Nucleation Of Nanocrystals Research Articles

Synthesis of hierarchical SAPO-11 via seeded crystallization

Hierarchical SAPO-11 molecular sieve was synthesized via a seeded crystallization approach as reported in this paper. SAPO-11 molecular sieve was first synthesized in common Al2O3-P2O5-Dipropylamine-H2O system. Nitrogen adsorption test indicated that the synthesized SAPO-11 has additional mesoporosity with a mesopore volume being 0.09 cm3/g. SEM and TEM analysis indicated the formation of a core (microporous SAPO-11)/shell (mesoporous SAPO-11 aggregate) structure. With the purpose to improve the mesoporosity, SAPO-11 seed was added into the Al2O3-P2O5-Dipropylamine-H2O system. XRD, SEM, TEM, and nitrogen adsorption tests indicated hierarchical SAPO-11 molecular sieve with mesopore volume up to 0.40 cm3/g can be synthesized in Al2O3-P2O5-Dipropylamine-H2O system with 2–10% SAPO-11 molecular sieve as seed. SEM and TEM studies indicate the formation of SAPO-11 nanorods with ultra-small diameter (5 nm). A crystallization kinetic study indicated that 6 h is sufficient for the formation of highly crystalline hierarchical SAPO-11 molecular sieve. The texture and acidity of hierarchical SAPO-11 can be controlled by changing the crystallization time. Based on the experimental results, the formation of hierarchical SAPO-11 is an integrated effect of the burst nucleation and special rod shape of SAPO-11 nanocrystal and the role of SAPO-11 seed is promoted nucleation by increasing the surface area of the liquid–solid interface.

Effects of Reaction Parameters on the Growth and Optical Properties of PbSe Nanocrystals

Colloidal syntheses of PbSe nanocrystals (NCs) have been widely investigated and the properties of nanocrystals have been shown to vary with reaction conditions, time, concentration and chemistry of reagents as well as the surfactants used. In this work the effects of reaction temperature, solvents, ligand purity, lead and selenium sources on the optical and structural properties of PbSe nanocrystals were investigated. PbSe NCs synthesized at 90 °C were observed to be spherical and had a narrower size distribution as compared to those synthesized at higher temperatures. 1-octadecene, trioctylphosphine and oleylamine were investigated as solvents for NC synthesis with the non-coordinating solvent octadecene showing the fastest growth rate with medium sized NCs. The coordinating solvents trioctylphosphine and oleylamine produced larger and smaller NCs respectively; this could be attributed to solvent interference during NC nucleation and growth phases. Oleate ligands were used during these syntheses and the ligand purity was not observed to have a significant effect on the NC optical and structural properties. The selenium precursor used affected the NC size and their optical properties while the lead source influenced both the NC shape and size. Lead acetate produced cubic NCs which were larger than the spherical NCs obtained when lead oxide was used.

Effect of seed particles on crystallization and crystallite size of anatase TiO2 nanocrystals by solvothermal treatment

Commercial TiO2 nanoparticles (Degussa P25) with a mean diameter of ca. 20nm and of predominately anatase phase were deliberately added in sol–gel-prepared amorphous TiO2 particles as “seed” before being subjected altogether to a mild solvothermal treatment over a temperature range from 100 to 200°C. The presence of seed particles reduced the crystallization temperature moderately from 127.2 to 122.4°C when the seed of up to 10wt.% was added, resulted in crystalline anatase nanocrystals. On the other hand, crystallite size of the anatase nanocrystals increased up to an average of 28nm (+40%) with the seed. This seed-induced grain growth appeared to occur preferentially at vicinity of the seed particles. As temperature was raised above the crystallization temperature (∼120°C), homogeneous nucleation and growth of the anatase TiO2 nanocrystals prevailed so that a massive anatase structure with a crystal dimension of 8–12nm resulted after the solvothermal treatment.

