The integration of metal oxides and carbon materials provides a great potential for enhancing the high energy and power densities of supercapacitors, but the rational design and scalable fabrication of such composite materials still remain a challenge. Herein, we report a fast, scalable, and one-pot hydrodynamic synthesis for preparing ion conductive and defect-free graphene from graphite and MnO 2 /graphene nanocomposites. The use of this hydrodynamic method using Taylor−Couette flow allows us to efficiently fast shear-exfoliate graphite into large quantities of high-quality graphene sheets. Deposition of MnO 2 on graphene is subsequently performed in a fluidic reactor within 10 min. The prepared MnO 2 /graphene nanocomposite shows outstanding electrochemical performances, such as a high specific capacitance of 679 F/g at 25 mV/s, a high rate capability of 74.7% retention at an extremely high rate of 1000 mV/s, and an excellent cycling characteristic (∼94.7% retention over 20 000 cycles). An asymmetric supercapacitor device is fabricated by assembling an anode of graphene and a cathode of MnO 2 / graphene, which resulted in high energy (35.2 W h/kg) and power (7.4 kW/kg) densities (accounting for the mass of both electrodes and the electrolyte) with a high rate capability and long cycle life.
We report on the high-throughput production of heterogeneous catalysts of RuO2-deposited graphene using a hydrodynamic process for selective alcohol oxidation. The fluid mechanics of a hydrodynamic process based on a Taylor–Couette flow provide a high shear stress field and fast mixing process. The unique fluidic behavior efficiently exfoliates graphite into defect-free graphene sheets dispersed in water solution, in which ionic liquid is used as the stabilizing reagent to prevent the restacking of the graphene sheets. The deposition of RuO2 on a graphene surface is performed using a hydrodynamic process, resulting in the uniform coating of RuO2 nanoparticles. The as synthesized RuO2/IL–graphene catalyst has been applied efficiently for the oxidation of a wide variety of alcohol substrates, including biomass-derived 5-hydroxymethylfurfural (HMF) under environmentally benign conditions. The catalyst is mechanically stable and recyclable, confirming its heterogeneous nature.
The oxidation reactions of alcohols and amines to their
respective
aldehydes/ketones and nitriles are important reactions in the laboratory
and industry. A highly robust and activated ruthenium-supported anodic
aluminum oxide (Ru@AAO) has been synthesized through the sonochemical
method. The sonochemical technique allowed a short synthesis time
and uniform distribution of Ru on the AAO surface as confirmed by
the scanning electron microscopy, transmission electron microscopy,
X-ray diffraction analysis, and BET surface-area analysis. The synthesized
catalyst was employed for the oxidation of alcohols and amines in
the presence of atmospheric air at a relatively lower temperature.
The synthesized catalyst showed excellent conversions of both alcohols
and amines with high selectivities toward their respective aldehydes/ketones
and nitriles. The function of the AAO support in Ru@AAO catalytic
activity has also been elaborated in the present investigation.
The efficiency of a heterogeneous ruthenium zirconia catalyst (Ru(OH)x/ZrO2) was demonstrated to the selective oxidative transformation of alkenes or alkynes. The scissions of C-C double bonds to aldehydes and triple bonds to diketones or carboxylic acids were carried out with (diacetoxyiodo)benzene as an oxidant under dichloromethane (5 mL)/water (0.5 mL) solvent system at 30 ℃ for wide range of substrates. The Ru(OH)x/ZrO2 composite showed higher catalytic activity and selectivity than other ruthenium-based homogeneous or heterogeneous catalysts for the scission reaction. The catalyst exhibited a high mechanical stability, and no leaching of the metal was observed during the reaction. These features ensured the reusability of the catalyst for several times for the oxidative cleavage of unsaturated hydrocarbons.
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