Reinforcing the carrier separation is the key issue to maximize the photocatalytic hydrogen evolution (PHE) efficiency of graphitic carbon nitride (g-C N ). By a surface engineering of gradual doping of graphited carbon rings within g-C N , suitable energy band structures and built-in electric fields are established. Photoinduced electrons and holes are impelled into diverse directions, leading to a 21-fold improvement in the PHE rate.
Covalent organic frameworks (COFs)
with porphyrins as
structural
units are a new kind of porous organic polymers, which have a regular
and ordered structure, abundant porosity, and good stability. In the
past, the construction of porphyrin COFs was generally synthesized
by routes such as a Schiff base reaction. Here, we report a new COF
structure by linking the porphyrin with the triazine ring. Using a
cyano group-terminated porphyrin as a structural unit precursor, a
new triazine-porphyrin hyperconjugated COF (TA-Por-sp2-COF)
was constructed through the cyano group’s self-polymerization.
The extension of porphyrin units in two directions that stemmed from
the cyano group at para-positions accounts for the
establishment of a highly ordered two-dimensional topological structure.
Attributing to the collaboration of electron-donating and withdrawing
blocks for photo-induced carrier separation and adequate porosity
for mass diffusion, this hyperconjugated system showed high photocatalytic
performance in organic reactions such as the aerobic coupling reaction
of benzylamine and thioanisole selective oxidation.
Inter-site interaction in densely populated single-atom catalysts has been demonstrated to have a crucial role in regulating the electronic structure of metal atoms, and consequently their catalytic performances. We herein report a general and facile strategy for the synthesis of several densely populated single-atom catalysts. Taking cobalt as an example, we further produce a series of Co single-atom catalysts with varying loadings to investigate the influence of density on regulating the electronic structure and catalytic performance in alkene epoxidation with O2. Interestingly, the turnover frequency and mass-specific activity are significantly enhanced by 10 times and 30 times with increasing Co loading from 5.4 wt% to 21.2 wt% in trans-stilbene epoxidation, respectively. Further theoretical studies reveal that the electronic structure of densely populated Co atoms is altered through charge redistribution, resulting in less Bader charger and higher d-band center, which are demonstrated to be more beneficial for the activation of O2 and trans-stilbene. The present study demonstrates a new finding about the site interaction in densely populated single-atom catalysts, shedding insight on how density affects the electronic structure and catalytic performance for alkene epoxidation.
In the exploration of synthesizing graphitic carbon nitride (g-C3N4), the existence of secondary anime bridging units shows the incompleteness of related theories.
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