of particle self-assembly as a strategy for materials discovery is presented, focusing on key advances in both synthesis and measurement of emergent properties to describe the current state of the field. Several key challenges for further advancement of nanoparticle assembly are also outlined, establishing a roadmap of critical research areas to enable the next generation of nanoparticle-based materials synthesis.

Using small-angle scattering to guide functional magnetic nanoparticle design

Magnetic nanoparticles offer unique potential for various technological, biomedical, or environmental applications thanks to the size-, shape- and material-dependent tunability of their magnetic properties. To optimize particles for a specific application, it is crucial to interrelate their performance with their structural and magnetic properties. This review presents the advantages of small-angle X-ray and neutron scattering techniques for achieving a detailed multiscale characterization of magnetic nanoparticles and their ensembles in a mesoscopic size range from 1 to a few hundred nanometers with nanometer resolution. Both X-rays and neutrons allow the ensemble-averaged determination of structural properties, such as particle morphology or particle arrangement in multilayers and 3D assemblies. Additionally, the magnetic scattering contributions enable retrieving the internal magnetization profile of the nanoparticles as well as the inter-particle moment correlations caused by interactions within dense assemblies. Most measurements are used to determine the time-averaged ensemble properties, in addition advanced small-angle scattering techniques exist that allow accessing particle and spin dynamics on various timescales. In this review, we focus on conventional small-angle X-ray and neutron scattering (SAXS and SANS), X-ray and neutron reflectometry, gracing-incidence SAXS and SANS, X-ray resonant magnetic scattering, and neutron spin-echo spectroscopy techniques. For each technique, we provide a general overview, present the latest scientific results, and discuss its strengths as well as sample requirements. Finally, we give our perspectives on how future small-angle scattering experiments, especially in combination with micromagnetic simulations, could help to optimize the performance of magnetic nanoparticles for specific applications.

Programming "Atomic Substitution" in Alloy Colloidal Crystals Using DNA

Although examples of colloidal crystal analogues to metal alloys have been reported, general routes for preparing 3D analogues to random substitutional alloys do not exist. Here, we use the programmability of DNA (length and sequence) to match nanoparticle component sizes, define parent lattice symmetry and substitutional order, and achieve faceted crystal habits. We synthesized substitutional alloy colloidal crystals with either ordered or random arrangements of two components (Au and Fe₃O₄ nanoparticles) within an otherwise identical parent lattice and crystal habit, confirmed via scanning electron microscopy and small-angle X-ray scattering. Energy dispersive X-ray spectroscopy reveals information regarding composition and local order, while the magnetic properties of Fe₃O₄ nanoparticles can direct different structural outcomes for different alloys in an applied magnetic field. This work constitutes a platform for independently defining substitution within multicomponent colloidal crystals, a capability that will expand the scope of functional materials that can be realized through programmable assembly.

Influence of Surfactant-Mediated Interparticle Contacts on the Mechanical Stability of Supraparticles

Colloidal supraparticles are micron-scale spherical assemblies of uniform primary particles, which exhibit emergent properties of a colloidal crystal, yet exist as a dispersible powder. A prerequisite to utilize these emergent functionalities is that the supraparticles maintain their mechanical integrity upon the mechanical impacts that are likely to occur during processing. Understanding how the internal structure relates to the resultant mechanical properties of a supraparticle is therefore of general interest. Here, we take the example of supraparticles templated from water/fluorinated oil emulsions in droplet-based microfluidics and explore the effect of surfactants on their mechanical properties. Stable emulsions can be generated by nonionic block copolymers consisting of a hydrophilic and fluorophilic block and anionic fluorosurfactants widely available under the brand name Krytox. The supraparticles formed in the presence of both types of surfactants appear structurally similar, but differ greatly in their mechanical properties. While the nonionic surfactant induces superior mechanical stability and ductile fracture behavior, the anionic Krytox surfactant leads to weak supraparticles with brittle fracture. We complement this macroscopic picture with Brillouin light spectroscopy that is very sensitive to the interparticle contacts for subnanometer-thick adsorbed layers atop of the nanoparticle. While the anionic Krytox does not significantly affect the interparticle bonds, the amphiphilic nonionic surfactant drastically strengthens these bonds to the point that individual particle vibrations are not resolved in the experimental spectrum. Our results demonstrate that seemingly subtle changes in the physicochemical properties of supraparticles can drastically impact the resultant mechanical properties.

