Multiscale Phase Separations for Hierarchically Ordered Macro/Mesostructured Metal Oxides

A Straightforward Solvent-Pair-Enabled Multicomponent Coassembly Approach toward Noble-Metal-Nanoparticle-Decorated Mesoporous Tungsten Oxide for Trace Ammonia Sensing

The straightforward synthesis of noble-metal-nanoparticle-decorated ordered mesoporous transition metal oxides remains a great challenge due to the difficulty of balancing the interactions between precursors and templates. Herein, a solvent-pair-enabled multicomponent coassembly (SPEMC) strategy is developed for straightforward synthesis of noble-metal-nanoparticle-decorated nitrogen-doped ordered mesoporous tungsten oxide (abbreviated as NM/N-mWO3, NM = Pt, Rh, Pd). The amphiphilic poly(ethylene oxide)-block-polystyrene (PEO-b-PS) copolymers coassemble with ammonium metatungstate (AMT) clusters and different kinds of hydrophilic noble metal precursors without phase separation. SPEMC synthesis requires no direct interaction between PEO-b-PS and AMT, thus the assembly equilibriums between noble metal precursors and PEO-b-PS can be readily controlled. The obtained NM/N-mWO3 nanocomposites possess ordered mesopores, abundant oxygen vacancies, and metal-metal oxide interfaces. As a result, the Pt/N-mWO3 sensors exhibit superior ammonia sensing performances with high sensitivity, an ultralow limit of detection (51.2 ppb), good selectivity, and long-term stability. Spectroscopic analysis reveals that ammonia is oxidized stepwise to NO, NO2 -, and NO3 - during the sensing process. Moreover, a portable wireless module based on Pt/N-mWO3 sensor can recognize ppm-level concentration of ammonia, which lays a solid foundation for its application in various fields.

Spinodal Decomposition-Driven Structural Hierarchy of Mesoporous Inorganic Materials for Energy Applications

ConspectusMesoporous inorganic materials (MIMs) directed by block copolymers (BCPs) have attracted tremendous attention due to their high surface area, large pore volume, and tunable pore size. The structural hierarchy of inorganic materials with designed meso- and macrostructures combines the benefits of mesoporosity and tailored macrostructures in which macropores have increased ion/mass transfer and large capacity to carry guest material and have a macroscale particle morphology that permits close packing and a low surface energy. Existing methods for hierarchically structured MIMs require complicated multistep procedures including preparation of sacrificial macrotemplates (e.g., foams and colloidal spheres). Despite considerable efforts to control the macrostructures of mesoporous materials, major challenges remain in the formation of a structural hierarchy with ordered mesoporosity.In polymer science, spinodal decomposition (SD) is a physical phenomenon that spontaneously produces a wide variety of macroscale heterostructures from interconnected networks to isolated droplets. Exploitation of SD is a promising method to achieve precise control of the macrostructure (e.g., macropore, particle morphology) and mesostructure (e.g., pore size and structure, composition) of inorganic materials. However, this approach for tailoring the structural hierarchy of MIMs is unexplored due to the lack of effective systems that can control the complex thermodynamic interactions of inorganic precursor/polymer blends and the phase-separation kinetics.In this Account, we present our recent research progress on the development of synthesis systems that combine unique SD behaviors and BCP self-assembly in polymer blends. To generate macropores in MIMs, we have exploited interconnected macrostructures of SD induced by designed quench conditions of multicomponent blends containing BCP. These strategies enable control of the size of the macropores of the nanostructures independently and can be extended to various compositions (e.g., carbon, SiO2, TiO2, WO3, TiNb2O7, TiN). We also control the macroscopic morphology of the MIMs into spherical particles (e.g., solid and hollow mesoporous spheres) by using SD induced by increasing the mixing entropy penalty of polymer blends that consist BCP, homopolymer(s), and inorganic precursors. Furthermore, interfacial tension between polymers determines the macroscopic morphology of MIMs, from isotropic to anisotropic mesoporous particles (e.g., oblate, bowl, 2D nanosheet). The interfacial states of the homopolymer determine the pore orientation and particle morphology of BCP-directed MIMs.We also highlight the application of the hierarchically structured MIMs in energy storage devices. Generated macropores facilitate ion/mass transfer in lithium-ion batteries and stable accommodation of a large amount of sulfur in lithium-sulfur batteries. Designed morphologies of MIMs are beneficial to achieve high packing density as electrode materials in potassium-ion batteries and thereby achieve high volumetric capacities.Recent advances in SD-driven synthesis for the structural hierarchy of MIMs will inspire how polymer science can be used as a platform for preparing the designed inorganic materials. Additionally, broadening the polymer and composition repertoire will guide in novel frontiers in the design and applications of MIMs in various fields.

Alkaloid Precipitant Reaction Inspired Controllable Synthesis of Mesoporous Tungsten Oxide Spheres for Biomarker Sensing

Highly porous sensitive materials with well-defined structures and morphologies are extremely desirable for developing high-performance chemiresistive gas sensors. Herein, inspired by the classical alkaloid precipitant reaction, a robust and reliable active mesoporous nitrogen polymer sphere-directed synthesis method was demonstrated for the controllable construction of heteroatom-doped mesoporous tungsten oxide spheres. In the typical synthesis, P-doped mesoporous WO3 monodisperse spheres with radially oriented channels (P-mWO3-R) were obtained with a diameter of ∼180 nm, high specific surface area, and crystalline skeleton. The in situ-introduced P atoms could effectively adjust the coordination environment of W atoms (Wδ+-Ov), giving rise to dramatically enhanced active surface-adsorbed oxygen species and unusual metastable ε-WO3 crystallites. The P-mWO3-R spheres were applied for the sensing of 3-hydroxy-2-butanone (3H2B), a biomarker of foodborne pathogenic bacteria Listeria monocytogenes (LM). The sensor exhibited high sensitivity (Ra/Rg = 29 to 3 ppm), fast response dynamics (26/7 s), outstanding selectivity, and good long-term stability. Furthermore, the device was integrated into a wireless sensing module to realize remote real-time and precise detection of LM in practical applications, making it possible to evaluate food quality using gas sensors conveniently.

