Stable and improved visible-light photocatalytic hydrogen evolution using copper(ii)–organic frameworks: engineering the crystal structures

Abstract

Relatively high photocatalytic H₂ production activities can be exhibited by metal–organic framework (MOF) materials using a compulsory cocatalyst or photosensitizer. However, no study has focused on the effect of the crystal structures of MOF materials on the photocatalytic H₂ evolution activity when using the same organic ligand and metal ion. Therefore, by connecting the 4′-(2,4-disulfophenyl)-3,2′:6′,3′′-terpyridine (H₂DSPTP) organic ligand with CuSO₄·5H₂O, different MOF photocatalyst crystalline structures, (1) and (2), were obtained. These products were then respectively characterized and employed for photocatalytic H₂ evolution. In the absence of any photosensitizer and cocatalyst, compounds 1 and 2 exhibited efficient visible-light-driven photocatalytic H₂ production at maximum rates of 5.77 μmol h⁻¹ and 6.99 μmol h⁻¹. Interestingly, compounds 1 and 2 also exhibited photocatalytic H₂ generation when irradiated with near-infrared light. Compound 2 showed outstanding long-term stability, as evidenced by eight-cycle tests over 24 h. The charge separation and transfer process of the compounds were verified using PL, time-resolved PL spectroscopy, and photocurrent measurements.