Direct Probing of the Oxygen Evolution Reaction at Single NiFe2O4 Nanocrystal Superparticles with Tunable Structures

Due to the precisely controllable size, shape, and composition, self-assembled nanocrystal superlattices exhibit unique collective properties and find wide applications in catalysis and energy conversion. Identifying their intrinsic electrocatalytic activity is challenging, as their averaged properties on ensembles can hardly be dissected from binders or additives. We here report the direct measurement of the oxygen evolution reaction at single superparticles self-assembled from ∼8 nm NiFe₂O₄ and/or ∼4 nm Au nanocrystals using scanning electrochemical cell microscopy. Combined with coordinated scanning electron microscopy, it is found that the turnover frequency (TOF) estimated from single NiFe₂O₄ superparticles at 1.92 V vs RHE ranges from 0.2 to 11 s^-1 and is sensitive to size only when it is smaller than ∼800 nm in diameter. After the incorporation of Au nanocrystals, the TOF increases by ∼6-fold and levels off with further increasing Au content. Our study demonstrates the first direct single entity electrochemical study on individual nanocrystal superlattices with tunable structures and unravels the intrinsic structure-activity relationship that is not accessible by other methods.

Quantitative 3D real-space analysis of Laves phase supraparticles

Assembling binary mixtures of nanoparticles into crystals, gives rise to collective properties depending on the crystal structure and the individual properties of both species. However, quantitative 3D real-space analysis of binary colloidal crystals with a thickness of more than 10 layers of particles has rarely been performed. Here we demonstrate that an excess of one species in the binary nanoparticle mixture suppresses the formation of icosahedral order in the self-assembly in droplets, allowing the study of bulk-like binary crystal structures with a spherical morphology also called supraparticles. As example of the approach, we show single-particle level analysis of over 50 layers of Laves phase binary crystals of hard-sphere-like nanoparticles using electron tomography. We observe a crystalline lattice composed of a random mixture of the Laves phases. The number ratio of the binary species in the crystal lattice matches that of a perfect Laves crystal. Our methodology can be applied to study the structure of a broad range of binary crystals, giving insights into the structure formation mechanisms and structure-property relations of nanomaterials.

3D real-space analysis of thick nanoparticle crystals is non-trivial. Here, the authors demonstrate the structural analysis of a bulk-like Laves phase by imaging an off-stoichiometric binary mixture of hard-sphere-like nanoparticles in spherical confinement by electron tomography, enabling defect analysis on the single-particle level.

Anisotropic nanocrystal shape and ligand design for co-assembly

The use of nanocrystal (NC) building blocks to create metamaterials is a powerful approach to access emergent materials. Given the immense library of materials choices, progress in this area for anisotropic NCs is limited by the lack of co-assembly design principles. Here, we use a rational design approach to guide the co-assembly of two such anisotropic systems. We modulate the removal of geometrical incompatibilities between NCs by tuning the ligand shell, taking advantage of the lock-and-key motifs between emergent shapes of the ligand coating to subvert phase separation. Using a combination of theory, simulation, and experiments, we use our strategy to achieve co-assembly of a binary system of cubes and triangular plates and a secondary system involving two two-dimensional (2D) nanoplates. This theory-guided approach to NC assembly has the potential to direct materials choices for targeted binary co-assembly.

Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

A luminescent view of the clickable assembly of LnF3 nanoclusters

Nanoclusters (NCs) bridge the gap between atoms and nanomaterials in not only dimension but also physicochemical properties. Precise chemical and structural control, as well as clear understanding of formation mechanisms, have been important to fabricate NCs with high performance in optoelectronics, catalysis, nanoalloys, and energy conversion and harvesting. Herein, taking advantage of the close chemical properties of Ln³⁺ (Ln = Eu, Nd, Sm, Gd, etc.) and Gd³⁺–Eu³⁺ energy transfer ion-pair, we report a clickable LnF₃ nanoparticle assembly strategy allowing reliable fabrication of diversely structured NCs, including single-component, dimeric, core-shelled/core-shell-shelled, and reversely core-shelled/core-shell-shelled, particularly with synergized optical functionalities. Moreover, the purposely-embedded dual luminescent probes offer great superiority for in situ and precise tracking of tiny structural variations and energy transfer pathways within complex nanoarchitectures.

Precisely controlling the chemical composition and structure of nanoclusters is an ongoing challenge. Here, the authors report a clickable assembly strategy to construct widely varied lanthanide nanoclusters with synergized optical functionalities.

Self-assembly of colloidal inorganic nanocrystals: nanoscale forces, emergent properties and applications

The self-assembly of colloidal nanoparticles has made it possible to bridge the nanoscopic and macroscopic worlds and to make complex nanostructures. The nanoparticle-mediated assembly enables many potential applications, from biodetection and nanomedicine to optoelectronic devices. Properties of assembled materials are determined not only by the nature of nanoparticle building blocks, but also by spatial positions of nanoparticles within the assemblies. A deep understanding of nanoscale interactions between nanoparticles is a prerequisite to controlling nanoparticle arrangement during assembly. In this review, we present an overview of interparticle interactions governing their assembly in a liquid phase. Considerable attention is devoted to examples that illustrate nanoparticle assembly into ordered superstructures using different types of building blocks, including plasmonic nanoparticles, magnetic nanoparticles, lanthanide-doped nanophosphors, and quantum dots. We also cover the physicochemical properties of nanoparticle ensembles, especially those arising from particle coupling effects. We further discuss future research directions and challenges in controlling self-assembly at a level of precision that is most crucial to technology development.

Self-limiting self-assembly of supraparticles for potential biological applications

Nanotechnology has largely spurred the development of biological systems by taking advantage of the unique chemical, physical, optical, magnetic, and electrical properties of nanostructures. Self-limiting self-assembly of supraparticles produce new nanostructures and display great potential to create biomimicking nanostructures with desired functionalities. In this minireview, we summarize the recent developments and outstanding achievements of colloidal supraparticles, such as the driving forces for self-limiting self-assembly of supraparticles and properties of constructed supraparticles. Their application values in biological systems have also been illustrated.

Binary Nanoparticle Superlattices for Plasmonically Modulating Upconversion Luminescence

Engineering a facile and controllable approach to modulate the spectral properties of lanthanide-doped upconversion nanoparticles (UCNPs) is always an ongoing challenge. Herein, long-range ordered, distinct two-dimensional (2D) binary nanoparticle superlattices (BNSLs) composed of NaREF₄ :Yb/Er (RE = Y and Gd) UCNPs and plasmonic metallic nanoparticles (Au NPs), including AB, AB₃ , and AB₁₃ lattices, are fabricated via a slow evaporation-driven self-assembly to achieve plasmonic modulation of upconversion luminescence (UCL). Optical measurements reveal that typical red-green UCL from UCNPs can be effectively modulated into reddish output in BNSLs, with a drastically shortened lifetime. Notably, for AB₃ - and AB₁₃ -type BNSLs with more proximal Au NPs around each UCNP, modified UCL with fine-structured spectral lineshape is observed. These differences could be interpreted by the interplay of collective plasmon resonance introduced by 2D periodic Au arrays and spectrally selective energy transfer between UCNPs and Au. Thus, fabricating UCNP-Au BNSLs with desired lattice parameters and NP configurations could be a promising way to tailor the UCL through controlled plasmonic modulation.

