The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (H NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.
The flexible self-supporting electrode can maintain good mechanical and electrical properties while retaining high specific capacity, which meets the requirements of flexible batteries. Lithium-sulfur batteries (LSBs), as a new generation of energy storage system, hold much higher theoretical energy density than traditional batteries, and they have attracted extensive attention from both the academic and industrial communities. Selection of a proper substrate material is important for the flexible self-supporting electrode.Carbon materials, with the advantages of light weight, high conductivity, strong structural plasticity, and low cost, provide the electrode with a large loading space for the active material and a conductive network. This makes the carbon materials meet the mechanical and electrochemical requirements of flexible electrodes. In this paper, the commonly used fabrication methods and recent research progresses of the flexible self-supporting cathode with a carbon material as the substrate are introduced. Various sulfur loading methods are summarized, which provides useful information for the structural design of the cathode. As the first review article of the carbon-based flexible self-supporting LSB cathodes, it provides valuable guidance for the researchers working in the field of LSB.
In the present work, coal fly ash-derived mesoporous silica material (CFA-MS) has been successfully fabricated without employing any extra silica source. The obtained CFA-MS was characterized by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption measurement, powder X-ray diffraction and transmission electron microscopy. Nitrogen adsorption-desorption measurement disclosed that CFA-MS possesses Brunauer-Emmett-Teller-specific surface area of 497 m 2 Ág À1 and pore volume of 0.49 cm 3 Ág À1 , respectively. Furthermore, CFA-MS was evaluated for the adsorptive removal of methylene blue from aqueous solution. Several influence parameters on the removal of methylene blue including contact time, pH, initial concentration and temperature were studied in detail. Moreover, Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were employed for interpretation of the adsorption process, while the pseudo-first-order and pseudo-second-order kinetics equations were applied to investigate the adsorption kinetics. Results in the current work demonstrate that CFA-MS can be used as an efficient adsorbent for methylene blue removal.
With the extensive use of palladium derivatives in the industry, their environmental pollution has become more and more serious. Herein, allyl functionalized hydrazone 2D COFs (XB-COFs) were found for selective fluorescent detection of Pd 2+ (detection concentration of 0.29 μM) in water. The stable structure of the hydrazone bond and the complexation ability of allyl to Pd 2+ cause XB-COF to have a good fluorescence sensing effect in both acid and alkaline solutions, and its adsorption capacity for Pd 2+ is up to 120 mg g −1 .During the interaction between XB-COF and Pd 2+ , a part of Pd 2+ can be reduced to Pd nanoparticles with a diameter of about 10 nm. A fluorescent test paper was prepared by the in situ growth of XB-COF onto a filter paper, which can realize visualization detection of Pd 2+ in 10 s with the naked eye or under a 365 nm UV lamp. This is the first time a fluorescent test paper based on in the situ growth of COFs has been applied for the detection of heavy metal ions, which provides a new platform for the application of COF materials in the medical health field, food safety, and environmental protection.
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