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The challenge of improving the activity of TiO2 by modifying it with metals and using it for targeted applications in microreactor environments is an active area of research. Recently, microreactors have emerged as successful candidates for many photocatalytic reactions, especially for the selective oxidation process. The current work introduces ultrasound-assisted catalyst deposition on the inner walls of a perfluoro-alkoxy alkane (PFA) microtube under mild conditions. We report Cu-Au/TiO2 and Fe-Au/TiO2 nanoparticles synthesized using the sol–gel method. The obtained photocatalysts were thoroughly characterized by UV–Vis diffuse-reflectance spectroscopy (DRS), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and N2 physisorption. The photocatalytic activity under UV (375 nm) and visible light (515 nm) was estimated by the oxidation of lignin-based model aromatic alcohols in batch and fluoropolymer-based flow systems. The bimetallic catalyst exhibited improved photocatalytic selective oxidation. Herein, four aromatic alcohols were individually investigated and compared. In our experiments, the alcohols containing hydroxy and methoxy groups (coniferyl and vanillin alcohol) showed high conversion (93% and 52%, respectively) with 8% and 17% selectivity towards their respective aldehydes, with the formation of other side products. The results offer an insight into ligand-to-metal charge transfer (LMCT) complex formation, which was found to be the main reason for the activity of synthesized catalysts under visible light. [ABSTRACT FROM AUTHOR]

The herein presented low‐power high‐frequency (500 kHz) ultrasound‐assisted precipitation synthesis (LPHF‐US) leads to a unique multiphase nano‐structured titanium dioxide, grafted with oxygen‐containing organic functionalities. The material exhibits a high porosity (surface area 326 m2 g−1 and total pores volume 0.484 cm3 g−1) and heterogeneous surface chemistry. In the used LPHF‐US synthetic protocol, the energy‐demanding calcination step leading to crystallization is eliminated and an organic residue is simultaneously grafted to the surface. That organic residue affects the anatase nanocrystals, size (4–7 nm), which are embedded in an amorphous titanium hydroxide network. This nanomaterial shows superior performance as a heterogenous photocatalyst either in a gaseous phase by decomposing toxic vapors of chemical warfare agents (a mustard‐gas surrogate), or in a liquid phase by selectively oxidizing benzyl alcohol, a model lignin‐biomass‐derived compound. The grafted organic phase enhances the catalyst's photoreactivity under visible light, by acting as a photosensitizer (antenna effect) and/or as a source of chromophores. [ABSTRACT FROM AUTHOR]

A new field where the utilization of mechanochemistry can create new opportunities is materials chemistry, and, more interestingly, the synthesis of novel nanomaterials. Ball-milling procedures and ultrasonic techniques can be regarded as the most important mechanochemical synthetic tools, since they can act as attractive alternatives to the conventional methods. It is also feasible for the utilization of mechanochemical forces to act synergistically with the conventional synthesis (as a pre-treatment step, or simultaneously during the synthesis) in order to improve the synthetic process and/or the material's desired features. The usage of ultrasound irradiation or ball-milling treatment is found to play a crucial role in controlling and enhancing the structural, morphological, optical, and surface chemistry features that are important for heterogeneous photocatalytic practices. The focus of this article is to collect all the available examples in which the utilization of sonochemistry or ball milling had unique effects as a synthesis tool towards zero- or one-dimensional nanostructures of a semiconductor which is assumed as a benchmark in photocatalysis, titanium dioxide. [ABSTRACT FROM AUTHOR]

Abstract: We present a facile and green approach to produce crystalline TiO2 nanoparticles on a surface of different carbonaceous materials derived from lignocellulosic biomass such as STARBON‐800® obtained by carbonization at 800 °C and biochar‐SWP700 (Soft Wood Pellets (SWP) obtained by pyrolysis at 700 °C) via novel low‐temperature ultrasound‐promoted green methodology coupled with citric acid as a cross‐linking agent. In comparison to other methods, the developed method has several significant benefits such as simplicity, great ability to get crystalline TiO2 particles (elimination of high‐temperature treatment (material calcination at >300 °C) needed in the conventional sol‐gel method, which is extremely important in transforming amorphous TiO2 into a photoactive crystalline phase) elimination of risky chemicals and oxidizing agent, and also ability to change some parameters (e. g. ultrasound intensity). Prepared materials were characterized by XRD, DR UV−vis, N2 physisorption, HR‐XPS, XRF, HR‐TEM, FT‐IR and subsequently tested for their photocatalytic activities both in photocatalytic phenol degradation (in water) and oxidation of methanol (in air) under UV and visible light irradiation. [ABSTRACT FROM AUTHOR]