Non-classical Crystallization Mechanism Research Articles

Visualizing the Internal Nanocrystallinity of Calcite Due to Nonclassical Crystallization by 3D Coherent X-Ray Diffraction Imaging.

The internal crystallinity of calcite is investigated for samples synthesized using two approaches: precipitation from solution and the ammonium carbonate diffusion method. Scanning electron microscopy (SEM) analyses reveal that the calcite products precipitated using both approaches have a well-defined rhombohedron shape, consistent with the euhedral crystal habit of the mineral. The internal structure of these calcite crystals is characterized using Bragg coherent diffraction imaging (BCDI) to determine the 3D electron density and the atomic displacement field. BCDI reconstructions for crystals synthesized using the ammonium carbonate diffusion approach have the expected euhedral shape, with internal strain fields and few internal defects. In contrast, the crystals synthesized by precipitation from solution have very complex external shapes and defective internal structures, presenting null electron density regions and pronounced displacement field distributions. These heterogeneities are interpreted as multiple crystalline domains, created by a nonclassical crystallization mechanism, where smaller nanoparticles coalescence into the final euhedral particles. The combined use of SEM, X-ray diffraction (XRD), and BCDI allows for structurally differentiating calcite crystals grown with different approaches, opening new opportunities to understand how grain boundaries and internal defects alter calcite reactivity.

A non-classical crystallization mechanism of microbially-induced disordered dolomite

Non-classical crystallization pathways, involving the formation of complex precursors prior to nucleation, have been observed during the calcification process of invertebrate skeletons and shells. However, these pathways were rarely documented in microbially-induced carbonate precipitation. In this study, we presented experimental evidence demonstrating that a halophilic bacterium (Halomonas sp. strain JBHLT-1) catalyzed the biomineralization of disordered dolomite through an amorphous calcium-magnesium carbonate (ACMC) with a stoichiometry near that of dolomite. During the ACMC formation, strain JBHLT-1 significantly enhanced the incorporation of Mg2+ ions compared to abiotic ACMC that was synthesized without any microbial biomass. In the stage of ACMC crystallization, the presence of microbial biomass reduced the dissolution-reprecipitation rate and induced bias towards a solid-state reaction pathway. This observation was supported by the negligible loss of structural Mg2+ ions in the presence of cells of strain JBHLT-1. The microbially-induced growth of disordered dolomite appeared to follow a spherulitic growth mechanism, as evidenced by its hierarchical structure composed of coalesced nano-spheres, eventually growing into micron-sized spheroids and dumbbells with extended incubation times. Since disordered dolomite is considered as a crucial crystalline precursor of ordered sedimentary dolomite, the findings of this study have important implications for understanding the formation mechanism of natural dolomite.

Quantification of classical and non-classical crystallization pathways in calcite precipitation

Crystal precipitation from aqueous solution occurs through multiple pathways. Besides the classical ion-by-ion addition, non-classical crystallization mechanisms, such as multi-ion polymer and nano-particle attachment, could be significant. These non-classical crystallization processes have been observed with advanced microscopy, yet detailed quantification of their contributions remains challenging. Building from paired Ca and Sr isotope observations, we develop a theoretical framework to quantify the contributions of classical and non-classical crystallization pathways on the precipitation of the calcium carbonate mineral calcite, a common precipitate in nature. We demonstrate that the classical crystallization pathway alone is insufficient to account for the observed isotope behaviors and, thus, the entire calcite precipitation process. We further present a surface kinetic model that incorporates non-classical crystallization pathways. This model enables the characterization of the roles of classical and non-classical crystallization mechanisms in calcite precipitation. The results suggest that the relative contribution of non-classical crystallization pathways increases with saturation state and can, under high supersaturation levels, be comparable to or greater than the classical pathway. The presented theoretical framework readily explains observed trace element partitioning and isotope fractionation behaviors during calcite precipitation and can be further expanded onto other mineral systems to gain insights into crystal growth mechanisms.

Earthworm granules: A model of non-classical biogenic calcium carbonate phase transformations.

