Piezocatalysis, a newly emerging catalysis technology that relies on the piezopotential and piezoelectric properties of the catalysts, is attracting unprecedented research enthusiasm for applications in energy conversion, organic synthesis, and environmental remediation. Despite the rapid development in the past three years, the mechanism of piezocatalysis is still under debate. A fundamental understanding of the working principles of this technology should enable the future design and optimization of piezocatalysts. Herein, we provide an overview of the two popular theories used to explain the observed piezocatalysis: energy band theory and screening charge effect. A comprehensive discussion and clarification of the differences, relevance, evidence, and contradiction of the two mechanisms are provided. Finally, challenges and perspectives for future mechanistic studies are highlighted. Hopefully, this Review can help readers gain a better understanding of piezocatalysis and enable its application in their own research.

Carbon quantum dots (CQDs) as novel types of emerging materials have aroused tremendous attention in recent years. Herein, we report for the first time a new application of 3D CQD-based composite aerogels as excellent electrode materials for alkaline aqueous batteries. The scalable graphitic CQDs are prepared with high yields (>40%) and further utilized to fabricate the novel nitrogen-doped CQDs/ reduced graphene oxide/porous Fe 2 O 3 (N-CQDs/rGO/ Fe 2 O 3 ) composite aerogels with different contents of Fe 2 O 3 . Benefiting from the unique 3D network composite aerogel structure with a high surface area and hierarchical porous structure as well as the synergistic effect of high-capacity Fe 2 O 3 and highly conductive and stable N-CQDs/rGO, the composite aerogels achieve enhanced electrochemical properties with ultrahigh specific capacity, admirable rate property, and superior cycling performance. Furthermore, the N-CQDs/rGO/Fe 2 O 3 -1 electrode (Fe 2 O 3 , 34.9 wt %) exhibits the best rate capability (72.1, 58.9, and 46.2% capacity retention at 5, 50, and 100 A g −1 , respectively) and cycle performance (80.4% capacity retention at 3 A g −1 over 5000 cycles), while the N-CQDs/rGO/Fe 2 O 3 -3 electrode (Fe 2 O 3 , 62.3 wt %) displays the highest specific capacity (274.1 mA h g −1 at 1 A g −1 ). The current research provides a valuable guidance for developing highperformance 3D CQD-based composite aerogels for application in energy storage systems.

Meeting the escalating demand for clean water resources is one of the key challenges to ensure a sustainable future. Catalysis plays an important role to advance the chemical reactions required for wastewater efficient remediation. How to exploit high-performance catalysts to boost the pivotal reaction kinetics always attracts researchers' enthusiasm. Perovskite oxides as a novel class of functional materials can be tuned to confer compositional flexibilities and provide rich and unique structural properties. As the rising-star material, it has been widely probed for electrocatalysis, photocatalysis, and membrane-catalysis for energy conversion, but received less attention in water treatment. In this review, the advances of perovskite oxides for advanced oxidation processes (AOPs) in water remediation are comprehensively elaborated. A fundamental understanding of the crystal structures and properties of perovskite oxides as well as the basic principles of AOPs is firstly provided. Then, emphasis is placed on how to tune the perovskite oxides to suit various AOPs. The strategies to design novel perovskite oxides to enhance the catalytic activities in AOPs have been highlighted. It is expected that after reading this review, readers will have a clearer vision of the background, the state of the art development, and general guidelines for future directions regarding research in this area.

Small vibration on the order of nanometers poses challenges for the application of aerostatic bearings in ultra-precision machine tools and metrology equipments. In this article, the flow field in aerostatic bearings is numerically investigated and air vortices in the recess are analyzed. Vibration of the aerostatic bearing is also experimentally measured. Design and functioning parameters are varied to study their effects on the air vortices and nano-vibration of aerostatic bearings, and a direct relationship is established between the gas vortices and nanovibration in aerostatic bearings. It is demonstrated that vibration energy of the aerostatic bearing increases with the strength of air vortices.

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An impeller blade with a slot structure can affect the velocity distribution in the impeller flow passage of the centrifugal pump, thus affecting the pump’s performance. Various slot structure geometric parameter combinations were tested in this study to explore this relationship: slot position p, slot width b1, slot deflection angle β, and slot depth h with (3–4) levels were selected for each factor on an L16 orthogonal test table. The results show that b1 and h are the major factors influencing pump performance under low and rated flow conditions, while p is the major influencing factor under the large flow condition. The slot structure close to the front edge of the impeller blade can change the low-pressure region of the suction inlet of the impeller flow passage, thus improving the fluid velocity distribution in the impeller. Optimal slot parameter combinations according to the actual machining precision may include a small slot width b1, slot depth h of ¼ b, slot deflection angle β of 45°–60°, and slot position p close to the front edge of the blade at 20–40%.

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