Layered double hydroxides (LDHs) are promising cathode materials for supercapacitors because of the enhanced flow efficiency of ions in the interlayers. However, the limited active sites and monotonous metal species further hinder the improvement of the capacity performance. Herein, cobalt sulfide quantum dots (Co9S8‐QDs) are effectively created and embedded within the interlayer of metal‐organic‐frameworks‐derived ternary metal LDH nanosheets based on in situ selective vulcanization of Co on carbon fibers. The hybrid CF@NiCoZn‐LDH/Co9S8‐QD retains the lamellar structure of the ternary metal LDH very well, inheriting low transfer impedance of interlayer ions. Significantly, the selectively generated Co9S8‐QDs expose more abundant active sites, effectively improving the electrochemical properties, such as capacitive performance, electronic conductivity, and cycling stability. Due to the synergistic relationship, the hybrid material delivers an ultrahigh electrochemical capacity of 350.6 mAh g−1 (2504 F g−1) at 1 A g−1. Furthermore, hybrid supercapacitors fabricated with CF@NiCoZn‐LDH/Co9S8‐QD and carbon nanosheets modified by single‐walled carbon nanotubes display an outstanding energy density of 56.4 Wh kg−1 at a power density of 875 W kg−1, with an excellent capacity retention of 95.3% after 8000 charge–discharge cycles. Therefore, constructing hybrid electrode materials by in situ‐created QDs in multimetallic LDHs is promising.
Multistage pump can provide high-pressure liquid, which is widely used in various areas of national economy. In order to improve the stability and reduce the noise of multistage pump, the relationships among the pressure fluctuation, vibration, and noise were studied deeply by using computational fluid dynamics and experimental measurement. Based on the unsteady numerical calculation, the phase of the pressure fluctuation wave in the middle section of the impeller and the diffuser was obtained, and the unsteady velocity distribution was acquired in the rotor-stator interaction (RSI) region between the rotational impeller and the stationary diffuser. Moreover, the vibration and noise tests of a five-stage pump with radial diffuser were performed. The results show that the phase distribution of the pressure fluctuation wave in the impeller and diffuser can be divided into four regions: the impeller flow channel region, the impeller transition region, the diffuser transition region, and the diffuser flow channel region. In addition, the pressure fluctuation, vibration and noise of the multistage pump are strongly related to each other, that is, RSI induces strong unsteady flow and pressure fluctuation in the pump, which makes the pump produce serious vibration and cause the corresponding noise. The key to controlling the vibration and noise is to reduce the effect of RSI between the impeller and the diffuser.
Development of efficient photocatalysts for environmental remediation under visible light conditions has obtained much attention in recent years. In this study, the novel BiVO 4 / Ag 3 VO 4 heterojunction has been successfully fabricated via a hydrothermal process and a facile precipitation reaction. The organic dye Rhodamine B (RhB) was chosen to explore the photocatalytic performance, and it was found that the synthetic sample at 10:1 mol ratio of BiVO 4 :Ag 3 VO 4 had the highest photocatalytic activity among all the photocatalysts. The RhB was completely degraded (95.9%) under visible light irradiation in 20 min, which was 10 times and 3.4 times higher than those of pristine BiVO 4 and Ag 3 VO 4, respectively. Furthermore, the A/10B sample also showed superior degradation activity on the other organic dyes such as methyl blue (MB), methyl red (MR), and methyl violet (MV). It is assumed that the enhanced photocatalytic property could be ascribed to the heterojunction, leading to an effective separation of the photogenerated charges carriers. The responsible photocatalytic mechanism is discussed based on the active species trapping experiments and ESR, and it was found that h + and •OH are for the photocatalytic process.
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