Different non-classical crystallization mechanisms have been invoked to explain structural and compositional properties of biocrystals. The identification of precursor amorphous nanoparticle aggregation as an onset process in the formation of numerous biominerals (crystallization via particle attachment) constituted a most important breakthrough for understanding biologically mediated mineralization. A comprehensive understanding about how the attached amorphous particles transform into more stable, crystalline grains has yet to be elucidated. Here, we document structural, biogeochemical, and crystallographic aspects of the formation as well as the further phase transformations of the amorphous calcium carbonate particles formed by cultured specimens of earthworm Lumbricus terrestris. In-situ observations evidence the formation of proto-vaterite after dehydration of earthworm-produced ACC, which is subsequently followed by proto-vaterite transformation into calcite through nanoparticle attachment within the organic framework. In culture medium spiked with trace amounts of Mn2+, the cauliflower-like proto-vaterite structures become longer-lived than in the absence of Mn2+. We propose that the formation of calcite crystals takes place through a non-classical recrystallization path that involves migration of proto-vaterite nanoparticles to the crystallization site, and then, their transformation into calcite via a dissolution-recrystallization reaction. The latter is complemented by ion-by-ion crystal growth and associated with impurity release. These observations are integrated into a new model of the biocrystallization of earthworm-produced carbonate granules which highlights the sensibility of this process to environmental chemical changes, its potential impact on the bioavailability of contaminants as well as the threat that chemical pollution poses to the normal development of its early stages. STATEMENT OF SIGNIFICANCE: Understanding the mechanisms of nucleation, stabilization and aggregation of amorphous calcium carbonate (ACC) and factors controlling its further transformation into crystalline phases is fundamental for elucidation of biogenic mineralization. Some species of earthworms are natural workbench to understand the biogenic ACC, stabilization and the transformation mechanisms, because they create millimeter-sized calcareous granules from amorphous calcium carbonate, which crystallize to a more stable mineral phase (mostly calcite). This study undergoes into the mechanisms of ACC stabilization by the incorporation of trace elements, as manganese, and the ulterior precipitation of calcareous granules by a coupled process of amorphous particle attachment and ion-by-ion growth. The study points to sensibility of this process to environmental chemical changes.

The nonclassical crystallization mechanism and growth kinetics of densely packed fluorapatite nanorod arrays: effects of the ion transportation rate and fluoride concentration

FAP arrays form via a nanoparticle assembly route and an appropriate ion transportation rate and increasing fluoride concentration can accelerate the mineralization rate.

Nonclassical Growth of Atomically Flat Two‐Dimensional Organic Single Crystals on a Liquid Surface through Fusion

AbstractOrganic single crystals with low defect density are key functional materials for next‐generation electronics. Classical crystallization commonly results in a high density of molecular steps, which are defects that can trap charge carriers and reduce the mobility of organic semiconductors. Herein, a novel nonclassical crystallization mechanism involving nucleation, fusion, and growth is designed. The introduction of the fusion stage changes the crystal growth mode from three‐dimensional island growth to two‐dimensional layer‐by‐layer growth and leads to large‐area two‐dimensional molecular crystals with almost no molecular steps. Therefore, the average mobility is observed to improve from 1.26 to 2.07 cm2 V−1 s−1. The nonclassical crystallization mechanism paves the way for atomically flat single crystals to probe the intrinsic optoelectronic properties of organic semiconductors.

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.

