The influence of non-noble metal-induced MOF defectivity on light-driven CO2 reductionBridge of knowledge

Sustainable development requires both CO2 emission reduction and management of existing greenhouse gases. Utilizing CO2 as a substrate in light-assisted catalytic reactions is promising, particularly with metal-organic frameworks (MOFs) due to their high surface area and selectivity. However, achieving sufficient charge separation remains crucial for larger-scale application. To enhance MOFs' light-driven CO2 photoconversion capabilities, defect engineering has been employed to modify their structure. Herein, two MOFs – UiO-66 and NH2-UiO-66 – were modified by synthetical incorporation and post-synthetical photodeposition of Cu, Co and Ni, resulting in an increased amount of both missing linkers and clusters. Notably, the highest photocatalytic activity was observed for NH2-UiO-66 modified by photodeposition of Co (Codep-NUiO), portrayed by 35% higher yield of reduction of CO2 to HCOOH in solid-liquid system and an increased number of missing linkers and clusters up to 30% and 12%, respectively, compared to the pristine sample. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed the ability of Codep-NUiO to photoreduce CO2 to CO in solid-gas system. Overall, the modification by photodeposition yielded higher number of formed defects and efficiency of CO2 photoreduction than by incorporation. To provide holistic understanding of the experimental results, adsorption properties were modeled using DFT and classical simulations to assess binding energy and geometries among others. Simulations revealed change of frontier orbitals location after the introduction of Co, which enabled metal-to-metal transfer. The presented results provide the foundations for further increase of MOFs effectiveness in photocatalysis by adjusting the defectivity and chemical composition.