Oriented Attachment Research Articles

Precise control of water content on the growth kinetics of ZnO quantum dots

The growth kinetics of quantum dots (QDs) is of great importance to control and understand their particle size evolution. Water content is an important parameter for the growth of ZnO QDs during the sol-gel process, which has not been precisely studied until now. Herein, a modified sol-gel method was proposed to prepare uniform and mono-dispersed ZnO QDs. In this method, water content was precisely controlled, which facilitated the thorough investigation concerning the effects of water content on growth kinetics of ZnO QDs. When the water content was low (≤90 mM), the precursor solution was stable and the generation of ZnO QDs could not be triggered. When the water content was too high (3 M), Zn-HDS was generated instead of ZnO. When the water content was in an appropriate range (360 mM-900 mM), the growth of ZnO QDs followed two stages: the oriented attachment (OA) and the Ostwald ripening (OR) stage. Based on our particle size calculation results by Sarma Model, which showed more distinct differentiation and better pertinence than EMA Model, it has been proved that the increase in the water content could not only promote the growth rate of OA stage, but also the OR stage. This results changed our previous thinking that water content has no influence to the OR stage.

Mono- and Multilayer Silicene-Type Honeycomb Lattices by Oriented Attachment of PbSe Nanocrystals: Synthesis, Structural Characterization, and Analysis of the Disorder.

Nanocrystal (NC) solids are commonly prepared from nonpolar organic NC suspensions. In many cases, the capping on the NC surface is preserved and forms a barrier between the NCs. More recently, superstructures with crystalline connections between the NCs, implying the removal of the capping, have been reported, too. Here, we present large-scale uniform superstructures of attached PbSe NCs with a silicene-type honeycomb geometry, resulting from solvent evaporation under nearly reversible conditions. We also prepared multilayered silicene honeycomb structures by using larger amounts of PbSe NCs. We show that the two-dimensional silicene superstructures can be seen as a crystallographic slice from a 3-D simple cubic structure. We describe the disorder in the silicene lattices in terms of the nanocrystals position and their atomic alignment. The silicene honeycomb sheets are large enough to be used in transistors and optoelectronic devices.

Surface characterisation and reaction kinetics of silver nanoparticles mediated by the leaf and flower extracts of French marigold (Tagetes patula).

In this study, French marigold's leaf and flower were used for the synthesis of silver nanoparticles (SNPs) in order to explore their potentials towards bioreduction of Ag+ to Agᵒ. The as-synthesised SNPs were characterised using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction, transmission electron microscopy, and zeta-potential analysis. The results obtained showed that the particles are polydispersed with sizes in the range 15.8-42.8 nm. The bioreduction was believed to be due to the amides, aldehyde functional groups, and essential oils present in the extracts as confirmed by the FTIR analysis. The growth mechanism involved in the reaction was studied which revealed oriented attachment (OA) onwards Ostwald ripening in the case of the flower-mediated synthesis and typical OA in the leaf-mediated synthesis. The studied kinetics of the particle formation showed that the reaction is possibly a pseudo-first-order reaction with some diffusion-controlled mechanism which is driven by high surface area to volume ratio in both the leaf- and flower-mediated synthesis.

Material’s Design beyond Lateral Attachment: Twin-Controlled Spatial Branching of Rutile TiO2

Crystallization by oriented attachment (OA) is changing our conventional understanding of crystal growth and holds promise for creative design of diverse hierarchic mesostructures. To achieve angular branching of mesostructures, we can exploit twinning. Here we show that in rutile TiO2 twin-based OA can be realized in a solvothermal process from Ti(IV)-butoxide under mild acidic conditions that favor precipitation of rutile with short-prismatic morphology. The aspect ratio of precipitated nanocrystals was shown to decrease linearly with the acidity of the medium; i.e., lower it is, higher is the affinity for twin OA. For a given aspect ratio, the frequency of twinning is controlled by precursor concentration. Through the control of lateral {110} and twin {101} OA in rutile, we are able to generate diverse fractal-like multiply twinned inorganic mesostructures for nanotechnology applications. To quantify branching, we define a morphology factor, fm, a new generally applicable criterion, which provides a qu...

