| Sumario: | Simulated sunlight driven overall water splitting has been carried out using porphyrin-based PCN-222 metal-organic frameworks having none or Zn, Fe, Mn and Co metal ion at the porphyrin linker. Influence of the transition metal on the photocatalytic water splitting reaction was systematically studied filling the existing gap. Under simulated sunlight irradiation, PCN-222(Zn) shows the highest H evolution reaction (HER) efficiency, reaching almost 1.5 mmol of H per gram of photocatalyst by using MeOH, which corresponds to the HER rate of 65.8 μmol g h that is higher than some examples of porphyrinic MOFs with Pt. In addition to this, as the valence band (VB) levels of PCN-222(M) gets more positive than that of water oxidation potential, O evolution was detected in a quasi stoichiometric ratio respect to H. To gain insights into the mechanism of the H and O evolution, transient absorption (TA) spectroscopy measurements were carried out, providing a strong evidence of the generation of a charge separated state and that the positive holes are able to oxidize HO in the microsecond time. This study not only provides new insights for overall water splitting applications of porphyrin-based MOFs without using noble metal co-catalysts, but also shed light on future experiments for construct sustainable photocatalysts for important yet thermodynamically uphill reactions.
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