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Metal-free Semiconductor Photocatalysis for sp2 C-H Functionalization with Molecular Oxygen
摘要： Designing metal-free catalysts for solar energy conversion is a long-standing challenge in semiconductor photoredox catalysis (SPC). With visible-light-responsive hexagonal boron carbon nitride (h-BCN) as a non-metal photocatalyst, this system affords C–H/N–H coupling products with broad substitution tolerance and high efficiency with molecular oxygen as the terminal oxidant. The catalyst exhibits remarkable performance for the selective C-H functionalization of electron-rich arenes to C-N products (yields up to 95%) and good stability (6 recycles). Both nitrogen heteroarenes and amine salts are competent coupling nucleophiles. Mechanically, the reactive oxygen species are superoxide anion radical (O2??) and H2O2, which are proved by electron spin resonance (ESR) data, KI-starch, and control experiments. In addition, kinetic isotope effect (KIE) experiments indicate that C–H bond cleavage is not involved in the rate limiting step. This semiconductor-based photoredox system allows for C–H amination free of any metals, ligands, strong oxidants, and additives. It provides a complementary avenue to C–H functionalizations and enables synthetic applications efficiently in a sustainable manner.
关键词： Radical,Semiconductor Photoredox Catalysis,Heterogeneous Catalysis,Visible Light,C-H Fuctionalizaition
更新于2025-09-10 09:29:36
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An Integration of Photo-Fenton and Membrane Process for Water Treatment by a PVDF@CuFe2O4 Catalytic Membrane
摘要： Membrane fouling always decreases the separation efficiency and shortens the membrane life, which severely hinders the practical application of the membrane technology. The photo-Fenton process can degrade various foulants with the generation of hydroxyl radicals, and its integration with membrane filtration may become an efficient way to improve the antifouling property and filtration performance of the membrane. In this study, the CuFe2O4 particles were synthesized and doped in the PVDF@CuFe2O4 membranes with increasing concentration from 0 to 1.0%. The degradation measurement of methylene blue (MB) solution shows the optimal conditions for the photo-Fenton process as CuFe2O4 concentration of 1.0%, pH of 3.0, and H2O2 dosage of 400 μL. With the photo-Fenton cleaning process, the PVDF@CuFe2O4 membrane (1.0%) exhibits versatile antifouling property to different types of foulants, including organic dyes (e.g. MB and rhodamine B (RhB)), nature organic matter (e.g. humic acid (HA)), and protein (e.g. bovine serum albumin (BSA)). With the integration of photo-Fenton and membrane process, the PVDF@CuFe2O4 membrane (1.0% of CuFe2O4) dramatically enhanced the separation efficiency, with the results of 99.77% to MB, 81.02% to RhB, 36.35% to HA, and 82.94% to BSA. The flux and rejection have been increased respectively to threefold and double of the corresponding data from the membrane filtration alone. Moreover, even after fifteen cycles of experiments, the average MB rejection is still higher than 70%, which further indicates the good stability and reusability of the PVDF@CuFe2O4 membrane. Therefore, this study provides a promising methodology for the successful fabrication of high-performance membrane through the integration of photo-Fenton and membrane process, and further proposes a new strategy on the design and application of functional materials for new generation of catalytic membranes.
关键词： Membrane,Antifouling,Integration,Filtration,Photo-Fenton Catalysis,CuFe2O4
更新于2025-09-10 09:29:36
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Sol-gel synthesis of Ag-loaded TiO2-ZnO thin films with enhanced photocatalytic activity
摘要： Ag-loaded TiO2-ZnO thin films, with low ZnO content, were synthesized by a one-step sol-gel process. The Ag content varied in the interval 0-4 mol% Ag. The films were deposited on glass substrates and post-annealed at 500 °C to induce crystallinity. By using the Tauc model, it was determined that the higher the Ag concentration the higher the optical band-gap energy of the films, a result attributed to the Burstein-Moss effect. Images obtained by scanning electron microscopy and transmission electron microscopy depicted aggregated particles with grain size close to 20 to 25 nm for the oxides with no Ag, whereas the particle size decreased with the addition of Ag. X-ray photoelectron spectroscopy measurements indicated the formation of the Ti4+ and Zn2+ oxidation states, while Ag was found in the metallic state. A depth profile analysis, performed by secondary ion mass spectrometry, confirmed the presence of Ti, Zn, and Ag in the films. X-ray diffraction patterns displayed the anatase phase of TiO2. For (TiO2)0.95-(ZnO)0.05 thin films, a BET analysis showed that the specific surface area increased from 4.56 up to 48.84 m2/g as a consequence of Ag doping. The photocatalytic degradation of the materials under UV irradiation was assessed by using methylene blue as a model pollutant. For (TiO2)1-x-(ZnO)x compounds with no Ag, the highest response corresponded to x = 0.05. In addition, the optimum photodegradation was found for (TiO2)0.95-(ZnO)0.05 thin films with 2 mol% Ag.
