[Show abstract][Hide abstract] ABSTRACT: We report on the preparation of hierarchically doubled shells of different porosity on monodispersive silica nanocores by the direct formation of the outer shell with larger mesopores (D > ~2.5 nm) on the surface of the initial single shell of smaller mesopores (D < ~2.5 nm). An organic template solution containing cetyl-trimethylammonium bromide, 1,3,5-trimethylbenzene, and decane was used for the formation of the larger mesoporous shells, while the initial shell was prepared with the use of only one type of structure-directing agent, namely cetyltrimethylammonium bromide. The resulting core–shell silica nanoparticles are spherical, monodispersive, and show a distinct bimodal porosity. Pore sizes of those shells were easily controlled by varying the molar ratio of the pore expansion agents.
Bulletin- Korean Chemical Society 03/2015; 36(3):789-892. DOI:10.1002/bkcs.10146 · 0.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Foam stability was investigated by varying the amount of silica nanoparticles in a decontamination foam containing a surfactant and a stabilizer. In addition, a study on the oxide dissolution of a corroded specimen using a decontamination foam was performed to evaluate the decontamination efficiency of the foam. The decontamination foam prepared with Elotant™ Milcoside 440N (EM440N) as a non-ionic surfactant displayed the highest foam stability compared with that of foam containing other surfactants such as SDS and Triton X-100 in acidic pH. For the decontamination foam prepared using silica nanoparticles, the liquid volume in the foam was enhanced by a factor of 2 compared with that of the foam prepared using only a surfactant. Silica nanoparticles are thought to play a key role as an effective stabilizer of decontamination foam in acidic pH. The decontamination efficiency toward dissolving iron was improved by up to approximately 94% when using a decontamination foam in 1.0% EM440N consisting of the mixture of 3.0 wt.% silica nanoparticles and 0.1 wt.% xanthan gum compared with that of the chemical decontamination agent alone. This result indicates that an increase in foam stability enhanced the oxide dissolution of the decontamination foam owing to an increase in the contact time between the decontaminant foam and the corroded specimen.
Annals of Nuclear Energy 11/2014; 73:168–174. DOI:10.1016/j.anucene.2014.06.046 · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The shape and crystal structure of TiO2 nanomaterials synthesized by the hard-template method can be controlled by simply changing the calcination temperature. In this work, SiO2 nanoparticles were used as a hard template and TiO2 was coated onto the surface of the silica core, resulting in core-shell nanoparticles, which were then calcined at various temperatures to induce shape transformation and crystallization of the TiO2 shell. After etching of the silica cores, spherical hollow nanocapsules with anatase crystal phase were obtained by calcination at 400-1000 degrees C, while urchin-like hollow capsules and small-sized particulates were obtained at temperatures below 400 degrees C and above 1000 degrees C, respectively. The core-shell nanoparticles exhibited greatly enhanced anatase phase stability (up to approximately 1200 degrees C), which was attributable to the effect of the core material. The phase stability was found to be dependent on the shell thickness of the nanocapsules, also supporting the effect of the core material.
Journal of Nanoscience and Nanotechnology 09/2013; 13(9):6069-73. DOI:10.1166/jnn.2013.7657 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3 nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8 nm) and macropores (ca 300 nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909 m/g) and large pore volume (ca 0.73 cm/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.
[Show abstract][Hide abstract] ABSTRACT: We report on the fabrication of the nanoporous TiO2 hollow capsules using core-shell silica nanoparticle templates. The thickness of the capsules can be simply controlled by varying the amount of the TiO2 precursor. The resulting nanoporous capsules exhibited the high specific surface area and the large pore volume of 103-180 m2/g and 0.40-0.86 cm3/g, respectively. Photocatalytic activity of the TiO2 hollow capsules was also investigated and compared to that of the commercial TiO2 nanoparticles.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1604-7. DOI:10.1166/jnn.2012.4611 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A wavelength-dispersive X-ray fluorescence (WDXRF) technique that uses the scattered radiation of the X-ray tube lines and the fluorescence radiation of an element present in a powder sample is proposed as a non-destructive method for the determination of the water content in silica powder. Although direct X-ray fluorescence analysis of water using WDXRF is not adequate for the quantitative determination of water in powder, due to the very low fluorescence yield for hydrogen and oxygen, the fluorescence signal of silicon (Si) in silica powder is attenuated by water, and is shown to decrease in proportion to the water content in silica powder. In addition, it is demonstrated that the Compton- and Rayleigh-scattering of the X-ray tube lines is proportional to the water content. The coefficients of determination, R2, of the linear regression equations obtained from the calibration curves for all individual scattered radiations and for the fluorescence radiation of Si were >0.90. The sum of the peak intensities of the four scattering signals, i.e. the Rayleigh-scattered Rh K–L2,3 and Rh K–M2,3 lines, and Compton-scattered Rh K–L2,3 and Rh K–M2,3 lines, also showed fairly good linearity and sensitivity over a very wide range of water content from 0wt.% to 61.5wt.%. However, porosity had a significant effect on the X-ray signal at low water content, in the range from 0wt.% to 7.5wt.%, where the sensitivity for the silica nanopowder with well-defined mesopores (~3nm in diameter) decreased to 0.40kcps/wt.%, from 0.99kcps/wt.% for the non-porous silica nanopowder. The use of the Si fluorescence signal along with the scattered radiation of the X-ray tube lines expands the applicability of conventional XRF spectrometers to the quantitative determination of water content in silica powder.