Polyoxometalate-Bridged Synthesis of Superstructured Mesoporous Polymers and Their Derivatives for Sodium-Iodine Batteries

Despite the impressive progress in mesoporous materials over past decades, for those precursors having no well-matched interactions with soft templates, there are still obstacles to be guided for mesoporous structure via soft-template strategies. Here, a polyoxometalate-assisted co-assembly route is proposed for controllable construction of superstructured mesoporous materials by introducing polyoxometalates as bifunctional bridge units, which weakens the self-nucleation tendency of the precursor through coordination interactions and simultaneously connects the template through the induced dipole-dipole interaction. By this strategy, a series of meso-structured polymers, featuring highly open radial mesopores and dendritic pore walls composed of continuous interwoven nanosheets can be facilely obtained. Further carbonization gave rise to nitrogen-doped hierarchical mesoporous carbon decorated uniformly with ultrafine γ-Mo2 N nanoparticles. Density functional theory proves that nitrogen-doped carbon and γ-Mo2 N can strongly adsorb polyiodide ions, which effectively alleviate polyiodide dissolving in organic electrolytes. Thereby, as the cathode materials for sodium-iodine batteries, the I2 -loaded carbonaceous composite shows a high specific capacity (235 mA h g-1 at 0.5 A g-1 ), excellent rate performance, and cycle stability. This work will open a new venue for controllable synthesis of new hierarchical mesoporous functional materials, and thus promote their applications toward diverse fields.

Spinodal Decomposition Method for Structuring Germanium-Carbon Li-Ion Battery Anodes

To increase the energy density of lithium-ion batteries (LIBs), high-capacity anodes which alloy with Li ions at a low voltage against Li/Li⁺ have been actively pursued. So far, Si has been studied the most extensively because of its high specific capacity and cost efficiency; however, Ge is an interesting alternative. While the theoretical specific capacity of Ge (1600 mAh g^-1) is only half that of Si, its density is more than twice as high (Ge, 5.3 g cm^-3; Si, 2.33 g cm^-3), and therefore the charge stored per volume is better than that of Si. In addition, Ge has a 400 times higher ionic diffusivity and 4 orders of magnitude higher electronic conductivity compared to Si. However, similarly to Si, Ge needs to be structured in order to manage stresses induced during lithiation and many reports have achieved sufficient areal loadings to be commercially viable. In this work, spinodal decomposition is used to make secondary particles of about 2 μm in diameter that consist of a mixture of ∼30 nm Ge nanoparticles embedded in a carbon matrix. The secondary structure of these germanium-carbon particles allows for specific capacities of over 1100 mAh g^-1 and a capacity retention of 91.8% after 100 cycles. Finally, high packing densities of ∼1.67 g cm^-3 are achieved in blended electrodes by creating a bimodal size distribution with natural graphite.

Direct Visualization of the Self-Alignment Process for Nanostructured Block Copolymer Thin Films by Transmission Electron Microscopy

Herein, this work aims to directly visualize the morphological evolution of the controlled self-assembly of star-block polystyrene-block-polydimethylsiloxane (PS-b-PDMS) thin films via in situ transmission electron microscopy (TEM) observations. With an environmental chip, possessing a built-in metal wire-based microheater fabricated by the microelectromechanical system (MEMS) technique, in situ TEM observations can be conducted under low-dose conditions to investigate the development of film-spanning perpendicular cylinders in the block copolymer (BCP) thin films via a self-alignment process. Owing to the free-standing condition, a symmetric condition of the BCP thin films can be formed for thermal annealing under vacuum with neutral air surface, whereas an asymmetric condition can be formed by an air plasma treatment on one side of the thin film that creates an end-capped neutral layer. A systematic comparison of the time-resolved self-alignment process in the symmetric and asymmetric conditions can be carried out, giving comprehensive insights for the self-alignment process via the nucleation and growth mechanism.

Rheology and dynamics of a solvent segregation driven gel (SeedGel)

Bicontinuous structures promise applications in a broad range of research fields, such as energy storage, membrane science, and biomaterials. Kinetically arrested spinodal decomposition is found responsible for stabilizing such structures in different types of materials. A recently developed solvent segregation driven gel (SeedGel) is demonstrated to realize bicontinuous channels thermoreversibly with tunable domain sizes by trapping nanoparticles in a particle domain. As the mechanical properties of SeedGel are very important for its future applications, a model system is characterized by temperature-dependent rheology. The storage modulus shows excellent thermo-reproducibility and interesting temperature dependence with the maximum storage modulus observed at an intermediate temperature range (around 28 °C). SANS measurements are conducted at different temperatures to identify the macroscopic solvent phase separation during the gelation transition, and solvent exchange between solvent and particle domains that is responsible for this behavior. The long-time dynamics of the gel is further studied by X-ray Photon Correlation Spectroscopy (XPCS). The results indicate that particles in the particle domain are in a glassy state and their long-time dynamics are strongly correlated with the temperature dependence of the storage modulus.