Control of one‐dimensional hydroxyapatite nanocrystals at mild conditions: organic additive effects

One-dimensional hydroxyapatite (HAp, Ca10(PO4)6(OH)2) nanocrystals have been successfully synthesised via the simple precipitation-hydrolysis process on mild solution conditions. At the first precipitation step, the precursor samples of monetite phase CaHPO4 were prepared with three kinds of organic additives. The results of X-ray diffraction (XRD) patterns show that the structure and crystallinity of CaHPO4 prepared with the different organic additives are different, which indicates that the organic additives exert influence on the crystal growth of CaHPO4. During the second process, the HAp nanocrystals with high aspect ratio grew up under a high pH condition. The XRD patterns show that the preference of every nanocrystal growth is the (002) plane. Transmission electron microscopy micrographs indicate that the HAp nanocrystals were affected by the reaction temperature and the pH values of the solution. The organic additives influenced the aspect ratio of HAp nanocrystals, and Fourier transform infrared spectra show that the organic additives were completely dissolved in the aqueous system. This indicates that the organic additives affected the formation of nucleation and growth of HAp nanocrystals, and the influence gradually decreased with the extension of the hydrolysis time, until the organic additives were detached from the HAp crystals.

Substrate-induced assembly of PtAu alloy nanostructures at choline functionalized monolayer interface for nitrite sensing

PtAu alloy nanostructures (nanoclusters) with desired surface structure and properties were constructed at choline functionalized monolayer interface. The significance of choline substrate was to provide a suitable local microenvironment with –N+(CH3)3 polar head groups, which was favorable for the progressive nucleation of alloy nanocrystals, as well as the mass transfer of AuCl4− and PtCl62−. The formation process and mechanism of the nanoclusters were investigated, and the physicochemical properties of the nanoclusters were characterized. Electrochemical experimental results demonstrated that the as-prepared nanoclusters exhibited remarkable electrocatalytic activity towards the oxidation of nitrite due to the ensemble effect and ligand effect of alloy material. Based on the catalytic performance of alloy nanoclusters, the electrode reaction kinetics of nitrite oxidation was studied. Moreover, the analysis of nitrite was realized in real samples including pond water, industrial wastewater, and milk samples, suggesting that the system is beneficial for environmental monitoring and food safety assessment.

Photocatalytic degradation of phenol over novel rod shaped Graphene@BiPO4 nanocomposite

Graphene@BiPO4 nanocomposite with unique rod shape morphology of BiPO4 has been successfully fabricated by the simple microwave assisted hydrothermal method. The crucial role of graphene oxide in the growth of rod shaped BiPO4 crystals has been attempted to explain in this article. Graphene oxide acts as a structure-directing and morphology-controlling agent in the nucleation and growth of nanocrystals. The as prepared organic–inorganic hybrid Graphene@BiPO4 nanocomposite photocatalyst was characterized by various techniques i.e. X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy. The results were promising and shown enhanced photocatalytic activity than pure BiPO4 for phenol degradation. The effect of graphene loading on the rates of photocatalytic degradation of phenol in solution is investigated. The result shows that the optimum photocatalytic activity of Graphene@BiPO4 composite at 5wt% of graphene under visible light is almost three times higher than pure BiPO4.

Facile synthesis of high-temperature (1000 °C) phase-stable rice-like anatase TiO2 nanocrystals

High-temperature phase-stable rice-like anatase TiO2 nanocrystals were synthesized by one-pot solvothermal method using soluble titania xerogel and isopropyl alcohol (IPA) as the precursor and the solvent, respectively. Sample characterization was carried out by powder X-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscope, X-ray photoelectron spectroscopy, and N2 adsorption–desorption isotherms. The results showed that TiO2 nanocrystals had rice-like shapes with an average size of 5 nm in width and 35 nm in length. The BET surface area was 153 m2/g. Unexpectedly, the rice-like TiO2 nanocrystals exhibited high-temperature phase stability, which could remain as pure anatase phase after calcinations at 1000 °C. Growth mechanism investigation revealed that the IPA solvent played a key role in nucleation and growth of rice-like anatase TiO2 nanocrystals. The photodegradation of rhodamine B demonstrated that rice-like anatase TiO2 nanocrystals exhibited enhanced photocatalytic activity under visible light irradiation.

Synthesis and characterization of Cu2ZnSnS4 nanocrystals by hot-injection method

Cu2ZnSnS4 (CZTS) nanocrystals were synthesized by hot injection method. The n-dodecanethiol (DDT) is used as coordinating ligand which is expected to have great effect on the nucleation and growth of the final CZTS nanocrystals. The influences of the amount of DDT on the structure, morphology and optical properties of CZTS nanocrystals were investigated in detail. The results show that the structures of the as-synthesized CZTS products are kesterite structure, the morphology of the nanocrystals changed from hexagonal to spherical and the average diameter of CZTS nanocrystals changed in the range of 13–23 nm. The band gap energy of the as-synthesized CZTS nanocrystals changed from 1.61 to 1.31 eV with increase of the amount of DDT. The obtained CZTS nanocrystals are suitable for using as an absorber layer in low-cost solar cells.

