Formation Of Mesocrystals Research Articles

Kinetics of Oriented Attachment of Mica Crystals.

Oriented attachment (OA), that is, the coalescence of crystals through attachment on coaligned crystal faces, is a nonclassical crystal growth process. Before attachment, a mesocrystal consisting of coaligned parallel crystals but with liquid separating them was observed. Fundamental questions such as why OA is kinetically favored and whether a mesocrystal stage is a prerequisite for OA are raised. Through combining brute-force molecular dynamics simulations and path samplings based on extensive umbrella simulations, we address these questions with a case study on the OA of a mica nanocrystal onto a mica crystal substrate in water. Brute-force simulations show that if two mica crystals are attached but largely misaligned, coalignment hardly appears. Thus, if OA is possible, then coalignment must appear before the attachment between crystals. Electrophoresis of the nanocrystal toward the substrate surface is spontaneous, but mesocrystal formation is occasional, also shown by brute-force simulations. Free energies along different pathways show that OA is spontaneous and kinetically favored over non-OA, and a mesocrystal formation is just a bifurcation in the pathway. OA is through a pathway in which the nanocrystal is tilted with respect to the substrate. Part of the nanocrystal is attached to the substrate first, and then, OA is gradually completed. Once a mesocrystal is occasionally formed, then a jump event is needed for the nanocrystal to get back to the OA pathway. The sampling technique here can hopefully guide the design of nanostructured materials facilitated by OA.

Formation and properties of spindle-shaped aragonite mesocrystals from Mg-bearing solutions.

The formation of aragonite under ambient conditions is typically linked to Mg-rich aqueous environments. The grains that form in such environments show peculiar properties such as aggregate-like appearance and mesocrystalline character. We tested the effect of dissolved Mg2+ ions on the formation of aragonite mesocrystals by synthesizing aragonite with an automatic titrator at constant pH and at different dissolved Mg : Ca ratios, and by studying the properties of the precipitated material with various scanning transmission electron microscopy (STEM) techniques. At all studied Mg : Ca ratios the firstly condensed carbonate phase was Mg-bearing amorphous calcium carbonate (Mg-ACC) that transformed into aragonite during the synthesis experiments. The aragonite grains had typically aggregate-like appearance and spindle shapes, with the external morphologies of the spindles unaffected by variation in solution chemistry. The alignment of the nanocrystals within the aggregates was crystallographically highly coherent, the [001] directions of nanocrystals showing only a small misorientation with respect to one another; however, both parallel and twin assembly of neighbouring crystals occurred. An increase in the dissolved Mg concentration decreased the crystallographic coherence between the aragonite nanocrystals, suggesting an important role of Mg2+ ions in the assembly of aragonite spindles. Whereas the mesoscale-ordered arrangement of nanocrystals implies a particle-mediated assembly, the observed differences in particle size and composition between the amorphous precursor and the crystalline end-product suggest that the crystallization includes at least partial dissolution and re-precipitation. These findings provide insight into the formation of aragonite and could contribute to the understanding of important aspects of the formation of mesocrystals and hierarchically structured biogenic minerals.

Crystallographic disorder-order transition of self-assembly FeCo mesocrystals independent of ligand

Mesocrystal with aligned small grains is an important type of block in building high performance artificial bulk materials. But it is difficult to obtain mesocrystal particles without the assistant of surface ligands due to their unclear formation process. In this study, mesocrystal FeCo nanoparticles were successfully synthesized by co-precipitation of Fe and Co atoms using hydrazine hydrate as reducing agent with an appropriate addition rate. A non-classic nucleation process and the formation of mesocrystal FeCo nanoparticles had been observed. Microstructure characterization reveals that the arrangement of grains inside particles gradually change from multi-orientation to mono-orientation with the change of addition rate of hydrazine. The hydrazine addition rate, ie the reducing rate of metal atoms plays an important role for the formation of mesocrystal particles. The obtained mesocrystal FeCo particles show good magnetic performance (the highest magnetization and lowest coercivity). The discovery of the influence of synthesis conditions on the formation of mesocrystals provide a useful way to control the microstructure and the performance of consisting nanostructures.