Multilevel Self-Assembly of Block Copolymers and Polymer Colloids for a Transparent and Sensitive Gas Sensor Platform

The recent emerging significance of the Internet of Things (IoT) demands sensor devices to be integrated with many different functional structures and devices while conserving their original functionalities. To this end, optical transparency and mechanical flexibility of sensor devices are critical requirements for optimal integration as well as high sensitivity. In this work, a transparent, flexible, and sensitive gas sensor building platform is introduced by using multilevel self-assembly of block copolymers (BCPs) and polystyrene (PS) colloids. For the demonstration of an H₂ gas sensor, a hierarchically porous Pd metal mesh structure is obtained by overlaying the two different patterned template structures with synergistic, distinctive characteristic length scales. The hierarchical Pd mesh shows not only high transparency over 90% but also superior sensing performance in terms of response and recovery time owing to enhanced Pd-to-hydride ratio and short H₂ diffusion lengths from the enlarged active surface areas. The hierarchical morphology also endows high mechanical flexibility while securing reliable sensing performance even under severe mechanical deformation cycles. Our scalable self-assembly based multiscale nanopatterning offers an intriguing generalized platform for many different multifunctional devices requiring hidden in situ monitoring of environmental signals.

Two-dimensional demixing within multilayered nanoemulsion films

Benefiting from the demixing of substances in the two-phase region, a smart polymer laminate film system that exhibits direction-controlled phase separation behavior was developed in this study. Here, nanoemulsion films (NEFs) in which liquid nanodrops were uniformly confined in a polymer laminate film through the layer-by-layer deposition of oppositely charged emulsion nanodrops and polyelectrolytes were fabricated. Upon reaching a critical temperature, the NEFs exhibited a micropore-guided demixing phenomenon. A simulation study based on coarse-grained molecular dynamics revealed that the perpendicular diffusion of oil droplets through the micropores generated in the polyelectrolyte layer is crucial for determining the coarsening kinetics and phase separation level, which is consistent with the experimental results. Considering the substantial advantages of this unique and tunable two-dimensional demixing behavior, the viability of using the as-proposed NEF system for providing an efficient route for the development of smart drug delivery patches was demonstrated.

Small-Molecular-Weight Additives Modulate Calcification by Interacting with Prenucleation Clusters on the Molecular Level

Small-molecular-weight (MW) additives can strongly impact amorphous calcium carbonate (ACC), playing an elusive role in biogenic, geologic, and industrial calcification. Here, we present molecular mechanisms by which these additives regulate stability and composition of both CaCO₃ solutions and solid ACC. Potent antiscalants inhibit ACC precipitation by interacting with prenucleation clusters (PNCs); they specifically trigger and integrate into PNCs or feed PNC growth actively. Only PNC-interacting additives are traceable in ACC, considerably stabilizing it against crystallization. The selective incorporation of potent additives in PNCs is a reliable chemical label that provides conclusive chemical evidence that ACC is a molecular PNC-derived precipitate. Our results reveal additive-cluster interactions beyond established mechanistic conceptions. They reassess the role of small-MW molecules in crystallization and biomineralization while breaking grounds for new sustainable antiscalants.

Hierarchical Design in Nanoporous Metals

Hierarchically porous metals possess intriguing high accessibility of matter molecules and unique continuous metallic frameworks, as well as a high level of exposed active atoms. High rates of diffusion and fast energy transfer have been important and challenging goals of hierarchical design and porosity control with nanostructured metals. This review aims to summarize recent important progress toward the development of hierarchically porous metals, with special emphasis on synthetic strategies, hierarchical design in structure-function and corresponding applications. The current challenges and future prospects in this field are also discussed.

Dynamic Coassembly of Amphiphilic Block Copolymer and Polyoxometalates in Dual Solvent Systems: An Efficient Approach to Heteroatom-Doped Semiconductor Metal Oxides with Controllable Nanostructures

Dynamic coassembly of block copolymers (BCPs) with Keggin-type polyoxometalates (POMs) is developed to synthesize heteroatom-doped tungsten oxide with controllable nanostructures, including hollow hemispheres, nanoparticles, and nanowires. The versatile coassembly in dual n-hexane/THF solvent solution enables the fomation of poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/POMs (e.g., silicotungstic acid, H₄SiW₁₂O₄₀) nanocomposites with different morphologies such as spherical vesicles, inverse spherical micelles, and inverse cylindrical micelles, which can be readily converted into diverse nanostructured metal oxides with high surface area and unique properties via in situ thermal-induced structural evolution. For example, uniform silicon-doped WO₃ (Si-WO₃) hollow hemispheres derived from coassembly of PEO-b-PS with H₄SiW₁₂O₄₀ were utilized to fabricate gas sensing devices which exhibit superior gas sensing performance toward acetone, thanks to the selective gas-solid interface catalytic reaction that induces resistance changes of the devices due to the high specific surface areas, abundant oxygen vacancies, and the Si-doping induced metastable ε-phase of WO₃. Furthermore, density functional theory (DFT) calculation reveals the mechanism about the high sensitivity and selectivity of the gas sensors. On the basis of the as-fabricated devices, an integrated gas sensor module was constructed, which is capable of real-time monitoring the environmental acetone concentration and displaying relevant sensing results on a smart phone via Bluetooth communication.

