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Covalent organic framework as an efficient, metal-free, heterogeneous photocatalyst for organic transformations under visible light
摘要： Visible-light active, heterogeneous, and organic photocatalysts exhibit a more sustainable and environmentally friendly alternative to classical metal-based catalysts. Two-dimensional covalent organic frameworks (2D-COFs) with permanent porosity, columnar π-arrays and excellent stability, that can become an excellent platform for heterogeneous photocatalysis of organic transformations. Here we report a predesigned imine-based COF with electron donor and acceptor structure. And new framework possesses large surface area, high crystallinity, outstanding stability and broad absorption range in the visible-light region as well as good photoelectric response characteristics. Importantly, it was found to be a highly effective heterogeneous photocatalyst for reductive dehalogenation of phenacyl bromide derivatives and α-alkylation of aldehydes under irradiation of visible-light. In addition, the COF gave good recyclability and could be reused after a simple separation manipulation. The current present still reveals a great prospect for 2D-COFs as metal-free, heterogeneous photocatalysts for organic transformations.
关键词： visible light,photocatalysis,heterogeneous catalysis,metal-free,covalent organic frameworks
更新于2025-09-23 15:23:52
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2D-montmorillonite-dispersed g-C3N4/TiO2 2D/0Dnanocomposite for enhanced photo-induced H2 evolution from glycerol-water mixture
摘要： Montmorillonite (MMT) dispersed g-C3N4/TiO2 hybrid nanocomposite for enhanced photo-catalytic hydrogen production from glycerol-water mixture has been investigated. The newly designed composite photo-catalysts were fabricated through a sol-gel assisted hydrothermal method and were characterized by XRD, XPS, SEM, EDX, TEM, FTIR, UV–Vis, Raman and PL spectroscopy. Well-designed g-C3N4/MMT/TiO2 heterojunction composite was obtained with 2D MMT structure, which promoted both visible light absorption and hindered charges recombination rate. The modification of 2D/0D g-C3N4/TiO2 heterojunction with 2D MMT sheets enhances H2 production due to MMT works as a mediator for effective charges trapping and transportation within the composite structure. The g-C3N4/MMT/TiO2 photo-catalyst exhibits highest H2 production of 4425 ppm h?1 g?1 at pH 7.0, which was 2.12 times higher than the pure TiO2 (2085 ppm h?1 g?1). In addition, increasing catalyst loading promotes more H2 evolution and among the different sacrificial reagents, glycerol-water mixture gave highest H2 production due to the presence of α-hydrogen atoms attached to carbon atoms. The enhanced photocatalytic efficiency can be attributed to synergistic effect of MMT with g-C3N4/TiO2 heterojunction composite, appropriate band structure and transportation of electrons–holes with their hindered recombination rate. These composite catalysts exhibited excellent photo-catalytic stability for H2 production in cyclic runs. Possible reaction mechanism for hydrogen production over g-C3N4/MMT/TiO2 composite has been explained based on the experimental results. The finding of this work would be fruitful for hydrogen production applications with all sustainable systems.
关键词： TiO2,Photo-catalysis,Montmorillonite,g-C3N4,Z-scheme,Hydrogen production
更新于2025-09-23 15:23:52
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C5-Selective Trifluoromethylation of 8-Amino quinolines via Photoredox Catalysis
摘要： A new protocol for C5-selective C–H trifluoromethylation of 8-aminoquinolines via photoredox catalysis was developed. It allows rapid access to various C5-trifluoromethyl 8-amino quinoline derivatives in MeCN/H2O enabled by Eosin Y as photocatalysts.
关键词： para-selective C-H activation,Photoredox catalysis,Trifluoromethylation,8-Aminoquinolines
更新于2025-09-23 15:23:52
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Enlightening developments in 1,3-P,N-ligand-stabilized multinuclear complexes: A shift from catalysis to photoluminescence
摘要： 1,3-P,N-ligands provide the ideal spatial separation to facilitate homo and hetero metal-metal interactions to access multinuclear complexes. The rich chemistry of such complexes includes applications in coordination chemistry, metal-activation and (cooperative) catalysis. However, it has been especially the fruitful combination in photoluminescent P,N-coinage metal complexes which has renewed interest in these ligands. While the field classically focused on dinuclear species, now also coinage metal clusters have been studied for use in catalysis and photophysical applications. Reviewed are recent developments from 2009 to mid-2017.
