Dual-Functional Ln-OFs for Efficient Luminescence Sensing and Photoreduction of Cr(VI) without Additional Photosensitizers and Cocatalysts

Six isostructural stable lanthanide metal–organic Frameworks (Ln-OFs), namely, [Ln(ADBA)(HCOO)(DMF)] (Ln = Sm(1), Tb(2), Dy(3), Ho(4), Er(5), Eu(6), H2ADBA = 4,4′-(anthracene-9,10-diyl)dibenzoate, DMF = N,N-dimethylformamide), have been successfully obtained by the solvothermal method based on an aromatic carboxylic acid ligand H2ADBA. 1–6 have a similar three dimensional (3D) network structure with pts topology based on dinuclear metallic clusters {Ln2}. 1–6 all have excellent chemical and thermal stabilities, which is beneficial to carrying out fluorescence sensing and achieving catalytic reactions. 1–6 show admirable fluorescent properties in aqueous solution and can quickly and efficiently detect Fe3+, Cr2O72–, and nitrofurazone (NZF) with high selectivity and excellent sensitivity. Remarkably, upon completion of detection, the Cr2O72– ion in wastewater can be reduced into Cr3+ by photocatalyst 1, which is ascribed to its broad-range visible-light absorption and recyclable stability. During the reduction process, ethanol is an optimal hole scavenger; 1 shows an excellent convert efficiency (99%), a high rate constant (k) of 0.066 min–1, and a high Cr(VI) reduction rate of 0.158 mgCr(VI)·g–1cata·min–1 at pH = 2. Furthermore, photocatalyst 1 can be reused for three cycles without significant loss of catalytic activity. Until now, it is the first example to report that the photocatalytic reduction of Cr(VI) is achieved only by using 3D rare earth MOFs without additional photosensitizers and cocatalysts. The reasonable mechanisms of luminescence sensing and photocatalytic reaction were also investigated systematically via indispensable testing technologies and theoretical simulated calculation.