Potassium and iodine codoped graphitic carbon nitride (CN-KI) photocatalysts were prepared via thermal polymerization of a mixture prepared by dissolving dicyandiamide into a KI solution. Several techniques were employed to characterize the CN-KI photocatalysts and elucidate the mechanisms of the K and I codoping. Compared to pristine CN, CN-KI exhibited a red shift in optical absorption edge, and the electron spin resonance analysis revealed that the enlargement of the visible light response mostly originated from I doping. Then, photoluminescence spectra showed that recombination of photogenerated carriers in CN-KI was retarded compared to that in pristine CN, and electrochemical impedance spectroscopy measurements suggested that the decrease in carrier recombination resulted from K doping because the doping with K into the CN network improved the charge transportation efficiency. Consequently, the K and I codoped g-C 3 N 4 sample with an optimal mass fraction of KI exhibited superior photocatalytic activity over those doped with only K or I owing to the synergistic effect of the K and I doping. This work might shed light on cation−anion codoping for developing high-performance g-C 3 N 4 photocatalysts.
We
report the guest-anion-induced photoluminescence enhancement
of metal–organic frameworks (UiO-66-NH2), first
based upon diffraction and computational evidence. We found that only
limited anions, namely, carbonate and fluoride, can lead to a significant
enhancement in photoluminescence, whereas their related anions, such
as acetate and chloride, cannot. The optimized crystal structures
reveal that the guest carbonate and fluoride ions interact with four
framework amino functional groups through hydrogen bonding (ca. 1.6–1.7
Å) that ultimately forms a quaternary (−N(H))4···X– molecular bridge around the
nodal center. Hence, the hydrogen-bonded molecular bridge not only
restricts the intermolecular C–C rotation of the linker molecules
but also greatly perturbs the electronic densities between the guest
anions and the framework amino groups.
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