Formation Of Mesocrystals Research Articles

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.

Hexagonal sodium yttrium fluoride mesocrystals: One-pot hydrothermal synthesis, formation mechanism and multicolor up-/down-converted luminescence for anti-counterfeiting and fingerprint detection

Abstract Currently, a precise architecture manipulation of mesocrystals with controllable morphology and tunable size remains a huge challenge and is highly desired for their practical applications. Here, we develop a facile one-pot strategy for the direct synthesis of uniform and monodispersed β-NaYF4 mesocrystals with cantaloupe-like shape and adjustable dimension. To investigate the formative mechanism of β-NaYF4 superstructures in depth, the evolution processes for the crystal structure and morphology of β-NaYF4 mesocrystals under different experimental conditions have been systematically researched and discussed. A series of experimental results demonstrate that intrinsic crystallographic structure and external factors govern the crystal growth process of hexagonal-phased NaYF4. The processes of dissolution-renucleation, anisotropic growth, subsequent oriented attachment and self-assembly are believed to be responsible for the formation of cantaloupe-shaped β-NaYF4 mesocrystals. Moreover, the luminescence properties of β-NaYF4:RE3+ (RE = Ce, Tb, Eu, Yb, Tm and Ho) mesocrystals are also studied and efficient multicolor upconverting and downshifting emissions can be easily realized. As a proof of concept experiment, the as-synthesized β-NaYF4:RE3+ phosphors are employed to demonstrate their promising applications in anti-counterfeiting and fingerprint identification.

Magnetic field-assisted assembly of iron oxide mesocrystals: a matter of nanoparticle shape and magnetic anisotropy.

This letter describes the formation and detailed characterization of iron oxide mesocrystals produced by the directed assembly of superparamagnetic iron oxide-truncated nanocubes using the slow evaporation of the solvent within an externally applied homogeneous magnetic field. Anisotropic mesocrystals with an elongation along the direction of the magnetic field can be produced. The structure of the directed mesocrystals is compared to self-assembled mesocrystalline films, which are formed without the influence of a magnetic field. The remarkable structural difference of mesocrystals produced within the external magnetic field from those self-assembled without field indicates that the specific nanoparticle ordering within the superstructure is driven by competing of two types of anisotropic interactions caused by particle shape (i.e., faceting) and orientation of the magnetic moment (i.e., easy axes: <111>magnetite). Hence, these findings provide a fundamental understanding of formation mechanisms and structuring of mesocrystals built up from superparamagnetic nanoparticles and how a magnetic field can be used to design anisotropic mesocrystals with different structures.

Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth

A subunit growth controlled orientation uncovering the formation mechanism of spherical calcium sulfate mesocrystals.

Developing Biopolymer Mesocrystals by Crystallization of Secondary Structures

Particle-based mesocrystals have been known for over 10 years; however, examples of biopolymer mesocrystals are rather scarce. The synthesis of particle precursors of biopolymers, the identification of particle-mediated crystallization processes, and thus the synthesis of mesocrystals of biopolymers are challenging. Here, we summarize the existing examples of biopolymer crystallization based on self-assembly of the secondary structures, which could induce the formation of biopolymer mesocrystals. As basic building units, simple secondary structures such as β-sheets or α-helixes could provide a useful tool for the design of biopolymer mesocrystals.

Hydrothermal crystallization of Pmn21 Li2FeSiO4 hollow mesocrystals for Li-ion cathode application

