The conversion of solar-powered carbon dioxide (CO2) into value-added fuels can help mitigate the greenhouse effect and achieve a sustainable society. Natural catalysts are attracting attention due to their environmentally friendly, efficient, and precise substrate specificity. The catalytic activity of enzymes in nature is usually higher than the metal sites they determine. For example, chloroplast's photosynthetic hydrolytic enzyme has a Mn4Ca cluster at its active site.
However, due to the inherent shortcomings of biocatalysts, such as poor thermal stability, poor acid and alkali resistance, and reduced performance in organic solvents, their widespread application still faces challenges. By simulating the key catalytic centers of natural enzymes, titanium oxide clusters with atomic precision with defined structures are expected to replace traditional metalloenzymes, and combine the advantages of homogeneous and heterogeneous catalysis to promote the development of biomimetic catalysis.
The structure and properties of titanium clusters depend primarily on the geometrical and electronic properties of the selected metal and organic nodes, where uncoordinated metal sites can be fully exposed, thereby activating the CO2 molecule. In addition, its precise crystal structure is conducive to understanding the reaction mechanism of photochemical reduction of CO2 from a molecular perspective.
Recently,Zhang Jian, Fujian Institute of Physical Structure, Chinese Academy of ScienceswithKing Abdullah University of Science and Technology (KAUST) Zhang HuabinA Ti4Mn3 cluster with a clear interface was designed for photocatalytic reduction of CO2. These Ti4Mn3 clusters are arranged into a superstructure with honeycomb channels, and this highly ordered packing gives them advanced structural arrangement and directed migration of photo-induced carriers, and photogenerated carriers can be efficiently utilized through surface reactions.
The experimental results showed that the CO yield of Ti4Mn3 clusters was as high as 378 mol g 1 h 1 at 365 nm with a quantum efficiency (qe) of CO2 photoreduction to Co is 001% with a turnover frequency (TOF) of 005 h−1。In addition, the activity of Ti4Mn3 clusters did not decrease significantly after three cycles, and the morphology and structure remained intact.
Spectral characterization and theoretical calculations showed that the high CO2 reduction activity of Ti4Mn3 clusters was attributed to the synergistic effect between the active Mn sites and the surrounding functional microenvironment.
Specifically, compared with the Ti4CO3 cluster and the Ti4 cluster, the ability to capture electrons at the Mn site in the Ti4M3 cluster is stronger, and the separation efficiency of photogenerated electron-hole pairs is higher. At the same time, compared with Co-Co*, Mn-Co* exhibited lower bond orbital filling and higher anti-bond gift, indicating that the interaction between the active site of Mn and the adsorbed Co* was relatively weak, which contributed to the release of Co products during the reaction.
In conclusion, the undercoordinated MN site not only reduces the reaction energy barrier, but also has a moderate CO* adsorption strength, thereby accelerating the charge separation kinetics and improving the CO2 photoreduction activity.
bioinspired polyoxo-titanium cluster for greatly enhanced solar-driven co2 reduction. nano letters, 2023. doi: 10.1021/acs.nanolett.3c03304