Post-synthetic exchange in a zirconium metal-organic framework for efficient photoreduction of CO2 to formate

The reduction of CO2 to useful products such as formic acid is of immense industrial importance. In the present report, we have studied the CO2 reduction performance of a Zr MOF and its titanium-exchanged analogs. A naphthalene diimide tetracarboxylic acid (TNDI) linker-based metal-organic framework with zirconium metal was synthesized for effective photocatalytic CO2 reduction in aqueous medium. This water-stable MOF was able to achieve formate production at a rate of 38 mu mol g(-1) h(-1). Higher production rates and yields were achieved through the post-synthetic metal exchange of Zr with Ti. The new mixed metal MOF with 20% and 30% exchange of Zr with Ti metal resulted in the reduction of the band gap of the pristine MOF, which led to higher production rates of 50 mu mol g(-1) h(-1) and 71 mu mol g(-1) h(-1) of formate, respectively. Detailed photocatalytic experiments have been carried out to understand the mechanism of the enhancement of the formate production upon exchange with Ti metal.