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05 January 2024

Benzene Bridged Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution

Turing the electronic structure by inserting certain functional groups in graphitic carbon nitride (g-C3N4, CN for short) skeleton through molecular doping is an effective way to improve its photocatalytic performance. Herein, we prepare a benzene bridged carbon nitride (BCN) by calcining urea and 1,3,5-tribromobenzene at elevated temperature. The introduction of benzene ring in g-C3N4 layers improves the separation efficiency and lifetime of photogenerated carriers, inhibits the recombination rate of electron/hole pairs, thus the performance of photocatalytic hydrogen evolution improves. The optimal hydrogen evolution rate of 1.5BCN reaches 1800 µmol/h·g, which is nine times that of the pure g-C3N4. DFT calculation proved the benzene bridged CN increased the distance of charge transfer (DCT) and the push-pull electronic effect of intramolecular electrons. This work may provide a pathway for preparing molecular doped g-C3N4 with improved photocatalytic performance.

Keywords: Graphitic carbon nitride; Photocatalysis; Hydrogen evolution; Photocatalysts; Molecular design


11 October 2023

Fibrous SiC-based Mesoporous Solids for the Photocatalytic Degradation of Organic Pollutants under Artificial Light

SiC-based mesoporous solids with fibrous nanostructure were prepared by impregnation of a polycarbosilane precursor on annealed polyacrylonitrile (PAN) fibers and subsequent pyrolysis. The obtained material exhibits a mesoporous structure and has a specific surface area of ~20 m2/g. It has a semiconducting electronic character with a bandgap of 2.65 eV, i.e., in the visible range. Adsorption tests of methylene blue were performed on the material under dark conditions, which showed an adsorption amount of 78 wt%. The photocatalytic activity of the material was then evaluated for the degradation of the dye under artificial daylight irradiation over a period of 7 h. A degradation of 94 wt% was achieved. Regeneration and reuse of the material was also tested and resulted in 97 wt% degradation after reuse, indicating potential interest of the material as a contactor in environmental remediation devices.

Keywords: Silicon carbide; Preceramic polymers; Ceramics; Photocatalysis; Fibers


31 August 2023

Potential Role of Exciton in Photocatalysis

This article commemorates the outstanding Russian scientists E.F. Gross and A.N. Terenin. It revisits their successors’ efforts to develop Terenin’s idea of using excitons, discovered by Gross, for photocatalytic redox reactions on wide-gap semiconductors. Terenin proposed ZnO as the subject of study. To explore the possibility of replacing photogenerated electrons and holes in a redox reaction by an exciton being a quasi-neutral particle, the test reaction of the photoactivated oxygen isotope exchange (POIE) was studied. It was found that many years of initial unsuccessful attempts were due to the fact that the exciton energy is spent on luminescence. In our experiments, the excitons decayed non-radiatively, and the long-lived electron-donor F-type and hole V-type active centers were formed by creating the 2D surface nanostructure ZnO/ZnO1−x/O. These centers allowed to obtain the reaction efficiency 5–8 times higher than with the interband transitions. Thus, the developed 2D surface nanostructure ZnO/ZnO1−x/O resolved the problem of using an exciton in photocatalysis and demonstrated the perspective of this nanostructure as an efficient photocatalyst.

Keywords: Photocatalysis; ZnO; Exciton; Photoactivated oxygen isotope exchange (POIE); Redox reactions


05 July 2023

Photocatalytic Efficiency of Suspended and Immobilized TiO2 P25 for Removing Myclobutanil, Penconazole and Their Commercial Formulations

Fungicide application in viticulture is a major source of surface and groundwater contamination. It is therefore essential to find solutions to stop this environmental pollution. Heterogeneous photocatalysis is an advanced oxidation method for the degradation and mineralization of organic pollutants in water. TiO2 P25 photocatalyst in suspension has been used for removing the fungicides Myclobutanil and Penconazol, and their respective commercial formulations Systhane and Topas, in contaminated water. The apparent kinetic constants kapp of fungicides removal over 30 min batch treatment was higher for a mixture of pure molecules of Myclobutanil and Penconazol than for a mixture of their commercial formulations (17.5 × 10−3 by comparison with 10.3 × 10−3 min−1 for Myclobutanil, and 10.0 × 10−3 by comparison with 2.80 × 10−3 min−1 for Penconazol). TOC removal constants kTOC were similar for the two mixtures, due to the presence of mineral and organic additives in the commercial formulations. To easily recover the photocatalyst after fungicide removal, TiO2 P25 has been supported on β-SiC foam. Fungicides degradation was lower with supported photocatalysts than with the suspension of photocatalyst nanoparticles (NPs) because of a lower concentration of active sites on the supported photocatalyst than in the catalyst suspension. However, catalyst recovery and reuse after fungicide removal is obviously easier with TiO2/β-SiC material than with a suspension of TiO2 which requires long and expensive filtration operations.

Keywords: Fungicides; Photocatalysis; Myclobutanil; Penconazol; TiO2/β-SiC


03 March 2023

SnS2 Quantum Dots Decorated MoS2 Nanosheets Enabling Efficient Photocatalytic H2 Evolution in CO2 Saturated Water

SnS2/MoS2 heterojunction nanocomposite was prepared by a one-step hydrothermal synthesis method. The nanocomposite exhibited much improved photocatalytic hydrogen evolution performance in CO2 saturated solution compared with pure MoS2 and SnS2 samples. The improved photocatalytic activity was attributed to the S-scheme heterojunction structure between SnS2 quantum dots and MoS2 nanosheets which facilitate electron-hole separation both in MoS2 and SnS2. In the S-scheme structure, the strong reduction ability of SnS2 quantum dots was well maintained for the improved H2 evolution. In situ DRIFT studies allowed us to suggest reaction pathways from CO2 and H2O to photocatalytic H2, CO, and CH4 generation.

Keywords: Photocatalysis; H2 evolution; CO2 hydrogenation; S-scheme


07 February 2023

Plasmon Enhanced Nickel(II) Catalyst for Photocatalytic Lignin Model Cleavage

Photocatalytic-induced cleaving of the ether C–O bond in model lignin compounds was studied with a closely-coupled compo-site material consisting of Ni(OH)2 and gold nanoparticles (NPs) on a zirconia support (Au/ZrO2–Ni(OH)2). The three important ether bond types consisting of α-O-4, β-O-4, and 4-O-5 linkages can all be cleaved using this catalyst at reaction temperatures 40, 85 and 95 °C when under low-flux visible light irradiation. The Au NPs action as a light-harvesting antenna provided light-generated hot electrons that reduced Ni2+ to Ni0. The Ni0 was the active catalytic site where reductive cleavage of ether C–O bonds occurred while it was oxidized to Ni2+ to complete the catalysis cycle. The plasmonic antenna system with supported Ni(OH)2 exhibited better ability for the catalytic reductive ether cleavages under visible light irradiation compared to photocata-lysts of Au NPs and Ni2+ ions immobilized on alumina fibers.

Keywords: Lignin model cleavage; Photocatalysis; LSPR effect; Mild conditions


06 September 2022