Lithium transition metal orthosilicates such as Li2FeSiO4 (LFS) have been recognized as promising cathode materials for application in Li-ion batteries because of their high theoretical energy density, safety, and benign/abundant element composition. Their development, however, has been hampered by the challenge of obtaining phase-pure and defect-free Li2FeSiO4 nanoparticles as non-optimized crystal properties have an adverse effect on structural stability and electrochemical performance. Considering the sustainable potential of hydrothermal synthesis in producing electrode materials, here we employ this process to systematically study critical synthesis parameters for optimal control of particle size, morphology, phase purity, and defects of Li2FeSiO4 crystallized in the orthorhombic crystal system with space group Pmn21. It is shown that via a combination of elevated FeSO4 concentration regime and use of EDTA as a complexing agent, phase-pure Pmn21 particle formation can be controlled. Synchrotron-based XRD Rietveld refinement and 57Fe Mössbauer spectroscopy reveal a significant reduction in Li-Fe antisite defects and presence of Fe3+. Additionally, the use of EDTA promotes the formation of unique peanut-shell looking hollow mesocrystals that are advantageous in maximizing electrode/electrolyte contact resulting in higher Li-ion storage capacity than dense LFS particles. On the basis of detailed XRD, SEM, and TEM characterizations, a four-step crystallization mechanism is proposed to explain the formation of the hollow mesocrystals. These findings bring new insight into our pursuit of optimization of Li2FeSiO4 as a cathode material for Li-ion batteries.

Superstructure Ta2O5 mesocrystals derived from (NH4)2Ta2O3F6 mesocrystals with efficient photocatalytic activity.

Superstructured mesocrystalline Ta2O5 nanosheets were successfully prepared from mesocrystalline (NH4)2Ta2O3F6 nanorods by the annealing method for the first time. The as-prepared mesocrystalline Ta2O5 nanosheets in this work showed remarkable visible light absorption, mainly due to the formation of oxygen vacancy defects in the mesocrystalline Ta2O5 nanosheets, which was also confirmed by XPS spectra, Raman spectra and EPR spectra. Besides, the mesocrystalline Ta2O5 nanosheets showed a highly enhanced photocatalytic activity of 11 268.24 μmol g-1 h-1, about 3.95 times that of commercial Ta2O5. Moreover, the specific surface area of the mesocrystalline Ta2O5-800 nanosheets was 16.34 m2 g-1, about 5.32 times that of the commercial Ta2O5 (3.072 m2 g-1). The valence band XPS spectra indicated a strong oxidizing ability of the mesocrystalline Ta2O5 nanosheets in comparison to that of commercial Ta2O5. The formation of superstructured Ta2O5 mesocrystals generated long lifetime carriers and effective conduction pathways, which greatly enhanced the photocatalytic activity for hydrogen production.

On mechanisms of mesocrystal formation: magnesium ions and water environments regulate the crystallization of amorphous minerals

Elucidating the emergence of crystalline superstructures from amorphous precursors, hydration environments and ionic constituents can guide transformation and structuration reactions towards distinct micro- and nano-structures.

High-Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions.

Mesocrystals of high-magnesian calcites are commonly found in biogenic calcites. Under ambient conditions, it remains challenging to prepare mesocrystals of high-magnesian calcite in aqueous solution. We report that mesocrystals of calcite with magnesium content of about 20 mol % can be obtained from the phase transformation of magnesian amorphous calcium carbonate (Mg-ACC) in lipid solution. The limited water content on the Mg-ACC surface would reduce the extent of the dissolution-reprecipitation process and bias the phase transformation pathway toward solid-state reaction. We infer from the selected area electron diffraction patterns and the dark-field transmission electron microscopic images that the formation of Mg-calcite mesocrystals occurs through solid-state secondary nucleation, for which the phase transformation is initiated near the mineral surface and the crystalline phase propagates gradually toward the interior part of the microspheres of Mg-ACC.

Mesoscale martensitic transformation in single crystals of topological defects

Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the double-twisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.

