Nanocrystal Rods Research Articles

TiO2 nanocrystal rods on titanium microwires: growth, vacuum annealing, and photoelectrochemical oxygen evolution

Titania nanocrystal rods grown hydrothermally onto titanium microwire are mechanically robust and photoelectrochemically active.

Anisotropic Diffusion and Phase Behavior of Cellulose Nanocrystal Suspensions.

In this paper, we use dynamic light scattering in polarized and depolarized modes to determine the translational and rotational diffusion coefficients of concentrated rodlike cellulose nanocrystals in aqueous suspension. Within the range of studied concentrations (1-5 wt %), the suspension starts a phase transition from an isotropic to an anisotropic state as shown by polarized light microscopy and viscosity measurements. Small-angle neutron scattering measurements also confirmed the start of cellulose nanocrystal alignment and a decreasing distance between the cellulose nanocrystals with increasing concentration. As expected, rotational and translational diffusion coefficients generally decreased with increasing concentration. However, the translational parallel diffusion coefficient was found to show a local maximum at the onset of the isotropic-to-nematic phase transition. This is attributed to the increased available space for rods to move along their longitudinal axis upon alignment. This increased parallel diffusion coefficient thus confirms the general idea that rodlike particles gain translational entropy upon alignment while paying the price for losing rotational degrees of freedom. Once the concentration increases further, diffusion becomes more hindered even in the aligned regions due to a reduction in the rod separation distance. This leads once again to a decrease in translational diffusion coefficients. Furthermore, the relaxation rate for fast mode translational diffusion (parallel to the long particle axis) exhibited two regimes of relaxation behavior at concentrations where significant alignment of the rods is measured. We attribute this unusual dispersive behavior to two length scales: one linked to the particle length (at large wavevector q) and the other to a twist fluctuation correlation length (at low wavevector q) along the cellulose nanocrystal rods that is of a larger length when compared to the actual length of rods and could be linked to the size of aligned domains.

TiO2 Nanocrystal Based Coatings for the Protection of Architectural Stone: The Effect of Solvents in the Spray-Coating Application for a Self-Cleaning Surfaces

A colloidal route was exploited to synthesize TiO2 anisotropic nanocrystal rods in shape (TiO2 NRs) with a surface chemistry suited for their dispersibility and processability in apolar organic solvents. TiO2 NRs were dispersed in chloroform and n-heptane, respectively, and the two resulting formulations were investigated to identify the optimal conditions to achieve high-quality TiO2 NR-based coatings by the spray-coating application. In particular, the two types of TiO2 NR dispersions were first sprayed on silicon chips as a model substrate in order to preliminarily investigate the effect of the solvent and of the spraying time on the morphology and uniformity of the resulting coatings. The results of the SEM and AFM characterizations of the obtained coatings indicated n-heptane as the most suited solvent for TiO2 NR dispersion. Therefore, an n-heptane dispersion of TiO2 NRs was sprayed on a highly porous limestone—Lecce stone—very commonly used as building material in historic constructions and monuments present in Apulia Region (Italy). A comprehensive physical-chemical investigation of the TiO2 NR based treatment on the surface of the stone specimens, including measurements of colour variation, static contact angle, water transfer properties, and morphological characterization were performed. Finally, the photocatalytic properties of the coatings were assessed under solar irradiation by using Lecce stone specimens and Methyl Red as a model target compound. The obtained results demonstrated that TiO2 NRs based coatings can be successfully applied by spray-coating resulting in an effective photocatalytic and hydrophobic treatment, which holds great promise as a material for the environmental protection of architectural stone in the field of cultural heritage conservation.

Freezing effect of metal droplets on the vapor liquid solid growth of nanocrystal rods

Indium tin oxide (ITO) films with different temperatures were prepared by an electron beam evaporation technique. The nanocrystal rods were synthesized by vapor–liqiud–solid (VLS) crystal growth method at the higher temperature 300 °C. The surface morphology of the samples was analyzed by scanning electron microscopy (SEM). There was a metal cap on the top of the nanocrystal rod, which was the typical morphology of VLS nanocrystalrod. The structure of crystalline rods was confirmed by X-ray diffraction (XRD). Transmission electron microscopy (TEM) of the single crystalrod displayed that the lattice was uncontinuous between the top cap and the rod. Metal droplets were considered to be metallic indium tin and its alloys. The shape and composition of droplets were affected by temperature, and the metal droplets were discovered to undergo a gradual freezing process during the VLS nanocrystal rod growth.