Revealing the Impact of Polystyrene Functionalization of Au Octahedral Nanocrystals of Different Sizes on the Formation and Structure of Mesocrystals

AbstractThe self‐assembly of anisotropic nanocrystals (stabilized by organic capping molecules) with pre‐selected composition, size, and shape allows for the creation of nanostructured materials with unique structures and features. For such a material, the shape and packing of the individual nanoparticles play an important role. This work presents a synthesis procedure for ω‐thiol‐terminated polystyrene (PS‐SH) functionalized gold nanooctahedra of variable size (edge length 37, 46, 58, and 72 nm). The impact of polymer chain length (Mw: 11k, 22k, 43k, and 66k g⋅mol−1) on the growth of colloidal crystals (e. g. mesocrystals) and their resulting crystal structure is investigated. Small‐angle X‐ray scattering (SAXS) and scanning transmission electron microscopy (STEM) methods provide a detailed structural examination of the self‐assembled faceted mesocrystals based on octahedral gold nanoparticles of different size and surface functionalization. Three‐dimensional angular X‐ray cross‐correlation analysis (AXCCA) enables high‐precision determination of the superlattice structure and relative orientation of nanoparticles in mesocrystals. This approach allows us to perform non‐destructive characterization of mesocrystalline materials and reveals their structure with resolution down to the nanometer scale.

Understanding Hierarchical Structure Construction Strategies and Biomimetic Design Principles: A Review

Organisms use gene and cell engineering to tailor the mineralization process and synthesize structure composites with special functions and favorable properties. This spurs scientists to design functional materials based on learning from nature. Herein, a systematic review of the biomimetic synthesis and hierarchical structure design of calcium carbonate–based minerals is presented. First, biomimetic synthesis strategies, including additive‐induced, template‐oriented, and gel‐mediated routes to direct the construction of the hierarchical structure, are reviewed. The molecular‐recognition technique and directional assembly pathway are then summarized to precisely describe the interactions between inorganic minerals and organic matter, and direct the mineral growth. Next, the underlying mineralization mechanisms governing the evolution of the complex morphology and structure are discussed. Nonclassical pathways that control mineral growth, including the theories of the amorphous phase, oriented attachment, mesocrystal formation, and liquid precursor, are concluded. Finally, herein, the applications of calcium carbonate–based minerals are discussed. Unique hierarchical structure endows minerals with special functions, including optical performance, biomedical applications, and environmental and ecological restoration. Overall, in this report, the biomimetic synthesis of calcium carbonate–based minerals is reviewed, covering the fundamental principles, construction of the hierarchical structure, underlying mechanisms of mineral growth, and functional designs.

Bioprocess inspired formation of calcite mesocrystals by cation-mediated particle attachment mechanism.

Calcite mesocrystals were proposed, and have been widely reported, to form in the presence of polymer additives via oriented assembly of nanoparticles. However, the formation mechanism and the role of polymer additives remain elusive. Here, inspired by the biomineralization process of sea urchin spine comprising magnesium calcite mesocrystals, we show that calcite mesocrystals could also be obtained via attachment of amorphous calcium carbonate (ACC) nanoparticles in the presence of inorganic zinc ions. Moreover, we demonstrate that zinc ions can induce the formation of temporarily stabilized amorphous nanoparticles of less than 20nm at a significantly lower calcium carbonate concentration as compared to pure solution, which is energetically beneficial for the attachment and occlusion during calcite growth. The cation-mediated particle attachment crystallization significantly improves our understanding of mesocrystal formation mechanisms in biomineralization and offers new opportunities to bioprocess inspired inorganic ions regulated materials fabrication.

Impact of peripheral alkyl chain length on mesocrystal assemblies of G2 dendrons.

