Fabrication Of Nanocrystals Research Articles

Concave Cu-Pd bimetallic nanocrystals: Ligand-based Co-reduction and mechanistic study

The synthesis of highly uniform alloy nanocrystals with a concave feature is desirable for applications in catalysis but is an arduous task. This article proposes an initiative protocol for the fabrication of novel Cu-Pd alloy nanocrystals, wherein the volume of decylamine (DA) in the reaction system was found to greatly influence the formation of different morphologies, including the tetrahedron (TH), concave tetrahedron (CTH), rhombohedral-tetrapod (RTP), and tetrapod (TP). The alloy structure of the products arises from the coordination interaction between the DA and metal ions, which affects the reduction potential of Cu and Pd species, and thus yields co-reduction. Other reaction parameters, such as the type of ligand, amount of reductant, and temperature, were also altered to study the growth mechanism, yielding consistent conclusions in the diffusion-controlled regime. As a catalyst, 48-nm Cu-Pd concave tetrahedral nanocrystals were highly active for the hydrogenation of 3-nitrostyrene and exhibited >99.9% chemoselectivity to C=C instead of -NO2.

Fabrication of Cellulose Nanocrystals from Agricultural Compost

ABSTRACTCellulose nanocrystals have emerged as replacements for man-made fibers to fabricate environmentally friendly green products. In this work, cellulose nanocrystals (CNCs) of mixed morphology were synthesized by acid hydrolysis of compost using sulfuric acid. Compost, an agro-based biomass feedstock, procured from water hyacinth (Eichhornia crassipes), cow dung, and saw dust (8:1:1) was utilized for the extraction of cellulose, followed by synthesis of CNCs. Compost was prepared using a rotary drum composter and was utilized for the production of CNCs. A two-step procedure for the extraction of CNCs was studied. Initial chemical treatments, including alkali treatment and bleaching, led to the gradual removal of lignin and hemicellulose, while the subsequent sulphuric acid (40%) hydrolysis step yields CNCs in an aqueous suspension. The synthesized CNCs have been studied by Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and particle size analyzer. The morphology and dimension of nanofibrils were studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques, which showed mixed morphology of rectangular cone type and spherical dimensions. Fabrication of such mixed morphology was found to be dependent on the selected biomass. The trace of metal elements present in the biomass was investigated by scanning electron microscopy-energy dispersive X-ray (SEM-EDX). We report a cost effective and feasible approach of utilizing inexpensive bioresources for production of value added products like CNCs, which could find potential application in the fields of healthcare, biomedical engineering, packaging, etc.

Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

Fabrication of 1D nickel sulfide nanocrystals with high capacitances and remarkable durability

Nickel sulfide (NiS) materials with a different 1D structure are successfully synthesized by strictly controlling the reaction time and temperature, using dodecanethiol as both solvent and sulfur source. The formation of the NiS nanomaterials results from a “dispersion–decomposition” mechanism. Remarkably, 1D NiS electrode materials show super specific capacitance and stability.

COLLOIDAL PREPARATION OF MONODISPERSE NANOCRYSTALS

In the field of nanoscience, the ability to prepare high-quality nanocrystals is crucial for fundamental research and technology development. Herein, we review a general route for the colloidal preparation of monodisperse nanocrystals, which is divided into five different stages, namely (i) nucleation, (ii) growth, (iii) Ostwald ripening, (iv) surfactant capping and (v) precipitation. Each of the five stages is discussed in detail to provide a comprehensive understanding of the mechanism behind nanocrystal formation and the subsequent processing steps. We put emphasis on the classical theories and experimental techniques that are most frequently practiced. These are useful for the successful design and fabrication of nanocrystals with properties that are beneficial for use in a plethora of technological applications.

In situ study of oxidative etching of palladium nanocrystals by liquid cell electron microscopy.

