Oriented Attachment Process Research Articles

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.

Self-assembly of birnessite nanoflowers by staged three-dimensional oriented attachment

Assembly of birnessite nanoflowers via a two-directional oriented attachment process.

General Synthetic Protocol for the Synthesis of Ru‐X (X=Rh, Pd, Ag) Heterogeneous Ultrathin Nanowires with a Tunable Composition

AbstractHerein, a wet‐chemical strategy was devised for the preparation of ultrathin Ru‐based (Ru‐Pd, Ru‐Ag, and Ru‐Rh) heterogeneous nanowires without the use of templates and organic solvents. The success of this synthetic strategy relies on the combination of heterogeneous nucleation and oriented attachment processes. In the synthesis, polyvinylpyrrolidone (PVP) and sodium iodide play very important roles in the growth of the ultrathin nanowires. PVP induces the linear attachment of Ru‐based nanostructures, and I− ions effectively tune the reaction kinetics of the reduction of the metal ions through the formation of more stable compounds. The average diameter of the Ru‐based nanowires is only 3 nm, approximately 12 atoms thick. Importantly, the components of the ultrathin nanowires can be tuned easily by changing the types of precursors and concentrations. As a result of the ultrathin structure and heterojunctions, the as‐synthesized Ru‐based ultrathin nanowires exhibit a good catalytic activity in the Suzuki–Miyaura reaction with a low loss of catalytic activity after several reuses.

Synthesis of hierarchical groove-like lepidorcocite-VOOH and applications in aqueous lithium ion batteries

One dimensional (1D) hierarchical layered Groove-like Lepidocrocite-VOOH (L-VOOH) was prepared by the synergy of in-suit Kirkendall effect and oriented attachment process. The H2V3O8 nanobelts serve as the self-sacrificed template reduced by the hydrazine hydrate. The electrical and magnetic properties of L-VOOH were studied. The hierarchical layered Groove-like L-VOOH was employed for aqueous lithium ion batteries (ALIBs) for its hierarchical layered structure and large BET surface areas.

Oriented self-assembly of PbS nanocrystals into 0D+1D ‘matchstick’ structures

We present a facile method to prepare a variety of Lead sulfide (PbS) anisotropic nanostructures, using aqueous solutions of Pb(NO3)2 and NaHS as precursors at room temperature. PbS nanostructures such as matchstick-, V- and rectangular-shaped were developed by an oriented attachment process, involving both spherical and cubic PbS nanoparticles, which were formed during the synthesis process. The nanostructures and oriented assembly were analyzed by Transmission Electron Microscopy. X-ray diffraction confirmed that PbS nanostructures were crystallized into the rock-salt structure. A brief description of the oriented self-assembly mechanism is provided too.

Concerted Growth and Ordering of Cobalt Nanorod Arrays as Revealed by Tandem in Situ SAXS-XAS Studies.

The molecular and ensemble dynamics for the growth of hierarchical supercrystals of cobalt nanorods have been studied by in situ tandem X-ray absorption spectroscopy-small-angle X-ray scattering (XAS-SAXS). The supercrystals were obtained by reducing a Co(II) precursor under H2 in the presence of a long-chain amine and a long-chain carboxylic acid. Complementary time-dependent ex situ TEM studies were also performed. The experimental data provide critical insights into the nanorod growth mechanism and unequivocal evidence for a concerted growth-organization process. Nanorod formation involves cobalt nucleation, a fast atom-by-atom anisotropic growth, and a slower oriented attachment process that continues well after cobalt reduction is complete. Smectic-like ordering of the nanorods appears very early in the process, as soon as nanoparticle elongation appears, and nanorod growth takes place inside organized superlattices, which can be regarded as mesocrystals.

Cold-bonding in sub-10 nm indium tin oxide nanorods

Cold-bonding in a typical metal oxide material nanostructure, indium tin oxide nanorods (ITONs), was observed and studied by combining precise in situ nano-manipulation, transmission electron microscopy (TEM) observation and on-line electrical properties measurements. Our studies revealed an oriented attachment process caused by enhanced atom mobility or diffusion and rearrangement at the contact, which worked efficiently in reconnecting the ITONs. Electrical measurements exhibited low contact resistance between the re-connectable ITON segments. Our observations indicate that small-sized nanostructures could be cold-bonded easily following a similar mechanism with their electrical properties retained.

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.

Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1-xMgxO system.

