Zeolite Catalysts with Tunable Hierarchy Factor by Pore‐Growth Moderators

The design of hierarchical zeolite catalysts is attempted through the maximization of the hierarchy factor (HF); that is, by enhancing the mesopore surface area without severe penalization of the micropore volume. For this purpose, a novel desilication variant involving NaOH treatment of ZSM‐5 in the presence of quaternary ammonium cations is developed. The organic cation (TPA⁺ or TBA⁺) acts as a pore‐growth moderator in the crystal by OH^?‐assisted silicon extraction, largely protecting the zeolite crystal during the demetallation process. The protective effect is not seen when using cations that are able to enter the micropores, such as TMA⁺ Engineering the pore structure at the micro‐ and mesolevel is essential to optimize transport properties and catalytic performance, as demonstrated in the benzene alkylation with ethylene, a representative mass‐transfer limited reaction. The hierarchy factor is an appropriate tool to classify hierarchically structured materials. The latter point is of wide interest to the scientific community as it not only embraces mesoporous zeolites obtained by desilication methods but it also enables to quantitatively compare and correlate various materials obtained by different synthetic methodologies.     

Beyond Creation of Mesoporosity: The Advantages of Polymer‐Based Dual‐Function Templates for Fabricating Hierarchical Zeolites

Direct synthesis of hierarchical zeolites currently relies on the use of surfactant‐based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual‐function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long‐range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single‐crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso‐ZSM‐5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM‐5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer‐based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof‐of‐concept experiment, unprecedented core–shell‐structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.     

MEL‐type Pure‐Silica Zeolite Nanocrystals Prepared by an Evaporation‐Assisted Two‐Stage Synthesis Method as Ultra‐Low‐k Materials

A MEL‐type pure‐silica zeolite (PSZ), prepared by spin‐on of nanoparticle suspensions, has been shown to be a promising ultra‐low‐dielectric‐constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two‐stage synthesis method was used to synthesize a MEL‐zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63%, the particle size is 80 nm, which has proved to be too large because it introduces a number of problems for the spin‐on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two‐stage synthesis method is modified into an evaporation‐assisted two‐stage method by adding a solvent‐evaporation process between the two thermal‐treatment steps. The modified method can yield much smaller particle sizes (e.g., 14 vs. 80 nm) while maintaining the same nanocrystal yields as the two‐stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation‐assisted two‐stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14 nm in size and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin‐on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67 ± 1.48 GPa vs. 7.82 ± 1.30 GPa), as well as a similar k value (1.91 ± 0.09 vs. 1.89 ± 0.08) to the previous two‐stage synthesized films.     

Interaction of Zoospores of the Green Alga Ulva with Bioinspired Micro‐ and Nanostructured Surfaces Prepared by Polyelectrolyte Layer‐by‐Layer Self‐Assembly

The interaction of spores of Ulva with bioinspired structured surfaces in the nanometer–micrometer size range is investigated using a series of coatings with systematically varying morphology and chemistry, which allows separation of the contributions of morphology and surface chemistry to settlement (attachment) and adhesion strength. Structured surfaces are prepared by layer‐by‐layer spray‐coating deposition of polyelectrolytes. By changing the pH during application of oppositely charged poly(acrylic acid) and polyethylenimine polyelectrolytes, the surface structures are systematically varied, which allows the influence of morphology on the biological response to be determined. In order to discriminate morphological from chemical effects, surfaces are chemically modified with poly(ethylene glycol) and tridecafluoroctyltriethoxysilane. This chemical modification changes the water contact angles while the influence of the morphology is retained. The lowest level of settlement is observed for structures of the order 2 µm. All surfaces are characterized with respect to their wettability, chemical composition, and morphological properties by contact angle measurement, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy.     

Unveiling the Mechanism of Water‐Triggered Diplex Transformation and Correlating the Changes in Structures and Separation Properties

Recently, great attention has been devoted to the initial and final structures of single‐crystal to single‐crystal (SCSC) transformations and dissolution‐recrystallization structural transformations (DRSTs), whereas the isolation and characterization of crucial intermediates and the unequivocal mechanism of the dynamic conversion process receive comparatively little consideration. Herein, a Cu^II‐based porous coordination polymer (PCP), which possesses a Kagomé lattice, is solvothermally synthesized. Triggered by water, the 2D Kagomé lattice (PCP‐1) primarily undergoes a reversible SCSC transformation to a distorted Kagomé intermediate (PCP‐2), which is followed by a DRST process to form a 3D NbO framework (PCP‐3) in situ. To the best of our knowledge, this is the first demonstration of a mixed SCSC and DRST transformation process. Notably, the sequential transformations result in the formation of the intermediate and the final product, which could not be obtained by direct synthesis. Regarding the intermediate, we have characterized the transformation separately and propose a plausible mechanism. More interestingly, the adsorption isotherms of water, methanol, and ethanol for the activated materials are distinctly different from one another. PCP‐2′ can uptake all three vapors with different adsorption capacities; however, the 3D transformed material PCP‐3′ only significantly absorbs water, which is concomitant with an amorphous‐to‐crystalline transformation, leading to the selective extraction of water from alcohol.     

