Herein, the visible-light-induced dehydrogenation of N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, and indolines in O2-containing suspensions of a commercially available titanium dioxide photocatalyst yielding the corresponding heteroarenes is presented. 4-Amino-2,2,6,6-tetramethylpipiridinyloxyl (4-amino-TEMPO) was found to exhibit a beneficial role, as it increased the yield and improved the selectivity of the dehydrogenation reaction. Both the selectivity and the yield are further enhanced by grafting 0.1 wt % of Ni­(II) ions onto the TiO2 surface. It is proposed that the basic reactant adsorbs at Lewis acid sites present at the TiO2 surface. The dehydrogenation reaction is initiated by visible-light excitation of the resulting surface complex and a subsequent single-electron transfer from the excited N-heterocycle via the conduction band of TiO2 to O2. Ni­(II) ions possibly serve as an electron transfer bridge between the conduction band of TiO2 and O2, while the TEMPO derivative is assumed to act as a selective redox mediator involved in reactions of the generated reactive oxygen species.

TiO2 is an effective and extensively employed photocatalyst, but its practical use in visible-light-mediated organic synthesis is mainly hindered by its wide band gap energy. Herein, we have discovered that Rh-photodeposited TiO2 nanoparticles selectively dehydrogenate N-heterocyclic amines with the concomitant generation of molecular hydrogen gas in an inert atmosphere under visible light (λmax = 453 nm) illumination at room temperature. Initially, a visible-light-sensitive surface complex is formed between the N-heterocycle and TiO2. The acceptorless dehydrogenation of N-heterocycles is initiated by direct electron transfer from the HOMO energy level of the amine via the conduction band of TiO2 to the Rh nanoparticle. The reaction condition was optimized by examining different photodeposited noble metals on the surface of TiO2 and solvents, finding that Rh0 is the most efficient cocatalyst, and 2-propanol is the optimal solvent. Structurally diverse N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, indolines, and others bearing electron-deficient as well as electron-rich substituents underwent the dehydrogenation in good to excellent yields. The amount of released hydrogen gas evinces that only the N-heterocyclic amines are oxidized rather than the dispersant. This developed method demonstrates how UV-active TiO2 can be employed in visible-light-induced synthetic dehydrogenation of amines and simultaneous hydrogen storage applications.

Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate.

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Halide perovskites have shown great potential in photocatalytic applications. In order to enhance the charge transportation efficiency, the chemical stability, and the light absorption ability, we anchored a lead-free halide perovskite (Cs3Bi2I9) on UV100-TiO2 nanoparticles to build a visiblelight active photocatalysts. The as-prepared material exhibited excellent stability and a remarkable yield for photocatalytic oxidation of methanol to formaldehyde under visible light irradiation. The photocatalyst was characterized using X-ray diffraction, scanning electron microscopy, energydispersive X-ray spectroscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, Brunauer-Emmett-Teller surface area measurement, and photoelectrochemical properties. The analyses confirmed a remarkable improvement of visible-light absorption, a favorable decrease in the recombination of photoinduced charge carriers, and a suitable bandgap for visible-light photocatalytic applications. 2Recycle experiments showed that the composites still presented significant photocatalytic activity after three successive cycles. A possible underlying mechanism of the composite accounting for the enhanced photocatalytic activity under visible light irradiation was proposed.Our study aims to open new possibilities of using lead-free halide perovskites for photocatalytic applications.