[Show abstract][Hide abstract] ABSTRACT: The hydrophobicity of a perfluoropolyether bisurethane methacrylate polymer film was investigated along with the formation of nano-hairs on its surface through reactive ion etching using gold nanoparticles (Au NPs) as masks. It was found that the hydrophobicity of the polymer film was strongly dependent on the number density of the nano-hairs which was determined by that of the Au NPs. The superhydrophobic surface was obtained when the number density was higher than 250 microm(-2). The effects of surface functionalization, Au NP immobilization, and etching time on the hydrophobicity of the polymer film were also examined extensively and discussed based on the results of the contact angle measurements and the scanning electron microscopy.
Journal of Nanoscience and Nanotechnology 07/2011; 11(7):6584-8. DOI:10.1166/jnn.2011.4457 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silica-based nanocasting synthesis of a nanostructured carbon replica inevitably involves the disposal of silica waste and toxic etchant after the time-consuming and costly etching processes for selective removal of silica template from a carbon/silica composite to produce the silica-free carbon replica, not only resulting in chemical waste, but also posing serious environmental concerns. Instead of removal of the silica template, the in situ recrystallization transformation of the silica into more useful functional nanostructured silica offers an attractive alternative to the problem of handling silica waste and toxic etchants. In this work, the novel composites composed of microporous zeolite ZSM-5 crystals and hollow core-mesoporous shell carbon (HCMSC) capsules are synthesized for the first time by such transformation process of sacrificial silica template in the carbon/solid core-mesoporous shell silica (SCMSS) composite through hydrothermal process under alkaline condition. Compared to the commercial filter materials, the zeolite/HCMSC composite (BET surface area: 532–600 m2/g) possessing a wide range of pore sizes, i.e., micropores from zeolites, mesopores from the outer shells, and macropores from the hollow core of the carbon capsules reveals the outstanding adsorption capacity for the typical malodorous acetaldehyde. Therefore, the recrystallization approach will be appealing as a simple, economical, environmentally benign, and efficient direct synthesis process for the preparation of new multifunctional composite materials for many advanced applications such as removal of volatile organic compounds, separation, energy storage, and catalysis. Recrystallization transformation approach of sacrificial silica in silica/carbon composites is reported for the first time for the formation of new composite materials composed of microporous ZSM-5 zeolite and hollow mesoporous carbon capsules. That is, the silica template waste is utilized to produce a new highly desirable crystalline microporous ZSM-5 silica material by this approach. The composite demonstrated high adsorption capacity for acetaldehyde.
[Show abstract][Hide abstract] ABSTRACT: Carbon capsules with hierarchical pore structures were fabricated by using core-shell silica nanoparticles as templates and phenolic resin as a carbon precursor. Carbon capsules with hierarchical pore structures were obtained via in-situ polymerization of the phenolic resin on the surface of the silica nanoparticles followed by the carbonization and removal of the silica templates. The hierarchically pored carbon capsules exhibited multimodal porosity with a high specific surface area (approximately 1834 m2/g) and a large pore volume (approximately 1.83 cm3/g).
Journal of Nanoscience and Nanotechnology 01/2011; 11(1):656-60. DOI:10.1166/jnn.2011.3187 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple and easy sol–gel approach has been developed to directly synthesize in situ three-dimensionally interconnected uniform ordered bimodal porous silica (BPS) incorporating both the macroporosity and mesoporosity in the lattice without extra synthesis process performed in previous work. Multimodal porous carbon (MPC) was fabricated through the inverse replication of the BPS. The unique structural characteristics such as well-developed 3-D interconnected ordered macropore framework with open mesopores embedded in the macropore walls, large surface area (1120m2g−1) and mesopore volume (1.95cm3g−1) make MPC very attractive as an anode catalyst support in polymer exchange membrane fuel cell. The MPC-supported Pt-Ru alloy catalyst has demonstrated much higher power density toward hydrogen oxidation than the commercial carbon black Vulcan XC-72-supported ones.