关键词： Optical spectroscopy,Catalysis,X-ray diffraction,Sol-gel process,Thin films,Oxide materials
更新于2025-09-10 09:29:36
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Concurrent Asymmetric Reactions Combining Photocatalysis and Enzyme Catalysis: Direct Enantioselective Synthesis of 2,2-Disubstituted Indol-3-ones from 2-Arylindoles
摘要： The combination of photoredox and enzymatic catalysis for the direct asymmetric one-pot synthesis of 2,2-disubstituted indol-3-ones from 2-arylindoles through concurrent oxidization and alkylation reactions is described. 2-Arylindoles can be photocatalytically oxidized to 2-arylindol-3-one with subsequent enantioselective alkylation with ketones catalyzed by wheat germ lipase (WGL). The chiral quaternary carbon center at C2 of the indoles was directly constructed. This mode of concurrent photobiocatalysis provides a mild and powerful strategy for one-pot enantioselective synthesis of complex compounds. The experiments proved that other lipases containing structurally analogous catalytic triad in the active site also can catalyze the reaction in the same way. This reaction is the first example of combining the non-natural catalytic activity of hydrolases with visible-light catalysis for enantioselective organic synthesis and it does not require any cofactors.
关键词： photochemistry,enzymes,heterocycles,synthetic methods,asymmetric catalysis
更新于2025-09-10 09:29:36
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[Topics in Organometallic Chemistry] || Functionalization of C(sp2)–H Bonds of Arenes and Heteroarenes Assisted by Photoredox Catalysts for the C–C Bond Formation
摘要： The formation of C–C bonds from arenes and heteroarenes through transition metal-catalyzed C–H bond functionalizations is one of the major achievements of these last decades. It is now possible to perform such transformations under mild reaction conditions with the help of visible light photocatalysis leading to eco-friendly and safer process to build organic molecules or materials. This chapter will focus on photoredox catalysis which involves a C(sp2)–H bond functionalization step for the formation of C(sp2)–C bonds [i.e., direct arylations and (per?uoro)alkylations] and will show how this hot topic contributes to the development of green chemistry.
关键词： MLTC photoredox catalysis,C(sp2)–H bond,Visible light,C–C bond formation
更新于2025-09-10 09:29:36
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Benzyl Alcohol Oxidation Using Gold Catalysts Derived from Au8 Clusters on TiO2
摘要： Atomically-precise gold clusters have gained attraction in catalysis due to high fraction of low-coordinated gold atoms, unique structural geometry and ligand effect. Phosphine-ligated gold clusters offer an advantage in the light of the labile gold-phosphorous bond for easy ligand removal. Here, heterogeneous gold catalysts were prepared by depositing atomically-precise phosphine-ligated gold clusters, Au8(PPh3)8(NO3)2 onto anatase-phase TiO2 nanoparticles. The catalysts were then calcined under two different conditions: O2 (Au8/TiO2:O2) and O2 followed by H2 (Au8/TiO2:O2–H2) at 200 °C, to dislodge phosphine ligands from the Au core. It was found that Au8/TiO2:O2–H2 catalyst showed a decent catalytic activity in benzyl alcohol oxidation while Au8/TiO2 and Au8/TiO2:O2 were completely inactive. Such results imply that small-size gold clusters (2–3 nm) alone do not always contribute to high catalytic activity of gold catalysts. It is suggested that the presence of NO3 species defines the catalytic activity of supported gold clusters in benzyl alcohol oxidation in the case of these catalysts and reinforces our initial claim in the previous work.
关键词： Heterogeneous catalysis,Oxidation,Alcohols,Green chemistry
更新于2025-09-10 09:29:36
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Disorder Engineering in Monolayer Nanosheets Enabling Photothermic Catalysis for Full Solar Spectrum (250 <b>-</b> 2500?nm) Harvesting
摘要： A persistent challenge in classical photocatalyst systems with extended light absorption is the unavoidable trade-off between maximizing light harvesting and sustaining high photoredox capability. Alternatively, cooperative energy conversion through photothermic activation and photocatalytic redox is a promising yet unmet scientific proposition that critically demands a spectrum-tailored catalyst system. Here, we construct a solar thermal-promoted photocatalyst, an ultrathin “biphasic” ordered–disordered D-HNb3O8 junction, which performs two disparate spectral selective functions of photoexcitation by ordered structure and thermal activated conversion via disordered lattice for combinatorial photothermal mediated catalysis. This in situ synthetically immobilized lattice distortion, constrained to a single-entity monolayer structure not only circumvents interfacial incompatibility but also triggers near-field temperature rise at the catalyst–reactant complexes’ proximity to promote photoreaction. Ultimately, a generic full solar conversion improvement for H2 fuel production, organic transformation and water purification is realized.