A Mesocrystal‐Like Morphology Formed by Classical Polymer‐Mediated Crystal Growth

AbstractGrowth by oriented assembly of nanoparticles is a widely reported phenomenon for many crystal systems. While often deduced through morphological analyses, direct evidence for this assembly behavior is limited and, in the calcium carbonate (CaCO3) system, has recently been disputed. However, in the absence of a particle‐based pathway, the mechanism responsible for the creation of the striking morphologies that appear to consist of subparticles is unclear. Therefore, in situ atomic force microscopy is used to investigate the growth of calcite crystals in solutions containing a polymer additive known for its ability to generate crystal morphologies associated with mesocrystal formation. It is shown that classical growth processes that begin with impurity pinning of atomic steps, leading to stabilization of new step directions, creation of pseudo‐facets, and extreme surface roughening, can produce a microscale morphology previously attributed to nonclassical processes of crystal growth by particle assembly.

Mesocrystals: Past, Presence, Future

In this review, we briefly summarize the history of mesocrystal research. We introduce the current structural definition of mesocrystals and discuss the appropriate base for the classification of mesocrystals and their relations with other classes of solid state materials in terms of their structure. Building up on this, we comment on the problems in mesocrystal research both fundamental and methodological. Additionally, we make the short overview of the mesocrystal formation principles and synthetic routes used for their fabrications. As an outlook into the future, we highlight the most notable trends in mesocrystal research and developments.

Trends in mica–mica adhesion reflect the influence of molecular details on long-range dispersion forces underlying aggregation and coalignment

Oriented attachment of nanocrystalline subunits is recognized as a common crystallization pathway that is closely related to formation of nanoparticle superlattices, mesocrystals, and other kinetically stabilized structures. Approaching particles have been observed to rotate to achieve coalignment while separated by nanometer-scale solvent layers. Little is known about the forces that drive coalignment, particularly in this "solvent-separated" regime. To obtain a mechanistic understanding of this process, we used atomic-force-microscopy-based dynamic force spectroscopy with tips fabricated from oriented mica to measure the adhesion forces between mica (001) surfaces in electrolyte solutions as a function of orientation, temperature, electrolyte type, and electrolyte concentration. The results reveal an ∼60° periodicity as well as a complex dependence on electrolyte concentration and temperature. A continuum model that considers the competition between electrostatic repulsion and van der Waals attraction, augmented by microscopic details that include surface separation, water structure, ion hydration, and charge regulation at the interface, qualitatively reproduces the observed trends and implies that dispersion forces are responsible for establishing coalignment in the solvent-separated state.

Spindle-Shaped Apatite La–Silicate Mesocrystals Grown via a Multistep Nucleation and Growth Mechanism, A New Strategy for Preparing Ordered Nanoscale Superstructures

A precise control over the growth of mesocrystals composed of crystallographically aligned nanocrystals is necessary to exploit their collective properties for potential applications. Here, we describe a successful preparation of spindle-shaped apatite La–silicate (ap-LSO) mesocrystals with an ordered arrangement of elongated nanocrystals along c-axis through a solvothermal process, as revealed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy–selected area electron diffraction, and high-resolution transmission electron microscopy. It has been shown that a multistep nucleation and growth mechanism would be responsible for the formation of the mesocrystals. This novel mesocrystal formation mechanism breaks through the classical crystallization norm and opens a new way to constructing mesocrystals with nanoscale superstructures.

Hierarchically nanostructured shuttle-like aragonite mesocrystals: Preparation, characterization, growth mechanism, and removal ability to La(III)

Hierarchically nanostructured Shuttle-like aragonite mesocrystals have been successfully achieved in a water/ethylene glycol (EG) binary solvent system by a facile microwave-assisted method without using any other organic additives. The synthesized products were characterized by a wide range of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption analysis. The effects of the ratio of EG to water, and calcium sources on the formation of the special structured aragonite were studied systematically. The results indicate that the cooperation of EG and acetate ions are indispensable to the formation of shuttle-like aragonite mesocrystals, and a plausible oriented attachment formation mechanism is proposed. Moreover, the removal ability of the hierarchical aragonite mesocrystals for La(III) was also tested. Batch experiments reveal that the aragonite possesses excellent removal efficiency to La(III), suggesting that the shuttle-like aragonite mesocrystals can be potentially applied in the removal of rare earth elements (REEs) entering the water environment.