[Show abstract][Hide abstract] ABSTRACT: The preparation of mesoporous nanocompartment films composed of both hollow silica capsules and silica particles by using layer-by-layer (LbL) adsorption is described. The resultant nanocompartment films exhibit stepwise release of encapsulated water molecules without application of external stimuli. The hollow hierarchic pore structure of the silica capsules, including their internal void and mesoporous walls, is a key factor for the regulation and stepwise release of water, and is probably caused by the non-equilibrated concurrent evaporation of material from the mesopore and capillary penetration into the mesopores. The number of release steps and rate of release can be tuned by variation of several parameters including water content, ambient temperature, layer multiplicity, and co-adduct particle size. Application of the mesoporous nanocompartment films for the release of substances, including therapeutic agents and fragrances, indicates that the stepwise material release can be applied for a wide range of liquid substances. The films should lead to a novel material release system useful even for biomedical applications capable of controlled and sustained delivery of drug molecules.
[Show abstract][Hide abstract] ABSTRACT: Hollow core mesoporous shell (HCMS) carbon has been explored for the first time as a cathode catalyst support in direct methanol fuel cells (DMFCs). The HCMS carbon consisting of discrete spherical particles possesses unique structural characteristics including large specific surface area and mesoporous volume and well-developed interconnected void structure, which are highly desired for a cathode catalyst support in low temperature fuel cells. Significant enhancement in the electrocatalytic activity toward oxygen reduction reaction has been achieved by the HCMS carbon-supported Pt nanoparticles compared with carbon black Vulcan XC-72-supported ones in the DMFC. In addition, much higher power was delivered by the Pt/HCMS catalysts (i.e., corresponding to an enhancement of ca. 91–128% in power density compared with that of Pt/Vulcan), suggesting that HCMS carbon is a unique cathode catalyst support in direct methanol fuel cell.
[Show abstract][Hide abstract] ABSTRACT: Stable, homogeneous ultrathin films of uniformly dimensioned dual-pore carbon capsules with mesoporous walls and macroscopic empty cores were fabricated using layer-by-layer methods based on electrostatic interaction between a polyelectrolyte and a surfactant coating of the carbon capsules. The resulting dual-porous carbon capsule films were investigated as a sensor substrate for vapors of different organic solvents. The carbon capsule films have much higher adsorption capacities than conventional electrolyte films and even than noncapsular mesoporous carbon films. The dual-pore carbon capsules have greater affinities for aromatic volatiles over their aliphatic counterparts, probably due to stronger pi-pi interactions. Additionally, the adsorption selectivity can be designed. Impregnation of additional recognition components into the carbon capsules permits further control over adsorption selectivity between aromatic and nonaromatic substances and between acids and bases in the prevailing atmosphere. Therefore, it is anticipated that the dual-pore carbon capsule films developed in this work will find application in sensing and separation applications because of their designable selectivity.
Journal of the American Chemical Society 05/2009; 131(12):4220-1. DOI:10.1021/ja9010354 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Large mesoporous silica microspheres with bimodal pore size distributions will be very promising in a special application. Silica microspheres of 10-100 microm in size were synthesized using n-dodecylamine and polymeric surfactant as co-templating agents at room temperature. Surface area and large pore volume of the mesoporous silica microspheres were 884-1009 m2/g and 1.25-1.68 cm3/g, respectively, depending on the reaction conditions. Mesoporous silica microspheres prepared using a short-chained alkylamine surfactant and a long-chained polymeric surfactant exhibited distinct bimodal pore size distribution, that is, small (< 3 nm) and large mesopores (> 20 nm). Pluronic F108, which is a poly(ethylene glycol)-poly(propylene glycol) triblock copolymer, played an important role in the formation of the large mesopores as well as the formation of stable silica microspheres without strong aggregation between particles.
Journal of Nanoscience and Nanotechnology 10/2008; 8(10):5261-5. DOI:10.1166/jnn.2008.1045 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mesoporous nanocompartment films composed of silica particles and hallow silica capsules were prepared by the layer-by-layer (LbL) technique. The resulting mesoporous nanocompartment films possess special molecular encapsulation and release capabilities so that stimuli-free auto-modulated stepwise release of water or drug molecules was achieved through the mesopore channels of robust silica capsule containers embedded in the film. Stepwise release of water was reproducibly observed that originates in the non-equilibrated rates between evaporation of water from the mesopore channels to the exterior and the capillary penetration of water from container interior to the mesopore channels. It was generalized to evaporation of other substances, fragrances, limonene. Application was also tested in the controlled release of the sunscreen UV-absorber (UV-S1) for circumvention of its rapid dissolution in water and prolongation of its prophylactic effect toward harmful ultraviolet radiation. UV-S1 was successfully entrapped within the mesoporous nanocompartment films and was released in a prolonged stepwise mode. The nanocompartment films developed in this research are promising materials for drug delivery since they allow gradual release of therapeutic agents with likely related improvements in their efficacy.