Surface engineering of magnetic iron oxide nanoparticles by polymer grafting: synthesis progress and biomedical applications

Magnetic iron oxide nanoparticles (IONPs) have wide applications in magnetic resonance imaging (MRI), biomedicine, drug delivery, hyperthermia therapy, catalysis, magnetic separation, and others. However, these applications are usually limited by irreversible agglomeration of IONPs in aqueous media because of their dipole-dipole interactions, and their poor stability. A protecting polymeric shell provides IONPs with not only enhanced long-term stability, but also the functionality of polymer shells. Therefore, polymer-grafted IONPs have recently attracted much attention of scientists. In this tutorial review, we will present the current strategies for grafting polymers onto the surface of IONPs, basically including "grafting from" and "grafting to" methods. Available functional groups and chemical reactions, which could be employed to bind polymers onto the IONP surface, are comprehensively summarized. Moreover, the applications of polymer-grafted IONPs will be briefly discussed. Finally, future challenges and perspectives in the synthesis and application of polymer-grafted IONPs will also be discussed.

Self-assembly of anisotropic nanoparticles into functional superstructures

Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technological applications. In this field, anisotropic NPs with size- and shape-dependent physical properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technological applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the experimental techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.

Boron doping-induced interconnected assembly approach for mesoporous silicon oxycarbide architecture

Despite desirable progress in various assembly tactics, the main drawback associated with current assemblies is the weak interparticle connections limited by their assembling protocols. Herein, we report a novel boron doping-induced interconnection-assembly approach for fabricating an unprecedented assembly of mesoporous silicon oxycarbide nanospheres, which are derived from periodic mesoporous organosilicas. The as-prepared architecture is composed of interconnected, strongly coupled nanospheres with coarse surfaces. Significantly, through delicate analysis of the as-formed boron doped species, a novel melt-etching and nucleation-growth mechanism is proposed, which offers a new horizon for the developing interconnected assembling technique. Furthermore, such unique strategy shows precise controllability and versatility, endowing the architecture with tunable interconnection size, surface roughness and switchable primary nanoparticles. Impressively, this interconnected assembly along with tunable surface roughness enables intrinsically dual (both structural and interfacial) stable characteristics, achieving extraordinary long-term cycle life when used as a lithium-ion battery anode.

Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy

Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.

Shape-directed self-assembly of nanodumbbells into superstructure polymorphs

Self-assembly of colloidal nanoparticles into ordered superstructures provides a promising route to create novel/enhanced functional materials. Much progress has been made in self-assembly of anisotropic nanoparticles, but the complexity and tunability of superstructures remain restricted by their available geometries. Here we report the controlled packing of nanodumbbells (NDs) with two spherical lobes connected by one rod-like middle bar into varied superstructure polymorphs. When assembled into two-dimensional (2D) monolayer assemblies, such NDs with specific shape parameters could form orientationally ordered degenerate crystals with a 6-fold symmetry, in which these NDs possess no translational order but three allowed orientations with a rotational symmetry of 120 degrees. Detailed analyses identify the distinct roles of subunits in the ND assembly: the spherical lobes direct NDs to closely assemble together into a hexagonal pattern, and the rod-like connection between the lobes endows NDs with this specific orientational order. Such intralayer assembly features are well maintained in the two-layer superstructures of NDs; however, the interlayer stackings could be adjusted to produce stable bilayer superstructures and a series of metastable moiré patterns. Moreover, in addition to horizontal alignment, these NDs could gradually stand up to form tilted or even vertical packing based on the delicate control over the liquid-liquid interface and ND dimensions. This study provides novel insights into creating superstructures by controlling geometric features of nanoscale building blocks and may spur their novel applications.