Oxidative etching has widely prevailed in the synthesis of a crystal and played a critical role in determining the final growth behavior. In this Letter, we report an in situ microscopic study on the oxidative etching of palladium cubic nanocrystals by liquid cell scanning transmission electron microscopy. The etching was realized with oxidative radiation reactants from electron-water interaction in the presence of Br(-) ions. Dissolution dynamics of monodispersed and aggregated nanocrystals were both investigated and compared. Analyses on the dissolution kinetics of nanocrystals and the diffusion kinetics of the dissolved agents were carried out based on the scanning transmission electron microscopy characterizations. The results presented here pave a way toward the quantitative understanding of the oxidative etching reaction and its application in the functionally orientated fabrication of nanocrystals with certain sizes, structures, and morphologies.

Fabrication of dispersible calcium phosphate nanocrystals via a modified Pechini method under non-stoichiometric conditions

Various techniques for preparing ceramic nanoparticles have been developed; however, most of them start from a preparation of precursor nanoparticles that are generally amorphous or in poorly crystallized phases. Thermal treatments used to obtain crystalline phases typically result in the sintering of the products into large polycrystals. In this study, we developed a process to fabricate dispersible hydroxyapatite (HAp; Ca10(PO4)6(OH)2) nanocrystals via a modified Pechini method, which is a sol–gel like solid-state synthesis method for the preparation of multicomponent oxides. We demonstrated that the HAp nanocrystals sintered into large polycrystals ranging in size from several tens to several hundreds of microns via a conventional Pechini method using the stoichiometric Ca/P molar ratio of 1.67. When the Ca/P molar ratio in the precursor was >1.67, a mixture of HAp nanocrystals and removable CaO matrix was obtained. The HAp nanocrystals were dispersed in aqueous media mostly in the form of nanoparticles when the amount of CaO matrix was sufficiently greater than the amount of HAp.

Room temperature fabrication of silicon nanocrystals by pulsed laser deposition

In this work, a room temperature single-step physical vapour deposition process is presented for the fabrication of nanosized Si crystals (diameter below 10 nm) embedded in an amorphous matrix, together with unique novel nanostructures consisting of silicon amorphous-crystalline core–shell nanostructures. Pulsed laser deposition in a background atmosphere (Ar or a mixture of <3 vol% of H2 in Ar) is used to induce cluster nucleation in the gas phase and to vary the deposition kinetic energy, in order to grow Si films of different morphologies and porosities, at the nanoscale, as a function of gas pressure. Relatively high-pressure processing (100 Pa) leads to a hierarchically nanostructured film composed of Si nanocrystals embedded in a columnar porous amorphous matrix, as assessed by high resolution transmission electron microscopy. Raman spectroscopy analysis shows quantum-confinement-induced shift of the Si peak at 520 cm−1, thus confirming the occurrence of nanocrystals. Finally, in situ silicon oxidation has been effectively shown to be decreased after adaptation of a mixture of few-percent-hydrogen in argon as background gas.

Shape‐ and Size‐Controlled Synthesis of Mn3O4 Nanocrystals at Room Temperature

AbstractA versatile synthetic method has been developed for the fabrication of Mn3O4 nanocrystals with different sizes and shapes, such as square nanoplates, mesocrystal nanodisks, and nanopolyhedra. Manganese(II) acetate tetrahydrate and hydrazine monohydrate were the only two reactants used in aqueous solution, and no surfactant was employed. The key advantages of our approach are (1) the room‐temperature synthesis, (2) the facile operation, (3) the flexibility in shape‐ and size‐control, and (4) the ease of scale‐up. The exposed surfaces of the as‐prepared nanoparticles were carefully characterized and indexed. The catalytic properties of the nanoplates for the degradation of methylene blue were evaluated in detail. The catalytic properties are closely related to the shape and size of the Mn3O4 nanocrystals, and nanoplates with a size of 50 nm exhibited the best catalytic performance. The magnetic properties were investigated with a superconducting quantum interference device magnetometer.