Journal of the American Chemical Society 03/2008; 130(8):2376-7. DOI:10.1021/ja076139s · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Monodisperse spherical silica particles with solid core and mesoporous shell were synthesized by adopting silica particles as core host components and surfactant molecules as structure-directing agents for the mesoporous shell. Here, two different types of surfactant molecules, octadecyltrimethoxysilane (C18-TMS) and cetyltrimethylammonium bromide (C16-TMABr) were utilized as porogens for the formation of mesoporous shell over the spherical silica particles. While the C18-TMS generated solid core/disordered mesoporous shell (SCDMS) silica spheres, the C16-TMABr produced solid core/ordered mesoporous shell (SCOMS) silica spheres. Interestingly, the mesoporous channels generated in the SCOMS silica spheres were in the direction perpendicular to the silica surface. Also, the mesopores of the SCOMS silica spheres were expanded by addition of 1,3,5-trimethylbenzene (TMB) and decane mixture. The core sizes, shell thickness, and nanoporosity of the silica particles were controlled by monitoring the size of the silica sphere core, the amount and ratio of TEOS and C18-TMS or C16-TMABr added, additives and the thermal treatment.
Colloids and Surfaces A Physicochemical and Engineering Aspects 02/2008; 313:77-81. DOI:10.1016/j.colsurfa.2007.04.145 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Synthesis of mesoporous silica microspheres larger than 10 microm via surfactant template approach has rarely been reported. According to the previous studies, particle morphologies were highly variable, depending on the synthesis conditions and impeller design such as impeller type, size, and agitation speed. A new robust surfactant-template synthesis strategy for the stable suspension of large silica microspheres was investigated by introducing an additional cosurfactant. Di(2-ethylhexyl)phosphoric acid (HDEHP) as a cosurfactant played a key role in suspension stabilization without distorting the spherical morphology as well as in the formation of uniform pore structures. High quality of mesoporous silica microspheres was obtained and compared with the Kosuge's silica under different conditions such as stirring rate, acid concentration, the amount of solvent in a mother liquor.
Journal of Nanoscience and Nanotechnology 12/2007; 7(11):3862-6. DOI:10.1166/jnn.2007.098 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Both particle monodispersity and mesopore orientation have been considered in this work. Monodisperse spherical silica particles with a solid core and a mesoporous shell featuring mesopore channels perpendicular to the core surface were synthesized for the first time by adopting silica particles as the core component and by employing Cn-TAB (n = 12, 14, 16, 18), the structure-directing agent for the mesoporous shell. Micelles on the surface of the silica particles are formed from the electrostatic interaction between the partially negatively charged silica particles and the positively charged surfactant molecules under basic conditions. The particles synthesized in this work have a uniformly coated thin mesoporous shell of about 28–61 nm in thickness over the silica core and possess a surface area of ca. 370–500 m2 g−1, pore volume of ca. 0.2–0.35 cc g−1, and narrow pore size distribution.
[Show abstract][Hide abstract] ABSTRACT: Nanostructured polymer materials with interesting morphological variation, which include three dimensionally interconnected uniform nanoporous network arrays (volume- and surface-templated ordered arrays) and hollow core spheres were synthesized by inducing different polymerization process of phenol and formaldehyde as a precursor over silica templates (ordered silica colloidal crystals or individual silica particles). The pore sizes of the resulting nanostructured polymer materials can be easily controlled by monitoring the sizes of silica spheres, while their morphologies were modulated by controlling the initiation sites of the acid-catalyzed condensation reaction of the same polymer precursor and by modifying silica templates.
Current Applied Physics 10/2006; 6(6):1054-1058. DOI:10.1016/j.cap.2005.07.018 · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Synthesis of carbons with uniform spherical mesopores is explored from mesophase pitch and polymerized phenol-formaldehyde carbon precursors using porous templates prepared from silica colloids having diameters of 16, 31 and 46 nm. It is shown that the polymer-based carbons exhibited very large pore volumes (between 3.5 and 4.0 cc g−1) and complex pore size distributions because of incomplete filling of silica templates. In contrast, mesophase pitch filled all pores of the silica templates, which led to the carbons with uniform spherical mesopores reflecting the size of the silica colloids used. There is some evidence for mesostructural ordering in the pitch-based carbons obtained by using silica templates assembled from uniform colloids of diameters greater than 30 nm. This ordering is clearly visible for the pitch-based carbon obtained by using the silica template consisting of 46 nm colloids, which demonstrates the feasibility of colloidal crystal synthesis from uniform spheres of size below 50 nm. These unique structural properties of pitch-based carbons are reflected by paralleled capillary condensation and steep evaporation steps of nitrogen adsorption isotherm, which indicates high uniformity of mesopores and mesopore windows.