关键词： P,N-ligands,Coinage metal clusters,Photoluminescence,Transition metal complexes,Homogeneous catalysis,Metal-metal bonds
更新于2025-09-23 15:23:52
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Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide nanostructured catalyst
摘要： In this paper, we report an in-situ synthesis of silver supported on cobalt oxide (Ag/Co3O4) nanoparticles (NPs) and studied the catalytic activity of this material as an eco-friendly, simple, recyclable and efficient catalyst for one‐pot photocatalytic oxidation of aromatic alcohols. Ag nanoparticles with the sizes of 2–5 nm supported on spherical Co3O4 with the radius between 40 and 60 nm were synthesized by homogeneous chemical precipitation followed by hydrothermal heating. The as-synthesized catalyst was thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherm (BET) analysis. It was observed that the catalysts with 1 wt% of silver loading shows high activity and selectivity toward the target aldehyde product. The effects of different reaction parameters such as reaction time, oxidant and solvent were investigated and studied in detail. The synergistic effect between the surface Ag NPs and Co3O4 nanospheres plays a vital role toward very high catalytic activity.
关键词： Oxide materials,Chemical synthesis,Catalysis,X-ray diffraction
更新于2025-09-23 15:23:52
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Facile Synthesis and Self-assembly of Zinc (2-Diethoxy-phosphorylethynyl)porphyrins
摘要： The synthesis of zinc (2-diethoxyphosphorylethynyl)porphyrins and their self-organization in solid state and in solution are reported. Copper-cocatalyzed Sonogashira reaction of bromoporphyrins with diethyl ethynylphosphonate was used to prepare meso-substituted derivatives Zn4 and Zn5 bearing one or two ethynylphosphonate substituents at the macrocycle. In contrast, copper-free Sonogashira coupling of 2-bromoporphyrin with diethyl ethynylphosphonate is more convenient to prepare porphyrin Zn6 bearing this substituent at the b-pyrrolic position of the macrocycle. The structure of complexes Zn4a.C7H8, Zn4a.CHCl3, Zn4c and Zn5b.CH2Cl2 in crystals were elucidated by X-ray diffraction analysis. The supramolecular self-assembly through weak coordinative binding of the phosphoryl group of one porphyrin molecule to the zinc(II) ion located in the center of another macrocyclic cavity is observed in all crystals. However, Zn(II)-porphyrinates Zn4a and Zn5b exist in the solid state as mutually coordinated dimers while complex Zn4c displays a 1D polymer structure. In all dimer complexes, neighboring porphyrin rings are spatially separated, with Zn–O and P=O bond distances being similar, while the interplanar porphyrin distance is variable to depend on weak intermolecular interactions in the crystals. The self-organization of (phosphorylethynyl)porphyrins is also observed in weakly polar chloroform and detectable by NMR and UV-vis spectroscopies. The mutually coordinated dimer of electron-deficient porphyrin Zn5b was observed in 5.x.10-3 M chloroform solution even at room temperature. Kinetic lability of this supramolecular complex was proven by NMR spectroscopy. The associates of more electron-donating porphyrins Zn4a and Zn4c are less stable and self-assembled dimers become the predominant species in 5.x.10-3 M chloroform solution only below 225 K. The self-assembly of porphyrin Zn4a and Zn5b in more diluted solutions (up to 10-6 M) was also investigated by UV-vis spectroscopy.
关键词： self-organization,phosphonate,porphyrin,catalysis,acetylene linker
更新于2025-09-23 15:23:52
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Fabrication of electrochemically nonporous NiO–ZnO/TiO2 nanotubes/Ti plates for photocatalytic disinfection of microbiological pollutants
摘要： Nonporous NiO–ZnO/TiO2 nanotubes/Ti photocatalyst plates were fabricated via facile electrochemical method. The structural and morphological properties of the modified plates were investigated by scanning electron microscopy and X-ray diffraction, while their photoelectrochemical (PEC) characterizations were evaluated by transient photocurrent responses and electrochemical impedance spectroscopy. Antimicrobial activities of the fabricated plates against Escherichia coli bacteria and Candida albicans fungi were studied under UV light irradiation. The results indicated that the photocatalytic and PEC activities of the NiO–ZnO/TiO2 nanotubes/Ti plates are much higher than those of TiO2 nanotubes/Ti, ZnO/TiO2 nanotubes/Ti and NiO/TiO2 nanotubes/Ti. The synergetic effect among NiO, ZnO and TiO2 nanotubes motivated a fast charge separation as well as a slow electron/hole recombination, thus increasing the photocatalytic performance of the nonporous NiO–ZnO/TiO2 nanotubes/Ti photocatalyst plate.