Oxide-on-Oxide Porous Electrodes Revealing Superior Reversible Li+-Coupled Electron-Transfer Properties by Unconventional Heterojunction Effects

Internal spacing of electrodes is a key point for controlling electron-transfer (ET)-related phenomena. However, their disordered porous structures often prevent the observation of microscopic effects. It hampers the development of modern electrochemical theories. The development of model porous electrodes therefore provides an ideal platform to discover intriguing fundamental principles of electrode processes. We developed a new synthetic strategy for all-oxide monolithic ruthenium dioxide (RuO₂)/antimony-doped tin oxide (ATO) electrodes with a controlled hierarchically porous structure and oxide-oxide heterojunction. The use of the obtained RuO₂/ATO electrodes as model electrodes suppressed influences related to different mass diffusion efficiencies between electrodes with heterojunctions of different types. Then, we showed unconventional oxide-oxide heterojunction effects, improving reversible Li⁺-coupled electron-transfer properties using model electrodes constituted of various nanostructured (nano-) RuO₂ on porous ATO. In addition to the superior electrochemical properties of the nano-RuO₂/ATO heterojunction, the quasi-two-dimensional (2D) RuO₂/ATO heterojunction led to improved specific capacity at a high rate and longer cycle life. We anticipate that this oxide-oxide heterojunction effect and developed all-oxide model porous electrodes can provide a path to develop advanced reversible energy storage devices.

Structural Evolution of a Polystyrene-Block-Poly(Ethylene Oxide) Block Copolymer in Tetrahydrofuran/Water Cosolvents

This study aims to quantitatively investigate the effect of water content on the self-assembly behavior of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) in tetrahydrofuran/water cosolvents by small-angle X-ray scattering. PS-b-PEO chains preferentially form fractal aggregates at a dilute concentration in neat tetrahydrofuran (THF). By adding a small amount of water into THF, PS-b-PEO forms gelled networks. The gelled networks have correlated inhomogeneities, which were generated through mesophase separation. These gelled networks are not present when PS-b-PEO is dissolved in THF/methanol and THF/ethanol cosolvents. The substitution of water with 12 M HCl reduces the viscosity of the gelled networks. Those results indicate that the gelled networks of PS-b-PEO need hydrogen bonds formed from surrounding water molecules to be bridging agents, which connect different PEO block chains together. Upon increasing the water content in THF/water cosolvents, dispersed micelles with a core-shell conformation or aggregated micelles preferentially coexist with fractal aggregates.

Block Copolymer Nanopatterning for Nonsemiconductor Device Applications

Block copolymer (BCP) nanopatterning has emerged as a versatile nanoscale fabrication tool for semiconductor devices and other applications, because of its ability to organize well-defined, periodic nanostructures with a critical dimension of 5-100 nm. While the most promising application field of BCP nanopatterning has been semiconductor devices, the versatility of BCPs has also led to enormous interest from a broad spectrum of other application areas. In particular, the intrinsically low cost and straightforward processing of BCP nanopatterning have been widely recognized for their large-area parallel formation of dense nanoscale features, which clearly contrasts that of sophisticated processing steps of the typical photolithographic process, including EUV lithography. In this Review, we highlight the recent progress in the field of BCP nanopatterning for various nonsemiconductor applications. Notable examples relying on BCP nanopatterning, including nanocatalysts, sensors, optics, energy devices, membranes, surface modifications and other emerging applications, are summarized. We further discuss the current limitations of BCP nanopatterning and suggest future research directions to open up new potential application fields.

Ordered Mesoporous Alumina with Tunable Morphologies and Pore Sizes for CO2 Capture and Dye Separation

We describe a versatile and scalable strategy toward long-range and periodically ordered mesoporous alumina (Al₂O₃) structures by evaporation-induced self-assembly of a structure-directing ABA triblock copolymer (F127) mixed with aluminum tri-sec-butoxide-derived sol additive. We found that the separate preparation of the alkoxide sol-gel reaction before mixing with the block copolymer enabled access to a relatively unexplored parameter space of copolymer-to-additive composition, acid-to-metal molar ratio, and solvent, yielding ordered mesophases of two-dimensional (2D) lamellar, hexagonal cylinder, and 3D cage-like cubic lattices, as well as multiscale hierarchical ordered structures from spinodal decomposition-induced macro- and mesophase separation. Thermal annealing in air at 900 °C yielded well-ordered mesoporous crystalline γ-Al₂O₃ structures and hierarchically porous γ-Al₂O₃ with 3D interconnected macroscale and ordered mesoscale pore networks. The ordered Al₂O₃ structures exhibited tunable pore sizes in three different length scales, <2 nm (micropore), 2-11 nm (mesopore), and 1-5 μm (macropore), as well as high surface areas and pore volumes of up to 305 m²/g and 0.33 cm³/g, respectively. Moreover, the resultant mesoporous Al₂O₃ demonstrated enhanced adsorption capacities of carbon dioxide and Congo red dye. Such hierarchically ordered mesoporous Al₂O₃ are well-suited for green environmental solutions and urban sustainability applications, for example, high-temperature solid adsorbents and catalyst supports for carbon dioxide sequestration, fuel cells, and wastewater separation treatments.

