Construction of the copper metal-organic framework (MOF)-on-indium MOF Z-scheme heterojunction for efficiently photocatalytic reduction of Cr (VI)

A novel two-dimensional (2D)-on-3D metal-organic framework (MOF) "dimensionality-hybrid" heterostructure was established by the anisotropic growth method and exploited as the robust photocatalyst to efficiently remove Cr(VI) ions in the polluted water system under visible irradiation. The 2D Cu-MOF nanosheet was in situ grown around the 3D In-MOF nanorods, thus forming the MOF-on-MOF Z-scheme heterojunction (denoted as CuMOF@In-MOF). Benefiting to the large specific surface area (718.1 m2 g-1) and promoted the photo absorption property within visible-light region, the attained Cu-MOF@In-MOF heterojunction exhibited the remarkably enhanced separation ability of photocarriers and electron transfer. Comparing with the sole MOFs (Cu-MOF and In-MOF) the 2D/3D Cu-MOF@In-MOF Z-scheme heterojunction demonstrated high photocatalytic reduction efficiency toward Cr(VI) (98%) within 1 h under visible-light irradiation (50 mg/L, pH 5.4), markedly higher than those of the sole MOFs and most of reported photocatalysts (50 mg/L, pH 5.4). Moreover, the photocatalysis mechanism of the Cr(VI) reduction by Cu-MOF@In-MOF was provided based on the analysis of energy band structure trapping experiments and electron spin resonance results. The presented MOF-on-MOF photocatalyst shows the synergistic effect of various components for efficiently photocatalytic removal of harmful pollutants in water, thus giving the great potential applications in environmental governance field.