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An unprecedented visible-light-driven photocatalytic system consisting of Pd nanoparticles stabilized on g-C3N4-imine-functionalized TiO2 nanoparticles was discovered for photoassisted hydrogen generation followed by olefin hydrogenation under mild conditions. The structural integrity of the as-synthesized photocatalyst was corroborated by Fourier transform infrared spectroscopy, X-ray powder diffraction, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-diffuse reflectance spectroscopy, Brunauer-Emmett-Teller measurements, and thermogravimetric analysis (TGA). Transmission electron microscopy and high-resolution scanning electron microscopy revealed the nanoscopic nature of the catalyst. The photocatalyst promoted several different transformations in a one-pot reaction sequence: hydrogen evolution through photocatalytic acceptorless formation of benzimidazoles as important therapeutic agents followed by visible-light-driven photocatalytic reduction of olefins with a high hydrogen utilization efficiency of up to 92% under mild conditions. A significant volume of H2 was produced under blue light-emitting diode (LED) irradiation during the selective formation of benzimidazole, while the selectivity reduced significantly under a Xe lamp or in the dark. The in situ-generated H2 could be activated by the as-prepared Pd-C3N4-imine/TiO2 photocatalyst to effectively hydrogenate olefins under mild conditions at appropriate time exposed to blue LED irradiation. The light-dependent photocatalytic performance of the title catalyst was assessed using action spectra by calculating the apparent quantum efficiency (AQE), which exhibited the maximum AQEs at 410 and 550 nm, at which the highest performance for styrene hydrogenation was obtained. The improved photoredox activity of the title nanohybrid could be caused by the synergistic effects of the heterojunction of carbon nitride-Pd on TiO2 nanoparticles evidenced by photoluminescence spectra and catalytic reactions. The catalyst proved to be air-stable, robust, recyclable, and very active in the absence of any undesirable additives and reducing agents. Thus, this work presents a new protocol for improving the photocatalytic properties of semiconducting materials for various photocatalytic applications under environmentally friendly conditions.

The incorporation of Cu(OAc)2 into ascorbic acid coated TiO2 nanoparticles easily provided a new heterogeneous visible-light active titania-based photocatalyst (TiO2-AA-Cu(II)) which was characterized by different techniques such as FT-IR, XPS, ICP-AES, TGA and TEM. A red-shift of the band-edge and a reduction of the band-gap (2.8 eV vs. 3.08 for TiO2) were demonstrated by UV-DRS and Tauc plots. The combination of the as-prepared TiO2-AA-Cu(II) nanoparticles with TEMPO and molecular oxygen (air) afforded an active catalytic system for the selective oxidation of diverse set of benzylic alcohols under solvent-free conditions. A photoassisted pathway was confirmed for oxidation reactions evidenced by good correlation between apparent quantum yield (AQY) and diffuse reflectance spectra (DRS) of the as-prepared nanohybrid. The spectral data and recycling experiments demonstrated the structural stability of the title copper photocatalyst during oxidation reactions.

In this study, synthesis, characterization and photocatalytic performance of surface-modified TiO2 nanoparticles with ascorbic acid-stabilized Pd nanoparticles are presented. The structure, composition and morphology of as-prepared nanophotocatalyst were characterized by UV-DRS, FT-IR, ICP-AES, TEM and XPS analysis. Ascorbic acid-stabilized Pd nanoparticles induced visible light driven photocatalytic property on the surface of TiO2 which are otherwise insensitive to visible light owing to the wide band gap. The catalytic system worked well for the Suzuki–Miyaura cross-coupling and Ullmann homocoupling under compact fluorescent light as a visible source with significant activity, selectivity and recyclability. Good to excellent yields of biaryl products were obtained for various aryl halides having different electronic demands and even aryl chlorides. Our results proposed that the improved photoactivity predominantly benefits from the synergistic effects of ascorbic acid-stabilized Pd nanoparticles on TiO2 nanoparticles that cause efficient separation and photoexcited charge carriers and photoredox capability of nanocatalyst. Thus, tuning of band gap of TiO2 making a visible light sensitive photocatalyst, demonstrates a significant advancement in the photocatalytic Suzuki–Miyaura and Ullmann coupling reactions.

In this study, we performed a visible light-mediated aerobic photo-cross dehydrogenative coupling (CDC) reaction between aldehydes and N-hydroxyimides using TiO2–AA–Co as a photocatalyst for the synthesis of active esters. The synergistic and selective effects of the cobalt ascorbic acid complex (Co–AA) and TiO2 nanoparticles on the visible-light photocatalytic activity were explored. The method possesses some advantages such as environmentally friendly conditions, easy work-up procedure, reusability, and scalability.

In this study, we developed methods for the one pot environmentally benign synthesis of benzimidazoles by cobalt ascorbic acid complex coated on TiO2 nanoparticles via aerobic photooxidative cyclization reactions. Easy work-up procedure, reusability of the catalyst and scalable to the multi-mole scale, which is valuable for an industrial process make these catalytic systems highly attractive. Also, the combination of photocatalytic and catalytic reactions presented here may help to develop a new strategy towards the development of photocatalysis-based organic synthesis.

A visible-light-driven photocatalytically active nanocrystalline TiO2 was prepared by surface modification with a cobalt–ascorbic acid complex. The photocatalyst exhibited high activity and excellent chemo-, diastereo-, and stereoselectivities in the aerobic epoxidation of olefins under visible-light irradiation in the absence of a reducing agent. The catalyst proved efficient and could be recycled at least five times.

The incorporation of Co(OAc)2 into ascorbic acid-coated TiO2 nanoparticles easily provided a new heterogeneous visible-light active titania-based photocatalyst (TiO2/AA/Co) which was characterized by different techniques such as FT-IR, XPS, ICP-AES, TGA and TEM. A red-shift of the band-edge and a significant reduction of the band-gap (2.8 eV) were demonstrated by UV-DRS. The as-prepared TiO2/AA/Co nanoparticles possess excellent photocatalytic properties under visible light for the aerobic benzylic C–H oxidation of a structurally diverse set of benzylic alcohols and benzylic hydrocarbons in ethyl acetate as a safe solvent. The spectral results and leaching experiments revealed that the structural integrity of the solid catalyst is well preserved after being reused many times.