To construct photocatalytically active MOFs, various strategies have recently been developed. We have synthesized and characterized a new metal-organic framework (MOF-253-Pt) material through immobilizing a platinum complex in 2,2 0 -bipyridine-based microporous MOF (MOF-253) using a post-synthesis modification strategy.The functionalized MOF-253-Pt serves both as a photosensitizer and a photocatalyst for hydrogen evolution under visible-light irradiation. The photocatalytic activity of MOF-253-Pt is approximately five times higher than that of the corresponding complex. The presence of the short Pt/Pt interactions in the framework was revealed with extended X-ray absorption fine structure (EXAFS) spectroscopy and low temperature luminescence. These interactions play an important role in improving the photocatalytic activity of the resulting MOF.
Vacancy
engineering, that is, self-doping of vacancy in semiconductors,
has become a commonly used strategy to tune the photocatalytic performances.
However, there still lacks fundamental understanding of the role of
the vacancies in semiconductor materials. Herein, the g-C3N4 nanosheets with tunable nitrogen vacancies are prepared
as the photocatalysts for H2 evolution and CO2 reduction to CO. On the basis of both experimental investigation
and DFT calculations, nitrogen vacancies in g-C3N4 induce the formation of midgap states under the conduction band
edge. The position of midgap states becomes deeper with the increasing
of nitrogen vacancies. The g-C3N4 nanosheets
with the optimized density of nitrogen vacancies display about 18
times and 4 times enhancement for H2 evolution and of CO2 reduction to CO, respectively, as compared to the bulk g-C3N4. This is attributed to the synergistic effects
of several factors including (1) nitrogen vacancies cause the excitation
of electrons to midgap states below the conduction band edge, which
results in extension of the visible light absorption to photons of
longer wavelengths (up to 598 nm); (2) the suitable midgap states
could trap photogenerated electrons to minimize the recombination
loss of photogenerated electron–hole pairs; and (3) nitrogen
vacancies lead to uniformly anchored small Pt nanoparticles (1–2
nm) on g-C3N4, and facilitate the electron transfer
to Pt. However, the overintroduction of nitrogen vacancies generates
deeper midgap states as the recombination centers, which results in
deterioration of photocatalytic activities. Our work is expected to
provide new insights for fabrication of nanomaterials with suitable
vacancies for solar fuel generation.
A nitrogen-doped Co3(PO4)2@nanocarbon hybrid was developed as an oxygen reduction reaction (ORR) catalyst and exhibits outstanding catalytic performance with high activity, long-term stability and a four-electron transfer pathway.
Cobalt
phosphate is considered to be one of the most active catalysts
for the oxygen evolution reaction (OER) in neutral or near-neutral
pH media, but only a few transition-metal phosphates are investigated
in alkaline media, probably due to their poor intrinsic electrical
conductivity and/or tendency to aggregate. Herein, in situ-formed
cobalt phosphate decorated with N-doped graphitic carbon was prepared
using phosphonate-based metal–organic frameworks (MOFs) as
the precursor. It can serve as a highly active OER catalyst in alkaline
media, affording a current density of 10 mA cm–2 at a small overpotential of 215 mV on the Ni foam. A combination
of X-ray absorption spectroscopy and high-resolution XPS elucidates
the origin of the high activity. Our observations unveil that cobalt
diphosphate having the distorted metal coordination geometry with
long Co–O and Co–Co distances is mainly responsible
for the high OER activity. These results not only demonstrate the
potential of a low-cost OER catalyst derived from phosphonate-based
MOF but also open a promising avenue into the exploration of highly
active and stable catalysts toward replacing noble metals as oxygen
evolution electrocatalysts.
Photocatalytic reduction of CO2 to value‐added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to maximumly expose the active sites is the key to activate CO2 molecules and determine the reaction selectivity. Herein, we synthesize a well‐defined copper‐based boron imidazolate cage (BIF‐29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO2. Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady‐state and time‐resolved fluorescence spectra show these Cu sites promote the separation of electron–hole pairs and electron transfer. As a result, the cage achieves solar‐driven reduction of CO2 to CO with an evolution rate of 3334 μmol g−1 h−1 and a high selectivity of 82.6 %.
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