Alkalinity-controlled zeolite nucleation and growth: ultrafast synthesis of total-morphology zeolite L mesocrystals and adsorption evaluation

Owing to the intrinsic complexity of crystallization and the heterogeneity of precursors, the specific stages and corresponding behaviors of an actual crystallization system remain ambiguous, which makes the univariate-controlled crystallization-kinetics-regulated synthesis and design of zeolite morphology and porosity an unrealized blueprint. In this study, a facile and univariate modulation (i.e., OH-/SiO2) strategy was developed to regulate zeolite crystallization kinetics, and zeolite L mesocrystals were synthesized rapidly (within 1-2 h) with almost all LTL morphologies (from cylindrical or disc-like shapes to nanoclusters or nanocrystals) in the simplest SiO2-Al2O3-K2O-H2O system. Using time-resolved analysis of the change in the solid-liquid Si/Al nutrient and crystallinity evolution, the intertwined and complex crystallization processes of zeolite L were clearly distinguished into four distinct stages: induction, nucleation, growth, and ripening. Under alkalinity-controlled conditions, the reactivity, Si/Al distribution, and state of aluminosilicates were critical to the formation of short-range order in the amorphous matrix, which greatly influenced the nucleation frequency and assembly state. Subsequently, these nucleation differences evoked correspondingly different kinetic growth behaviors. A putative alkalinity-controlled nonclassical crystallization mechanism was uncovered, and its validity was evaluated by analyzing morphology evolution, NH4F etching, and the effects of modifiers. Furthermore, adsorption tests demonstrated the high adsorption capacity of a series of zeolite L for guest molecules with various sizes and properties (e.g., gaseous aromatic hydrocarbon, aqueous dye, and protein).

Facile synthesis of ZSM-5 mesocrystal via novel pathway of crystallization: Fast precipitation, deconstruction and reorganization

Mesocrystal zeolite with well-defined morphology owns mesoporous channels and single crystal characteristics, which could promote diffusion efficiency, stability and catalytic activity. Thus, we performed the controllable synthesis of ZSM-5 mesocrystal without special additives and complex methods. Selected area electron diffraction (SAED) and fast Fourier transform (FFT) showed diffraction spots regardless of crystallization time, which indicated the well oriented feature of synthesized ZSM-5 zeolites. The crystallization process was further investigated. The oriented particle attachment (OPA) effectively guided the synthesis process of mesocrystals, which followed the nonclassical crystallization mechanism. The crystallinity curve exhibited valley-like shape, which manifested that the crystallization pathway went through three stages: fast precipitation, deconstruction and reorganization. The plausible formation mechanism was proposed, which might be useful for the fabrication of ZSM-5 mesocrystal. The prepared zeolites showed superior catalytic performance in aldol condensation reaction between benzaldehyde and 2-hydroxyacetophenone, obtaining 93% of the conversion. The fast precipitation gave rise to perfect oriented feature. Then, the synthesized zeolites deconstructed due to OH − ions, the lighter bule indicated imperfect crystallized crystal due to the damage of OH − ions. Finally, the reorganization happened due to further ripening of deconstructed nanoparticles. The planar graph embedded in the circle demonstrated the structure of inter domain. •ZSM-5 mesocrystal with tunable Si/Al ratio was synthesized without special additives and complex methods. •The synthesis of ZSM-5 mesocrystal underwent unusual crystallization pathway: fast precipitation, deconstruction and reorganization. •ZSM-5 mesocrystal showed excellent catalytic performance in the Claisen‐Schmidt condensation reaction.

Polymer-Directed Crystallization of Luteolin, Quercetin, and Myricetin

for active pharmaceutical ingredients, the bioavailability, stability, and processability critically depend on crystal habit and size. The presence of polymers in a crystallization solution can engineer broader ranges of crystal habit and size, but only in certain cases. To elucidate the underlying mechanism of this selectivity, polymer-directed crystallization was systematically investigated here for a series of natural polyphenols, namely luteolin, quercetin, and myricetin. Significant changes in crystal habit and size were observed in the cases of quercetin and myricetin. Peak broadening in X-ray diffraction profiles and significant amounts of polymer within the crystallized particles suggested possible composite structure formation via a non-classical crystallization mechanism. Polyethyleneimine and poly(vinyl alcohol) showed relatively stronger crystal engineering effects than poly(ethylene glycol). The results facilitate understanding of the specific interactions important for crystal engineering and thus preparing polyphenols to attain wide ranges of habit and particle size for various applications.