Rod-like cellulose nanocrystal/cis-aconityl-doxorubicin prodrug: A fluorescence-visible drug delivery system with enhanced cellular uptake and intracellular drug controlled release

Rod-like nanomedicines facilitate cellular uptake. This research is aimed to develop fluorescence-visible rod-like nanomedicines with enhanced cellular uptake and intracellular drug controlled release based on cis-aconityl-doxorubicin (CAD) labeled cellulose nanocrystal rods (CNR). Particularly, CAD was synthesized by the ring-opening reaction between cis-aconitic anhydride (CAA) and the amino group of Doxorubicin (DOX). Amidation reaction occurred between the 6-carboxylic groups of CAD and the amino groups of aminated CNR to give CAD labeled CNR (CAD@CNR). Compared with CNR, CAD@CNR showed similar morphology and crystal structure. The mean length of CAD@CNR was ca. 118 nm with aspect ratio ranging from 12 to 15, facilitating their endocytosis. CAD@CNR prodrug was rather stable in pH 7.4 phosphate buffer solution but tended to be hydrolyzed to release DOX under acidic condition, due to the rapid degradation of amide bonds between DOX and cis-aconitic acid via an intramolecular acid-catalyzed mechanism. CAD@CNR prodrug showed sustained drug release profiles over 40 h, and the cumulative drug release showed a tendency to increase from 36 to 80% with the pH value decreasing from 7.4 to 5.0. The half maximal inhibitory concentration (IC50) of CAD@CNR prodrug against NCI H 460 cells without NH4Cl (lysosomotropic weak bases) pretreatment was 1.75 times higher than that with 40 mM NH4Cl pretreatment, further confirmed that the DOX release from the CAD@CNR prodrug was triggered by the low pH value of lysosome (pH 5.0). Compared with DOX·HCl, CAD@CNR prodrug showed enhanced cellular uptake ability during 12 or 24 h of incubation due to the endocytosis mechanism of CAD@CNR prodrug. After incubation with cells, CAD@CNR prodrug could be observed by using fluorescence microscope due to the red fluorescence of DOX. In a word, CAD@CNR showed great potential as fluorescence-visible drug delivery system with enhanced cellular uptake and intracellular drug release due to its rod-like morphology, suitable aspect ratio, and acid-triggered drug release.

Effect of Eu3+ Ion Concentration on Phase Transition, Site Symmetry and Quantum Efficiency of ZrO² Nanocrystal Rods.

This work report the influence of Eu3+ ion concentration on the photophysical properties of zirconia nanocrystal rods including its intrinsic quantum efficiency (IQE). A simple chemical route was employed in the synthesis procedure. X-ray diffraction results show mixed phases of monoclinic and tetragonal structures. Phase transition occurred at low (1 mol%) and high (7 and 8 mol%) Eu3+ concentrations. There are three forms of excitations for this phosphor; band edge excitation at 216 nm, charge transfer state transition at 247 and 263 nm, and direct excitation at 362, 395 and 535 nm. Photoluminescence emission for all the doped samples at room temperature appeared to be entirely from intraconfigurational Eu3+ emissions and depends both on the site symmetry as well as the Eu3+ concentration. Low temperature measurements indicate the presence of defect bands associated with oxygen vacancies. Defects were also shown to be temperature dependent. The Eu3+ ions were distributed in both phases especially at high ion concentrations (7 and 8 mol% Eu3+). Two multipolar processes where found to be responsible for the luminescence quenching process in the mixed-structure; the dipole-dipole and the dipole-quadrupole transitions. The intensity parameters (Ω2, Ω4), asymmetry ratio, R0 and the average decay lifetime of the nanocrystals show dependence on concentration and excitation wavelength. High IQE values were obtained at 1, 7 and 8 mol% Eu3+ where the monoclinic phase is dominant. The CIE coordinates values are comparable to existing red phosphors and in combination with high average IQE of 55% makes this phosphor a good candidate for red emitting phosphor application.