Assembly by solvent evaporation: equilibrium structures and relaxation times

We present a study describing the dynamics and equilibrium of the assembly of nanostructures by solvent evaporation. We first consider N nanocrystals stabilized by capping ligands in a spherical droplet of liquid solvent coexisting with its gas and show that, as the liquid solvent evaporates slowly, NCs crystallize into clusters of high symmetry based on tetrahedral and octahedral units: tetrahedron (N = 4), octahedron (N = 6), icosahedron (N = 13), Archimedean truncated tetrahedron (N = 16) and Z₂₀ (N = 21). We derive explicit formulas for the process and rigorously compute relaxation times, which drastically increase when the packing parameter reaches the hard-sphere liquid-solid transition η = 0.49. This result shows that contrary to what occurs in an evaporation of a single component system, the relaxation times are not determined by the diffusion constant of the vapor, but rather, are dominated by the residence time of solvent molecules trapped within the capping ligands. Our theory provides a number of predictions that enable the design of new structures while improving the control and quality of their assembly.

Facile synthesis of PdFe alloy tetrahedrons for boosting electrocatalytic properties towards formic acid oxidation

The controllable synthesis of multi-metal nanocrystals with a tetrahedral shape is significant for constructing high-efficiency electrocatalysts. However, due to the great distinction among the thermodynamic reduction potentials of different metal precursors, it is difficult to achieve tetrahedron-shaped alloy nanocrystals with a uniform {111} crystal surface and low surface energy. Herein, we reported a one-pot hydrothermal synthetic strategy to achieve high-yield PdFe alloy tetrahedrons. The unique structure endowed an impressive surface area-to-volume ratio, well distribution of Pd and Fe sites, and essential electronic effects, due to which they could be employed as formic acid oxidation reaction (FAOR) catalysts. As expected, the PdFe alloy tetrahedrons exhibited 4.8 and 2.4 times higher mass activity (595.8 A g-1) and specific activity (33.4 A m-2) compared to commercial Pd black, respectively; they also showed enhanced electrocatalytic stability and good resistance to CO poisoning. This work demonstrates the potential applications of bimetal Pd-based tetrahedrons as promising anode catalysts in a direct formic acid fuel cell.

Colloidal Self-Assembly of Inorganic Nanocrystals into Superlattice Thin-Films and Multiscale Nanostructures

The self-assembly of colloidal inorganic nanocrystals (NCs) offers tremendous potential for the design of solution-processed multi-functional inorganic thin-films or nanostructures. To date, the self-assembly of various inorganic NCs, such as plasmonic metal, metal oxide, quantum dots, magnetics, and dielectrics, are reported to form single, binary, and even ternary superlattices with long-range orientational and positional order over a large area. In addition, the controlled coupling between NC building blocks in the highly ordered superlattices gives rise to novel collective properties, providing unique optical, magnetic, electronic, and catalytic properties. In this review, we introduce the self-assembly of inorganic NCs and the experimental process to form single and multicomponent superlattices, and we also describe the fabrication of multiscale NC superlattices with anisotropic NC building blocks, thin-film patterning, and the supracrystal formation of superlattice structures.

Free Energy Landscape of Colloidal Clusters in Spherical Confinement

The structure of finite self-assembling systems depends sensitively on the number of constituent building blocks. Recently, it was demonstrated that hard sphere-like colloidal particles show a magic number effect when confined in emulsion droplets. Geometric construction rules permit a few dozen magic numbers that correspond to a discrete series of completely filled concentric icosahedral shells. Here, we investigate the free energy landscape of these colloidal clusters as a function of the number of their constituent building blocks for system sizes up to several thousand particles. We find that minima in the free energy landscape, arising from the presence of filled, concentric shells, are significantly broadened, compared to their atomic analogues. Colloidal clusters in spherical confinement can flexibly accommodate excess particles by ordering icosahedrally in the cluster center while changing the structure near the cluster surface. In between these magic number regions, the building blocks cannot arrange into filled shells. Instead, we observe that defects accumulate in a single wedge and therefore only affect a few tetrahedral grains of the cluster. We predict the existence of this wedge by simulation and confirm its presence in experiment using electron tomography. The introduction of the wedge minimizes the free energy penalty by confining defects to small regions within the cluster. In addition, the remaining ordered tetrahedral grains can relax internal strain by breaking icosahedral symmetry. Our findings demonstrate how multiple defect mechanisms collude to form the complex free energy landscape of colloidal clusters.