Electrochemical and Top‐Down 3D Ion‐Carving to Change Magnetic Properties

It is challenging to develop new top‐down approaches to tailor particles into subnanometer size structures on a large scale to further reveal their structure‐dependent physicochemical properties. Here, we demonstrate a non‐conventional, electrochemical, 3D ion‐carving process to tailor particles into subscale flower‐like nanostructures at room temperature. The technology is based on the electrochemical insertion/extraction of lithium ions as a carving “knife” to carve the single‐crystalline particle precursor into higher‐order, flower‐like nanostructures with hexagonal nanopetals as the building units. Our study demonstrates that the morphology of the as‐carved, flower‐like nanostructures can be controlled by the electrochemical parameters, such as the current density and the number of cycles. Particularly interesting is that dramatically different magnetic properties can be achieved depending on the morphology through careful tuning by the electrochemical ion‐carving process. The as‐carved, flower‐like particles may find many important applications, including magnetic nanodevices. Our approach, in principle, is applicable to prepare various kinds of 3D‐structured materials with different compositions.     

Structure–Property Relations in All‐Organic Dye‐Sensitized Solar Cells

A structure–property relationship in all‐organic dye solar cells is revealed by first‐principles molecular dynamics and real‐time time‐dependent density functional theory simulations, accompanied with experimental confirmation. An important structural feature at the interface, Ti–N anchoring, for a broad group of all‐organic dyes on TiO₂ is inferred from energetics, vibrational recognition, and electronic data. This fact is contrary to the usual assumption; however, it optimizes electronic level alignment and photoelectron injection dynamics, greatly contributing to the observed efficiency improvement in all‐organic cyanoacrylate dye sensitized solar cells.     

Epitaxial Ferroelectric Heterostructures with Nanocolumn‐Enhanced Dynamic Properties

The possibility to tailor ferroelectricity by controlling epitaxial strain in thin films and heterostructures of complex metal oxides is well established. Here it is demonstrated that apart from this mechanism, 3D film growth during heteroepitaxy can be used to favor specific domain configurations that lead to step‐like polarization switching and a giant nonlinear dielectric response in sub‐switching ac electric fields. A combination of cube‐on‐cube epitaxial growth and the formation of columnar structures during pulsed laser deposition of Pb_0.5Sr_0.5TiO₃ films on La_0.5Sr_0.5CoO₃ bottom electrode layers and MgO (001) substrates stabilizes ferroelectric nanodomains with enhanced dynamic properties. In the Pb_0.5Sr_0.5TiO₃ films, a‐ and c‐oriented epitaxial columns grow from the bottom to the top of the film leading to random polydomain architectures with strong associations between the ferroelectric domains and the nanocolumns. Polarization switching in the two domain populations is initiated at distinctive fields due to domain wall pinning on column boundaries. Moreover, piezoelectric coupling between ferroelectric domains leads to strong interdomain elastic interactions, which result in an enhanced Rayleigh‐type dielectric nonlinearity. The growth of epitaxial films with 3D columnar structures opens up new routes towards the engineering of enhanced ferroelectric and electromechanical functions in a broad class of complex oxide materials.     

In Situ Preparation of Sandwich MoO3/C Hybrid Nanostructures for High‐Rate and Ultralong‐Life Supercapacitors

This work presents a design of sandwich MoO₃/C hybrid nanostructure via calcination of the dodecylamine‐intercalated layered α‐MoO₃, leading to the in situ production of the interlayered graphene layer. The sample with a high degree of graphitization of graphene layer and more interlayered void region exhibits the most outstanding energy storage performance. The obtained material is capable of delivering a high specific capacitance of 331 F g^?1 at a current density of 1 A g^?1 and retained 71% capacitance at 10 A g^?1. In addition, nearly no discharge capacity decay between 1000 and 10 000 continuous charge–discharge cycles is observed at a high current density of 10 A g^?1, indicating an excellent specific capacitance retention ability. The exceptional rate capability endows the electrode with a high energy density of 41.2 W h kg^?1 and a high power density of 12.0 kW kg^?1 simultaneously. The excellent performance is attributed to the sandwich hybrid nanostructure of MoO₃/C with broad ion diffusion pathway, low charge‐transfer resistance, and robust structure at high current density for long‐time cycling. The present work provides an insight into the fabrication of novel electrode materials with both enhanced rate capability and cyclability for potential use in supercapacitor and other energy storage devices.     