关键词： Microbiological pollutants,Heterogeneous catalysis,Photocatalytic disinfection,NiO–ZnO hybrids
更新于2025-09-23 15:23:52
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Two-dimensional amorphous heterostructures of Ag/a-WO3- for high-efficiency photocatalytic performance
摘要： Synergistic photocatalysis is an important concept for designing the high-efficiency catalysis for fundamental research and technical applications. In this study a well-defined synergistic photocatalysis system is realized by the 2D amorphous heterostructures (2DAHs) Ag/a-WO3-x, which are constructed by Ag nanoparticles on 2D amorphous tungsten oxide (a-WO3-x) fabricated via supercritical CO2 method. We demonstrate theoretically that the oxygen evolution reactions (OER), characterized by photocurrent response, have been dramatically improved in Ag/a-WO3-x than those of both single a-WO3-x and Ag/WO3 systems. Such an enhanced photoelectrochemical performance attributes to the superposition effect of amorphous effect catalysis and local surface plasmon resonances (LSPR) catalysis. More interestingly, the ab initio density-functional theory calculations reveal that the amorphous effect catalysis ascribes to the unique d-d tail states coupling of both Ag and W atoms in the 2DAHs. Overall, our findings not only propose the prototype of synergistic photocatalysis, but also provide a new methodology to the design of novel catalyst.
关键词： 2D amorphous tungsten oxide,amorphous effect catalysis,synergistic photocatalysis,d-d tail states coupling,2D amorphous heterostructures Ag/a-WO3-x
更新于2025-09-23 15:23:52
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Abrupt changes in the graphene on Ge(001) system at the onset of surface melting
摘要： By combining scanning probe microscopy with Raman and x-ray photoelectron spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a function of the deposition temperature in close proximity to the Ge melting point, highlighting an abrupt change of the graphene’s quality, morphology, electronic properties and growth mode at 930 °C. We attribute this discontinuity to the incomplete surface melting of the Ge substrate and show how incomplete melting explains a variety of diverse and long-debated peculiar features of the graphene/Ge(001), including the characteristic nanostructuring of the Ge substrate induced by graphene overgrowth. We find that the quasi-liquid Ge layer formed close to 930 °C is fundamental to obtain high-quality graphene, while a temperature decrease of 10 degrees already results in a wrinkled and defective graphene film.
关键词： Chemical Vapor Deposition,Germanium,Scanning Tunneling Microscopy,Catalysis,Graphene
更新于2025-09-23 15:23:52
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La-modified TiO2/carbon nanotubes assembly nanocomposite for efficient photocatalytic hydrogen evolution from glycerol-water mixture
摘要： Lanthanum (La) modified TiO2 embedded over carbon nanotubes (CNTs) to develop nanocomposite for enhanced photocatalytic hydrogen evolution from glycerol-water mixture has been investigated. The samples, synthesized by sol-gel assisted hydrothermal method, were characterized by XRD, FESEM, HRTEM, FTIR, BET, UVeVisible, Raman and PL spectroscopy. La/TiO2 anchored CNTs has larger surface area with uniform distribution of La3+ ions. The performance of hybrid assembly was evaluated in a continuous flow slurry photoreactor system under UVevisible light irradiations. The highest H2 evolution rate of 17265 ppm g-cat-1 h-1 was obtained over 5% La-5% CNTs/TiO2 NRs, 1.14 folds the amount produced over 5% La-5% CNTs/TiO2 NPs, 1.53 time than 5% La/TiO2 and 4.10 folds than using pure TiO2 NPs. This significant improvement in the photo-activity was obviously due to synergistic effect between La and CNTs, larger BET surface area, cleavage of glycerol by La, appropriate band structure, and hindered charges recombination rate. Among the sacrificial reagents, highest H2 evolution was obtained using glycerol due to the presence of a-hydrogen atoms attached to carbon atoms. A correlation between BET surface area and photonic flux in terms of photocatalytic H2 production rate was established to understand the performance of hybrid nanostructures. It was observed that BET surface area and photo-flux utilization for the generation of charge carriers with their efficient separation has significant contribution towards improved H2 production rate. More interestingly, catalyst persisted prolonged stability with a steady H2 production in cyclic runs. This study provides promising pathway for constructing composite of La/TiO2 coupled CNTs for efficient H2 production under visible light.
关键词： La/TiO2,Glycerol,TiO2/CNTs hybrid,H2 production,Visible light,Photo-catalysis
更新于2025-09-23 15:23:52