Modulating central metals in 2D POMOFs for enhanced photocatalytic reduction of Cr(vi), oxidation of CEES and decolorization of MB

Abstract

Photocatalysis has attracted extensive attention in the field of environmental protection and monitoring due to its eco-friendly and highly efficient characteristics. In this work, three new two-dimensional (2D) polyoxomolybdate (POMo)-based metal–organic complexes (POMo-MOCs), namely [Fe^II(bcbpy)₂(θ-Mo₈O₂₆)_0.5]·2H₂O (BHU-7), [Cu(bcbpy)₂(θ-Mo₈O₂₆)_0.5]·4H₂O (BHU-8) and [Zn(bcbpy)₂(θ-Mo₈O₂₆)_0.5]·2H₂O (BHU-9) (Hbcbpy = 1-(4-carboxybenzyl)-4,4′-bipyridinium), were designed and successfully synthesized by modulating metal centers under hydrothermal conditions, which were constructed from 2D metal-bcbpy networks and [Mo₈O₂₆]⁴⁻ clusters, aiming to investigate the impact of different metal centers on their photocatalytic properties. These POMOFs were well characterized by the infrared (IR) spectra, elemental analysis and powder/single-crystal X-ray diffraction, which exhibited excellent photocatalytic activity toward the reduction of hexavalent chromium (Cr(VI)), oxidation of 2-chloroethyl ethyl sulfide (CEES) and degradation of methylene blue (MB). Among them, BHU-8 exhibited the most impressive photocatalytic activity, which achieved a 99.2% reduction in Cr(VI) within 75 min, a 99.4% conversion rate of CEES with a selectivity for 2-chloroethyl ethyl sulfoxide (CEESO) of 98.1%, and a 96.24% decolorization rate of MB within 70 min. Moreover, the photocurrent, electrochemical impedance spectroscopy and fluorescence spectroscopy measurement results indicated that BHU-8 possessed a higher efficiency in charge separation and migration, leading to its enhanced photocatalytic performance. The photocatalytic mechanism was also investigated in detail.