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

Sustainable development requires both CO 2 emission reduction and management of existing greenhouse gases. Utilizing CO 2 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 CO 2 photoconversion capabilities, defect engineering has been employed to modify their structure. Herein, two MOFs – UiO-66 and NH 2 -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 NH 2 -UiO-66 modified by photodeposition of Co (Co dep -NUiO), portrayed by 35% higher yield of reduction of CO 2 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 Co dep -NUiO to photoreduce CO 2 to CO in solid-gas system. Overall, the modification by photodeposition yielded higher number of formed defects and efficiency of CO 2 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. • UiO-66 and NH 2 -UiO-66 were modified during and post synthesis with Ni, Cu, Co. • Photoreduction of CO 2 to HCOOH under Vis and UV-Vis irradiation was investigated. • Presence of missing linkers and missing clusters can improve the photoactivity. • In the presence of Co, the HOCO position in MOF was shifted to the deposited metal. • MMCT is responsible for efficiency boost.