Synthesis of hierarchically porous 3D polymeric carbon superstructures with nitrogen-doping by self-transformation: a robust electrocatalyst for the detection of herbicide bentazone

Bentazone (BEZ) is one of the utmost selective problematic contact-past herbicide with high toxicity for humans owing to feasible contamination of surface and ground water. In this work, an electrochemical sensor has been developed for the sensitive detection of BEZ, based on hierarchically porous three-dimensional (3D) carbon superstructures (CS)-modified electrodes. The CSs (namely, CS_HEX, CS_PY, CS_ACN, and CS_NOS) were prepared by the pyrolysis process from organic porous polyacrylonitrile (PAN) superstructure particles (namely, PAN_HEX, PAN_PY, PAN_ACN, and PAN_NOS) obtained by free radical polymerization method using different solvents (hexane, pyridine, acetonitrile, and also no solvent). The assembly with the working electrode of CSs causes the electrocatalytic BEZ oxidation by rapid electron transfer compared to the PAN superstructures and bare electrodes. Intriguingly, compared to all electrodes, CS_HEX-modified electrode showed the superior electrochemical detection of BEZ at a working potential of 0.99 V (vs. Ag/AgCl), very low detection limit (0.002 μM), wide dynamic linear range (0.03 to 200 μM), high sensitivity (9.95 μA μM^-1 cm^-2), and excellent reliability. The advanced sensors displayed an intensification of oxidation peak current of BEZ with high selectivity, remarkable sensitivity, and reproducibility for BEZ detection and received satisfactory outcomes designating the application of sensors for the determination of BEZ in river water samples.

A Polymer-Assisted Spinodal Decomposition Strategy toward Interconnected Porous Sodium Super Ionic Conductor-Structured Polyanion-Type Materials and Their Application as a High-Power Sodium-Ion Battery Cathode

A general polymer-assisted spinodal decomposition strategy is used to prepare hierarchically porous sodium super ionic conductor (NASICON)-structured polyanion-type materials (e.g., Na3 V2 (PO4 )3 , Li3 V2 (PO4 )3 , K3 V2 (PO4 )3 , Na4 MnV(PO4 )3 , and Na2 TiV(PO4 )3 ) in a tetrahydrofuran/ethanol/H2 O synthesis system. Depending on the boiling point of solvents, the selective evaporation of the solvents induces both macrophase separation via spinodal decomposition and mesophase separation via self-assembly of inorganic precursors and amphiphilic block copolymers, leading to the formation of hierarchically porous structures. The resulting hierarchically porous Na3 V2 (PO4 )3 possessing large specific surface area (≈77 m2 g-1 ) and pore volume (≈0.272 cm3 g-1 ) shows a high specific capacity of 117.6 mAh g-1 at 0.1 C achieving the theoretical value and a long cycling life with 77% capacity retention over 1000 cycles at 5 C. This method presented here can open a facile avenue to synthesize other hierarchically porous polyanion-type materials.

Graphene-Based Two-Dimensional Mesoporous Materials: Synthesis and Electrochemical Energy Storage Applications

Graphene (G)-based two dimensional (2D) mesoporous materials combine the advantages of G, ultrathin 2D morphology, and mesoporous structures, greatly contributing to the improvement of power and energy densities of energy storage devices. Despite considerable research progress made in the past decade, a complete overview of G-based 2D mesoporous materials has not yet been provided. In this review, we summarize the synthesis strategies for G-based 2D mesoporous materials and their applications in supercapacitors (SCs) and lithium-ion batteries (LIBs). The general aspect of synthesis procedures and underlying mechanisms are discussed in detail. The structural and compositional advantages of G-based 2D mesoporous materials as electrodes for SCs and LIBs are highlighted. We provide our perspective on the opportunities and challenges for development of G-based 2D mesoporous materials. Therefore, we believe that this review will offer fruitful guidance for fabricating G-based 2D mesoporous materials as well as the other types of 2D heterostructures for electrochemical energy storage applications.

Controlling Bicontinuous Structures through a Solvent Segregation-Driven Gel

The past decade has seen increased research interest in studying bicontinuous structures formed via colloidal self-assembly due to their many useful applications. A new type of colloidal gel, solvent segregation-driven gel (SeedGel), has been recently demonstrated as an effective approach to arrest bicontinuous structures with unique and intriguing properties, such as thermoreversibility, structural reproducibility, and sensitive temperature response. Here, using a model system with silica particles in the 2,6-lutidine/water binary solvent, we investigate the factors controlling the domain size of a SeedGel system by varying the particle concentration, solvent ratio, and quenching protocol. A phase diagram is identified to produce SeedGels for this model system. Our results indicate that by adjusting the sample composition, it is possible to realize bicontinuous domains with well-controlled repeating distances (periodicities). In addition, the effect of quenching rate on the domain size is systematically investigated, showing that it is a very sensitive parameter to control domain sizes. By further heating SeedGel up into the spinodal region, the structure evolution under high temperatures is also investigated and discussed. These results provide important insights into how to control bicontinuous structures in SeedGel systems.

Tunable thermo-reversible bicontinuous nanoparticle gel driven by the binary solvent segregation

Bicontinuous porous structures through colloidal assembly realized by non-equilibrium process is crucial to various applications, including water treatment, catalysis and energy storage. However, as non-equilibrium structures are process-dependent, it is very challenging to simultaneously achieve reversibility, reproducibility, scalability, and tunability over material structures and properties. Here, a novel solvent segregation driven gel (SeedGel) is proposed and demonstrated to arrest bicontinuous structures with excellent thermal structural reversibility and reproducibility, tunable domain size, adjustable gel transition temperature, and amazing optical properties. It is achieved by trapping nanoparticles into one of the solvent domains upon the phase separation of the binary solvent. Due to the universality of the solvent driven particle phase separation, SeedGel is thus potentially a generic method for a wide range of colloidal systems.

Bicontinuous porous materials made by colloidal self-assemblies have many applications. Xi et al. utilize colloidal particles dispersed in a binary solvent to form thermo-reversible bicontinuous gel structures with good reproducibility and scalability, and tunable structural and optical properties.

