Aran Kim

Ultrathin graphene nanosheets derived from rice husks for sustainable supercapacitor electrodes

Graphene nanosheets are synthesized via the carbonization of brown-rice husks followed by a one-stage KOH-activation process for the design of a sustainable electrochemical energy-storage electrode. The graphene nanosheets exhibit an ultra-thin crumpled-silk-veil-wave, sheet-like structure with a high surface area of ∼1225 m2 g−1 and a high porosity. The graphene-nanosheet electrode shows a specific capacitance of 115 F g−1 at 0.5 mA cm−2 and a high energy density of 36.8 W h kg−1 at a power density of 323 W kg−1, with an excellent cyclic stability of 88% over 2000 cycles. The observed good electrochemical energy-storage performance of the biomaterial-derived graphene-nanosheet electrode is due to the synergistic effect of the intrinsically large electrochemically active surface area, an enhanced ion diffusion, and an improved electrical conductivity.

Selective stabilisation of blue phase liquid crystal induced by distinctive geometric structure of additives

ABSTRACT We successfully stabilised liquid crystalline blue phases (BPs) by introducing two suitable additives with different geometric molecular structures, linear-shaped cobalt oleate complex (Co-OL) or tetrahedral-shaped tetraoctadecylammonium bromide (TODAB), into a liquid crystal (mixture of 4ʹ-pentyl-4-biphenylcarbonitrile, JC-1041XX and chiral dopant). The BPs temperature range and phase sequence depending on the addition amount and shape of additives were systematically investigated to determine the optimal concentration and shape dependency required to achieve a stabilising effect for BPs. From the polarising optical microscope results, the BPs temperature range for all of the samples with additives was not only broadened but also shifted to room temperature compared to that of BPs without additives. The widest BPs temperature range was increased to 15.3°C by the addition of 3 wt% Co-OL. According to the UV-vis reflection spectroscopy results, the Co-OL has a more significant stabilisation effect on BP I than on BP II, and the widest BP I range increases to 11.0°C. On the other hand, TODAB is effective for BP II stabilisation with the broadest BP II range reaching 1.8°C. These selective stabilisation effects are attributed to the specific shape of additives that closely match the structures of the disclination lines of the BPs. Graphical Abstract

Pore Parameters-Dependent Adsorption Behavior of Volatile Organic Compounds on Graphene-Based Material

Mesoporous graphenes (MPGs) with interpenetrating porous networks are successfully obtained by the pyrolysis of composite gel consisting of graphite oxide (GO) and the amphiphilic triblock copolymer (Pluronic P123) under Ar atmosphere, wherein P123 is used as a soft-template. The as-prepared composite gel is obtained following self-assembly and freeze-drying. The obtained MPGs have high BET specific surface area (531-746 m2 g-1 and ink-bottle like pores with three dimensional interconnected network. Furthermore, the specific surface area and porous parameters such as pore volume, pore size, and pore size distribution of MPGs can be rationally controlled by regulating the initial mass ratio of P123 to GO. With the increase of P123 ratio, the average mesopore size is decreased from ∼16.4 nm to ∼9.5 nm, which is similar to the diameter size of P123 micelles. Also, the adsorption capacities of MPG-20 for 52 indoor air standard components (100 μg mL-1, Supelco) are compared with two different materials, namely commercial porous polymers (2,6-diphenyleneoxide) and reduced graphene oxide (RGO). The result shows that MPG-20 has significantly better adsorption capacity than RGO but also similar or slightly better than commercial porous polymer. The mesoporous structure and surface chemistry of MPGs were the most important factors for the enhancement of the adsorption efficiency for volatile organic compounds.

Development of Latent Fingermarks on Nonporous and Semiporous Substrates Using Photoluminescent Eu(Phen)2 Complex Intercalated Clay Hybrids with Enhanced Adhesion

In forensic science, developing latent fingermarks using powders is a critical, general method to identify individuals. Photoluminescent Eu(Phen)2 complex intercalated clay hybrids have been used to improve the visualization of fingermarks on nonporous (glass and polymer film) and semiporous (euro and dollar banknotes) substrates. An ion exchange reaction has been successfully used to intercalate Eu(Phen)2 complex ions into the interlayer spacing of two different Na+‐clays, Na+‐montmorillonite and Na+‐hectorite, with different primary particle sizes. To change the surface properties of the obtained hybrid to be more lipophilic, the hydroxyl groups at the edge of the hectorite hybrid were modified with hexadecyltrimethoxysilane via silylation. We investigated the correlation of the size and surface properties of the hybrids with their adhesion to fingermark residues. Fingermarks were successfully visualized using hybrids under UV illumination. In particular, ridge details on semiporous substrates can be more clearly seen using hybrids with smaller primary particles and greater lipophilicity.