For the first time, magnetic force microscopy (MFM) is used to characterize the mechanically exfoliated single- and few-layer MoS2 and graphene nanosheets. By analysis of the phase and amplitude shifts, the magnetic response of MoS2 and graphene nanosheets exhibits the dependence on their layer number. However, the solution-processed single-layer MoS2 nanosheet shows the reverse magnetic signal to the mechanically exfoliated one, and the graphene oxide nanosheet has not shown any detectable magnetic signal. Importantly, graphene and MoS2 flakes become nonmagnetic when they exceed a certain thickness.
Several different reactions have been studied to determine whether they occur more rapidly than conventionally heated reactions at atmospheric pressure. Small rate enhancements have been observed for some reactions carried out under microwave reflux in a modified domestic microwave oven. The Knoevenagel reaction of acetophenone with ethyl cyanoacetate was shown to have a rate enhancement of 2.5 times. However this reaction showed no rate increase over conventional heating, at the same temperature, in a variable-frequency microwave oven. It is therefore probable that the small rate enhancements observed in these experiments, using microwave heating, were due to hot spots or superheating of the solvent rather than to nonthermal effects.Key words: microwave, nonthermal effects, superheating, hot spots.
An asymmetric supercapacitor offers opportunities to effectively utilize the full potential of the different potential windows of the two electrodes for a higher operating voltage, resulting in an enhanced specific capacitance and significantly improved energy without sacrificing the power delivery and cycle life. To achieve high energy and power densities, we have synthesized an all-solid-state asymmetric supercapacitor with a wider voltage range using Fe-doped CoO and three-dimensional reduced graphene oxide (3DrGO) as the positive and negative electrodes, respectively. In contrast to undoped CoO, the increased density of states and modified charge spatial separation endow the Fe-doped CoO electrode with greatly improved electrochemical capacitive performance, including high specific capacitance (1997 F g and 1757 F g at current densities of 1 and 20 A g, respectively), excellent rate capability, and superior cycling stability. Remarkably, the optimized all-solid-state asymmetric supercapacitor can be cycled reversibly in a wide range of 0-1.8 V, thus delivering a high energy density (270.3 W h kg), high power density (9.0 kW kg at 224.2 W h kg), and excellent cycling stability (91.8% capacitance retention after 10 000 charge-discharge cycles at a constant current density of 10 A g). The superior capacitive performance suggests that such an all-solid-state asymmetric supercapacitor shows great potential for developing energy storage systems with high levels of energy and power delivery.
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