Morphology Control in Solution‐Processed Bulk‐Heterojunction Solar Cell Mixtures

The efficiency of bulk‐heterojunction solar cells is very sensitive to the nanoscale structure of the active layer. In the past, the final morphology in solution‐processed devices has been controlled by varying the casting solvent and by curing the layer using heat tempering or solvent soaking. A recipe for making the “best‐performing” morphology can be achieved using these steps. This article presents a review of several new techniques that have been developed to control the morphology in polymer/fullerene heterojunction mixtures. The techniques fall into two broad categories. First, the morphology can be controlled by preparing nanoparticle suspensions of one component. The size and shape of the nanoparticles in solution determine the size and shape of the domain in a mixed layer. Second, the morphology can be controlled by adding a secondary solvent or an additive that more strongly affects one component of the mixture during drying. In both cases, the as‐cast efficiency of the solar cell is improved with respect to the single‐solvent case, which strongly argues that morphology control is an issue that will receive increasing attention in future research.     

Enhancement of Thermoelectric Figure‐of‐Merit by a Bulk Nanostructuring Approach

Recently a significant figure‐of‐merit (ZT) improvement in the most‐studied existing thermoelectric materials has been achieved by creating nanograins and nanostructures in the grains using the combination of high‐energy ball milling and a direct‐current‐induced hot‐press process. Thermoelectric transport measurements, coupled with microstructure studies and theoretical modeling, show that the ZT improvement is the result of low lattice thermal conductivity due to the increased phonon scattering by grain boundaries and structural defects. In this article, the synthesis process and the relationship between the microstructures and the thermoelectric properties of the nanostructured thermoelectric bulk materials with an enhanced ZT value are reviewed. It is expected that the nanostructured materials described here will be useful for a variety of applications such as waste heat recovery, solar energy conversion, and environmentally friendly refrigeration.     

Br‐Doped Li4Ti5O12 and Composite TiO2 Anodes for Li‐ion Batteries: Synchrotron X‐Ray and in situ Neutron Diffraction Studies

Synchrotron X‐ray diffraction data were used to determine the phase purity and re‐evaluate the crystal‐structure of Li₄Ti₅O_12‐xBr_x electrode materials (where the synthetic chemical inputs are x = 0.05, 0.10 0.20, 0.30). A maximum of x′ = 0.12 Br, where x′ is the Rietveld‐refined value, can be substituted into the crystal structure with at least 2% rutile TiO₂ forming as a second phase. Higher Br concentrations induced the formation of a third, presumably Br‐rich, phase. These materials function as composite anodes that contain mixtures of TiO₂, Li₄Ti₅O_12‐xBr_x, and a Br‐rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li₄Ti₅O_12‐xBr_x where x′ ～ 0.1 were found to correspond to the optimum in electrochemical properties, while larger quantities of the secondary phases contributed to the degradation of the performance. In situ neutron diffraction of a composite anatase TiO₂/Li₄Ti₅O₁₂ anode within a custom‐built battery was used to determine the electrochemical function of the TiO₂ component. The Li₄Ti₅O₁₂ component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO₂ (1.7 V). This enabled Li insertion/extraction to be tuned through the choice of voltage range in both components of this composite or in the anatase TiO₂ phase only. The use of composite materials may facilitate the development of multi‐component electrodes where different active materials can be cycled in order to tune power output.     

Domain Engineering of Lead‐Free Li‐Modified (K,Na)NbO3 Polycrystals with Highly Enhanced Piezoelectricity

Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO₃ (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d₃₃ can be increased up to 324 pC N^?1 even from a considerably high value (190 pC N^?1) by means of a re‐poling treatment after room‐temperature aging. Such a high d₃₃ value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics.     

Defect Creation in HKUST‐1 via Molecular Imprinting: Attaining Anionic Framework Property and Mesoporosity for Cation Exchange Applications

Discovering new methods to tailor the physical and chemical properties of metal–organic frameworks (MOFs) for their numerous potential applications is highly desired. In this work, engineering defects in MOF via a molecular imprinting approach is developed to endow HKUST‐1, a well‐studied classical MOF, with hierarchical structure, mesoporosity, and anionic framework property. Ringlike anionic HKUST‐1 (HKUST‐1‐R) and a wide variety of metal‐doped isostructural analogues (M/HKUST‐1‐R, M = Ca, Cd, Ce, Co, Li, Mn, Na, Ni, or Zn) are obtained. The benefits of transforming imprinted HKUST‐1‐R to M/HKUST‐1‐R are further demonstrated for various applications. This synthetic strategy is therefore suitable for rational design and functionalization of MOFs in addition to their morphological control in nanoscale.     