Ultrathin Gold Nanoribbons Synthesized within the Interior Cavity of a Self-Assembled Peptide Nanoarchitecture

There is increasing interest in gold nanocrystals due to their unique physical, chemical, and biocompatible properties. In order to develop a template-assisted method for the fabrication of gold nanocrystals, we demonstrate here the de novo design and synthesis of a β-sheet-forming nonapeptide (RU006: Ac-AIAKAXKIA-NH2, X = L-2-naphthylalanine) which undergoes self-assembly to form disk-like nanoarchitectures approximately 100 nm wide and 2.5 nm high. These self-assemblies tend to form a network of higher-order assemblies in ultrapure water. Using RU006 as a template molecule, we fabricated ultrathin gold nanoribbons 50-100 nm wide, 2.5 nm high, and micrometers long without external reductants. Furthermore, in order to determine the mechanism of ultrathin gold nanoribbon formation, we synthesized four different RU006 analogues. On the basis of the results obtained using RU006 and these analogues, we propose the following mechanism for the self-assembly of RU006. First, RU006 forms a network by the cooperative association of disk-like assemblies in the presence of AuCl4(-) ions that are encapsulated and concentrated within the interior cavity of the network architectures. This is followed by electron transfer from the naphthalene rings to Au(III), resulting in slow growth to form ultrathin gold nanoribbons along the template network architectures under ambient conditions. The resulting ribbons retain the dimensions of the cavity of the template architecture. Our approach will allow the construction of diverse template architectural morphologies and will find applications in the construction of a variety of metallic nanoarchitectures.

Fabrication of hollow ZnO hexahedral nanocrystals grown on Si(100) substrate by a facile route

Using a facile two-step of wet chemical procedure to synthesize hollow hexahedral zinc oxide on a Si(100) substrate is described. The X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to investigate the structure and morphology of products, also the photocatalytic and ferromagnetic properties were examined. The results showed that the diameter of ZnO with hollow structure is 200nm and a hole with diameter of 100nm, which is expected to be utilized as a catalyst support material in environmental remediation. The formation mechanism of hollow hexahedral ZnO is based on a dehydration reaction of Zinc 4-coordinated complexes and a preferential defect-etching process. Further investigation on the photocatalytic activity of the products showed the degradation of tetracycline is high to 98% in 120min, also the hollow ZnO nanocrystals were proved having ferromagnetic property.

Fabrication and optical properties of water soluble CdSeS nanocrystals using glycerin as stabilizing agent.

Herein we present an unusual phosphine-free method to fabricate water soluble CdSeS nanocrystals in cubic structure. In this method, glycerin was used as a stabilizing agent replacing tri-n-octylphosphine oxide (TOPO). Water solution of Na2SeO3 in polyethylene glycol was utilized as Se source. 3-Mercaptopropionic acid (MPA) provides S source. The phosphine-free Se and S sources were found to be highly reactive and suitable for the synthesis of CdSeS nanocrystals. XRD and HRTEM images confirm the formation of CdSeS nanocrystals in zinc blende structure. The absorption peaks on UV-vis spectra of as-prepared CdSeS nanocrystals are tunable from 330 nm to 440 nm, which blue shifts to shorter wavelength side in comparison with that of pure CdSe nanocrystals. The cubic CdSeS nanocrystals demonstrate narrow PL emissions spectra between 464 and 615 nm. Transmission electron microscopy images show the uniformity for the size distribution of the ternary QDs. Series water soluble CdSe1–xSx (x = 0∼1) nanocrystals have also been synthesized using Na2SeO3 and Na2S solution as the Se-S co-sources. Tunable band gap energies of CdSe1–xSx (x = 0∼1) nanocrystals upon chemical composition x have been achieved, the gap ranges from 290 nm to 558 nm.

