Hankwon Chang

A glucose biosensor based on TiO2–Graphene composite

A novel glucose biosensor was developed based on the adsorption of glucose oxidase at a TiO(2)-Graphene (GR) nanocomposite electrode. A TiO(2)-GR composite was synthesized from a colloidal mixture of TiO(2) nanoparticles and graphene oxide (GO) nanosheets by an aerosol assisted self-assembly (AASA). The particle morphology of all TiO(2)-GR composites was spherical in shape. It was observed that micron-sized TiO(2) particles were encapsulated by GR nanosheets and that the degree of encapsulation was proportional to the ratio of GO/TiO(2). The amperometric response of the glucose biosensor fabricated by the TiO(2)-GR composite was linear against a concentration of glucose ranging from 0 to 8mM at -0.6 V. The highest sensitivity was noted at about 6.2 μA/mMcm(2). The as prepared glucose biosensor based on the TiO(2)-GR composite showed higher catalytic performance for glucose redox than a pure TiO(2) and GR biosensor.

Oil absorbing graphene capsules by capillary molding

Oil absorbing graphene capsules are synthesized by capillary molding of graphene oxide (GO) sheets against a polystyrene bead template in evaporating aerosol droplets, followed by simultaneous reduction of GO and decomposition of the polymer template during ultrasonic spray pyrolysis.

3D label-free prostate specific antigen (PSA) immunosensor based on graphene-gold composites.

Highly sensitive and label-free detection of the prostate specific antigen (PSA) remains a challenge in the diagnosis of prostate cancer. Here, a novel three-dimensional (3D) electrochemical immunosensor capable of sensitive and label-free detection of PSA is reported. This unique immunosensor is equipped with a highly conductive graphene (GR)-based gold (Au) composite modified electrode. The GR-based Au composite is prepared using aerosol spray pyrolysis and the morphology of the composite is the shape of a crumpled GR ball decorated with Au nanoparticles. Unlike the previous research, this novel 3D immunosensor functions very well over a broad linear range of 0-10 ng/mL with a low detection limit of 0.59 ng/mL; furthermore, it exhibits a significantly increased electron transfer and high sensitivity toward PSA. The highest rate of current change with respect to the PSA concentration is 5 μA/(ng/mL). Satisfactory selectivity, reproducibility, and stability of the 3D immunosensor are also exhibited.

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.

Continuous Single-Step Fabrication of Nonaggregated, Size-Controlled and Cubic Nanocrystalline Y2O3:Eu3+ Phosphors Using Flame Spray Pyrolysis

Continuous single-step fabrication of cubic nanocrystalline Y2O3:Eu3+ phosphor particles using flame spray pyrolysis was successfully conducted without any post-heat treatments. The morphology of the as-prepared particles was spherical and nonaggregated. The mean size of as-prepared particles was easily controlled by adjusting the precursor concentration. On varying the overall concentration of the precursor solution from 0.01 to 0.5 M, the crystallite size and geometric mean particle diameter varied from 38.4 nm to 50.6 nm and 263 nm to 741 nm, respectively. XRD spectra of as-prepared particles indicated that all products, regardless of the precursor concentration, showed the cubic phase with high crystallinity without any post-treatments, although residence times in the flame were very short. Upon excitation with 254 nm light, all of the as-prepared particles showed bright red emission due to the 4f–4f transitions of Eu3+ ions, and the highest photoluminescent intensity at 611 nm was found at a Eu3+ content of about 12 mol%. These results indicate the possibility of the fabrication of cubic nanocrystalline Y2O3:Eu3+ phosphors with a high production rate and high purity.

One Step Synthesis of Pt-nanoparticles-Laden Graphene Crumples By Aerosol Spray Pyrolysis and Evaluation of Their Electrocatalytic Activity

Pt-nanoparticles-laden graphene (GR) crumples were directly synthesized from a colloidal mixture of aqueous chloroplatinic acid (H2PtCl6) and graphene oxide (GO) sheets via aerosol spray pyrolysis (ASP). Effects of Pt content in the Pt/GR composite and temperature of heating zone on the particle morphology, diffraction pattern, and specific surface area were investigated. The morphology of Pt/GR was the shape of a crumpled sheet of paper and the average size of the composite was around 1.3 μm in diameter. As Pt content increased from 2 to 20 wt%, higher numbers of Pt nanoparticles are observed on the GR at higher Pt content and the specific surface area of the composite also increased from 122 to 146 m2/g. Also, the intensity of the GR peak decreased, but that of the Pt peak increased. As temperature increased from 500°C to 900°C, an increase of the particle size of Pt due to sintering was observed. Electrocatalytic application of the Pt/GR composites was examined through methanol oxidation reaction. The 20 wt% Pt/GR synthesized at 900°C showed higher performance on methanol oxidation than a commercial 20 wt% Pt/carbon black catalyst. Copyright 2013 American Association for Aerosol Research