Three‐Dimensional Bulk Heterojunction Morphology for Achieving High Internal Quantum Efficiency in Polymer Solar Cells

Here, an investigation of three‐dimensional (3D) morphologies for bulk heterojunction (BHJ) films based on regioregular poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) is reported. Based on the results, it is demonstrated that optimized post‐treatment, such as solvent annealing, forces the PCBM molecules to migrate or diffuse toward the top surface of the BHJ composite films, which induces a new vertical component distribution favorable for enhancing the internal quantum efficiency (η_IQE ) of the devices. To investigate the 3D BHJ morphology, novel time‐of‐flight secondary‐ion mass spectroscopy studies are employed along with conventional methods, such as UV‐vis absorption, X‐ray diffraction, and high‐resolution transmission electron microscopy studies. The η_IQE of the devices are also compared after solvent annealing for different times, which clearly shows the effect of the vertical component distribution on the performance of BHJ polymer solar cells. In addition, the fabrication of high‐performance P3HT:PCBM solar cells using the optimized solvent‐annealing method is reported, and these cells show a mean power‐conversion efficiency of 4.12% under AM 1.5G illumination conditions at an intensity of 100 mW cm^?2.     

Mesomorphic Organization and Thermochromic Luminescence of Dicyanodistyrylbenzene‐Based Phasmidic Molecular Disks: Uniaxially Aligned Hexagonal Columnar Liquid Crystals at Room Temperature with Enhanced Fluorescence Emission and Semiconductivity

A new dicyanodistyrylbenzene‐based phasmidic molecule, (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(3,4,5‐tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT). GDCS molecules self‐assemble into supramolecular disks consisting of a pair of molecules in a side‐by‐side disposition assisted by secondary bonding interactions of the lateral polar cyano group, which, in turn, constitute the hexagonal columnar LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystalline states, respectively, in contrast to the total absence of fluorescence emission in the isotropic melt state according to the characteristic aggregation‐induced enhanced emission (AIEE) behavior. The AIEE and two‐color luminescence thermochromism of GDCS are attributed to the peculiar intra‐ and intermolecular interactions of dipolar cyanostilbene units. It was found that the intramolecular planarization and restricted molecular motion associated with a specific stacking situation in the liquid/solid crystalline phases are responsible for the AIEE phenomenon. The origin of the two‐color luminescence was elucidated to be due to the interdisk stacking alteration in a given column driven by the specific local dipole coupling between molecular disks. These stacking changes, in turn, resulted in the different degree of excited‐state dimeric coupling to give different emission colors. To understand the complicated photophysical properties of GDCS, temperature‐dependent steady‐state and time‐resolved PL measurements have been comprehensively carried out. Uniaxially aligned and highly fluorescent LC and crystalline microwires of GDCS are fabricated by using the micromolding in capillaries (MIMIC) method. Significantly enhanced electrical conductivity (0.8 × 10^?5 S?cm^?1/3.9 × 10^?5 S?cm^?1) of the aligned LC/crystal microwires were obtained over that of multi‐domain LC sample, because of the almost perfect shear alignment of the LC material achieved in the MIMIC mold.     

The Performance of Small‐Pore Microporous Aluminophosphates in Low‐Temperature Solar Energy Storage: The Structure–Property Relationship

The utilization of the reversible chemical and physical sorption of water on solids provides a new thermal energy storage concept with a great potential for lossless long‐term storage. The performance of microporous aluminophosphates in heat storage applications is highlighted by a comparative thermogravimetric and calorimetric study of three known materials (SAPO‐34, AlPO₄‐18, APO‐Tric) and is correlated with their structural features. The maximum water sorption capacity is similar for all three samples and results in a stored energy density of 240 kWh m^?3 in the 40–140 °C range. The elemental composition influences the gradual (silicoaluminophosphate SAPO‐34) or sudden (aluminophosphates AlPO₄‐18, APO‐Tric) water uptake, with the latter being favourable in storage systems. The driving force for the determined sorption process is the formation of highly ordered water clusters in the pores, which is enabled by rapid and reversible changes in the Al coordination and optimal pore diameters. The ease with which changes in the Al coordination can occur in APO‐Tric is related to the use of the fluoride route in the synthesis. The understanding of these fundamental structure/sorption relationships forms an excellent basis for predicting the storage potential of numerous known or new microporous aluminophosphates and other porous materials from their crystal structures.