Well-Dispersed Ruthenium in Mesoporous Crystal TiO2 as an Advanced Electrocatalyst for Hydrogen Evolution Reaction.

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1- xRu xO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ GH).

In-situ liquid cell transmission electron microscopy investigation on oriented attachment of gold nanoparticles

Inside a liquid solution, oriented attachment (OA) is now recognized to be as important a pathway to crystal growth as other, more conventional growth mechanisms. However, the driving force that controls the occurrence of OA is still poorly understood. Here, using in-situ liquid cell transmission electron microscopy, we demonstrate the ligand-controlled OA of citrate-stabilized gold nanoparticles at atomic resolution. Our data reveal that particle pairs rotate randomly at a separation distance greater than twice the layer thickness of adsorbed ligands. In contrast, when the particles get closer, their ligands overlap and guide the rotation into a directional mode until they share a common {111} orientation, when a sudden contact occurs accompanied by the simultaneous expulsion of the ligands on this surface. First-principle calculations confirm that the lower ligand binding energy on {111} surfaces is the intrinsic reason for the preferential attachment at this facet, rather than on other low-index facets.

Oriented attachment growth of hundred-nanometer-size LaTaON2 single crystals in molten salts for enhanced photoelectrochemical water splitting

Largely-sized single crystal photocatalyst was prepared by oriented attachment (OA) in molten salt.

Formation mechanism of bead-chain-like ZnO nanostructures from oriented attachment of Zn/ZnO nanocomposites prepared via DC arc discharge in liquid

Bead-chain-like ZnO nanoparticles (NPs) formed in colloidal solution from oriented attachment (OA) of spherical nanoparticles. Arc discharge in liquid is a cost-effective method for quick mass production of nanostructured materials without considerable environmental footprints. Applying voltage across two zinc rods as electrodes, which were immersed in water cause explosion of electrodes and plasma generation. Zn/ZnO nanocomposites produced by interaction of different active species in high-pressure and high-temperature plasma at the solid-liquid interface. Different sized nanoparticles with diameters of 26, 35, 40 and 60nm at applied discharge currents of 150, 100, 50 and 20A respectively, were fabricated in water without any chemical additives. The results showed bead-like oriented attachments appeared with increasing the applied current during synthesis. Length of aggregates increases from 114nm to 120nm with the applied current of the arc discharge. The mechanism of OA of ZnO NPs was investigated by calculating the attractive and repulsive forces based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for characterization of particle size, shape, and investigation of bead-like aggregates. X-ray diffraction (XRD) analysis was used to study the crystal structure and phase composition of the bead-chain like nanostructures. Finally, zeta potential analysis was used to measure surface charges and study the mechanism of oriented attachment. The results provide a simple and flexible method for synthesis of Zn/ZnO bead-chain like nanostructures.

Oriented assembly of anisotropic nanoparticles into frame-like superstructures

It is fascinating but challenging for nanoscientists to organize nanoparticles (NPs) into ordered architectures just as it is for chemists to manipulate atoms and molecules to form functional molecules and supramolecules. We explore a strategy to assemble anisotropic NPs into open frame-like superstructures via oriented attachment (OA), experimentally realizing a nanoscale analog to the bonding behavior in M8L12-type supramolecular cubes. We highlight the role of NP shape in the OA-involved assembly for constructing predictable superstructures. In addition, the frame-like superstructures can retain their basic structure when undergoing postcrystallization of the building blocks as well as annealing for conversion toward functional electrocatalytic materials. Our work enables fundamental insights into directional "bonding" among NPs and adds to the growing body of knowledge for bottom-up assembly of anisotropic NPs into sophisticated functional materials.

