The recombination of electron–hole
pairs severely detracts
from the efficiency of photocatalysts. This issue could be addressed
in metal–organic frameworks (MOFs) through optimization of
the charge-transfer kinetics via rational design of structures at
atomic level. Herein, a pyrazolyl porphyrinic Ni-MOF (PCN-601), integrating
light harvesters, active catalytic sites, and high surface areas,
has been demonstrated as a superior and durable photocatalyst for
visible-light-driven overall CO2 reduction with H2O vapor at room temperature. Kinetic studies reveal that the robust
coordination spheres of pyrazolyl groups and Ni-oxo clusters endow
PCN-601 with proper energy band alignment and ultrafast ligand-to-node
electron transfer. Consequently, the CO2-to-CH4 production rate of PCN-601 far exceeds those of the analogous MOFs
based on carboxylate porphyrin and the classic Pt/CdS photocatalyst
by more than 3- and 20-fold, respectively. The reaction avoids the
use of hole scavengers and proceeds in a gaseous phase which can take
full advantage of the high gas uptake of MOFs. This work demonstrates
that the rational design of coordination spheres in MOF structures
not only reconciles the contradiction between reactivity and stability
but also greatly promotes the interfacial charge transfer to achieve
optimized kinetics, providing guidance for the design of highly efficient
MOF photocatalysts.
Solution‐processed metal halide perovskites (MHPs) have attracted much attention for applications in light‐emitting diodes (LEDs) due to their wide color gamut, high color purity, tunable emission wavelength, balanced electron/hole transportation, etc. Although MHPs are very tolerant to defects, the defects in solution‐processed perovskite LEDs (PeLEDs) still cause severe nonradiative recombination and device instability. Here, molecular design of additives for dual passivation of both lead and halide defects in perovskites is reported. A bi‐functional additive, 4‐fluorophenylmethylammonium‐trifluoroacetate (FPMATFA), is synthesized by using a simple solution process. The TFA anions and FPMA cations can bond with undercoordinated lead and halide ions, respectively, resulting in dual passivation of both lead and halide defects. In addition, the bulky FPMA group can constrain the grain growth of 3D perovskite, enhancing electron–hole capture rates and radiative recombination rates. As a result, high‐performance PeLEDs with a peak external quantum efficiency reaching 20.9% and emission wavelength at 694 nm are achieved using formamidinium‐cesium lead iodide‐bromide (FA0.33Cs0.67Pb(I0.7Br0.3)3). Furthermore, the operational lifetime of PeLEDs is also greatly improved due to the low trap density in the perovskite film.
Hydrogen-bonded
organic frameworks (HOFs) show great potential
in many applications, but few structure–property correlations
have been explored in this field. In this work, we report that self-assembly
of a rigid and planar ligand gives rise to flat hexagonal honeycomb
motifs which are extended into undulated two-dimensional (2D) layers
and finally generate three polycatenated HOFs with record complexity.
This kind of undulation is absent in the 2D layers built from a very
similar but nonplanar ligand, indicating that a slight torsion of
ligand produces overwhelming structural change. This change delivers
materials with unique stepwise adsorption behaviors under a certain
pressure originating from the movement between mutually interwoven
hexagonal networks. Meanwhile, high chemical stability, phase transformation,
and preferential adsorption of aromatic compounds were observed in
these HOFs. The results presented in this work would help us to understand
the self-assembly behaviors of HOFs and shed light on the rational
design of HOF materials for practical applications.
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