Ferry Iskandar

Control of the morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol.

The control of the morphology of nanostructured particles prepared by the spray drying of nanoparticle sol was investigated experimentally and the results are qualitatively explained based on available theory. A theoretical analysis indicates that the structural stability of the droplet and the hydrodynamic effects during the drying process play important roles in controlling the morphology of the resulting particles. The size of the sol in the droplet, droplet size, viscosity of droplet, drying temperature, gas flow rate, and addition of surfactant are all crucial parameters that affect the morphology of particles. Experimentally, nanostructured silica particles were prepared from a nanosize silica sol under various preparation conditions. Doughnut-shaped particles can be produced when the droplet size is large, in conjunction with high temperature, high gas flow rate and in the presence of an added surfactant. Appropriate choice of the spray drying method permits control of the particle size and shape, ranging from spheres to ellipsoids as well as doughnut-shaped particles by varying the preparation conditions. The results open a new route to controlling the formation of a wide variety of nanostructured particles.

An experimental and modeling investigation of particle production by spray pyrolysis using a laminar flow aerosol reactor

The influence of operating parameters on the morphology of particles prepared by spray pyrolysis was investigated using a temperature-graded laminar flow aerosol reactor. Experimentally, zirconia particles were prepared by spray pyrolysis using an aqueous solution of zirconyl hydroxide chloride. Hollow particles were formed if the reactor temperature was high, the temperature gradient was too large, the flow rate of carrier gas was high, and the initial solute concentration was low. A numerical simulation of the pyrolysis process was developed using a combination of two previous models. The simulation results compared well with the experimental results. (c) 2000 Materials Research Society.

Preparation of functional nanostructured particles by spray drying

Abstract When particle dimensions are reduced to the order of several nanometers, their physical and chemical properties deviate significantly from the bulk properties of such materials. Because of this, there is abundant potential for their use in future technologies including electronic and optoelectronic, mechanical, chemical, cosmetic, medical, drug, and food technologies. However, due to their extremely small sizes, the particles suffer from many problems related to their surface and thermal stability, shape preservation, handling, assembly in devices, etc. It is therefore an important challenge to solve these problems by developing slightly larger particles (e. g. on the submicrometer scale) in which the properties generated by the nanoscale material are preserved. One approach to this is to trap nanoparticles in a micrometer-sized inert matrix. This approach allows the nanoscale properties to be retained, since nanoparticles are separated from each other in the inert matrix. The inert matrix also serves as a coating medium that inhibits any chemical changes to the surface of the nanoparticles. Their larger size allows easy handling or assembly in devices. A promising method for designing and fabricating these composite structures is a spray method, in which spherical particles can be produced. In this paper, we review the nanostructural processing (synthesis) of submicrometersized particles by a spray method, which provides a restricted reaction environment (such as pores or cages) in the matrix for their synthesis and handling. The characterization and potential applications of these composites are also discussed.

Stable photoluminescence of zinc oxide quantum dots in silica nanoparticles matrix prepared by the combined sol–gel and spray drying method

A sol–gel method was employed to produce a zinc oxide (ZnO) colloid consisting of ZnO nanocrystalline particles with an average diameter of ∼3 nm, and subsequently mixed with a silica (SiO2) colloid. The mixture was finally spray dried to form a powder nanocomposite. It was found that the green photoluminescence (PL) exhibited by the composite was very stable: the intensity, position, and shape do not change even after being aged over 30 days. Thus, the ZnO/SiO2 nanocomposite has a much improved PL stability over ZnO colloids, which is often found to undergo a significant redshift even after aging over a few days. Our results are expected to have significant technological implications.

Functional Nanostructured Silica Powders Derived from Colloidal Suspensions by Sol Spraying

The preparation of silica powders derived from sols with a variety of primary particle sizes from 4 to 100 nm and the influences of preparation conditions such as drying temperature and initial concentration of precursor on the final powders morphology were investigated for the first time. The prepared silica powders have spherical morphology, and the final diameter (between 0.1 and 2 um) was controlled by changing the concentration of starting colloidal suspension. The preparation of silica based luminescent powders was investigated by adding europium ion as the dopant. The Eu-doped silica powders showed a visible-luminescence with wavelength of 613 nm, a red emission, under excitation of 394 nm light source. The effects of Eu-doping concentration, operation temperature and primary particle size of silica sols on the luminescence were also investigated.

