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Solar photocatalysis is the key to resolve many environmental challenges but is usually hard to achieve over a metal oxide semiconductor. Therefore, assembling π-conjugated molecules onto semiconductors becomes an efficient approach to solar conversion via ligand-to-metal charge transfer. Here, a rational design of ligands for titanium dioxide (TiO 2 ) is presented to produce robust visible light photocatalysts. Three hydroxynaphthoic acids (HNAs) were selected as ligands by extending an extra benzene ring of salicylic acid (SA) at 3,4 or 4,5 or 5,6 positions. These ligands could regulate the performance of TiO 2 in which 2-hydroxy-1-naphthoic acid (2H1NA) endows the best outcome. In detail, blue light-powered cooperative photocatalysis of 2H1NA-TiO 2 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 5 mol%) inaugurates the expeditious formation of imines by oxidation of amines with atmospheric oxygen (O 2 ). Interestingly, the increase of the O 2 pressure from 1 atm to 0.4 MPa promoted the selective oxidation of benzylamine but thereafter declined with a further boost to 0.6 MPa. Notably, an electron transfer between the oxidatively quenched 2H1NA-TiO 2 and TEMPO is established, offering a new pathway for environmental applications. This work presents a strategy in designing cutting-edge visible light photocatalysts via altering semiconductors with surface ligands., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

[Display omitted] • Nb 2 O 5 nanorods are synthesized with a specific surface area of 166 m2/g. • The dissociative adsorption of amine on Nb 2 O 5 affords a surface complex. • The surface complex can facilitate selective oxidation of amine to imine. • TEMPO+PF 6 − acts as an electron–proton transfer mediator. • Superoxide is the dominant reactive oxygen species. Cooperative photocatalysis has gained increasing interest to better an existing redox reaction with a mediator. Herein, an ingenious system is constructed for the visible light-driven selective oxidation of a variety of amines by merging niobium oxide (Nb 2 O 5) photocatalysis with an electron–proton transfer mediator, 2,2,6,6-tetramethylpiperidine-1-oxoammonium hexafluorophosphate (TEMPO+PF 6 −). The visible light-driven dissociative adsorption of amine over Nb 2 O 5 nanorods gives rise to an amine–Nb 2 O 5 complex with a weak response to visible light (λ < 460 nm). With adding 4 mol% of TEMPO+PF 6 −, the conversion of benzylamine over Nb 2 O 5 is approximately 2.5 times that without TEMPO+PF 6 −. The proton and electron transfer between the amine–Nb 2 O 5 complex and TEMPO+PF 6 − is the key to assuring cooperative photocatalysis. Besides, the oxidant dioxygen is predominantly reduced to superoxide anion in affording the imine products. This work highlights it is feasible to ameliorate selective organic conversions over metal oxide photocatalysts with a suited mediator. [ABSTRACT FROM AUTHOR]

[Display omitted] • Semiconductor materials are the key to anchor visible light-active dye molecules. • 1D Nb 2 O 5 nanorods with a specific surface area of 264.3 m2•g−1 are synthesized. • Dye-Nb 2 O 5 nanorods can facilitate the green light-driven selective oxidation of amines in air. • TEMPO enhances photocatalytic efficiency. • Superoxide (O 2 •−) is the central reactive oxygen species. Visible light-driven photocatalysis over semiconductors has emerged as one of the most desired strategies for animating diverse selective chemical transformations. Herein, one-dimensional (1D) Nb 2 O 5 nanorods with a specific surface area of 264 m2•g−1 were synthesized via a straightforward hydrothermal method. Thereafter, an efficient visible light photocatalyst was constructed by in-situ anchoring of alizarin red S (ARS) onto the Nb 2 O 5 nanorods to afford ARS-Nb 2 O 5. Resultantly, the ARS-Nb 2 O 5 nanorods can facilitate the selective aerobic oxidation of amines into imines, affording about twice of the result over 3D hierarchical Nb 2 O 5. Notably, 2,2,6,6-tetramethylpiperidine- N -oxyl (TEMPO) could synchronize the intricate electron and proton transfers between ARS-Nb 2 O 5 nanorods, amines, and superoxide (O 2 •−). In most cases, the green light-driven primary and secondary amines into imines could be completed with about 95% selectivity within 2 h. This work highlights the dimension of designing semiconductor materials to anchor visible light-active molecules for selective oxidation reactions under benign conditions. [ABSTRACT FROM AUTHOR]

The selective aerobic oxidation of benzylamine by cooperative ARS-TNTs photocatalysis with TEMPO+BF 4 −. [Display omitted] • Anatase TNTs deliver outstanding photocatalytic activity. • ARS binds with TNTs through surface hydroxyl sites. • Electron transfer occurs smoothly between ARS-TNTs and TEMPO+BF 4 −. • With increased polarity, TEMPO+BF 4 − can increase cooperative photocatalysis. • Green light-driven selective aerobic oxidation of amines has been achieved. Visible light photocatalysis could offer an eco-friendly alternative for selective transformation of organic molecules. Herein, a cooperative system is created with alizarin red S (ARS), TiO 2 nanotubes (TNTs), and an extra redox mediator. The electron transfer between oxidatively quenched ARS-TNTs and the redox mediator is the key to secure cooperative photocatalysis. The selective aerobic oxidation of primary and secondary amines was constructed by cooperative photocatalysis of ARS-TNTs with 2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (TEMPO+BF 4 −) driven by green light. Specifically, the activity of anatase TNTs could reach about 2.2 times that of the P25 (Aeroxide P25) TiO 2 precursor. Due to increased polarity, TEMPO+BF 4 − serves more efficiently for electron transfer than (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), conferring above 1.5 times of activity that of TEMPO for the selective aerobic conversion of amines. This work features the potential of designing redox mediators in amplifying cooperative photocatalysis driven by visible light. [ABSTRACT FROM AUTHOR]