Hollow micro and nanostructures for therapeutic and imaging applications

Hollow particles have been extensively used in bioanalytical and biomedical applications for almost two decades due to their unique and tunable optoelectronic properties as well as their significantly high loading capacities. These intrinsic properties led them to be used in various bioimaging applications as contrast agents, controlled delivery (i.e. drugs, nucleic acids and other biomolecules) platforms and photon-triggered therapies (e.g. photothermal and photodynamic therapies). Since recent studies showed that imaging-guided targeted therapeutics have higher success rates, multimodal theranostic platforms (combination of one or more therapy and diagnosis modality) have been employed more often and hollow particles (i.e. nanoshells) have been one of the most efficient candidates to be used in multiple-purpose platforms, owing to their intrinsic properties that enable synergistic multimodal performance. In this review, recent advances in the applications of such hollow particles fabricated with various routes (either inorganic or organic based) were summarized to delineate strategies for tuning their properties for more efficient biomedical performance by overcoming common biological barriers. This review will pave the ways for expedited progress in design of next generation of hollow particles for clinical applications.

Ordered Bicontinuous Mesoporous Polymeric Semiconductor Photocatalyst

Owning triply periodic minimal surfaces and three-dimensional (3D) interconnected pores, bicontinuous porous materials have drawn enormous attention due to their great academic interest and potential applications in many fields including energy and catalysis. However, their synthesis has remained a great challenge. Here, we demonstrate the synthesis of a bicontinuous porous organic semiconductor photocatalyst, which involves the preparation of SiO₂ with a shifted double diamond (DD) structure through solvent evaporation-induced self-assembly of a polystyrene-block-poly(ethylene oxide) diblock copolymer and tetraethyl orthosilicate, followed by SiO₂-templated self-condensation of melamine monomers in a vacuum. Strikingly, the resultant DD-structured graphitic carbon nitride (g-CN) possesses two sets of 3D continuous mesopores with a mean diameter of 14 nm, which afford a high specific surface area of 131 m² g^-1 and an optical band gap of 2.8 eV. Being a visible-light-driven photocatalyst, the bicontinuous mesoporous g-CN exhibits high catalytic activity for water splitting to generate H₂ (6831 μmol g^-1 h^-1) with excellent cycling stability. This study provides a protocol for the construction of ordered mesoporous materials containing 3D continuous channels, which holds promise for catalysis applications.

Bicontinuous phase separation of lithium-ion battery electrodes for ultrahigh areal loading

Ultrathick battery electrodes are appealing as they reduce the fraction of inactive battery parts such as current collectors and separators. However, thick electrodes are difficult to dry and tend to crack or flake during production. Moreover, the electrochemical performance of thick electrodes is constrained by ion and electron transport as well as fast capacity degradation. Here, we report a thermally induced phase separation (TIPS) process for fabricating thick Li-ion battery electrodes, which incorporates the electrolyte directly in the electrode and alleviates the need to dry the electrode. The proposed TIPS process creates a bicontinuous electrolyte and electrode network with excellent ion and electron transport, respectively, and consequently achieves better rate performance. Using this process, electrodes with areal capacities of more than 30 mAh/cm² are demonstrated. Capacity retentions of 87% are attained over 500 cycles in full cells with 1-mm-thick anodes and cathodes. Finally, we verified the scalability of the TIPS process by coating thick electrodes continuously on a pilot-scale roll-to-roll coating tool.

Polymer blend directed anisotropic self-assembly toward mesoporous inorganic bowls and nanosheets

Anisotropic mesoporous inorganic materials have attracted great interest due to their unique and intriguing properties, yet their controllable synthesis still remains a great challenge. Here, we develop a simple synthesis approach toward mesoporous inorganic bowls and two-dimensional (2D) nanosheets by combining block copolymer (BCP)-directed self-assembly with asymmetric phase migration in ternary-phase blends. The homogeneous blend solution spontaneously self-assembles to anisotropically stacked hybrids as the solvent evaporates. Two minor phases-BCP/inorganic precursor and homopolystyrene (hPS)-form closely stacked, Janus domains that are dispersed/confined in the major homopoly(methyl methacrylate) (hPMMA) matrix. hPS phases are partially covered by BCP-rich phases, where ordered mesostructures develop. With increasing the relative amount of hPS, the anisotropic shape evolves from bowls to 2D nanosheets. Benefiting from the unique bowl-like morphology, the resulting transition metal oxides show promise as high-performance anodes in potassium-ion batteries.

Noninterference Revealing of "Layered to Layered" Zinc Storage Mechanism of δ-MnO2 toward Neutral Zn-Mn Batteries with Superior Performance

MnO2 is one of the most studied cathodes for aqueous neutral zinc-ion batteries. However, the diverse reported crystal structures of MnO2 compared to δ-MnO2 inevitably suffer a structural phase transition from tunneled to layered Zn-buserite during the initial cycles, which is not as kinetically direct as the conventional intercalation electrochemistry in layered materials and thus poses great challenges to the performance and multifunctionality of devices. Here, a binder-free δ-MnO2 cathode is designed and a favorable "layered to layered" Zn2+ storage mechanism is revealed systematically using such a "noninterferencing" electrode platform in combination with ab initio calculation. A flexible quasi-solid-state Zn-Mn battery with an electrodeposited flexible Zn anode is further assembled, exhibiting high energy density (35.11 mWh cm-3; 432.05 Wh kg-1), high power density (676.92 mW cm-3; 8.33 kW kg-1), extremely low self-discharge rate, and ultralong stability up to 10 000 cycles. Even with a relatively high δ-MnO2 mass loading of 5 mg cm-2, significant energy and power densities are still achieved. The device also works well over a broad temperature range (0-40 °C) and can efficiently power different types of small electronics. This work provides an opportunity to develop high-performance multivalent-ion batteries via the design of a kinetically favorable host structure.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

We give a comprehensive overview of how the morphology control is an effective and versatile way to control the physicochemical properties of metal oxides that can be transferred to metal–organic frameworks and porous carbon materials.

