A Cu-II-based Metal-Organic Framework as an Efficient Photocatalyst for Direct Hydroxylation of Benzene to Phenol in Aqueous Solution

A Cu-II-based metal-organic framework (MOF; 1), constructed with imidazole carboxylate ligands (5-(1H-imidazol-1-yl)isophthalic acid) and copper(II) ions was prepared and characterized in detail by XRD, Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and IR methods. Its catalytic performance for the direct hydroxylation of benzene to phenol has been investigated. A benzene conversion of 29% as well as a high phenol selectivity above 95% has been obtained at 60 degrees C in water. The cycling tests showed no significant decrease after five runs, indicating good stability and reuse properties of the Cu-II-based MOF (1). The effect of adding the hydroxyl radical scavenger, thiourea, and the ESR spectra of the catalytic system have confirmed the existence of hydroxyl radicals, which indicates the catalytic mechanism follows a Fenton-type route. This economically and environmentally friendly approach with Cu-II-based MOFs is expected to find applications in the hydroxylation of aromatics.