Optical properties of dense and porous spheroids consisting of primary silica nanoparticles

The light scattering by granular and macroporous silica spheroids consisting of nanometer-sized primary particles was systematically investigated using a laser particle counter coupled with a pulse height analyzer. The shape- and porosity-controlled spheroids as model particles were prepared using spray drying method by changing the particle size of colloidal suspension. The effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was also studied using a differential mobility analyzer and an electron microscope. The electrical mobility equivalent diameter of particles classified by the differential mobility analyzer was estimated by measuring Feret diameter and the projected area equivalent diameter from the SEM micrographs. The electrical mobility diameter of the spheroids was in good agreement with the projected area equivalent diameter regardless of the primary particle size and porosity. The measured partial scattering cross section of dense and porous silica particles with same mobility diameter showed significant differences. As the primary particle size of granules and the porosity of porous particles increased at parity of electrical mobility diameter, the scattering intensity decreased. The effective refractive indices of dense and porous particles were computed by best fitting of the scattering intensity measurements. The porosities of dense and porous spheroids were calculated using the effective refractive indices as obtained by the effective medium theory. The porosities were also measured by a comparison of particle size before and after annealing at 1700°C. By comparing these porosities, the effective refractive indices of the spheroidal particles were confirmed.

Aerosol-Assisted Extraction of Silicon Nanoparticles from Wafer Slicing Waste for Lithium Ion Batteries

A large amount of silicon debris particles are generated during the slicing of silicon ingots into thin wafers for the fabrication of integrated-circuit chips and solar cells. This results in a significant loss of valuable materials at about 40% of the mass of ingots. In addition, a hazardous silicon sludge waste is produced containing largely debris of silicon, and silicon carbide, which is a common cutting material on the slicing saw. Efforts in material recovery from the sludge and recycling have been largely directed towards converting silicon or silicon carbide into other chemicals. Here, we report an aerosol-assisted method to extract silicon nanoparticles from such sludge wastes and their use in lithium ion battery applications. Using an ultrasonic spray-drying method, silicon nanoparticles can be directly recovered from the mixture with high efficiency and high purity for making lithium ion battery anode. The work here demonstrated a relatively low cost approach to turn wafer slicing wastes into much higher value-added materials for energy applications, which also helps to increase the sustainability of semiconductor material and device manufacturing.

3 D Network-Structured Crumpled Graphene/Carbon Nanotube/Polyaniline Composites for Supercapacitors

Crumpled graphene (CGR) is considered a promising supercapacitor material to achieve high power and energy density because it could overcome the disadvantages of 2 D GR sheets such as aggregation during the electrode fabrication process, reduction of the available surface area, and limitation of the electron and ion transport. Even though CGR shows good results, carbon materials are limited in terms of their capacitance performance. Here, we report highly enhanced supercapacitor materials by fabricating a 3 D composite containing CGR, carbon nanotubes (CNTs), and polyaniline (PANI). The CNTs increased the basal spacing and bridged the defects for electron transfer between the GR sheets in CGR. PANI can enhance the rate of conduction of electrons and offer high pseudocapacitance originating from its redox reactions. The synergistic effect of the CNTs and PANI may also result in a higher electrochemical capacitance and better stability than each individual component as electrode materials for supercapacitors in a two-electrode system. More importantly, the performance of the supercapacitors can be further enhanced by employing 2 D GR as the binder for the composite electrodes, resulting in specific capacitance of 456 F g-1 , rate capability of 89 %, and cyclic stability of 97 % after 1000 cycles.

Experimental evaluation of the optical properties of porous silica/carbon composite particles

Light scattering by porous spheroidal silica and several silica/carbon composite particles having different carbon contents was systematically investigated using a laser particle counter coupled with a pulse height analyzer (LPC-PHA). A new and simple method for the measurements of the effective complex refractive index of silica/carbon composite particles using a conventional LPC-PHA system and a differential mobility analyzer was introduced and tested. Challenge particles, from pure silica to silica/carbon compounds having a gradually increasing porous structure, were prepared by spray-drying methods for use in testing of the inversion method. By representing the deviation of the real part of the refractive index of a porous silica particle versus the size on a topographical map, the inversion method for the determination of the real part of the refractive indices was found to have a satisfactory precision. Furthermore, the method can be applied to the measurement of the complex refractive index of silica/carbon composite particles by extending the best fitting method to complex refractive indices. The effective complex refractive index of silica/carbon composite particles as a function of their carbon content is reported. Both the real and imaginary parts of the complex refractive index were increased with increasing carbon content of the composite particles.