Suk Bon Yoon

Fabrication of Carbon Capsules with Hollow Macroporous Core/Mesoporous Shell Structures**

By Suk Bon Yoon, Kwonnam Sohn, Jeong Yeon Kim,Chae-Ho Shin, Jong-Sung Yu,* and Taeghwan Hyeon*In this report, the fabrication of carbon capsules with hol-low core/mesoporous shell (HCMS) structures will be pre-sented. Various nanoporous carbon materials have been fabri-cated using inorganic templates, including zeolites,

Layer-by-Layer Films of Dual-Pore Carbon Capsules with Designable Selectivity of Gas Adsorption

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.

Stimuli-free auto-modulated material release from mesoporous nanocompartment films

Mesoporous nanocompartment films composed of silica particles and hollow 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.

Synthesis of monodisperse spherical silica particles with solid core and mesoporous shell: mesopore channels perpendicular to the surface

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.

Synthesis and characterization of spherical carbon and polymer capsules with hollow macroporous core and mesoporous shell structures

Abstract The synthesis and characterization of spherical carbon hollow capsules with mesoporous shell (HCMS) structures is reported. Silica spheres with sub-micrometer sized solid cores and mesoporous shell (SCMS) structures were used as templates in the synthesis. The resulting carbon capsules inversely replicated the morphology of the silica template and had uniform pores with a narrow pore size distribution centered at 3 nm. The carbon capsules exhibited a BET surface area of >1000 m 2 /g and a total pore volume of >1.0 cm 3 /g. The diameter of the hollow core and the mesoporous shell thickness of the carbon capsules could easily be controlled using appropriate SCMS silica materials as templates. Using a similar synthetic procedure, hollow poly(divinylbenzene) capsules were also synthesized.

Synthesis of highly ordered mesoporous polymer networks

Synthesis of highly ordered three-dimensionally interconnected mesoporous hydrocarbon polymer networks exhibiting Bragg X-ray diffraction is reported by replicating the mesoporous MCM-48 and SBA-15 channel frameworks.

Synthesis of highly ordered nanoporous carbon molecular sieves from silylated MCM-48 using divinylbenzene as precursor

Calcined pure silica MCM-48 is modified by silylating its mesopores with trimethylsilyl chloride; such pore modification along with polymerization and carbonization of divinylbenzene as a carbon precursor is found to be a very efficient way of fabricating highly ordered carbon molecular sieves with three-dimensionally interconnected uniform pore arrays, greatly improving structural integrity and thermal stability.

Adsorption and structural properties of mesoporous carbons obtained from mesophase pitch and phenol-formaldehyde carbon precursors using porous templates prepared from colloidal silica

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.

A direct template synthesis of nanoporous carbons with high mechanical stability using as-synthesized MCM-48 hosts.

A simple and efficient synthetic method for highly ordered nanoporous carbons with high mechanical and thermal stability has been performed through a direct template carbonization using as-synthesized MCM-48 hosts.

Fabrication of nanocapsules with Au particles trapped inside carbon and silica nanoporous shells

Carbon capsules with hollow cores and mesoporous shells (HCMS) containing entrapped Au particles were prepared by template replication from solid core/mesoporous shell silica spheres with encapsulated Au particles. The resulting HCMS carbon capsules were then nanocast one step further to generate Au-trapping hollow core silica capsules with nanostructured shells.