Nitrogen dopants of carbon materials remarkably improve the stability and tune the catalytic performance of supported metal nanoparticles. However, it is still controversial how the Pd−N metal−support-interaction (MSI) influences the catalysis. Herein, the density function theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) were combined to rationalize the Pd−N MSI. DFT calculations suggested that Pd adsorbs on N-doped carbon nanotubes (N@CNTs) and donates electrons to pyridinic nitrogen. It was further experimentally proved using XPS through a titration method by gradually increasing Pd content or changing the N content of support by a postheat-treatment. The Pd catalysts display electron-deficiency depending on the intensity of MSI between Pd and pyridinic nitrogen, measured by Pd 3d binding energy. It paves the way to the rational synthesis of Pd catalysts with a tunable electronic state for the targeted catalytic reaction. Using the hydrogenation of nitrobenzene as the probe reaction, it was revealed that the reaction activity can be facilely tuned by the Pd−N MSI, due to the strong adsorption of nitro-groups on electron-deficient Pd nanoparticles.
Na-ion cathode materials cycling at high voltages with long cycling life and high capacity are of imminent need for developing future high-energy Na-ion batteries. However, the irreversible anionic redox activity of Na-ion layered cathode materials results in structural distortion and poor capacity retention upon cycling. Herein, we develop a facile doping strategy by incorporating copper into the layered cathode material lattice to relieve the irreversible oxygen oxidation at high voltages. On the basis of a comprehensive comparison with the Cu-free material, both the overoxidation of O 2− to trapped molecular O 2 and Mn-related Jahn−Teller distortion have been effectively inhibited by restraining both the oxygen activity and participation of Mn 4+ /Mn 3+ redox activity. Not limited to discovering stable cycling behavior at high voltages after Cu substitution, our findings also highlight an effective strategy to stabilize the anionic redox activity and elucidate the stabilization mechanism of Cu substitution, thus paving the way for further improvement of layered oxide cathode materials for high-energy Na-ion batteries.
Engineering
biological interfaces represents a powerful means to improve the performance
of biosensors. Here, we developed a DNA-engineered nanozyme interface
for rapid and sensitive detection of dental bacteria. We employed
DNA aptamer as both molecular recognition keys and adhesive substrates
to functionalize the nanozyme. Utilizing different immobilization
strategies and DNA designs, a range of DNA nanoscale biointerfaces
were constructed to modulate enzymatic and biological properties of
the nanozyme systems. These functional biointerfaces improved the
accessibility of bacteria to the nanozyme surface, providing large
signal change range at optimal DNA probe density. The DNA-functionalized
nanozymes demonstrate a rapid, label-free, and highly sensitive direct
colorimetric detection of Streptococcus mutans, with a detection limit of 12 CFU mL–1, as well
as excellent discrimination from other dental bacteria. We demonstrate
the use of this biological nanointerface for identifying dental bacteria
in salivary samples, showing its potential in clinical prevention
and diagnosis of dental diseases.
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