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic-NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces.

Investigation of disclinations in Marks decahedral Pd nanoparticles by aberration-corrected HRTEM

Temperature plays a vital role in the nucleation and growth of nanocrystals in the hydrothermal method, but the heating methods would cause some side reactions during the temperature rising period. Here, we modify the synthesis process of Marks decahedral Pd nanoparticles and do a detailed analysis of the internal structure of a Marks decahedral Pd Nanoparticle using aberration-corrected high resolution transmission electron microscopy (HRTEM) and the geometric phase analysis (GPA). The yield rate of Marks decahedral Pd nanoparticles increases to more than 60%. Our measurements confirm the existence of disclinations, which is consistent with the results given by the inhomogeneous strain model.

Hierarchical ZnO with twinned structure: Morphology evolution, formation mechanism and properties

Various hierarchical ZnO architectures constructed by twinned structures have been synthesized via a trisodium citrate assisted hydrothermal method on a large scale. The probable formation mechanisms of hierarchical ZnO structures with twinned structure were proposed and discussed. The hierarchical ZnO with twinned structures are composed of two hemispheres with a center concave junction to join them together at their waists. The ZnO microspheres with rough surfaces were obtained when the concentration of trisodium citrate is 0.1 M. However, the football-like microspheres consisted of hexagonal nanosheets were formed when adding glycerol into the water, which should be attributed to the slower nucleation and growth rate of nanocrystals. The hamburger-like ZnO with different aspect ratio and nonuniform ZnO microspheres were generated due to the different quantity of initial nuclei and growth units when simply modulating the concentration of trisodium citrate. The surface area of football-like ZnO is about 3.51 times of microspheres composed of irregular particles. However their photocatalytic performances are similar under UV light irradiation, which indicates that pore sizes of the sample have more important influences on the photocatalytic activity.

Ion Irradiation Induced Crystallization In Iron Phosphate Glass – TEM Investigations

Iron phosphate glass (IPG) is considered as a suitable matrix for the immobilization of nuclear waste containing higher concentration of Cs, rare earth, Mo and Cr. The central issue, while disposing nuclear waste in glass matrices, is the damage in glass matrices due to the ballistic processes caused by atomic displacements due to α-particles and the recoiling of heavy nuclei resulting from actinide decay. Ion irradiation produces similar kind of damage, and hence the samples are irradiated with 4 MeV O + (self) ion. The microstructural studies were carried out using transmission electron microscopy (TEM) for as-prepared, annealed and ion irradiated samples. It is observed that ion irradiation in IPG leads to the formation of nanocrystals with different phases containing Fe, P and O. Thermally activated crystallization process is ruled out based on the non-equilibrium experimental conditions. In the present experiments, stress driven crystallization mechanism was invoked. The stress, around the ion track formed during ion irradiation, is larger than the yield strength of the glass and hence, the surrounding matrix undergoes substantial deformation resulting in the formation of shear bands. Nucleation of nanocrystals is driven by the stress in the vicinity of the shear bands. Copyright © 2015 VBRI press.

Utilizing Sn Precursor To Promote the Nucleation of PbSe Quantum Dots with in Situ Halide Passivation

The lead chalcogenide quantum dots with a size smaller than 3 nm and good chemical stability were difficult to synthesize due to the poor chemical reactivity of commonly used phosphine-free chalcogen and lead sources. Here we report the synthesis of small and surface passivated PbSe quantum dots (QDs) by addition of SnCl2 as the nucleation promoting agent and PbCl2 as the in situ passivation agent. Common PbCl2 (dissolved in oleylamine, oleic acid, and 1-octadecene) and elemental Se (dissolved in oleylamine) were used to synthesize small PbSe QDs by addition of SnCl2 to promote the fast nucleation of PbSe nanocrystals. The sizes of the PbSe QDs are between 3 and 8 nm and are tunable by controlling the ratio of PbCl2/SnCl2 and the reaction time. High photostability of PbSe QDs approved by the XPS analysis and photoluminescence spectra of PbSe QDs was also achieved by the in situ formation of thin halide adlayers on the surface of QDs. This new method is green with accessible raw materials and simple in sit...

Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes

Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.

Alteration, adsorption and nucleation processes on clay–water interfaces: Mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale

Nano-scale processes on the solid–water interface of clay minerals control the mobility of metals in the environment. These processes can occur in confined pore spaces of clay buffers and barriers as well as in contaminated sediments and involve a combination of alteration, adsorption and nucleation processes of multiple species and phases. This study characterizes nano-scale processes on the interface between clay minerals and uranyl-bearing solution near neutral pH. Samples of clay minerals with a contact pH of ∼6.7 are collected from a U mill and mine tailings at Key Lake, Saskatchewan, Canada. The tailings material contains Cu-, As-, Co-, Mo-, Ni-, Se-bearing polymetallic phases and has been deposited with a surplus of Ca(OH)2 and Na2CO3 slaked lime. Small volumes of mill-process solutions containing sulfuric acid and U are occasionally discharged onto the surface of the tailings and are neutralized after discharge by reactions with the slaked lime. Transmission electron microscopy (TEM) in combination with the focused ion beam (FIB) technique and other analytical methods (SEM, XRD, XRF and ICP-OES) are used to characterize the chemical and mineralogical composition of phases within confined pore spaces of the clay minerals montmorillonite and kaolinite and in the surrounding tailings material. Alteration zones around the clay minerals are characterized by different generations of secondary silicates containing variable proportions of adsorbed uranyl- and arsenate-species and by the intergrowth of the silicates with the uranyl-minerals cuprosklodowskite, Cu[(UO2)2(SiO3OH)2](H2O)6 and metazeunerite, Cu[(UO2)(AsO4)2](H2O)8. The majority of alteration phases such as illite, illite–smectite, kaolinite and vermiculite have been most likely formed in the sedimentary basin of the U-ore deposit and contain low amounts of Fe (<5at.%). Iron-enriched Al-silicates or illite–smectites (Fe >10at.%) formed most likely in the limed tailings at high contact pH (∼10.5) and their structure is characterized by a low degree of long-range order. Adsorption of U and nucleation of metazeunerite and cuprosklodowskite are strongly controlled by the presence of the adsorbed oxy-anion species arsenate and silica on the Fe-enriched silicates. Heterogeneous nucleation of nano-crystals of the uranyl minerals occurs most likely on adsorption sites of binary uranyl-, arsenate- and silica-complexes as well as on ternary uranyl–arsenate or uranyl–silicate complexes. The uranyl minerals occur as aggregates of misoriented nano-size crystals and are the result of supersaturated solutions and a high number of nucleation sites that prevented the formation of larger crystals through Oswald ripening. The results of this study provide an understanding of interfacial nano-scale processes between uranyl species and altered clay buffers in a potential Nuclear Waste repository as similar alteration conditions of clays may occur in a multi-barrier system.

Renewable chitin from marine sponge as a thermostable biological template for hydrothermal synthesis of hematite nanospheres using principles of extreme biomimetics

AbstractChitin originating from marine sponges possesses a unique nanofibrillar network structure that is the basic element of the microtubular scaffold-like skeleton of these organisms. Sponge chitin represents an intriguing example of thermostability, as it is stable up to 400 °C. It also constitutes a renewable biological source due to the high regeneration ability of Aplysina sponges under marine farming conditions. These properties can be exploited for the facile and environmentally friendly creation of novel, biocompatible organic-inorganic hybrid materials with a range of uses. Here, chitin-based scaffolds isolated from the skeleton of marine demosponge Aplysina aerophoba were used as a template for the in vitro formation of iron oxide from a saturated iron(III) chloride solution, under hydrothermal conditions (pH~1.5, 90 °C). The resultant chitin-Fe2O3 three dimensional composites, prepared for the first time via hydrothermal synthesis route, were thoroughly characterized using light, fluorescence and scanning electron microscopy; as well as with analytical methods like Raman spectroscopy, electron diffraction and HR-TEM. The results show that this versatile method allows for efficient chitin mineralization with respect to hematite. Additionally, we demonstrate that chitin nanofibers template the nucleation of uniform Fe2O3 nanocrystals.