New insights into polymer mediated formation of anatase mesocrystals

The reaction between (NH4)2TiF6 and H3BO3 in the presence of varying quantities of PEG-6000 was used to form NH4TiOF3 mesocrystals (MCs). The amount of PEG-6000, employed as a template, is crucial to the formation of defect free, non-agglomerated NH4TiOF3 MCs; high concentrations lead to MC agglomeration, lower ones result in centralized defects. This polymer-mediated formation process may be understood using an analogy with known polymerization reactions. The oxofluorotitanate MCs readily undergo a thermal topotactic transformation to give anatase MCs with photocatalytic activity. The TiO2 MCs are porous, with highly orientated lamellar crystallites that form part of the larger mesocrystal structure.

Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops.

Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

Self‐Assembled Magnetite Mesocrystalline Films: Toward Structural Evolution from 2D to 3D Superlattices

This study describes synthesis and detailed characterization of 2D and 3D mesocrystalline films produced by self‐assembly of iron oxide (magnetite) truncated nanocubes. The orientational relations between nanocrystals within the superlattice are examined and atomistic models are introduced. In the 2D case, two distinct superstructures (i.e., translational order) of magnetite nanocubes can be observed with p4mm and c2mm layer symmetries while maintaining the same orientational order (with [100]magnetite perpendicular to the substrate). The 3D structure can be approximated by a slightly distorted face‐centered cubic (fcc) superlattice. The most efficient space filling within the 3D superstructure is achieved by changing the orientational order of the nanoparticles and following the “bump‐to‐hollow” packing principle. Namely orientational order is determined by the shape of the nanoparticles with the following orientational relations: [001]SL||[310]magnetite, [001]SL||[301]magnetite, [001]SL||[100]magnetite. Overall the presented data provide a fundamental understanding of a mesocrystal formation mechanism and their structural evolution. Structure, composition, and magnetic properties of the synthesised nanoparticles are also characterized.

Cuboctahedral Sb2O3Mesocrystals Organized from Octahedral Building Blocks: More than Self-Similarity

Assembly of nanoparticle building blocks over multiple length scales into hierarchically ordered structures plays an essential role in the nonclassical crystallization pathway. Although random particle aggregates are constantly observed in crystallization experiments, mesocrystals with well-shaped morphology and ordered hierarchical structure have been seldomly reported. Here, we describe the successful production of remarkable cuboctahedral Sb2O3 mesocrystals with hierarchical three-dimensional superstructures through a simple solution route. This is the first example of well-defined polyhedral mesocrystals with a cuboctahedral external morphology differing from the octahedral morphology of the building subunits. Electrostatic interactions between cetyltrimethylammonium cations (CTA+) and tartrate anions and hydrophobic interactions between the cetyltrimethylammonium bromide tails were supposed to be the driving force for the aggregation-based growth process. This novel mesocrystal formation breaks through the classical crystallization pattern and opens up a new pathway to construct mesoscale-transformed mesocrystals with hierarchical superstructures.

Experimental Observation of Fullerene Crystalline Growth from Mesocrystal to Single Crystal

Fullerene hierarchical mesocrystals were first prepared by antisolvent induced precipitation method. Their morphologies and sizes can be controlled by adjusting the antisolvent type and the ratio between the solvent (toluene) and antisolvent (ethyl acetate or tetrahydrofuran). The formation of fullerene mesocrystals and their transformation to single crystal were observed by time-dependent experiments with SEM and TEM. Fullerene mesocrystals can be separated from the solution and are stable for several months. HRTEM revealed that mesocrystals were made up of highly oriented nanoparticles. The formation of fullerene mesocrystals and their transformation to single crystals provide a new way for the construction of fullerene nanostructures with different applications.