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

Abstract

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 μmol 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 μmol g⁻¹ h⁻¹ and 71 μmol 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.