Heterogenization of Homogeneous Photocatalysts Utilizing Synthetic and Natural Support Materials

Homogeneous photocatalysis has considerably contributed to the green applications such as energy production and environmental decontamination. Currently, researchers mainly focus on the search for sustainable processes that can generate valuable...

Highlights on Recent Developments of Heterogeneous and Homogeneous Photocatalysis

Photocatalysis emerged in the last decades as a versatile technology, whose applications range from environmental remediation to hydrogen production, energy harvesting, and organic synthesis, with exciting examples also in medicine, electronics, and advanced functional materials [...]

Photocatalytic (Hetero)Arylation of C(sp3)–H Bonds with Carbon Nitride

Polymeric graphitic carbon nitride materials have attracted significant interest in recent years and found applications in diverse light-to-energy conversions such as artificial photosynthesis, CO₂reduction or degradation of organic pollutants. However, their utilization in synthetic photocatalysis especially in the direct functionalization of C(sp³)−H bonds remains underexplored. Herein, we report mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst for direct arylation of sp³ C−H bonds <i>via </i>a combination of<i> </i>hydrogen atom transfer and nickel catalysis. Our protocol has a broad synthetic scope (>70 examples including late-stage modification of densely functionalized bio-active molecules), is operationally simple, and shows high chemo- and regioselectivity. Facile separation and recycling of the mpg-CN catalyst in combination with its low preparation cost, innate photochemical stability and low toxicity are beneficial features overcoming typical shortcomings of homogeneous photocatalysis. Additionally, mechanistic investigations indicate that an unprecedented energy transfer process (EnT) from the organic semiconductor to the nickel complex is operating.

Photocatalytic (Hetero)Arylation of C(sp3)–H Bonds with Carbon Nitride

Polymeric graphitic carbon nitride materials have attracted significant interest in recent years and found applications in diverse light-to-energy conversions such as artificial photosynthesis, CO₂reduction or degradation of organic pollutants. However, their utilization in synthetic photocatalysis especially in the direct functionalization of C(sp³)−H bonds remains underexplored. Herein, we report mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst for direct arylation of sp³ C−H bonds <i>via </i>a combination of<i> </i>hydrogen atom transfer and nickel catalysis. Our protocol has a broad synthetic scope (>70 examples including late-stage modification of densely functionalized bio-active molecules), is operationally simple, and shows high chemo- and regioselectivity. Facile separation and recycling of the mpg-CN catalyst in combination with its low preparation cost, innate photochemical stability and low toxicity are beneficial features overcoming typical shortcomings of homogeneous photocatalysis. Additionally, mechanistic investigations indicate that an unprecedented energy transfer process (EnT) from the organic semiconductor to the nickel complex is operating.

Water-Soluble Polymeric Carbon Nitride Colloidal Nanoparticles for Highly Selective Quasi-Homogeneous Photocatalysis

Heptazine-based polymeric carbon nitrides (PCN) are well established as promising photocatalysts for light-driven redox transformations. However, the activity of these materials is hampered by their low surface area translating into low concentration of active sites accessible for reactants. Herein, we report, for the first time, a bottom-up preparation of PCN nanoparticles with a narrow size distribution (~10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months, and allow carrying out photocatalysis under <i>quasi</i>-homogeneous conditions. The rate of selective (up to 100%) photooxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde was enhanced by the factor of 6.5 as compared to conventional solid PCN and was accompanied by simultaneous H₂O₂ production <i>via</i> reduction of oxygen. The dissolved photocatalyst can be easily recovered and re-dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity. This work thus establishes a new paradigm of easily operable <i>quasi-</i>homogeneous photocatalysis with PCN, and opens up a route for other applications in which liquid aqueous operation or processing of PCN is required.

Water-Soluble Polymeric Carbon Nitride Colloidal Nanoparticles for Highly Selective Quasi-Homogeneous Photocatalysis

Heptazine-based polymeric carbon nitrides (PCN) are well established as promising photocatalysts for light-driven redox transformations. However, the activity of these materials is hampered by their low surface area translating into low concentration of active sites accessible for reactants. Herein, we report, for the first time, a bottom-up preparation of PCN nanoparticles with a narrow size distribution (~10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months, and allow carrying out photocatalysis under <i>quasi</i>-homogeneous conditions. The rate of selective (up to 100%) photooxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde was enhanced by the factor of 6.5 as compared to conventional solid PCN and was accompanied by simultaneous H₂O₂ production <i>via</i> reduction of oxygen. The dissolved photocatalyst can be easily recovered and re-dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity. This work thus establishes a new paradigm of easily operable <i>quasi-</i>homogeneous photocatalysis with PCN, and opens up a route for other applications in which liquid aqueous operation or processing of PCN is required.