Understanding the effect of homovalent cation alloying in wide band gap ZnO and the formation of metal-semiconductor heterostructures is very important for maximisation of the photophysical properties of ZnO. Nearly monodisperse ZnO nanopyramid and Mg alloyed ZnO nanostructures have been successfully synthesized by one pot decomposition of metal stearate by using oleylamine both as activating and capping agent. The solid solubility of Mg(ii) ions in ZnO is limited to ∼30% without phase segregation. An interesting morphology change is found on increasing Mg alloying: from nanopyramids to self-assembled nanoflowers. The morphology change is explained by the oriented attachment process. The introduction of Mg into the ZnO matrix increases the band gap of the materials and also generates new zinc interstitial (Zni) and oxygen vacancy related defects. Plasmonic magnetic Ag@Ni core-shell (Ag as core and Ni as shell) nanocrystals are used as a seed material to synthesize Ag@Ni/Zn1-xMgxO complex heterostructures. Epitaxial growth is established between Ag(111) and ZnO(110) planes in the heterostructure. An epitaxial metal-semiconductor interface is very crucial for complete electron-hole (e-h) separation and enhancement of the exciton lifetime. The alloyed semiconductor-metal heterostructure is observed to be highly photocatalytically active for dye degradation as well as photodetection. Incorporation of magnetic Ni(0) makes the photocatalyst superparamagnetic at room temperature which is found to be helpful for catalyst regeneration.

Multistage growth of monocrystalline ZnO nanowires and twin-nanorods: oriented attachment and role of the spontaneous polarization force

Our understanding of crystal growth mechanisms has changed deeply in the past few decades. Particularly, the oriented attachment of intermediate nanoparticles has been accepted to be a crucial crystal growth mechanism that is distinct from the traditional one involving nucleation and Ostwald ripening. However the details of the oriented attachment process are not readily observed experimentally, and little is known about the driving force and the dynamics involved in oriented attachment. In this respect, ZnO is an ideal material because it possesses strong spontaneous polarization which may easily drive oriented attachment during its crystal growth. We study experimentally and theoretically the complete crystal growth process (from primitive amorphous nanoclusters to ultimate single nanocrystals) of one-dimensional ZnO nanocrystals growing in water/ethanol at high temperatures. The results reveal that both axial (along the direction of the polarization axis) and lateral oriented attachment of the intermediates occurs during the growth process of the one-dimensional ZnO nanocrystals. Calculation based on the force and interaction model reveals that the axial oriented attachment driven by the spontaneous polarization force dominates the crystal growth of ZnO nanocrystals, and the van der Waals force also plays a role in driving oriented attachment. The study shows that oriented attachment of intermediate nanoparticle ensembles induces formation of the symmetric twin-nanorods. These results improve our understanding of the growth mechanism of nanocrystals in a liquid medium.

A Novel Mesoporous Single-Crystal-Like Bi2WO6 with Enhanced Photocatalytic Activity for Pollutants Degradation and Oxygen Production

The porous single-crystal-like micro/nanomaterials exhibited splendid intrinsic performance in photocatalysts, dye-sensitized solar cells, gas sensors, lithium cells, and many other application fields. Here, a novel mesoporous single-crystal-like Bi2WO6 tetragonal architecture was first achieved in the mixed molten salt system. Its crystal construction mechanism originated from the oriented attachment of nanosheet units accompanied by Ostwald ripening process. Additionally, the synergistic effect of mixed alkali metal nitrates and electrostatic attraction caused by internal electric field in crystal played a pivotal role in oriented attachment process of nanosheet units. The obtained sample displayed superior photocatalytic activity of both organic dye degradation and O2 evolution from water under visible light. We gained an insight into this unique architecture's impact on the physical properties, light absorption, photoelectricity, and luminescent decay, etc., that significantly influenced photocatalytic activity.

Solvent-induced oriented attachment growth of air-stable phase-pure pyrite FeS2 nanocrystals.

We report here the selective synthesis of air-stable phase-pure pyrite FeS2 nanocubes, spheroidal nanocrystals, and microspheres by solvent-induced oriented attachment (OA). It was found that the solvents could control the OA process and thus the morphologies of the products. Solvent exchange experiments and detailed Raman analysis revealed that 1-octanol contributed to the long-term stability of these pyrite nanomaterials.

