Facile preparation of ultrathin Bi2MoO6 nanosheets for photocatalytic oxidation of toluene to benzaldehyde under visible light irradiation

Toluene Oxidation: CO2 vs Benzaldehyde: Current Status and Future Perspectives

Toluene is a common and significant volatile organic compound (VOC). Although it finds extensive application in various industrial processes (chemical manufacturing, paint and adhesive production, and as a solvent), it creates a huge environmental impact when emitted freely into the atmosphere. Two solutions were found to mitigate the emission of this pollutant: the total oxidation to CO2 and H2O and the selective oxidation into benzaldehyde. This review discusses the two main alternatives for tackling this problem: converting the toluene into carbon dioxide by total oxidation or into benzaldehyde by selective oxidation. It presents new catalytic advances, new trends, and the advantages and disadvantages of both methods.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Recent advances in catalytic oxidation of VOCs by two-dimensional ultra-thin nanomaterials

Catalytic oxidation, an end-of-pipe treatment technology for effectively purifying volatile organic compounds (VOCs), has received widespread attention. The crux of catalytic oxidation lies in the development of efficient catalysts, with their optimization necessitating a comprehensive analysis of the catalytic reaction mechanism. Two-dimensional (2D) ultra-thin nanomaterials offer significant advantages in exploring the catalytic oxidation mechanism of VOCs due to their unique structure and properties. This review classifies strategies for regulating catalytic properties and typical applications of 2D materials in VOCs catalytic oxidation, in addition to their characteristics and typical characterization techniques. Furthermore, the possible reaction mechanism of 2D Co-based and Mn-based oxides in the catalytic oxidation of VOCs is analyzed, with a special focus on the synergistic effect between oxygen and metal vacancies. The objective of this review is to provide valuable references for scholars in the field.

Fabrication of Bi2MoO6 Nanosheets/TiO2 Nanorod Arrays Heterostructures for Enhanced Photocatalytic Performance under Visible-Light Irradiation

Bi2MoO6/TiO2 heterostructures (HSs) were synthesized in the present study by growing Bi2MoO6 nanosheets on vertically aligned TiO2 nanorod arrays using a two-step solvothermal method. Their morphology and structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Excellent visible-light absorption was observed by UV-Vis absorption spectroscopy, which was attributed to the presence of the Bi2MoO6 nanosheets with a narrow-band-gap. The specific surface area and pore volume of the photocatalysts were significantly increased due to the hierarchical structure composed of Bi2MoO6 nanosheets and TiO2 nanorods. The photoluminescence and photoelectrochemical characterizations showed improved separation and collection efficiency of the Bi2MoO6/TiO2 HSs towards the interface charge carrier. The photocatalytic analysis of the Bi2MoO6/TiO2 HSs demonstrated a significantly better methylene blue (MB) degradation efficiency of 95% within 3 h than pristine TiO2 nanorod arrays under visible-light irradiation. After three photocatalytic cycles, the degradation rate remained at ~90%. The improved performance of the Bi2MoO6/TiO2 HSs was attributed to the synergy among the extended absorption of visible light; the large, specific surface area of the hierarchical structure; and the enhanced separation efficiency of the photogenerated electron-hole pairs. Finally, we also established the Bi2MoO6/TiO2 HSs band structure and described the photocatalytic dye degradation mechanism. The related electrochemical analysis and free-radical trapping experiments indicated that h+, ·O2- and ·OH have significant effects on the degradation process.

Recent advances in non-noble metal-based oxide materials as heterogeneous catalysts for C–H activation

This perspective article summarizes the recent developments of non-noble metal-based oxides, as a new class of catalysts for C−H bond activation, focusing on their essential surface properties.

Recent Advances in Heterogeneous Photo-Driven Oxidation of Organic Molecules by Reactive Oxygen Species

The photo-driven oxidation of organic molecules into corresponding high-value-added products has become a promising method in chemical synthesis. This strategy can drive thermodynamically non-spontaneous reactions and achieve challenging thermocatalytic processes under ambient conditions. Reactive oxygen species (ROS) are not only significant intermediates for producing target products via photoinduced oxidation reactions but also contribute to the creation of sustainable chemical processes. Here, the latest advances in heterogeneous photo-driven oxidation reactions involving ROS are summarized. The major types of ROS and their generation are introduced, and the behaviors of various ROS involved in photo-driven processes are reviewed in terms of the formation of different bonds. Emphasis is placed on unraveling the reaction mechanisms of ROS and establishing strategies for their regulation, and the remaining challenges and perspectives are summarized and analyzed. This Review is expected to provide an in-depth understanding of the mechanisms of ROS involved in photo-driven oxidation processes as an important foundation for the design of efficient catalysts. Clarifying the role of ROS in oxidation reactions has important scientific significance for improving the atomic and energy efficiency of reactions in practical applications.

Theoretical study on the effect of the optical properties and electronic structure for the Bi-doped CsPbBr3

Metal doping, including Bi, Yb, Eu, Sb and so on, are important means to improve the photoelectric properties and stability of metal halide perovskite materials. Among these works, Bi-doped CsPbBr₃ especially has attracted much attention for both experimental and theoretical investigation. But there are still some arguments to be solved. One view thinks that Bi doping in CsPbBr₃ not only influences the band structure, but also improves the charge transfer (Raihana et al 2017 J. Am. Chem. Soc. 139 731-7). The other supported the points that there are no changes in the valence band structure of Bi-doped CsPbBr₃ and the concept of the band-gap engineering in Bi-doped CsPbBr₃ halide perovskite is not valid (Olga et al 2018 J. Phys. Chem. Lett. 9 5408-11). They also have different opinions for the reason of the red-shift phenomenon caused by Bi-doped CsPbBr₃. In this work, the density functional theory (DFT) based first-principles methods is adopted to investigate the effect of the optical properties and electronic structure for Bi doping CsPbBr₃. The calculated results clarify that the red-shift phenomenon is caused by the slight reduction of band gap and the transition levels of Bi_i and Bi_Pb defects. The values of red-shift also were estimated about 150 meV for Bi_i defects, which is close the experimental value of about 140 meV. Moreover, our studies also show that the Bi doping does not affect the valence bands, but Bi_i defects change the electron distribution of the conduction band. Our work and experimental results support and confirm each other, which provides a useful reference for the study of Sb-doped CsPbBr₃, Eu-doped CsPbBr₃ and so on.

Design and fabrication of polyaniline/Bi2MoO6 nanocomposites for enhanced visible-light-driven photocatalysis

PANI/Bi₂MoO₆ composites with improved photoelectrochemical performance and accessible interfacial active sites were fabricated for enhanced visible-light-driven photocatalytic degradation of RhB.