The Crystallization Process of Vaterite Microdisc Mesocrystals via Proto-Vaterite Amorphous Calcium Carbonate Characterized by Cryo-X-ray Absorption Spectroscopy

Investigation on the formation mechanism of crystals via amorphous precursors has attracted a lot of interests in the last years. The formation mechanism of thermodynamically meta-stable vaterite in pure alcohols in the absence of any additive is less known. Herein, the crystallization process of vaterite microdisc mesocrystals via proto-vaterite amorphous calcium carbonate (ACC) in isopropanol was tracked by using Ca K-edge X-ray absorption spectroscopy (XAS) characterization under cryo-condition. Ca K-edge X-ray absorption near edge structure (XANES) spectra show that the absorption edges of the Ca ions of the vaterite samples with different crystallization times shift to lower photoelectron energy while increasing the crystallization times from 0.5 to 20 d, indicating the increase of crystallinity degree of calcium carbonate. Ca K-edge extended X-ray absorption fine structure (EXAFS) spectra exhibit that the coordination number of the nearest neighbor atom O around Ca increases slowly with the increase of crystallization time and tends to be stable as 4.3 (±1.4). Crystallization time dependent XANES and EXAFS analyses indicate that short-range ordered structure in proto-vaterite ACC gradually transform to long-range ordered structure in vaterite microdisc mesocrystals via a non-classical crystallization mechanism.

Development of a two-stage in vitro model system to investigate the mineralization mechanisms involved in idiopathic stone formation: stage 1-biomimetic Randall's plaque using decellularized porcine kidneys.

Idiopathic calcium oxalate (CaOx) stone formers form stones that are commonly attached to calcium phosphate (CaP) deposits in the renal tissue, known as Randall's plaques (RP). Plaques are suggested to originate in the renal tubular basement membrane, where they exhibit a morphology of concentrically laminated apatitic spherules, while in the interstitial regions, the collagen fibrils and vesicles become mineralized. We hypothesize that these minerals might form by non-classical crystallization mechanisms, such as via amorphous precursors, some of which might originate from a polymer-induced liquid-precursor (PILP) process. Thus, our goal is to identify mineralogical 'signatures' of various stone formation mechanisms. To do this for idiopathic CaOx stones, we are developing a two-stage model system of CaP-CaOx composite stones, consisting of stage (1) CaP mineralized plaque, followed by stage (2) CaOx overgrowth into a stone. For the studies presented here, decellularized porcine kidneys were mineralized with CaP using polyaspartic acid or the protein osteopontin (OPN) to induce the PILP process and create biomimetic RP. Analysis of the PILP-mineralized tissues shows features that resemble the native plaques, including mineral spherules and collagen with intrafibrillar mineral. In contrast, the classical crystallization produced large apatitic spherulites, which is a very different morphology, but one which is also found in some stones. An alternative hypothesis regarding Randall's plaque, and if or when it becomes pathological, is discussed.

Seeding Bundlelike MFI Zeolite Mesocrystals: A Dynamic, Nonclassical Crystallization via Epitaxially Anisotropic Growth

Direct synthesis by assembly of precursor nanoparticles is a promising strategy for preparing distinct mesoscopic-structured crystals, especially when high controllability is realized. However, uncertain properties of amorphous precursors and inner complicacy of crystallization mechanisms hamper controllable synthesis of zeolite mesocrystals. Here, we develop a salt-aided seed-induced organic-free method to facilely synthesize anisotropic MFI-type nanorod-bundle zeolite mesocrystals. An epitaxial, anisotropic assembly and crystallization of precursor particles on seed crystals is successfully achieved via a distinctively dynamic, nonclassical process, from relatively disordered to ordered attachment (OA), triggering an enhanced one-dimensional (1D) growth, thus constructing a unique core–shell–shell structure. This work sheds new light on the insights of both zeolite mesocrystal properties and a nonclassical crystallization mechanism. With an understanding of the mechanism, this nonclassical process can b...

Tuning crystallization pathways through sequence engineering of biomimetic polymers.