Shape evolution of 3D flower-like gold microstructures from gold nanosheets via oriented attachment

Herein, we present a shape evolution of 3D flower-like gold microstructures (3D-FLGMSs) from gold nanosheets induced by H2O2 with the presence of starch. A systematic investigation of the influence of the parameters on the size, morphology and structural evolution of 3D-FLGMSs was presented. Under the starch-stabilized environment, H2O2 plays a key role on the formation of 3D-FLGMSs as it promotes a rapid generation of small nanosheets with starch-bound {111} facet at the very early stage. At a high concentration of H2O2, the nanosheets undergo oriented attachment and transform into a large primary gold nanosheets with imperfect facet-binding. The oriented attachment (OA) and subsequent epitaxial growth of nanopetals from the imperfects turns the primary nanosheets into 3D-FLGMSs with lateral size as large as 30μm within 120min. Without starch, quasi-microspheres of gold with diameters of 5–7μm are the sole product. In addition, the 3D-FLGMSs can be employed as SERS substrates which allow the detection limit of Rhodamine 6G (R6G) at the concentration as low as 0.1μM. The developed green synthetic method utilizes non-toxic reducing and stabilizing agents while limiting the discharge of harmful chemical wastes.

Single-Crystalline Gold Nanowires Synthesized from Light-Driven Oriented Attachment and Plasmon-Mediated Self-Assembly of Gold Nanorods or Nanoparticles

Through the light-driven geometrically oriented attachment (OA) and self-assembly of Au nanorods (NRs) or nanoparticles (NPs), single-crystalline Au nanowires (NWs) were synthesized by the irradiation of a linearly-polarized (LP) laser. The process was conducted in a droplet of Au colloid on a glass irradiated by LP near-infrared (e.g. 1064 nm and 785 nm) laser beam of low power at room temperature and atmospheric pressure, without any additive. The FE-SEM images show that the cross sections of NWs are various: tetragonal, pentagonal or hexagonal. The EDS spectrum verifies the composition is Au, and the pattern of X-ray diffraction identifies the crystallinity of NWs with the facets of {111}, {200}, {220} and {311}. We proposed a hypothesis for the mechanism that the primary building units are aligned and coalesced by the plasmon-mediated optical torque and force to form the secondary building units. Subsequently, the secondary building units undergo the next self-assembly, and so forth the tertiary ones. The LP light guides the translational and rotational motions of these building units to perform geometrically OA in the side-by-side, end-to-end and T-shaped manners. Consequently, micron-sized ordered mesocrystals are produced. Additionally, the concomitant plasmonic heating causes the annealing for recrystallizing the mesocrystals in water.

Synthesis of Cuboctahedral CeO2 Nanoclusters and Their Assembly into Cuboid Nanoparticles by Oriented Attachment

AbstractHere, we describe a simple approach to control the oriented attachment process through selective ligand scavenging from the {100} facets of CeO2 nanoclusters. Aggregates of these nanoclusters smaller than 10 nm with controlled shapes and exposed facets were obtained. For the synthesis of the cuboctahedral CeO2 nanoclusters, we developed a solvent‐controlled synthesis approach based on a non‐hydrolytic sol–gel process and used an ester aminolysis reaction to control ligand scavenging from the {100} facets. First‐principle calculations allowed us to understand and interpret, at the atomic level, the effects of shape control on the synthesis. Fine‐tuning of the desired morphologies can be achieved by controlling the values of the surface energies, which leads to the formation of morphologies that the classic growth process does not allow.