Novel rare-earth-free tunable-color-emitting BCNO phosphors

We present a facile synthesis of novel, rare-earth (RE)-ion-free boron carbon oxynitride (BCNO) phosphors. The preparation method, chemical composition, luminescent properties and emission mechanisms, as well as current trends in BCNO phosphors are reviewed. The novel BCNO phosphors were synthesized from inexpensive and environmentally friendly raw materials by a straightforward route using liquid precursors at low temperatures under atmospheric pressure. The newly developed BCNO phosphors demonstrated tunable color emission, high quantum efficiency, and long-duration afterglow. The color emission of these phosphors can be tuned across almost the entire visible light spectrum by varying the molar ratios of the raw materials.

Formation of Highly Ordered Nanostructures by Drying Micrometer Colloidal Droplets

Nanoparticles with well-defined chemical compositions can act as building blocks for the construction of functional structures, such as highly ordered aggregates, as well as porous and hollow aggregates. In this work, a spray-drying technique is used to form a crystal-like structure with nanoparticle building blocks. When spray-drying uniform spherical particles, tightly packed aggregates with either simple or broken symmetries (quasicrystalline) were formed. Using polystyrene (PS) particles with varied zeta potentials as templates, it is also possible to form highly ordered porous and hollow aggregates from inorganic colloidal particles. Essential to the production of quasicrystalline structures is the use of monodisperse colloidal particles in spray drying, as the quasicrystalline form is not achievable when two different sizes of colloidal particles are used in the precursor suspension. With varying colloidal particles sizes, smaller colloidal particles fill the spaces formed between the larger particles, resulting in adjustment of colloidal crystallization. A geometric model that considers the tight packing of several spheres into frustrated clusters (quasicrystal form) with short-range icosahedral symmetry is compared to experimentally produced structures and found to quantitatively explain experimental observations.

Role of C-N Configurations in the Photoluminescence of Graphene Quantum Dots Synthesized by a Hydrothermal Route.

Graphene quantum dots (GQDs) containing N atoms were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of urea and citric acid, and the effect of the GQDs’ C–N configurations on their photoluminescence (PL) properties were investigated. High-resolution transmission electron microscopy (HR-TEM) images confirmed that the dots were spherical, with an average diameter of 2.17 nm. X-ray photoelectron spectroscopy (XPS) analysis indicated that the C–N configurations of the GQDs substantially affected their PL intensity. Increased PL intensity was obtained in areas with greater percentages of pyridinic-N and lower percentages of pyrrolic-N. This enhanced PL was attributed to delocalized π electrons from pyridinic-N contributing to the C system of the GQDs. On the basis of energy electron loss spectroscopy (EELS) and UV-Vis spectroscopy analyses, we propose a PL mechanism for hydrothermally synthesized GQDs.

Preparation of microencapsulated powders by an aerosol spray method and their optical properties

Abstract Microencapsulated powders were prepared by an aerosol spray method using a precursor comprised of a mixture of two types of sols as well as a sol-aqueous mixture precursor solution. Two different types of sols were used as precursors to prepare microencapsulated small-SiO 2 /large-SiO 2 and Al 2 O 3 /SiO 2 powders. A microencapsulated ZrO 2 /SiO 2 powder was also prepared from a mixture of SiO 2 sol and an aqueous precursor solution of zirconyl nitrate dihydrate. For preparing small-SiO 2 /large-SiO 2 powders, two different sizes, i.e. 6 and 109 nm, of SiO 2 sols were used as precursors. The results show that the larger SiO 2 particles were encapsulated with the smaller ones. A similar result was also observed in the preparation of an Al 2 O 3 /SiO 2 powder prepared from a mixture of Al 2 O 3 (18 nm) and a SiO 2 (109 nm) sol precursor. The Al 2 O 3 particles appeared on the surface of the prepared powder. In the case of the ZrO 2 /SiO 2 powder, the morphology indicates that the SiO 2 particles (109 nm) were encapsulated by a ZrO 2 shell. The effect of precursor ratios on the morphology of powders was also investigated. The light scattering characteristics of the prepared particles were also investigated using a laser particle counter coupled with a pulse height analyzer. The effective refractive indices of the microencapsulated powders varied considerably with the content of coating material.

Fabrication and Characterization of a Yellow-Emitting BCNO Phosphor for White Light-Emitting Diodes

A yellow-emitting phosphor comprised of boron, carbon, nitrogen, and oxygen (BCNO) atoms without any rare-earth ions as luminescence centers was successfully synthesized using a facile process at low temperature and atmospheric pressure. The synthesized BCNO powders showed a broad emission spectrum centered at 540 nm under excitation at 460 nm due to the radiation transitions of local 2 H g → 1 Σ - g luminescence provided in the BO - 2 species. Further analysis revealed that the BCNO yellow phosphor exhibited a high external quantum efficiency (60%) having a hexagonal-BN crystalline structure mixed with cubic-B 2 O 3 . The synthesized yellow-emitting BCNO phosphor is promising for high-efficiency phosphor conversion-based white light-emitting diodes.