Two-step nucleation pathways in which disordered, amorphous, or dense liquid states precede the appearance of crystalline phases have been reported for a wide range of materials, but the dynamics of such pathways are poorly understood. Moreover, whether these pathways are general features of crystallizing systems or a consequence of system-specific structural details that select for direct versus two-step processes is unknown. Using atomic force microscopy to directly observe crystallization of sequence-defined polymers, we show that crystallization pathways are indeed sequence dependent. When a short hydrophobic region is added to a sequence that directly forms crystalline particles, crystallization instead follows a two-step pathway that begins with the creation of disordered clusters of 10-20 molecules and is characterized by highly non-linear crystallization kinetics in which clusters transform into ordered structures that then enter the growth phase. The results shed new light on non-classical crystallization mechanisms and have implications for the design of self-assembling polymersystems.

Crystallization kinetics of cerium oxide nanoparticles formed by spontaneous, room-temperature hydrolysis of cerium(iv) ammonium nitrate in light and heavy water.

A stable sol of cerium oxide nanoparticles forms spontaneously when cerium(iv) ammonium nitrate (CAN) is dissolved in room-temperature water at mM concentrations. Electron microscopy experiments reveal the formation of highly crystalline cerium oxide particles several nm in diameter and suggest that they are formed from amorphous particles that are similar in size. Under the low pH conditions of the experiments, the nanoparticles form a stable dispersion and show no evidence of aggregation, even many months after synthesis. The absence of particles large enough to scatter light significantly makes it possible to observe the crystallization kinetics through dramatic changes in the UV-visible absorption spectra that occur during solution aging. Measurements show that the cerium oxide nanocrystals are formed roughly an order of magnitude more slowly in D2O than in H2O solution. This large solvent kinetic isotope effect (kH/kD ∼ 10), which is reported here for the first time for the crystallization of a solid metal oxide phase, indicates a rate-determining proton transfer reaction, which is assigned to the conversion of hydroxy to oxo bridges. In D2O solution, the absorption per mole of cerium ions increases by over 400% at 290 nm as the weakly absorbing precursor phase is transformed into nanocrystalline cerium oxide. An isosbestic point is detected at 368 nm, and the absorption spectra can be modeled throughout aging by the sum of spectra of just two interconverting species. Preliminary ultrafast transient absorption experiments confirm that the optical properties of the amorphous precursors differ greatly from those of the final, nanocrystalline phase. Crystallization of CeO2 from CAN in water has much in common with the crystallization of iron oxides from iron(iii) salts, including the importance of non-classical nucleation and growth pathways. It is an outstanding system for studying the poorly understood events that cause molecularly solvated ions to self-assemble into nanocrystals, following hydrolysis. At the same time, the strong susceptibility of CAN to spontaneously form CeO2 nanocrystals under the mildest of reaction conditions indicates that caution is needed when working with this common sacrificial oxidant.

Gel-Like Calcium Carbonate Precursors Observed by in situ AFM.

The debate about crystallization processes is still ongoing and nonclassical crystallization mechanisms attract more and more attention. This work indicates that polymer induced liquid precursor (PILP) phases play a role for nonclassical calcium carbonate crystallization and growth processes. Here we report the observation of gel-like precursors for the crystal growth on a calcite surface by means of an in situ AFM study. These precursors spread out on the surface with time supporting their liquid character. This study will give new insights into biomineralization and crystallization processes in general.

Growth and photoluminescence of Si-SiOx nanowires by catalyst-free chemical vapor deposition technique

We developed a one-step catalyst-free chemical vapor deposition process to synthesize Si-SiOx nanowires using tetraethoxysilane as the precursor. Observations using scanning electron microscopy showed that the Si-SiOx nanowires were 20–50nm in diameter and tens of microns in length. The high-resolution transmission electron microscope analysis and X-ray diffraction demonstrated that the nanowires consisted of crystal silicon and amorphous SiOx. The Si and O with an atomic ratio of the Si-SiOx NWs were 1:1.2 according to the energy dispersion X-ray spectroscope. A systematic study on the effect of the growth conditions, such as reaction temperature, the reaction time, and the TEOS vapor flow rate was performed. The formation of Si-SiOx nanowires was implemented by the non-classical crystallization mechanism. The charged nanoparticles acting as building blocks self-assembled into nanowires. The photoluminescence measurements were carried out and showed that the Si-SiOx nanowires emitted stable ultraviolet and green luminescence excited by ultraviolet light.

