• Clean Technology
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• v.28 no.1
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• pp.18-23
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• 2022

Using air as an insulator due to its low heat transfer coefficient has been studied and has been widely commercialized to save energy in the field of thermal insulation technology. In this study, we analyzed the heat insulating effect of hollow silica nanoparticles mixed in non-uniform size, and the maximum heat insulating efficiency of these particles given the limited number of particles that can be mixed with a medium such as paint. The hollow silica nanoparticles were synthesized via a sol-gel process using a polystyrene template in order to produce an air layer inside of the particles. After synthesis, the particles were analyzed for their insulation effect according to the size of the air layer by adding 5 wt % of the particles to paint and investigating the thermal insulation performance by a heat transfer experiment. When mixing the particles with white paint, the insulation efficiency was 15% or higher. Furthermore, the large particles, which had a large internal air layer, showed a 5% higher insulation performance than the small particles. By observing the difference in the insulation effect according to the internal air layer size of hollow silica nanoparticles, this research suggests that when using hollow particles as a paint additive, the particle size needs to be considered in order to maximize the air layer in the paint.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.467-467
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• 2011

Reflecting the growing importance of nanomaterials in science and technology, controlling the porosity combined with well-defined structural properties has been an ever-demanding pursuit in the related fields of frontier researches. A number of reports have focused on the synthesis of various nanoporous materials so far and, recently, the nanomaterials with multimodal porosity are getting an emerging importance due to their improved material properties compared with the mono porous materials. However, most of those materials are obtained in bulk phases while the spherical nanoparticles are one of the most practical platforms in a great number of applications. Here, we report on the synthesis of the core-shell silica nanoparticles with double mesoporous shells (DMSs). The DMS nsnoparticles are spherical and monodispersive and have two different mesoporous shells, i.e., the bimodal porosity. It is the first example of the core-shell silica nanoparticles with the different mesopores coexisting in the individual nanoparticles. Furthermore, the carbon and silica hollow capsules were also fabricated via a serial replication process.

• Membrane Journal
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• v.30 no.5
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• pp.326-332
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• 2020

In this study, polymer-fluorinated silica composite hollow fiber membranes were fabricated and applied to a membrane contactor for the recovery of methane dissolved in the anaerobic effluent. To prepare the composite membranes, porous hollow fiber substrates were fabricated with Ultem^®, a commercial polyetherimide (PEI). Subsequently, fluorinated silica particles were synthesized and coated on the surface via strong covalent bonding. Due to the high porosity, our membrane showed a CH₄ flux of 8.25 × 10^-5 ㎤ (STP)/㎠·s at the liquid velocity of 0.03 m/s which is much higher that that of commercial polypropylene membrane designed for degassing processes. This is attributed to our membrane's high porosity as well as a superior surface hydrophobicity (120~122°) resulted from the coating with fluorinated silica nanoparticles.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.78-82
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• 2015

Hollow silica particles were prepared using sodium silicate and organic templates. Polystyrene latex (PSL) particles produced by dispersion polymerization were used as organic templates. PSL particles ranged from $1{\mu}m$ to $3{\mu}m$ in diameter were synthesized by adjusting the amount of 2,2'-azobisisobutyronitrile (AIBN). The PSL/$SiO_2$ core-shell particles were prepared by coating of silica nanoparticles originated from sodium silicate using sol-gel method. The organic templates were removed by the organic solvent, tetrahydrofuran (THF). Morphology of hollow silica particles was investigated with respect to types of the reaction medium and pH during the process. By changing the solvent from ethanol to water, hollow silica particles were successfully formed. Hollow silica particles with the uniform shell thickness were produced at low pH as well. The reflectivity of the as-prepared silica particles was measured in the range of the wavelength of UV and visible light. Hollow silica particles showed much better reflective properties than the commercial light reflector, Insuladd.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.1-1
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• 2011

We developed a new generalized synthetic procedure, called as "heat-up process," to produce uniform-sized nanocrystals of many transition metals and oxides without a size selection process. We were able to synthesize uniform magnetite nanocrystals as much as 1 kilogram-scale from the thermolysis of Fe-oleate complex. Clever combination of different nanoscale materials will lead to the development of multifunctional nano-biomedical platforms for simultaneous targeted delivery, fast diagnosis, and efficient therapy. In this presentation, I would like to present some of our group's recent results on the designed fabrication of multifunctional nanostructured materials based on uniform-sized magnetite nanoparticles and their medical applications. Uniform ultrasmall iron oxide nanoparticles of <3 nm were synthesized by thermal decomposition of iron-oleate complex in the presence of oleyl alcohol. These ultrasmall iron oxide nanoparticles exhibited good T1 contrast effect. In in vivo T1 weighted blood pool magnetic resonance imaging (MRI), iron oxide nanoparticles showed longer circulation time than commercial gadolinium complex, enabling high resolution imaging. We used 80 nm-sized ferrimagnetic iron oxide nanocrystals for T2 MRI contrast agent for tracking transplanted pancreatic islet cells and single-cell MR imaging. We reported on the fabrication of monodisperse magnetite nanoparticles immobilized with uniform pore-sized mesoporous silica spheres for simultaneous MRI, fluorescence imaging, and drug delivery. We synthesized hollow magnetite nanocapsules and used them for both the MRI contrast agent and magnetic guided drug delivery vehicle.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1127-1130
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• 2013