Lateral growth of Ge nanocrystals in a thin Ge-rich silicon nitride layer

Fabrication of Ge nanocrystals (NCs) in a thin Ge-rich silicon nitride layer was studied by structural, stress, phonon, compositional and optical characterisation. Multilayer films composed of alternating Ge-rich silicon nitride (GRN) and near stoichiometric Si3N4 barrier layers were prepared using rf-magnetron sputtering followed by a furnace annealing with variation to the temperature and the Ge content. Threshold Ge content for crystallisation was found and a narrow processing condition for spherical NCs also observed. Ge NCs in the Si3N4 matrix, without becoming a composite, experienced tensile stress shifting the phonon peak to lower wavenumber masking the phonon confinement induced peak shift. Results of the series of characterisation suggested that fairly high Ge content was required to precipitate NCs for this film structure and lateral growth of Ge NCs occurred readily with NCs formation in the Si3N4 matrix. The Si3N4 matrix is considered a dense matrix for large sized Ge atoms and so precipitation of excess Ge atoms seems challenging through the phase separation of GRN. Quantum confinement was found weak as demonstrated by slightly blue-shifted optical absorption edge in the 4nm NC film.

Synthesis of NaYF4, NaLuF4 and NaGdF4-Based Upconversion Nanocrystals with Hydro (Solvo) Thermal Methods

Serials of NaYF4, NaLuF4 and NaGdF4-based nanocrystals have been synthesized successfully by solvothermal and hydrothermal, respectively. The properties of the products were characterized and compared. The nanocrystals prepared by hydrothermal method exhibited uniform hexagonal phase and large size, while the nanocrystals prepared by solvothermal method displayed high upconversion luminescence (UCL) and small size. The UCL intensities of the nanocrystals prepared by solvothermal method were higher than that of nanocrystals from hydrothermal method. Whether using solvothermal or hydrothermal method, the UCL intensities of the nanocrystals were in the sequence (from strong to weak) of NaLuF4:Gd/Yb/Tm, NaLuF4:Yb/Tm, NaGdF4:Yb/Tm, NaYF4:Gd/Yb/Tm and NaYF4:Yb/Tm, respectively. This is the first time to systematically compare three kinds of host-based nanocrystals, which are prepared by two different approaches with various lanthanide ions doped. This work could provide new insight into fabrication of upconversion nanocrystals with intense UCL and controllable morphology and size via using suitable doping ions, host materials and efficient approaches.

Fabrication of fenofibrate nanocrystals by probe sonication method for enhancement of dissolution rate and oral bioavailability

Fenofibrate (FBT) is lipophillic drug used in hypercholesterolemia and hypertriglyceridemia having logP 5.375, low solubility (practically insoluble in water) and low oral bioavailability (36%). The purpose of work was to develop FBT nanocrystals for the enhancement of solubility and oral bioavailability. Fenofibrate nanosuspension was prepared using probe sonicator and transformed into dry powder using freeze drying and characterized by DSC, FTIR, XRPD, SEM, particle size, polydispersity index (PDI), zeta potential, solubility, in vitro dissolution, in vivo bioavailability and stability studies. Formulation FNS3 and pure drug exhibited the in vitro dissolution about 73.89% and 8.53% in 1% sodium lauryl sulfate (SLS) media, respectively. When the particle size reduced from 80,000±923nm to 460±20nm, saturation solubility was significantly increased. The saturation solubility of formulation FNS3 in 0.5% and 1% of SLS media found to be 67.51±1.5μg/mL and 107±1.9μg/mL, respectively. While, the saturation solubility of pure drug in 0.5% and 1% of SLS was found to be 6.02±1.51μg/ml and 23.54±1.54μg/ml, respectively. The pharmacokinetic study of optimized nanocrystals (FNS3) conducted in New Zealand white rabbits showed 4.73-fold increase in relative bioavailability than that of pure drug. Long term stability studies showed that there was no significant change in the mean particle size and PDI at 5°C±3°C after 180 days. This enhanced dissolution and bioavailability of fenofibrate nanocrystals could be the promising approach for oral delivery.