In situ growth and assembly of microporous aluminophosphate nanosheets into ordered architectures at low temperature and their enhanced catalytic performance

A low-temperature strategy to fabricate hierarchical aluminophosphate molecular sieves without using a secondary template.

Dual Morin transitions during the oriented attachment process

In this work, two Morin transitions were observed in hematite product at the intermediate stage during the oriented attachment process, which is universal and plays an important role in biogeochemical processes that shape Earth's near-surface environments. Seemingly, these Morin transitions originate from the existence of two sizes of hematite particles. While in-depth study reveals that they were also interdependent on the defreezing behaviors of two different spin configurations at their interfaces. Such pioneering study on the magnetic performance during the oriented attachment process provides a fundamental and new physical basis for the materials' potential applications.

Reaction Kinetics and Formation Mechanism of TiO2 Nanorods in Solution: An Insight into Oriented Attachment

The reaction kinetics and formation mechanism of oriented attachment for shaped nanoparticles in solution are not well-understood. We present the reaction kinetics and formation mechanism of organic-capped anatase TiO2 nanorods in solution as a case study for the oriented attachment process using small-angle X-ray scattering (SAXS) and transmission electronic microscopy. The SAXS analysis qualitatively and quantitatively provides in-depth understanding of the mechanism, including the structural evolution, interparticle interaction, and spatial orientation of nanoparticles developed from nanodots to nanorods during the nucleation, isotropic, and anisotropic growth steps. The present study demonstrates the growth details of oriented attachment of nanoparticles in solution. An ordered lamellar structure in the solution is constructed by the balance of interaction forces among surface ligands, functional groups, and solvent molecules serving as a natural template. The template allows the alignment of spherical nanoparticles into ordered chain arrays and facilitates simultaneous transformation from spherical to rod shape via proximity attachment. The proposed model reveals an insight into the oriented attachment mechanism. This multistep formation mechanism of TiO2 nanorods in solution can provide the fundamental understanding of how to tune the shape of nanoparticles and further control the aggregation of spatial nanorod networks in solution.

Understanding the crystallization mechanism of delafossite CuGaO2 for controlled hydrothermal synthesis of nanoparticles and nanoplates.

The delafossite CuGaO2 is an important p-type transparent conducting oxide for both fundamental science and industrial applications. An emerging application is for p-type dye-sensitized solar cells. Obtaining delafossite CuGaO2 nanoparticles is challenging but desirable for efficient dye loading. In this work, the phase formation and crystal growth mechanism of delafossite CuGaO2 under low-temperature (<250 °C) hydrothermal conditions are systematically studied. The stabilization of Cu(I) cations in aqueous solution and the controlling of the hydrolysis of Ga(III) species are two crucial factors that determine the phase formation. The oriented attachment (OA) growth is proposed as the crystal growth mechanism to explain the formation of large CuGaO2 nanoplates. Importantly, by suppressing this OA process, delafossite CuGaO2 nanoparticles that are 20 nm in size were successfully synthesized for the first time. Moreover, considering the structural and chemical similarities between the Cu-based delafossite series compounds, the understanding of the hydrothermal chemistry and crystallization mechanism of CuGaO2 should also benefit syntheses of other similar delafossites such as CuAlO2 and CuScO2.

Multipole Surface Plasmon Resonance in Electrodeposited Gold Nanoparticles

Electrodeposition is a convenient, economical and template-free tool to create the gold nanostructures. A two-electrode electrochemical process is used for the deposition process. In this method by controlling the deposition time and electrode potential, nearly spherical and rod-like gold nanostructures were synthesized through the reduction of Chlorauric acid with citric acid as a complexing agent. Spherical gold nanostructures of different size around 2 nm to 30 nm and rod-like nanostructures with an aspect ratio 0.5 were grown directly on fluorine-doped tin oxide (FTO)-coated glass substrate. The growth mechanism of gold nanostructures is explained with the help of oriented attachment process. The contact angle measurement showed the hydrophilic nature of gold nanostructures using water with contact angle of about 56°. The optical properties showed a dipole, quadrupole and an octupole plasmon resonance mode at around 625 nm, 530 nm and 422 nm respectively. The dipole resonance peak extends further to give a broad absorption band in the near infrared region of electromagnetic waves. The refractive index sensitivity of gold nanoparticles in various solvents was investigated by calculating the red shift of surface plasmon resonance (SPR) peaks. The quadrupole plasmon resonance mode showed maximum SPR sensitivity as compared to dipole and octupole plasmon resonance mode. The controlled formation of gold nanoparticles with variation of SPR over wide range of visible region supports the potential applications in biosensors, nanoelectronics and plasmon enhanced light absorption in photovoltaics, etc.