Micro-Blooming: Hierarchically Porous Nitrogen-Doped Carbon Flowers Derived from Metal-Organic Mesocrystals

Synthesis of 3D flower-like zinc-nitrilotriacetic acid (ZnNTA) mesocrystals and their conformal transformation to hierarchically porous N-doped carbon superstructures is reported. During the solvothermal reaction, 2D nanosheet primary building blocks undergo oriented attachment and mesoscale assembly forming stacked layers. The secondary nucleation and growth preferentially occurs at the edges and defects of the layers, leading to formation of 3D flower-like mesocrystals comprised of interconnected 2D micropetals. By simply varying the pyrolysis temperature (550-1000 °C) and the removal method of in the situ-generated Zn species, nonporous parent mesocrystals are transformed to hierarchically porous carbon flowers with controllable surface area (970-1605 m² g^-1 ), nitrogen content (3.4-14.1 at%), pore volume (0.95-2.19 cm³ g^-1 ), as well as pore diameter and structures. The carbon flowers prepared at 550 °C show high CO₂ /N₂ selectivity due to the high nitrogen content and the large fraction of (ultra)micropores, which can greatly increase the CO₂ affinity. The results show that the physicochemical properties of carbons are highly dependent on the thermal transformation and associated pore formation process, rather than directly inherited from parent precursors. The present strategy demonstrates metal-organic mesocrystals as a facile and versatile means toward 3D hierarchical carbon superstructures that are attractive for a number of potential applications.

Large-Pore Mesoporous CeO2 -ZrO2 Solid Solutions with In-Pore Confined Pt Nanoparticles for Enhanced CO Oxidation

Active and stable catalysts are highly desired for converting harmful substances (e.g., CO, NO_x ) in exhaust gases of vehicles into safe gases at low exhaust temperatures. Here, a solvent evaporation-induced co-assembly process is employed to design ordered mesoporous Ce_x Zr_{1- x} O₂ (0 ≤ x ≤ 1) solid solutions by using high-molecular-weight poly(ethylene oxide)-block-polystyrene as the template. The obtained mesoporous Ce_x Zr_{1- x} O₂ possesses high surface area (60-100 m² g^-1 ) and large pore size (12-15 nm), enabling its great capacity in stably immobilizing Pt nanoparticles (4.0 nm) without blocking pore channels. The obtained mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst exhibits superior CO oxidation activity with a very low T₁₀₀ value of 130 °C (temperature of 100% CO conversion) and excellent stability due to the rich lattice oxygen vacancies in the Ce_0.8 Zr_0.2 O₂ framework. The simulated catalytic evaluations of CO oxidation combined with various characterizations reveal that the intrinsic high surface oxygen mobility and well-interconnected pore structure of the mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst are responsible for the remarkable catalytic efficiency. Additionally, compared with mesoporous Pt/Ce_x Zr_{1- x} O₂ -s with small pore size (3.8 nm), ordered mesoporous Pt/Ce_x Zr_{1- x} O₂ not only facilitates the mass diffusion of reactants and products, but also provides abundant anchoring sites for Pt nanoparticles and numerous exposed catalytically active interfaces for efficient heterogeneous catalysis.

A Polymer-Oriented Self-Assembly Strategy toward Mesoporous Metal Oxides with Ultrahigh Surface Areas

Mesoporous metal oxides (MMOs) have attracted comprehensive attention in many fields, including energy storage, catalysis, and separation. Current synthesis of MMOs mainly involve use of surfactants as templates to generate mesopores and organic reagents as solvents to hinder hydrolysis and condensation of inorganic precursors, which is adverse to adjusting the interactions between surfactants and inorganic precursors. The resulting products have uncontrollable pore structure, crystallinity, and relatively lower surface areas. Here, a facile and general polymer-oriented self-assembly strategy to synthesize a series of MMOs (e.g., TiO2, ZrO2, NbO5, Al2O3, Ta2O5, HfO2, and SnO2) by using cationic polymers as porogens and metal alkoxides as metal oxide precursors in a robust aqueous synthesis system are reported. Nitrogen adsorption analysis and transmission electron microscopy confirm that the obtained MMOs have ultrahigh specific surface areas and large pore volumes (i.e., 733 m2 g-1 and 0.485 cm3 g-1 for mesoporous TiO2). Moreover, the structural parameters (surface area, pore size, and pore volume) and crystallinity can be readily controlled by tuning the interactions between cationic polymers and precursors. The as-synthesized crystalline mesoporous TiO2 exhibits promising performance in photocatalytic water splitting of hydrogen production and a high hydrogen production rate of 3.68 mol h-1 g-1.

