Porous Bimetallic Ti-MOFs for Photocatalytic Oxidation\nof Amines in Air

A family of microporous titanium-containing metal–organic\nframeworks (denoted as M<sub>2</sub>Ti-CPCDC, M = Mn, Co, Ni) has\nbeen synthesized by using a bimetallic [M<sub>2</sub>Ti(μ<sub>3</sub>-O)(COO)<sub>6</sub>] cluster and a tritopic carbazole-based\norganic ligand H<sub>3</sub>CPCDC. M<sub>2</sub>Ti-CPCDC are stable\nand display permanent porosity for N<sub>2</sub> and CO<sub>2</sub> uptake, ranking among the most porous titanium-based metal–organic\nframeworks. M<sub>2</sub>Ti-CPCDC crystals exhibit n-type semiconductor\nbehavior. Further catalytic studies demonstrate that all M<sub>2</sub>Ti-CPCDC materials are applicable for triggering photo-oxidative\nreactions of amines in air. More specifically, amines with electron-donating\ngroups afford the aldehydes as the main products, while amines bearing\nelectron-withdrawing groups give rise to imines as the main product.\nAmong them, Mn<sub>2</sub>Ti-CPCDC exhibit the best photocatalytic\nactivity, with conversion of benzylamine up to 99% and selectivity\nof 99%. Mn<sub>2</sub>Ti-CPCDC could be recycled in at least three\nruns while retaining crystallinity and catalytic activity. The reaction\nmechanism indicates that photoinduced hole (h<sup>+</sup>), superoxide\nradical anion (O<sub>2</sub><sup>·–</sup>), and singlet\noxygen (<sup>1</sup>O<sub>2</sub>) are the main active species involved\nin the photo-oxidation process.