Biological Niches within Human Calcified Aortic Valves: Towards Understanding of the Pathological Biomineralization Process.

Despite recent advances, mineralization site, its microarchitecture, and composition in calcific heart valve remain poorly understood. A multiscale investigation, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS), from micrometre up to nanometre, was conducted on human severely calcified aortic and mitral valves, to provide new insights into calcification process. Our aim was to evaluate the spatial relationship existing between bioapatite crystals, their local growing microenvironment, and the presence of a hierarchical architecture. Here we detected the presence of bioapatite crystals in two different mineralization sites that suggest the action of two different growth processes: a pathological crystallization process that occurs in biological niches and is ascribed to a purely physicochemical process and a matrix-mediated mineralized process in which the extracellular matrix acts as the template for a site-directed nanocrystals nucleation. Different shapes of bioapatite crystallization were observed at micrometer scale in each microenvironment but at the nanoscale level crystals appear to be made up by the same subunits.

Nano-Crystal Formation and Growth from High-Fluence Ion Implantation of Au, Ag or Cu in Silica

The linear and non-linear optical properties of silica may be tailored by the introduction of a random distribution of nanocrystallites of an immiscible metal within a near-surface region. The size, size distribution, and spatial distribution of these crystallites must be controllable in order to optimize the functional properties for device applications. In this paper, we present a novel fabrication technique that offers such control. Energetic metal ions are implanted in silica at room temperature. Subsequent heat treatment leads to diffusion of the implanted atoms, nucleation and growth of metal crystallites, and Ostwald ripening of the resulting clusters. We have observed the kinetics and effective activation energies describing the multiple processes involved, for the cases of Au, Ag or Cu implanted at MeV energies, at various fluences, and then annealed at fixed temperatures in the range 500°C-1000°C. Effective activation energies found for nanocrystal nucleation and growth at temperatures below 800°C (e.g. 64 meV for Ag) are replaced above this temperature range by much higher activation energies (e.g. 400 meV for Ag). We may attribute this to the depletion of un-attached mobile metal atoms (so that ripening of clusters will be limited by energy barriers for escape of such mobile atoms from small crystallites), and/or the annealing of implant-caused stress in the silica structure at high temperatures, that creates new channels for thermal diffusion of metal atoms within the silica host.

Nucleation-controlled vacancy formation in light-emitting wide-band-gap oxide nanocrystals in glass

Controlling nanocrystal nucleation in a solid host, as in the gallium-oxide nanophase grown in glass, provides a strategy for tailoring not only nanocrystal size but also light-emitting donor–acceptor population.

A multi-scale investigation of biological niches within human calcified aortic valves helps to understand the pathological biomineralization process

Calcific aortic valve stenosis (CAVS) is the most common form of heart valve disease in the industrialized countries, being an important public health problem [1]. Ectopic calcifications within aortic valve leaflets are strictly associated with CAVS, interfering with cusps opening, they lead to ventricular outflow obstruction [2]. Up to date no proven medical therapy stops CAVS course progression, so valve replacement is the only possible treatment of severe CAVS. Unfortunately, the degenerative valve calcification process, affects also bioprosthetic implants [3]. Being the molecular mechanisms leading to valve calcification still not understood, our aim was to carry on a multi-scale investigation using Scanning Electron Microscopy, Transmission Electron Microscopy and Energy Dispersive X-ray Spectrometry, to provide new insights into calcification process. Severely calcified aortic (tricuspid type, n = 29; bicuspid type, n = 3) and mitral valves (n = 4) were obtained from patients of both sexes (males=25) and different ages (mean age 72±10, range 41-90 years old) undergoing valve replacement due to severe aortic and mitral valve stenosis. We detected bioapatite crystals in two different mineralization sites: niches and extracellular matrix. This suggests the action of two different growth processes: the first occurs in biological niches and it is ascribed to a purely physico-chemical process; the second has the extracellular matrix acting ass the template for a site-directed nanocrystals nucleation. Different shapes of bioapatite crystallization were observed at micrometer scale in each microenvironment but at the nanoscale level crystals appear made up by the same subunits. We suggest that bioapatite nanocrystals in heart valve may activate a strong inflammatory process leading to irreversible pathological condition that, once activated,may aggravate the inflammatory response against bioapatite nanocrystals leading to a severe calcification process.