Formation of the monodisperse submicrospheres consisting of ionic palladium(II) complexes, $[(Me_4en)Pd(L)]_2(X)_4$($Me_4en$ = N,N,N',N'-tetramethylethylenediamine; L = bis(4-(4-pyridylcarboxyl)phenyl)methane; $X^-=BF_4{^-}$ and $ClO_4{^-}$), has been carried out without any templates or additives. The submicrospheres were coated with silicates, and then calcined in air at $550^{\circ}C$ for 1 h, to efficiently form hollow-spherical $SiO_2$ submicro-reactors dotted with palladium(0) nanoparticles (PdNPs). That is, the submicrospheres act as both a template and a source of the palladium metal nanoparticles. The submicro-reactors containing nano-catalysts have been characterized by means of SEM, TEM, and XPS. Notably, the reactors were proved to be very effective for Suzuki-Miyaura cross-coupling and hydrogenation reactions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.588-588
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• 2013

Nanoscale noble-metals have attracted enormous attention from researchers in various fields of study because of their unusual optical properties as well as novel chemical properties. They have possible uses in diverse applications such as devices, transistors, optoelectronics, information storages, and energy converters. It is well-known that nanoparticles of noble-metals such as silver and gold show strong absorption bands in the visible region due to their surface-plasmon oscillation modes of conductive electrons. Silver nanocubes stand out from various types of Silver nanostructures (e.g., spheres, rods, bars, belts, and wires) due to their superior performance in a range of applications involvinglocalized surface plasmon resonance, surface-enhanced Raman scattering, and biosensing. In addition, extensive efforts have been devoted to the investigation of Gold-based nanocomposites to achieve high catalytic performances and utilization efficiencies. Furthermore, as the catalytic reactivity of Silver nanostructures depends highly on their morphology, hollow Gold nanoparticles having void interiors may offer additional catalytic advantages due to their increased surface areas. Especially, hollow nanospheres possess structurally tunable features such as shell thickness, interior cavity size, and chemical composition, leading to relatively high surface areas, low densities, and reduced costs compared with their solid counterparts. Thus, hollow-structured noblemetal nanoparticles can be applied to nanometer-sized chemical reactors, efficient catalysts, energy-storage media, and small containers to encapsulate multi-functional active materials. Silver nanocubes dispersed in water have been transformed into Ag@Au nanoboxes, which show highly enhanced catalytic properties, by adding $HAuCl_4$. By using this concept, $SiO_2$-coated Ag@Au nanoboxes have been synthesized via galvanic replacement of $SiO_2$-coated Ag nanocubes. They have lower catalytic ability but more stability than Ag@Au nanoboxes do. Thus, they could be recycled. $SiO_2$-coated Ag@Au nanoboxes have been found to catalyze the degradation of 4-nitrophenol efficiently in the presence of $NaBH_4$. By changing the amount of the added noble metal salt to control the molar ratio Au to Ag, we could tune the catalytic properties of the nanostructures in the reduction of the dyes. The catalytic ability of $SiO_2$-coated Ag@Au nanoboxes has been found to be much more efficient than $SiO_2$-coated Ag nanocubes. Catalytic performances were affected noteworthily by the metals, sizes, and shapes of noble-metal nanostructures.

• Clean Technology
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• v.27 no.3
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• pp.223-231
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• 2021

In order to address many issues associated with large volume changes of silicon, which has very low electrical conductivity but offers about 10 times higher theoretical capacity than graphite (Gr), a silicon nanoparticles/hollow carbon (SiNP/HC) composite having bimodal-mesopores was prepared using silica nanoparticles as a template. A control SiNP/C composite without a hollow structure was also prepared for comparison. The physico-chemical and electrochemical properties of SiNP/HC were analyzed by X-ray diffractometry, X-ray photoelectron spectroscopy, nitrogen adsorption/desorption measurements for surface area and pore size distribution, scanning electron microscopy, transmission electron microscopy, galvanostatic cycling, and cyclic voltammetry tests to compare them with those of the SiNP/C composite. The SiNP/HC composite showed significantly better cycle life and efficiency than the SiNP/C, with minimal increase in electrode thickness after long cycles. A hybrid composite, SiNP/HC@Gr, prepared by physical mixing of the SiNP/HC and Gr at a 50:50 weight ratio, exhibited even better cycle life and efficiency than the SiNP/HC at low capacity. Thus, silicon/carbon composites designed to have hollow spaces capable of accommodating volume expansion were found to be highly effective for long cycle life of silicon-based composites. However, further study is required to improve the low initial coulombic efficiency of SiNP/HC and SiNP/HC@Gr, which is possibly because of their high surface area causing excessive electrolyte decomposition for the formation of solid-electrolyte-interface layers.