Oriented and Ordered Biomimetic Remineralization of the Surface of Demineralized Dental Enamel Using HAP@ACP Nanoparticles Guided by Glycine

Achieving oriented and ordered remineralization on the surface of demineralized dental enamel, thereby restoring the satisfactory mechanical properties approaching those of sound enamel, is still a challenge for dentists. To mimic the natural biomineralization approach for enamel remineralization, the biological process of enamel development proteins, such as amelogenin, was simulated in this study. In this work, carboxymethyl chitosan (CMC) conjugated with alendronate (ALN) was applied to stabilize amorphous calcium phosphate (ACP) to form CMC/ACP nanoparticles. Sodium hypochlorite (NaClO) functioned as the protease which decompose amelogenin in vivo to degrade the CMC-ALN matrix and generate HAP@ACP core-shell nanoparticles. Finally, when guided by 10 mM glycine (Gly), HAP@ACP nanoparticles can arrange orderly and subsequently transform from an amorphous phase to well-ordered rod-like apatite crystals to achieve oriented and ordered biomimetic remineralization on acid-etched enamel surfaces. This biomimetic remineralization process is achieved through the oriented attachment (OA) of nanoparticles based on non-classical crystallization theory. These results indicate that finding and developing analogues of natural proteins such as amelogenin involved in the biomineralization by natural macromolecular polymers and imitating the process of biomineralization would be an effective strategy for enamel remineralization. Furthermore, this method represents a promising method for the management of early caries in minimal invasive dentistry (MID).

Atomic imaging of the coherent interface between orientedly-attached Mn3O4 nanoparticles

In this paper, coherent interfaces between orientedly-attached (OA) Mn3O4 nanoparticles are fully reconstructed based on atomic-scale high angle annular dark field (HAADF) - scanning transmission electron microscopy (STEM) direct imaging technique. According to the characterization, five characteristics of the oriented attachment between Mn3O4 are proposed: (1) [100]Mn3O4 direction sharing; (2) crystallographic plane sharing for every two attached particles; (3) preference for O2−close-packed crystallographic planes to form the OA interface; (4) “defect transfers” compensating the deviation between the macroscopic interface and the atomic interface; (5) possible chemical state changes of the interfacial atoms.

Selective hydrothermally synthesis of hexagonal WS2 platelets and their photocatalytic performance under visible light irradiation

Hexagonal WS2 platelets have been synthesized via simple hydrothermal synthesis method. The hexagonal WS2 is formed by the oriented attachment (OA)-self-assembly (SA). The thickness of the WS2 platelets was between ∼20 and 100 nm. The specific surface area of these platelets is 94.63 m2 g−1. The hexagonal WS2 platelets exhibited excellent photocatalytic activity compared to irregular WS2 platelets for the degradation of rhodamine B (RhB) under visible light irradiation. This work paves the method for designing hexagonal shaped WS2 platelets with great potential for a wide spectrum of applications in photocatalysis. Moreover, this synthetic procedure may open up an opportunity to tailor the morphologies of the other nanomaterials especially transition metal sulfides.

Oriented attachment (OA) mediated characteristic growth of Gd2O3 nanorods from nanoparticle seeds

Herein, we demonstrated the oriented attachment (OA) driven formation and characterization of Gd2O3 nanorods. The nanorods were synthesized via a surfactant free, inexpensive hydrothermal route and considering ∼30 nm nanoparticles as the seed. While maintaining a cubic phase throughout the process, complete transformation of Gd2O3 nanoparticles to nanorods was found to occur at an elevated temperature (∼180 °C) of the hydrothermal reaction. The elongated Gd2O3 nanostructures, as revealed from transmission electron microscopic imaging, possessed an average diameter of ∼33 nm and an approximate length of 172 nm. From the kinetics of OA process, the activation energy of formation was estimated to be ∼25 kJ/mole. The existence of defect mediated radiative emission was ascertained from the asymmetric broadening of luminescence spectra. The defect emission arising from the Gd2O3 nanorods was nearly 1.4 times stronger than that of nanoparticles. The morphological evolution and growth kinetics were discussed along with the luminescence and electron paramagnetic resonance features.

The origin of facet selectivity and alignment in anatase TiO2 nanoparticles in electrolyte solutions: implications for oriented attachment in metal oxides.