Electrochemical response in aprotic ionic liquid electrolytes of TiO2 anatase anodes based on mesoporous mesocrystals with uniform colloidal size

Mesocrystals (superstructures of crystallographically-oriented inorganic nanocrystals) represent sophisticated configurations generated from biomineralization processes, and an example of nonclassical crystallization mechanisms. Being the closest relatives to single-crystals at the nanoscale, porous mesocrystals are considered as ideal configurations to improve functional properties, and to correlate structural and textural features with materials functionality. Here we show that TiO2 anatase mesoporous colloidal mesocrystals, synthesized by a self-assembly/seeding method, can be easily processed as active materials in anode composites. These anode composites can be efficiently infiltrated during battery operation with safe aprotic ionic liquid electrolytes down to the mesoporosity of mesocrystals (3–4 nm), and operate over a wider temperature window than organic carbonates. For example, after continuous galvanostatic cycling for 1 month at high temperatures (15 days at 60 °C + 15 days at 80 °C, ∼130 cycles), these anode composites sustain a capacity at 67 mA g−1 that is still remarkable for TiO2-based anodes (155 mAh g−1 or 200 mAh cm−3, coulombic efficiency of ∼99%). On contrast, in organic carbonates the capacity decays down to 80 mAh g−1 after only 15 days at 60 °C. Our results suggest that the principles derived from porous anatase mesocrystal/ionic liquid electrolyte combinations could constitute the basis for battery applications in which safety, durability and variability in operating temperature represent the primary concerns.

Li-doped ZnO nanorods with single-crystal quality – non-classical crystallization and self-assembly into mesoporous materials

The benefits and promise of nanoscale dimensions for the properties of (ceramic) semiconductors are widely known. 1-D nanostructures in particular have proven to be of extraordinary relevance due to their applicability in future electronic and optoelectronic devices. Key to successful technological implementation of semiconductor nanostructures is the control of their electronic properties via doping. Despite its tremendous importance, precise chemical doping of defined nano-objects has been addressed rarely so far. Frequent problems are the creation of secondary defects and related undesired property changes by incorporation of hetero-elements, and the difficulty in ensuring a uniform and precise positioning of the dopant in the nanocrystal lattice. Here, we present the synthesis of Li-doped zinc oxide nanorods, which possess excellent (single-crystal) quality. The method is based on a novel non-classical crystallization mechanism, comprising an unusually oriented disassembly step. Afterwards, the nanorods are incorporated into mesoporous layers using colloidal self-assembly. Proof-of-principle gas sensing measurements with these novel materials demonstrate the beneficial role of Li-doping, indicating not only better conductivity but also the occurrence of catalytic effects.

Oriented attachment and mesocrystals: Non-classical crystallization mechanisms based on nanoparticle assembly

In this review, we highlight particle based crystallization pathways leading to single crystals via mesoscopic transformation. In contrast to the classical mechanism of atom/molecule mediated growth of a single crystal, the particle mediated growth and assembly mechanisms are summarized as "non-classical crystallization", including exiting processes like oriented attachment and mesocrystal formation. Detailed investigations of non-classical crystallization mechanisms are a recent development, but evidence for these pathways is rapidly increasing in the literature. A major driving force for these investigations originates from biomineralization, because it seems that these crystallization routes are frequently applied by natural organisms. We give a non-exhaustive literature survey on these two mechanisms with a focus on recent examples and studies, which are dedicated to a mechanistic understanding. Furthermore, conditions are introduced for which these non-classical crystallization mechanisms can be expected, as they are always an alternative reaction pathway to classical crystallization.