Preparation of epoxy-functionalized hierarchically porous hybrid monoliths via free radical polymerization and application in HILIC enrichment of glycopeptides

Owing to their multiscale pore size regimes and unique properties, the materials with hierarchically porous structures have become an important family of functional materials in recent years. They have been applied from energy conversion and storage, catalysis, separation to drug delivery, etc. The synthesis of them is difficult by the need to employ multiple templates and take complicated steps. Herein, we successfully prepared epoxy-functionalized hierarchically porous hybrid monoliths (HPHMs) with micro/meso/macro-structures in an easy way. Firstly, a bulk monolithic material was formed via free radical polymerization between polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and allyl glycidyl ether (AGE) in the presence of polycaprolactone (PCL). Then PCL was degraded with hydrochloric acid solution, and the epoxy-functionalized HPHM was obtained. This approach was very simple and suitable for large-scale preparation. Hybrid monoliths with different specific surface area (from 5.4 to 636.7 m²/g) were prepared by adjusting the mole ratio of vinylPOSS to AGE and the content of PCL. The results of several characterization methods, including nitrogen adsorption/desorption measurements, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), showed that these materials contained not only micropores and mesopores but also macropores. The materials were further modified with penicillamine to be used as hydrophilic interaction chromatography (HILIC) adsorbents for enriching N-glycopeptides in IgG and serum protein tryptic digests. Up to 23 N-glycopeptides were identified from IgG digest, and 385 N-glycopeptides and 283 N-glycosylation sites were identified from human serum digest.

Approaching Ultrastable High-Rate Li-S Batteries through Hierarchically Porous Titanium Nitride Synthesized by Multiscale Phase Separation

Porous architectures are important in determining the performance of lithium-sulfur batteries (LSBs). Among them, multiscale porous architecutures are highly desired to tackle the limitations of single-sized porous architectures, and to combine the advantages of different pore scales. Although a few carbonaceous materials with multiscale porosity are employed in LSBs, their nonpolar surface properties cause the severe dissolution of lithium polysulfides (LiPSs). In this context, multiscale porous structure design of noncarbonaceous materials is highly required, but has not been exploited in LSBs yet because of the absence of a facile method to control the multiscale porous inorganic materials. Here, a hierarchically porous titanium nitride (h-TiN) is reported as a multifunctional sulfur host, integrating the advantages of multiscale porous architectures with intrinsic surface properties of TiN to achieve high-rate and long-life LSBs. The macropores accommodate the high amount of sulfur, facilitate the electrolyte penetration and transportation of Li⁺ ions, while the mesopores effectively prevent the LiPS dissolution. TiN strongly adsorbs LiPS, mitigates the shuttle effect, and promotes the redox kinetics. Therefore, h-TiN/S shows a reversible capacity of 557 mA h g^-1 even after 1000 cycles at 5 C rate with only 0.016% of capacity decay per cycle.

Generalized Access to Mesoporous Inorganic Particles and Hollow Spheres from Multicomponent Polymer Blends

Mesoporous inorganic particles and hollow spheres are of increasing interest for a broad range of applications, but synthesis approaches are typically material specific, complex, or lack control over desired structures. Here it is reported how combining mesoscale block copolymer (BCP) directed inorganic materials self-assembly and macroscale spinodal decomposition can be employed in multicomponent BCP/hydrophilic inorganic precursor blends with homopolymers to prepare mesoporous inorganic particles with controlled meso- and macrostructures. The homogeneous multicomponent blend solution undergoes dual phase separation upon solvent evaporation. Microphase-separated (BCP/inorganic precursor)-domains are confined within the macrophase-separated majority homopolymer matrix, being self-organized toward particle shapes that minimize the total interfacial area/energy. The pore orientation and particle shape (solid spheres, oblate ellipsoids, hollow spheres) are tailored by changing the kind of homopolymer matrix and associated enthalpic interactions. Furthermore, the sizes of particle and hollow inner cavity are tailored by changing the relative amount of homopolymer matrix and the rates of solvent evaporation. Pyrolysis yields discrete mesoporous inorganic particles and hollow spheres. The present approach enables a high degree of control over pore structure, orientation, and size (15-44 nm), particle shape, particle size (0.6-3 µm), inner cavity size (120-700 nm), and chemical composition (e.g., aluminosilicates, carbon, and metal oxides).

Amphiphilic Block Copolymers Directed Interface Coassembly to Construct Multifunctional Microspheres with Magnetic Core and Monolayer Mesoporous Aluminosilicate Shell

Core-shell magnetic porous microspheres have wide applications in drug delivery, catalysis and bioseparation, and so on. However, it is great challenge to controllably synthesize magnetic porous microspheres with uniform well-aligned accessible large mesopores (>10 nm) which are highly desired for applications involving immobilization or adsorption of large guest molecules or nanoobjects. In this study, a facile and general amphiphilic block copolymer directed interfacial coassembly strategy is developed to synthesize core-shell magnetic mesoporous microspheres with a monolayer of mesoporous shell of different composition (FDUcs-17D), such as core-shell magnetic mesoporous aluminosilicate (CS-MMAS), silica (CS-MMS), and zirconia-silica (CS-MMZS), open and large pores by employing polystyrene-block-poly (4-vinylpyridine) (PS-b-P4VP) as an interface structure directing agent and aluminum acetylacetonate (Al(acac)₃ ), zirconium acetylacetonate, and tetraethyl orthosilicate as shell precursors. The obtained CS-MMAS microspheres possess magnetic core, perpendicular mesopores (20-32 nm) in the shell, high surface area (244.7 m² g^-1 ), and abundant acid sites (0.44 mmol g^-1 ), and as a result, they exhibit superior performance in removal of organophosphorus pesticides (fenthion) with a fast adsorption dynamics and high adsorption capacity. CS-MMAS microspheres loaded with Au nanoparticles (≈3.5 nm) behavior as a highly active heterogeneous nanocatalyst for N-alkylation reaction for producing N-phenylbenzylamine with a selectivity and yields of over 90% and good magnetic recyclability.