Defect Tailoring in the Metal–Organic Framework Cu (BDC-NH2) for the High-Efficiency Photocatalytic Reduction of Cr(VI)

Mixed-linker metal–organic frameworks of Cu (BDC-NH2) have been fabricated in which the 2-aminoterephthalic acid (BDC-NH2) linker has been partially replaced by 3,5-pyridinedicarboxylic acid (PYDC) without obviously changing the crystal structure. The pyridine unit, as a defect site in the local coordination environment of the dimitic copper units, can alter the electronic structure. The experimental results of the photocatalytic reduction of Cr­(VI) reveal that defect engineering can effectively modify the performance of metal–organic framework (MOF) materials with a much improved charge separation efficiency, band gap energy, and light adsorption, resulting in a significantly enhanced photocatalytic activity. The apparent rate constant of Cr­(VI) reduction using defective Cu (BDC-NH2) of DE-15 is 3.6 times higher than that of defect-free Cu (BDC-NH2). More interestingly, DE-15 exhibits a relatively higher photocatalytic activity in contrast to the previously reported similar photocatalysts. The insight gained from this study will guide MOF defect engineering for enhancing the Cr­(VI) photocatalytic reduction capacity.