Unique sphere-packing mesophases such as Frank-Kasper (FK) phases have emerged from the viable design of intermolecular interactions in supramolecular assemblies. Herein, a series of Cn-G2-CONH2 dendrons possessing an identical core wedge are investigated to elucidate the impact of peripheral alkyl chain lengths (Cn) on the formation of the close-packed structures. The C18 and C14 dendrons, of which the contour lengths of the periphery Lp are longer than the wedge length Lw, assemble into a uniform sphere-packing phase such as body-centred cubic (BCC), whereas the C8 dendron with short (Lp < Lw) corona environment forms the FK A15 phase. Particularly in the intermediate C12 and C10 dendrons (Lp ≈ Lw), cooling the samples from an isotropic state leads to cooling-rate-dependent phase behaviours. The C12 dendron produces two structures of hexagonal columnar and sphere-packing phases (BCC and A15), while the C10 dendron generates the A15 and σ phases by the fast- and slow-cooling processes, respectively. Our results show the impact of peripheral alkyl chain lengths on the formation of mesocrystal phases, where the energy landscape of the dendrons at Lp/Lw ≈ 1 must be more complex and delicate than those with either longer or shorter peripheral alkyl chains.

Multistep Crystallization of Pharmaceutical Amorphous Nanoparticles via a Cognate Pathway of Oriented Attachment: Direct Evidence of Nonclassical Crystallization for Organic Molecules.

Crystallization of organic molecules is important in a wide range of scientific disciplines. However, in contrast to maturely studied crystallization of inorganic materials, the crystallization mechanisms of organic molecules involving nucleation and crystal growth are still poorly understood. Here, we used time-resolved cryogenic transmission electron microscopy to directly map the morphological evolution of amorphous cyclosporin A (CyA) nanoparticles during CyA crystallization. We successfully observed its initial nucleation and found that the amorphous CyA nanoparticles crystallized via a pathway cognate with oriented attachment, which is the nonclassical crystallization mechanism usually reported for inorganic compounds. Crystalline mesostructured intermediates (mesocrystals) were formed during crystallization. This study revealed clear and direct evidence of mesocrystal formation and oriented attachment in organic pharmaceuticals, providing new insights into the crystallization of organic molecules and theories of nonclassical crystallization.

Field-Assisted Formation of NH4CoF3 Mesocrystals toward Hierarchical Co3O4 Cuboids as Anode Materials for Lithium-Ion Batteries.

Porous NH4CoF3 mesocrystalline cuboids with highly exposed {100} facets are grown by in situ reaction of products produced by high field anodization of cobalt metal foil, via a nonclassical crystallization process involving oriented particle aggregation. 3D nano-micro hierarchical Co3O4 cuboids are obtained by thermal annealing of NH4CoF3 mesocrystals. The microstructure and morphology of products are characterized by electron microscopy and X-ray diffraction. The combination of small nanoparticle subunits, micrometer-sized overall particles, and porous structure provides the obtained hierarchical Co3O4 cuboids with large electrolyte-electrode contact areas, channels for large lithium ion flux, pore accessibility, and structural stability, leading to excellent rate and cyclic performance as lithium-ion battery (LIB) anodes.

Radiation Chemistry Provides Nanoscopic Insights into the Role of Intermediate Phases in CeO2 Mesocrystal Formation

AbstractThe role of intermediate phases in CeO2 mesocrystal formation from aqueous CeIII solutions subjected to γ‐radiation was studied. Radiolytically formed hydroxyl radicals convert soluble CeIII into less soluble CeIV. Transmission electron microscopy (TEM) and X‐ray diffraction studies of samples from different stages of the process allowed the identification of several stages in CeO2 mesocrystal evolution following the oxidation to CeIV: (1) formation of hydrated CeIV hydroxides, serving as intermediates in the liquid‐to‐solid phase transformation; (2) CeO2 primary particle growth inside the intermediate phase; (3) alignment of the primary particles into “pre‐mesocrystals” and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of “mineral bridges”. Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.