In-Situ Growth and Characterization of Indium Tin Oxide Nanocrystal Rods

Indium tin oxide (ITO) nanocrystal rods were synthesized in-situ by a vapor-liquid-solid (VLS) method and electron beam evaporation technique. When the electron-beam gun bombarded indium oxide (In2O3) and tin oxide (SnO2) mixed sources, indium and tin droplets appeared and acted as catalysts. The nanocrystal rods were in-situ grown on the basis of the metal catalyst point. The nanorods have a single crystal structure. Its structure was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface morphology was analyzed by scanning electron microscopy (SEM). During the evaporation, a chemical process was happened and an In2O3 and SnO2 solid solution was formed. The percentage of doped tin oxide was calculated by Vegard’s law to be 3.18%, which was in agreement with the mixture ratio of the experimental data. The single crystal rod had good semiconductor switch property and its threshold voltage of single rod was approximately 2.5 V which can be used as a micro switch device. The transmission rate of crystalline nanorods ITO film was over 90% in visible band and it was up to 95% in the blue green band as a result of the oxygen vacancy recombination luminescence.

Luminescence and energy transfer mechanism in Eu3+/Tb3+-co-doped ZrO2 nanocrystal rods

Nanocrystal rods of Eu3+/Tb3+-co-doped ZrO2 were synthesized using a simple chemical precipitation technique. Both ions were successfully doped into the Zr4+ ion site in a mixed structure containing both monoclinic and tetragonal phases. The Eu3+ or Tb3+ singly doped zirconia produced red and green luminescence which are characteristics of Eu3+ and Tb3+ ions, respectively. The co-doped zirconia samples produced blue emission from defect states transitions in the host ZrO2, red and green luminescence from dopant ions giving cool to warm white light emissions. The phosphors were efficiently excited by ultraviolet and near-ultraviolet/blue radiations giving white and red light, respectively. The decay lifetime was found to increase with increasing donor ion concentration contrary to conventional observations reported by previous researchers. Weak quadrupole–quatdrupole multipolar process was responsible for energy transfer from Tb3+ (donor) ion to Eu3+ ion. No energy back-transfer from Eu3+ to Tb3+ ion was observed from the excitation spectra. Temperature-dependent photoluminescence shows the presence of defects at low temperature, but these defects vanished at room temperature and beyond. The Eu3+/Tb3+-co-doped ZrO2 nanocrystal rod is a potential phosphor for white light application using UV as an excitation source. Thermoluminescence measurements show that the inclusion of Tb3+ ion increases trap depths in the host zirconia.

Microwave Hydrothermal Synthesis of GaN Nanorods

The GaOOH Nanocrystal rods were successfully synthesized by microwavehydrothermal method using Ga2O3 ,HNO3 and NH3·H2O as raw materials. Simple heat treatment of GaOOH in the flow of NH3 gas leads to the formation of submicron GaN rods even at 800°C through GaOOH. The resultant GaOOH and GaN nanomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism of GaOOH and GaN was proposed. The results indicate that the as synthesized GaN were hexagonal nanorods with average aspects ratio of 5:1(diameter 800 nm and length about 4μm). Photoluminescence spectrum shows that a blue emission peak originates at 473.5 nm, indicating that the GaN nanorods displayed luminescence emission in the blue-violet region, which was related to crystal defects, and may be helpful for electro-optical applications of GaN material.

Enhanced two-photon absorption of CdS nanocrystal rods

In this letter we report that CdS nanocrystals are reshaped into an elongated rod form for increasing two-photon absorption. CdS quantum rods with uniform rod dimensions have been synthesized and their two-photon absorption cross section in solution has been characterized using the z-scan method and the two-photon induced fluorescence study. The absorption cross section was found to be 20.9×10−46 cm4/s photon−1 under two-photon excitation at wavelength 800 nm, which is an order of magnitude larger than that of CdS quantum dots of similar diameters. The higher two-photon absorption coefficient establishes the potential of this class of quantum rods for various photonic applications.

Hybrid Organic–Nanocrystal Solar Cells

AbstractRecent results have demonstrated that hybrid photovoltaic cells based on a blend of inorganic nanocrystals and polymers possess significant potential for low-cost, scalable solar power conversion. Colloidal semiconductor nanocrystals, like polymers, are solution processable and chemically synthesized, but possess the advantageous properties of inorganic semiconductors such as a broad spectral absorption range and high carrier mobilities. Significant advances in hybrid solar cells have followed the development of elongated nanocrystal rods and branched nanocrystals, which enable more effective charge transport. The incorporation of these larger nanostructures into polymers has required optimization of blend morphology using solvent mixtures. Future advances will rely on new nanocrystals, such as cadmium telluride tetrapods, that have the potential to enhance light absorption and further improve charge transport. Gains can also be made by incorporating application-specific organic components, including electroactive surfactants which control the physical and electronic interactions between nanocrystals and polymer.