Amino-functionalized MIL-125(Ti) for photodenitrification of pyridine in fuels via coordination activation by unsaturated Ti 4+ centers.

Due to their explicit structure, metal-organic frameworks (MOFs) have been supposed to be credible platforms to research the micro-mechanism of heterogeneous photocatalysis. In this study, amino-functionalized MOFs (MIL-125(Ti)-NH (denoted as MTi), UiO-66(Zr)-NH (denoted as UZr) and MIL-68(In)-NH (denoted as MIn)) with three different metal centers were synthesized and applied for the denitrification of simulated fuels under visible light irradiation, during which pyridine was used as a typical nitrogen-containing compound. The results showed that MTi had the best activity among the above three MOFs, and the denitrogenation rate increased to 80% after 4 h of visible light irradiation. On the grounds of the theoretical calculation of pyridine adsorption and actual activity experiments, it can be presumed that the unsaturated Ti metal centers should be the key active sites. Meanwhile, the XPS and infrared results verified that the coordinatively unsaturated Ti sites facilitate the activation of pyridine molecules through the surface -N⋯Ti- coordination species. The coordination-photocatalysis synergism promotes the efficiency of photocatalytic performance and the corresponding mechanism is proposed.