Radiation Chemistry Provides Nanoscopic Insights into the Role of Intermediate Phases in CeO2 Mesocrystal Formation

The role of intermediate phases in CeO2 mesocrystal formation from aqueous CeIII solutions subjected to γ‐radiation was studied. Radiolytically formed hydroxyl radicals convert soluble CeIII into less soluble CeIV. Transmission electron microscopy (TEM) and X‐ray diffraction studies of samples from different stages of the process allowed the identification of several stages in CeO2 mesocrystal evolution following the oxidation to CeIV: (1) formation of hydrated CeIV hydroxides, serving as intermediates in the liquid‐to‐solid phase transformation; (2) CeO2 primary particle growth inside the intermediate phase; (3) alignment of the primary particles into “pre‐mesocrystals” and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of “mineral bridges”. Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.

Ionizing Radiation Induced Formation of CeO2 Mesocrystals: γ-Irradiation versus High-Energy Electron Irradiation

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Tailored Synthesis of Iron Oxide Nanocrystals for Formation of Cuboid Mesocrystals.

In this work, we systematically studied the shape- and size-controlled monodisperse synthesis of iron oxide nanocrystals (IONCs) for their use as building blocks in the formation of mesocrystals. For this aim, on understanding the influence of the oleic acid concentration, iron-oleate concentration, and heating rate on the synthesis of robust and reproducible IONCs with desired sizes and shapes, we synthesized highly monodisperse ∼11 nm sized nanocubes and nanospheres. Magnetic measurements of both cubic and spherical IONCs revealed the presence of mixed paramagnetic and superparamagnetic phases in these nanocrystals. Moreover, we observed that the magnetic moments of the nanocubes are more substantial compared to their spherical counterparts. We then demonstrated a simple magnetic-field-assisted assembly of nanocubes into three-dimensional (3D) cuboid mesocrystals while nanospheres did not form any mesocrystals. These findings indicate that small cubic nanocrystals hold great promise as potential building blocks of 3D magnetic hierarchical structures with their superior magnetic properties and mesocrystal assembly capability, which may have high relevance in various fields ranging from high-density data storage to biomedical applications.

Self-similar mesocrystals form via interface-driven nucleation and assembly.

Crystallization by particle attachment (CPA) is a frequently occurring mechanism of colloidal crystallization that results in hierarchical morphologies1-4. CPA has been exploited to create nanomaterials with unusual properties4-6 and is implicated in the development of complex mineral textures1,7. Oriented attachment7,8-a form of CPA in which particles align along specific crystallographic directions-produces mesocrystals that diffract as single crystals do, although the constituent particles are still discernible2,9. The conventional view of CPA is that nucleation provides a supply of particles that aggregate via Brownian motion biased by attractive interparticle potentials1,9-12. However, mesocrystals often exhibit regular morphologies and uniform sizes. Although many crystal systems form mesocrystals1-9 and individual attachment events have been directly visualized10, how random attachment events lead to well defined, self-similar morphologies remains unknown, as does the role of surface-bound ligands, which are ubiquitous in nanoparticle systems3,9,11. Attempts to understand mesocrystal formation are further complicated in many systems by the presence of precursor nanoparticles with a phase distinct from that of the bulk1,13,14. Some studies propose that such particles convert before attachment15, whereas others attribute conversion to the attachment process itself16 and yet others conclude that transformation occurs after the mesocrystals exceed a characteristic size14,17. Here we investigate mesocrystal formation by iron oxides, which are important colloidal phases in natural environments18,19 and classic examples of systems forming ubiquitous precursor phases and undergoing CPA accompanied by phase transformations15,19-21. Combining in situ transmission electron microscopy (TEM) at 80degrees Celsius with 'freeze-and-look' TEM, we tracked the formation of haematite (Hm) mesocrystals in the presence of oxalate (Ox), which is abundant in soils, where iron oxides are common. We find that isolated Hm particles rarely appear, but once formed, interfacial gradients at the Ox-covered surfaces drive Hm particles to nucleate repeatedly about two nanometres from the surfaces, to which they then attach, thereby generating mesocrystals. Comparison to natural and synthetic systems suggests that interface-driven pathways are widespread.