Oriented attachment (OA) is an important nonclassical pathway for crystal growth from solution, occurring by the self-assembly of nanoparticles and often leading to highly organized three-dimensional crystal morphologies. The forces that drive nanocrystal reorientation for face-selective attachment and exclude improperly aligned particles have remained unknown. Here we report evidence at the microscopic level that ion correlation forces arising from dynamically interacting electrical double layers are responsible for face-selective attraction and particle rotation into lattice co-alignment as particles interact at long range. Atomic-to-mesoscale simulations developed and performed for the archetype OA system of anatase TiO2 nanoparticles in aqueous HCl solutions show that face-selective attraction from ion correlation forces outcompetes electrostatic repulsion at several nanometers apart, drawing particle face pairs into a metastable solvent-separated captured state. The analysis of the facet and pH dependence of interparticle interactions is in quantitative agreement with the observed decreasing frequency of attachment between the (112), (001), and (101) face pairs, revealing an adhesion barrier that is largely due to steric hydration forces from structured intervening solvents. This finding helps open new avenues for controlling crystal growth pathways leading to highly ordered three-dimensional nanomaterials.

Li+ion induced three-dimensional aggregation growth of single-crystal perovskite octahedrons

Li+ ions were introduced into a hydrothermal system as surfactants to tailor the growth of perovskite tetragonal PbTiO3 (PT) nanocrystals, giving rise to single-crystal octahedrons with {111} facets exposed. Systematic investigations reveal that single-crystal PT octahedrons were formed via a three-dimensional (3D) aggregation growth process. In the initial stage, the intermediate phase primary nanoparticles, with a size of 2–5 nm, aggregated to form an octahedral shaped particle agglomeration with a size of 20–50 nm; then, the particle crystallized via an oriented attachment (OA) mechanism, resulting in the observed single-crystal PT octahedrons. During this process, the interplay of Li+ ions and the electrostatic force of the primary nanoparticles are essential for octahedral aggregation and subsequent crystallization. Moreover, the concentration of Li+ ions has been demonstrated to significantly modify the growth of PT, leading to nanostructures with various shapes from hexahedral particles to cubic conglomerates to cuboids. These nanostructures demonstrate shape-dependent visible light photocatalytic activity.

Study of the morphological evolution of vanadium pentoxide nanostructures under hydrothermal conditions

A detailed study on the morphological evolution of one-dimensional (1D) vanadium pentoxide (V2O5) nanostructures was performed. Small-angle X-ray scattering (SAXS) and electron microcopy techniques were used for the analyses of the influence of synthesis parameters on a hydrothermal synthesis method of V2O5 nanostructures based on the degradation of a peroxocomplex precursor. A mechanism that explains the morphological evolution under different experimental conditions is proposed and the role of the dehydration process as well as the importance of the oriented attachment (OA) mechanism is discussed.

Structural Correspondence of the Oriented Attachment Growth Mechanism of Crystals of the Pharmaceutical Dirithromycin.

The oriented attachment (OA) mechanism is promising for designing novel nanomaterials, yet an intensive understanding of the relationship between the crystal structure and attachment orientation is still lacking. In this work, we report layered hexagonal crystals of the pharmaceutical dirithromycin (DIR) containing multiple layers fabricated via a solvothermal method for a certain period of time at 40 °C. These elongated hexagonal crystals experience an OA that is preferentially on the face (001) of the initial crystals to assemble the final crystals into layered stacks. Through agreement with molecular modeling calculations, we predicted the final crystal growth morphology and confirmed the favored attachment surface based on the energy change ΔE following an OA event. These simulation results at the molecular level yielded good agreement with the crystal growth experiments. This study demonstrates the critical importance of combining experiments with a computational approach to understand the intrinsic molecular details of the OA growth mechanism of other compounds and to design nanomaterials with a desirable morphology and physical and chemical properties.