Photocatalytic reduction of environmental pollutant Cr (VI) in a pillared metal–organic framework by Solvent-Assisted Ligand exchange.

Metal–organic frameworks (MOFs) are an attractive class of hybrid materials that incorporate the rigidity of inorganic compounds with the flexibility and the tunability of organic materials.1 Solvent-assisted linker exchange (SALE) is a postsynthesis route that has been approved as a practical strategy to alter the structures and properties of MOFs.2 Organic ligand substitutions which take place at metal ions are essentially attributed to the reversible nature of the coordination bonds between metal ions and organic ligands in MOFs. SALE can provide pore engineering mechanisms including the control of the pore volume and environment while creating missing linker “defects” at metal centers.3 Moreover, SALE enhances MOF performance in gas uptake, catalysis, proton conductivity, etc.4 Herein, SALE was performed on a pillared metal–organic framework (MOF), [Zn2(oba)2(4-bpdb)]n•(DMF)2 (TMU-4), to tune their photocatalytic properties. The pillar ligands were successfully incorporated into this MOFs to generate daughter MOFs TMU-4′ and TMU-6′, which possess higher BET surface areas. Moreover, a study was performed to examine the photocatalytic performance of these parent and daughter MOF in photoreduction of Cr(VI) under visible light irradiation. Finally, the reduction mechanism was investigated by using various scavengers including AgNO3, t-butyl alcohol, BQ and ammonium oxalate