Insights from in situ and environmental TEM on the oriented attachment of α-Fe2O3nanoparticles during α-Fe2O3nanorod formation

Acicular α-Fe2O3 nanorods (NRs), at an intermediate stage of development, were isolated using a snapshot valve-assisted hydrothermal synthesis (HS) technique, for the purpose of complementary in situ transmission electron microscopy (iTEM) and environmental TEM (ETEM) investigations of the effect of local environment on the oriented attachment (OA) of α-Fe2O3 nanoparticles (NPs) during α-Fe2O3 NR growth. Observations of static snapshot HS samples suggested that α-Fe2O3 NPs undergo reorientation following initial attachment, consistent with an intermediate OA stage, prior to ‘envelopment’ with the developing NR to adopt a perfect single crystal. Conversely, the heating of partially developed α-Fe2O3 NRs up to 250 °C, under vacuum, during iTEM, demonstrated the progressive coalescence of loosely packed α-Fe2O3 NPs and the coarsening of α-Fe2O3 NRs, without any direct evidence for an intermediate OA stage. Direct evidence was obtained for the action of an OA mechanism prior to the consumption of α-Fe2O3 NPs at the tips of developing α-Fe2O3 NRs during ETEM investigation, under an He pressure of 5 mbar at 500 °C. However, α-Fe2O3 NPs more strongly attached to the side-walls of developing α-Fe2O3 NRs were more likely to be consumed through a local NP destabilisation and reordering process, in the absence of an OA mechanism. Hence, the emerging ETEM evidence suggests a competition between OA and diffusion processes at the α-Fe2O3 NP coalescence stage of acicular α-Fe2O3 NR crystal development, depending on whether the localised growth conditions facilitate freedom of NP movement.

Lattice defect quenching effects on luminescence properties of Eu3+-doped YVO4 nanoparticles

A room-temperature co-precipitation method was explored to synthesize Eu3+-doped YVO4 precursors as constructed by an aggregation of several primary particles. After calcination treatment, the primary particles underwent an oriented attachment process and grew into the regular square-like nanoparticles (NPs). These square-like NPs exhibited an improvement in quantum yield of luminescence emission, as indicated by greatly enhanced excitation intensity and lifetime. Further studies on these square-like NPs by electron paramagnetic resonance demonstrated a defect structure as characterized by lower valence state vanadium ions and oxygen vacancies that were produced during the growth process in nitrogen atmosphere. The formation of these defect structures was significantly influenced by the calcination atmospheres, which enables us to uncover the relationships between defect structures and luminescence properties of YVO4:Eu3+ nanocrystals.

Understanding the Growth Mechanism of α-Fe2O3 Nanoparticles through a Controlled Shape Transformation

The growth mechanism of α-Fe2O3 nanoparticles in solution has been elucidated from a comprehensive analysis on the shape and morphology of obtained particles. It is found that the hydrothermal synthesis of α-Fe2O3 nanoparticles from ferric chloride precursor follows two stages: the initial nucleation of α-Fe2O3 nuclei and the subsequent ripening of nuclei into various shapes. The initial nucleation involves the formation of polynuclears from hydrolysis of Fe3+ salt precursors, followed by the growth of β-FeOOH nanowires with an akaganeite structure, and then into two-line ferrihydrite nanoparticles through a dissolution–recrystallization process. In the subsequent ripening process, we suggest that the formation of large α-Fe2O3 particles follows the dissolution of two-line ferrihydrite and then precipitation and oriented aggregation of α-Fe2O3 nuclei rather than the oriented aggregation of ferrihydrite nanoparticles followed by phase transformation. The oriented attachment of {104} facets between α-Fe2O3 nuclei results in the formation of oblate spheroid nanocrystals (nanoflower-like particles) either in ethanol or in the beginning stage where the particles first undergo oriented aggregation. With the addition of water, Ostwald ripening process (dissolution–reprecipitation) will play an important role to convert the assembly of nanoflowers into a 3D rhombohedral shape with well-defined edges and surfaces. The proposed mechanism in this article not only allows us to better control the synthesis of iron oxide particles with designed shapes and structures but also provides guidance for theoretical simulations on the oriented attachment process for hematite formation.