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.