关键词： redox reaction,photothermic catalysis,defect engineering,order–disorder,full solar spectrum
更新于2025-09-10 09:29:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Deposition, Ligand Removal, and Applications of Atomically Precise, Chemically Synthesized Clusters on Metal Oxide Surfaces
摘要： It is now well established that the properties of metal particles can undergo dramatic changes in properties when they are reduced to the nanometer size regime. It is furthermore evident that these property changes become even more marked below 2 nm, into the nonscalar size regime. Such ultra-small “metal clusters” (also called “nanoclusters”) exhibit dynamic ?uxionality; thus they can barely be de?ned by one single shape. Moreover, their properties are observed to change with the addition or removal of just a single atom. These dramatic changes with cluster size arise because of the molecular-like energy levels present. These energy levels can not only affect the physical properties of the cluster but also its chemical reactivity and so there is a great expectation emerging that metal clusters could act as super-ef?cient catalysts.
关键词： light-emitting diodes,photocatalysis,nanoclusters,catalysis,metal clusters,photovoltaics,sensors
更新于2025-09-10 09:29:36
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Sensitizing effects of BiVO4 and visible light induced production of highly reductive electrons in the TiO2/BiVO4 heterojunction
摘要： BiVO4 is an e?cient and stable visible active photoanode material. However, due to its unfavorable conduction band position which falls below the H2 reduction potential, it fails to carry out the complete water splitting reaction. On the other hand, larger band gap TiO2 is able to photocatalytically split water, thanks to its negative conduction band energy. Aiming at verifying the possibility of sensitizing TiO2 with BiVO4 and employing the so obtained composite material in photocatalytic water splitting under visible light, we prepared and photoelectrochemically characterized TiO2/BiVO4 heterojunction electrodes. The photocatalytic reduction of methyl viologen, an electron acceptor probe with a reduction potential close to that of protons, was used to evaluate the reducing ability of the photoactive materials under visible light. An apparently counterintuitive electron transfer from photoexcited BiVO4 to the TiO2 conduction band occurs in the TiO2/BiVO4 heterojunction, resulting in TiO2 sensitization and production of highly reductive electrons, which appears to be favored by the band alignment occurring at the heterojunction.
关键词： Methyl viologen reduction,Photo(electro)catalysis,TiO2,BiVO4,Heterojunction,Visible light sensitization
更新于2025-09-10 09:29:36
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Modification of kaolinite from Pará/Brazil region applied in the anionic dye photocatalytic discoloration
摘要： The incorporation of titanium oxide and other transition metals on the surface of different materials has been shown to be a promising strategy to improve the efficiency of photocatalytic processes aiming at the decontamination of aqueous systems caused by persistent organic contaminants such as dyes. The objective of this work was to evaluate the catalytic properties of nanocomposites based on the kaolinite (Kaol) with TiO2 incorporated, obtained from the sol-gel method, used in discoloration of the coomasie brilliant blue dye (CBB) in aqueous solution. The nanocomposites were prepared from the reaction of titanium tetraisopropoxide with purified natural kaolinite and calcined at different temperatures. The samples were characterized by the XRD, FTIR, SEM-XED, BET-BJH and diffuse reflectance spectroscopy techniques, which demonstrated the structure, crystalline pattern, as well as the incorporation of titanium in the clay structure, changes caused by modification in morphology, texture and energy gap. The photocatalytic tests were performed using 5 × 10?5 mol L?1, 1.0 and 1.5 g L?1 concentration, respectively, to the CBB dye solution and to the synthesized materials. Among the nanocomposites, the sample calcined at 300 °C, KaolBT-300, presented the best photocatalytic performance. The addition of the H2O2 oxidant to the solution containing KaolBT-300 at the concentration of 1.5 g L?1 increased the discoloration percentage to 97.31% of the CBB solution dye after 120 min of irradiation. The discoloration kinetics of the CBB dye obeys the pseudo-first-order velocity law. Finally, the reuse of the KaolBT-300 sample in three consecutive cycles of photocatalysis demonstrated a significant adhesion stability of the TiO2 particles on the clay surface, indicating that it can be used in advanced oxidative processes for the degradation of organic pollutants.
关键词： Natural clay,Sol-gel synthesis,Heterogeneous catalysis,Titanium oxide,Water treatment,Dye
更新于2025-09-10 09:29:36