Tailoring the Assembly of Iron Nanoparticles in Carbon Microspheres toward High-Performance Electrocatalytic Denitrification

Electrocatalytic denitrification is considered as the most promising technology to transform nitrates to nitrogen gas in sewage so far. Although noble metal-based catalysts as a cathode material have reached decent removal capacity of nitrate, the high cost is the main hamper of electrocatalytic reduction. Therefore, the development of alternative catalysis toward highly effective denitrification is imperative yet still remains a significant challenge. Herein, a corchorifolius-like structure, where Fe nanoparticles are sealed in carbon microspheres (CL-Fe@C) with a rough surface, has been elaborately designed by self-assemble strategy. Impressively, the architectured CL-Fe@C microspheres are surrounded with a lot of small iron nanoparticles and contain the high iron content of ∼74%. As a result, an excellent removal capacity of 1816 mg N/g Fe and a high nitrogen selectivity of 98% under a very low nitrate concentration of 100 mg/L are achieved when using the CL-Fe@C microspheres as electrocatalytic denitrification. The present work not only explores high performance electrocatalysis for the denitrification but also promote new inspiration for the preparation of other iron-based functional materials for diverse applications.

Configurations of Nanocubes Floating and Clustering on Liquid Surfaces

The configurations of nanoparticles (NPs) floating on liquid surfaces can be largely affected by the NP shapes in combination with different NP-liquid coupling strengths. Here, the behavior of ligated nanocubes (NCs) on liquid surfaces is studied as an example of such NP floating by analytical methods and molecular dynamics simulations. Depending on the NC-liquid coupling strength, NCs can sit on the liquid surface (weak), be partly immersed in a tilted orientation (intermediate), or be fully immersed except for the top facet (strong). The simulations reveal that configurations of clusters of self-assembled NCs on liquid surfaces can be even more complex and also determined by the NC-liquid and NC-NC coupling strengths, thus providing a rich spectrum of possible superstructures formed.

Co3O4 Supraparticle-Based Bubble Nanofiber and Bubble Nanosheet with Remarkable Electrochemical Performance

Hollow nanostructures based on transition metal oxides (TMOs) with high surface-to-volumetric ratio, low density, and high loading capacity have received great attention for energy-related applications. However, the controllable fabrication of hybrid TMO-based hollow nanostructures in a simple and scalable manner remains challenging. Herein, a simple and scalable strategy is used to prepare hierarchical carbon nanofiber (CNF)-based bubble-nanofiber-structured and reduced graphene oxide (RGO)-based bubble-nanosheet-structured Co3O4 hollow supraparticle (HSP) composites (denoted as CNF/HSP-Co3O4 and RGO/HSP-Co3O4, respectively) by solution self-assembly of ultrasmall Co3O4 nanoparticles (NPs) assisting with polydopamine (PDA) modification. It is proved that the electrochemical performance of Co3O4 NPs can be greatly enhanced by the rationally designed nanostructure of bubble-like supraparticles combined with carbon materials as excellent electrodes for supercapacitors. The favorable structure and composition endow the hybrid electrode with high specific capacitance (1435 F g-1/1360 F g-1 at 1 A g-1/5 mV s-1) as well as fantastic rate capability. The asymmetric supercapacitors achieve an excellent maximum energy density of 51 W h kg-1 and superb electrochemical stability (92.3% retention after 10 000 cycles). This work suggests that the rational design of electrode materials with bubble-like superstructures provides an opportunity for achieving high-performance electrode materials for advanced energy storage devices.