Amino-functionalized MIL-125(Ti) for photodenitrification of pyridine in fuels via coordination activation by unsaturated Ti4+ centers

Abstract

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)–NH₂ (denoted as MTi), UiO-66(Zr)–NH₂ (denoted as UZr) and MIL-68(In)–NH₂ (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 Ti⁴⁺ metal centers should be the key active sites. Meanwhile, the XPS and in situ infrared results verified that the coordinatively unsaturated Ti⁴⁺ 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.