The controlled regulation of morphology and size of HKUST-1 by “coordination modulation method”

Three types of modulators, including sodium formate, sodium acetate and triethylamine were used to tailor the morphology and size of HKUST-1 crystals by “coordination modulation method”. Through exploring the reaction parameters during the synthesis of HKUST-1, fascinating crystals morphologies, including hierarchical octahedral-shape crystals and nanocrystals were obtained by a solvothermal treatment. This paper discloses two essential functions of the modulator for the fabrication of uniform nanocrystals: Adjusting the proper acid–base environment of the reaction medium which governs the nucleation process and capping groups capable of inhibiting crystallites from growing. Moreover, samples were fully characterized by various techniques and the formation mechanism of the hierarchical octahedral-shape crystals was deduced.

Ordered arrays of Si and Ge nanocrystals via dewetting of pre-patterned thin films

We develop self-organisation processes for the fabrication of 2D arrays of Si and Ge quantum dots. The processes make use of the dewetting phenomenon which involves the transformation of a 2D thin film into an array of isolated 3D islands through a morphological instability. We show that self-organization of monodisperse ultra-small nanocrystals (NCs) into large scale patterns with ad hoc features can be created via heterogeneous dewetting. The process involves dewetting of thin films nanopatterned by electron beam lithography (EBL) or liquid metal alloy source focused ion beam (LMAIS-FIB). Heterogeneous dewetting is initiated at the edges of the patterns. It provokes the retraction of the thin film following the kinetics of surface diffusion and ends by the formation of faceted monocrystalline NCs regularly positioned. Their geometrical features and lateral arrangements can be tuned by changing the pitch, size, and shape of the patterns. The process developed in this study is adapted to the fabrication of NCs based floating gate memories.

Fabrication of FeF3 nanocrystals dispersed into a porous carbon matrix as a high performance cathode material for lithium ion batteries

FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour–solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g−1 of charge capacity at a current density of 104, 520, and 1040 mA g−1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g−1 at 20.8 mA g−1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.

Phase- and shape-controlled hydrothermal synthesis of CdS nanoparticles, and oriented attachment growth of its hierarchical architectures

Hydrothermal strategies were successfully used to control the phases and morphologies of CdS nanocrystals. In the absence of an external direction-controlling process, the hexagonal and cubic phase well-defined leaf- and flower-like CdS nanocrystals were controlled obtained via adjusting the reaction duration or the concentration of surfactant. Oriented attachment growth modes were suggested for the formation of CdS superstructures, which was clarified through the tracing of temporal evolution of CdS nanoparticles. The CdS superstructures were structured by primary building nanoparticles, and held excellent visible emission with a peak in the green regions. This strategy is very helpful for studying the phase and morphology controlled fabrication of sulfides nanocrystals.

Kinetically Controlled Overgrowth of Ag or Au on Pd Nanocrystal Seeds: From Hybrid Dimers to Nonconcentric and Concentric Bimetallic Nanocrystals

This article describes a systematic study of the nucleation and growth of Ag (and Au) on Pd nanocrystal seeds. By carefully controlling the reaction kinetics, the newly formed Ag atoms could be directed to selectively nucleate and then epitaxially grow on a specific number (ranging from one to six) of the six faces on a cubic Pd seed, leading to the formation of bimetallic nanocrystals with a variety of different structures. In addition to changing the injection rate of precursor, we also systematically investigated other reaction parameters including the capping agent, reductant, and reaction temperature. Our results suggest that the site-selective growth of Ag on cubic Pd seeds could be readily realized by optimizing these reaction parameters. On the basis of the positions of Pd seeds inside the bimetallic nanocrystals as revealed by TEM imaging and elemental mapping, we could identify the exact growth pathways and achieve a clear and thorough understanding of the mechanisms. We have successfully applied the same strategy based on kinetic control to cubic Pd seeds with different sizes and octahedral Pd seeds of one size to generate an array of novel bimetallic nanocrystals with well-controlled structures. With cubic Pd seeds as an example, we have also extended this strategy to the Pd-Au system. We believe this work will provide a promising route to the fabrication of bimetallic nanocrystals with novel structures and properties for applications in plasmonics, catalysis, and other areas.