Ying-Feng Lee

Design and tailoring of a hierarchical graphene-carbon nanotube architecture for supercapacitors

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes (CNTs) to form a 3-D hierarchical structure which significantly enhances the electrochemical capacitive performances of GS-based composites. From SEM images, inserting proper quantity of CNTs as nanospacers can effectively impede the stacking of GS and enlarge the space between GS sheets, leading to obtain a highly porous nanostructure. The specific capacitance of GS-CNTs-9-1 (∼326.5 F g−1 at 20 mV s−1) is much higher than that of GS material (∼83 F g−1). Furthermore, the energy and power densities of GS-CNTs-9-1 are respectively as high as 21.74 Wh kg−1 and 78.29 kW kg−1, revealing that the hierarchical graphene-CNT architecture provides remarkable effects on enhancing the capacitive performance of GS-based composites. Therefore, the GS-CNT composites are promising carbon materials for supercapacitors.

Synthesis of activated carbon-surrounded and carbon-doped anatase TiO2 nanocomposites

A specially designed photocatalytic structure, i.e., carbon-doped anatase-TiO2 (A-TiO2−xCx) nanocrystallites surrounded with activated carbon (AC), is synthesized by a simple one-step carbonization of a self-assembled matrix consisting of titanium tetra-isopropoxide (TTIP) and triblock copolymer. The self-assembled copolymer homogeneously disperses TTIP and possesses a steric inhibition of A-TiO2 grain growth and aggregation during the carbonization step, reducing the average grain size of the A-TiO2 nanocrystallites. An additional merit of this simple process, the facile formation of visible-light-driven photocatalysts through carbon-doping, is attributable to the retention of few-nanometre-sized A-TiO2 clusters during the carbonization step. The porous AC of high specific surface area within the novel A-TiO2−xCx-AC nanocomposites shows excellent adsorption ability for concentrating organics at the vicinity of A-TiO2−xCx nanocrystallites. Unlike the A-TiO2 crystals, the synergy between C-doped A-TiO2 and AC definitely promotes the visible-light photo-induced degradation efficiency of organics.

Microstructure tuning of mesoporous silica prepared by evaporation-induced self-assembly processes: interactions among solvent evaporation, micelle formation/packing and sol condensation

By varying the vapor pressure of solvents through changing the alkyl length of aliphatic alcohols or the aging temperature, the microstructures, including mesopore ordering length, porosity, and specific surface area, of silica templates are controllable in an evaporation-induced self-assembly (EISA) process. The microstructures of various silica powders are systematically characterized and compared by the small-angle X-ray scattering (SAXS), nitrogen adsorption/desorption isotherms, as well as scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images. The microstructure ordering length of silica powders is found to decrease with reduction of the solvent evaporation rate tuned by the length of alkyl groups of alcohols, which is confirmed by the almost identical microstructure of silica powders prepared by using methanol and tetrahydrofuran (THF) which exhibit similar vapor pressures. The rate of micelle formation relative to the rate of silica precursor condensation, strongly depending on the solvent evaporation rate, determines the resultant organization of micelles and may cause morphological distortion and microdomain disorientation of silica templates. This concept is confirmed by the presence of completely and partially ordered microstructures of silica powders synthesized from the ethanol- and butanol-based precursor solutions, respectively, which are dried completely at a higher temperature in the aging process. The microstructure of mesoporous silica can thus be simply tuned by varying solvents and aging temperatures in the EISA process, which are promising for many applications.

Graphene: a novel template for controlling the microstructures of mesoporous silica

This study presents the use of graphene sheets as a novel template to control the microstructure of mesoporous silica. The impurity-doped silica is confirmed to be under the pseudo-softening state at temperatures ≥600 °C. The mechanical strength of graphene sheets, catalytically formed in the same temperature range by the presence of Co catalysts, forces the partial transformation of mesoporous impurity-doped silica from 2D hexagonal (p6mm) to the lamellar phase. A mechanism for tailoring the microstructure of mesoporous silica is proposed in this work. This study opens a new way for simply controlling the microstructure of mesoporous silica.