Shigenori Kuga

Activated carbon from nitrogen rich watermelon rind for high-performance supercapacitors

Watermelon rind (WR) is proposed as a nitrogen rich precursor of nitrogen-doped activated carbon (WRAC) for possible energy storage applications in supercapacitors. The WRAC gives rise to a large surface area of up to 2277 m2 g−1 and provides an efficient pathway for ions to diffuse into the interior surfaces of bulk electrodes. The nitrogen-doped WRAC electrode gives a high gravimetric specific capacitance (333.42 F g−1) in 6 M KOH at a current density of 1 A g−1 with an adequate nitrogen content of 2.48%, in which the specific capacitance is higher than most previously reported synthetic nitrogen-doped carbon materials. It also exhibits excellent high rate performance, low impedance and good cycle stability (96.82% capacitance reserved after 10 000 cycles). These excellent electrochemical performances are attributed to the high surface area, unique pore size distribution and appropriate nitrogen content.

Influence of solvent polarity on surface-fluorination of cellulose nanofiber by ball milling

Ball mill-assisted surface-fluorination of cellulose nanofiber was studied for two solvents with different polarity as dispersion/reaction medium. Milling cellulose in neat toluene gave irregular-shaped decrystallized cellulose particles; addition of pentafluorobenzoyl chloride (PFBC) to the system gave partially fluorinated cellulose as thin flakes with smooth surfaces, which maintained original crystallinity. Milling in neat dimethyl formamide (DMF) caused partial dispersion of nanofibers without decrystallization; milling in PFBC/DMF gave more enhanced dispersion of surface-fluorinated nanofibers. Both fluorinated materials were hydrophobic, with water contact angles of 103°–113°. Bulk degree of esterification was 0.20 for toluene and 0.57 for DMF systems. These results show characteristic influences of solvent species in reactive ball milling of cellulose in terms of fibrillation and surface esterification of nanofibers.

Hydrophobic nanocoating of cellulose by solventless mechanical milling

The solventless mechanical treatment of native cellulose in a polytetrafluoroethylene (PTFE) vessel was found to cause friction transfer of PTFE to comminuted cellulose particles, resulting in their nanocoating. Cellulose particles after milling were irregular-shaped platelets, with typical sizes of 2–10 μm wide and 0.1–0.4 μm thick (28 h milled). Add-on of PTFE onto cellulose was assessed by weight gain of powder or weight loss of the pot. The PTFE-coated particles were highly hydrophobic and completely repelled from water, with a water contact angle of 110–121°. SEM-EDS analysis showed nearly continuous coverage of cellulose particles by PTFE layers of approx. 10 nm thick, which agreed well with peak-width analysis of X-ray diffraction. This finding may open a new class of solid-phase processing for nanocoating of particles.

One‐Pot Green Synthesis of Nitrogen‐Doped Carbon Quantum Dots for Cell Nucleus Labeling and Copper(II) Detection

The doping of nitrogen into carbon quantum dots is vitally important for improved fluorescence performance. However, the synthesis of nitrogen-doped carbon quantum dots (N-CQDs) is usually conducted under strong acid and high temperature, which results in environmental pollution and energy consumption. Herein, the N-CQDs were prepared by a mild one-pot hydrothermal process. The hydrothermal reaction temperature was adjusted to control the particle size, nitrogen/carbon atomic ratio, and quantum yield. The products were water soluble with a narrow particle size distribution and good dispersion stability over a wide pH range. The N-CQDs could penetrate into the HeLa cell nucleus without any further functionalization. Moreover, the fluorescence of N-CQDs could be selectively quenched by Cu2+ , which suggested applications for the detection of Cu2+ in human plasma.

Antistatic PVC-graphene Composite through Plasticizer-mediated Exfoliation of Graphite

Multilayer graphene was prepared by mechanical exfoliation of natural graphite with dioctyl phthalate (DOP) as milling medium without solvent. The obtained mixture could be directly mixed with poly(vinyl chloride) (PVC) for melt-forming, with DOP acting as plasticizer and graphene acting as conductive filler for antistatic performance. The composite showed surface resistance of 2.5 × 106 Ω/□ at 1 wt% carbon additive, significantly lower than approx. 7 wt% of raw graphite required for achieving the same level. This value is low enough for practical antistatic criterion of 3 × 108 Ω/□. The effect of filler addition on mechanical performance was minimal, or even beneficial for the milled carbon in contrast to the case of raw graphite.