Formation of magnesium calcite mesocrystals in the inorganic environment only by using Ca2+ and Mg2+ and its biological implications

Magnesium calcite (Mg-calcite) mesocrystal is widespread in the biominerals with specific functions. Until now, it remains challenging to obtain Mg-calcite mesocrystals without organic additives and the formation mechanism of Mg-calcite mesocrystals in the ocean is not clear yet. We report here the synthesis of corn-like Mg-calcite mesocrystals from pure amorphous calcium carbonate (ACC) via a facile method only by using Ca2+ and Mg2+. The obtained Mg-calcite is composed of many nanocubes with common crystallographic orientation, which shows very good single crystal feature. In the crystallizing procedure, the ACC nanospheres rapidly agglomerate into Mg-calcite corn-like mesocrystal by oriented attachment (OA) in a certain direction, which belongs to the non-classical nucleation. By this method, the molar ratio of Ca2+ and Mg2+ plays a vital role in the whole crystallization procedure, which may shed a new light on disclosing the mechanism behind for the effect of seawater in the formation of biological Mg-calcite in nature.

A New Pathway for the Formation of Co-aligned Hierarchical Mesocrystals

A New Pathway for the Formation of Co-aligned Hierarchical Mesocrystals

Co-crystallization of racemic amino acids with ZnCl2: an investigation of chiral selectivity upon coordination to the metal centre

A preference for racemic vs. meso-crystal formation has been observed upon the cocrystallization of dl-amino acids with ZnCl2, as a result of homo vs. heterochiral competition.

Observing Oriented Attachment during Mesocrystal Growth with in Situ Dynamic Light Scattering (DLS)

Despite rapidly growing interest in the application of mesocrystals in catalysis, energy storage, and sensing, the understanding of mesocrystal formation mechanisms remains a relatively unexplored ...

Secondary carbonates in edaphic components of ecosystems

The paper considers some examples of secondary carbonates in edaphic ecosystem components (soils, river and lake bottom sediments, suspensions). In addition to calcite, more soluble and less stable polymorphic modifications of calcite vaterite and aragonite, which are important precursors of carbonate-forming systems, are diagnosed. Microforms of vaterite are formed in presence of low molecular weight amino acids. In turn, microforms of aragonite are associated with extremely high salinity of water. According to the nonclassical mesocrystal concept, stability of vaterite and aragonite in situ is explained by the formation of mesocrystals – hierarchically organized superstructures from nanocrystals. The mesocrystal concept may be an important key to understanding the micro-and macroaggregates in soils.

Symbiosis of Silica Biomorphs and Magnetite Mesocrystals

AbstractSilica biomorphs are extraordinary inorganic superstructures formed via autocatalytic co‐precipitation and bottom‐up self‐assembly of alkaline‐earth carbonates and silica. However, they show no inherent functionality except for their striking textural motifs and curved morphologies. This work presents strategies to magnetize silica biomorphs, thus creating thermally stable ceramic microswimmers with unique elaborate shapes. This is achieved by growing super paramagnetic magnetite mesocrystals on and around the complex curved surfaces of biomorphs, while keeping their morphology and maintaining mesocrystal integrity. Selective mesocrystal formation on certain parts of the substrates is induced by chemical modification of the biomorph surface, increasing the loading of magnetite on the silica–carbonate structures and, in suitable cases, rendering them able to respond to external magnetic fields and move as microswimmer entities. In this way, the complex ultrastructure of silica biomorphs is successfully used as a template for functional ceramics. Furthermore, selective dissolution of the carbonate core from the biomorphs leads to hollow magnetic structures that could be filled with actives, thus serving as microcarriers with considerable loading capacity.