N-hydroxyphthalimide-TiO2 complex visible light photocatalysis

• Published in: Applied catalysis. B, Environmental Environmental, 2019-06, Vol.246, p.149-155
• Main Authors: Hao, Huimin, Shi, Ji-Long, Xu, Hui, Li, Xia, Lang, Xianjun
• Format: Article
• Language: English
• Subjects: Amines; Binding sites; Catalysis; Catalysts; Electron transfer; Energy conversion; Imines; Irradiation; Molecular oxygen; N-hydroxyphthalimide; Organic chemistry; Oxidation; Photocatalysis; Photocatalysts; Radiation; Reactive oxygen species; Redox reactions; Superoxide; Surface complex; TEMPO; Titanium dioxide
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.01.037

[Display omitted] •N-hydroxyphthalimide (NHPI) can be complexed with TiO2 surface with covalent bonding.•NHPI-TiO2 complex an efficient visible light photocatalyst for selective oxidation.•Cooperative photocatalysis strategy was applied in the system.•NHPI is especially stable surface ligand for aerobic oxidation.•Selective aerobic oxidation of amines into imines has been accomplished with NHPI-TiO2 complex. TiO2 is the most established semiconductor photocatalyst. The prominence of TiO2 is becoming increasingly obvious because its interfacial redox reactions have implication on a wide range processes such as energy conversion and environmental remediation. Herein, we exploited the surface complex created by the interaction between organic molecules with binding sites and accommodating surface of TiO2 for visible light-driven selective aerobic oxidation reactions. A novel surface complex formed between N-hydroxyphthalimide (NHPI) and TiO2 was discovered. The NHPI-TiO2 complex turned out to be an outstanding visible light photocatalyst and was successfully used in the selective oxidation of amines into imines with atmosphere O2 under blue LED irradiation. The stability of the NHPI-TiO2 complex was preserved by 3 mol% of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) acting as a cooperative catalyst. Moreover, selectivities for the imine products were also promoted by TEMPO. Superoxide anion radical (O2−) were evidenced to be the primary reactive oxygen species (ROS) to execute the oxidative conversions. This work suggests that TiO2 surface complexes can be robust photocatalysts for visible light-driven selective aerobic reactions, provided that an appropriate cooperative redox catalyst exists to channel the photocatalytic electron transfer.