Solvent-controlled synthesis of Ti-based porphyrinic metal–organic frameworks for the selective photocatalytic oxidation of amines

Twin boundary defect engineering in Au cocatalyst to promote alcohol splitting for coproduction of H2 and fine chemicals

The microstructure of Au metal cocatalyst has been shown to significantly influence its optical and electronic properties. However, the impact of Au defect engineering on photocatalytic activity remains underexplored. In this study, we synthesize different Au-TiO2 composites by in-situ hybridizing face-centered cubic (F-Au) and twin boundary defect Au (T-Au) nanoparticles (NPs) onto the surface of TiO2. We find that T-Au NPs with twin defects serve as highly efficient cocatalysts for converting alcohols into their corresponding aldehydes while also generating H2. The optimized T-Au/TiO2 composite yields an H2 evolution rate of 6850 µmol h-1 g-1 and a BAD formation rate of 6830 µmol h-1 g-1, about 38 times higher than that of blank TiO2. Compared to F-Au/TiO2, the T-Au/TiO2 composite enhances charge separation, extends the lifetime of electrons, and provides more active sites for H2 reduction. The twin defect also improves alcohol reactant adsorption, boosting overall photocatalytic performance. This research paves the way for more studies on defect engineering in metal cocatalysts for enhanced catalytic activities in organic synthesis and H2 evolution.

Porphyrin-Based Metal-Organic Framework Materials: Design, Construction, and Application in the Field of Photocatalysis

Metal-organic frameworks (MOFs) are a novel category of porous crystalline materials with an exceptionally high surface area and adjustable pore structure. They possess a designable composition and can be easily functionalized with different units. Porphyrins with conjugated tetrapyrrole macrocyclic structures can absorb light from ultraviolet to visible light regions, and their structures and properties can be facilely regulated by altering their peripheral groups or central metal ions. Porphyrin-based MOFs constructed from porphyrin ligands and metal nodes combine the unique features of porphyrins and MOFs as well as overcoming their respective limitations. This paper reviewed the design and construction, light absorption and charge transfer pathways, and strategy for improving the photocatalytic performance of porphyrin-based MOFs, and highlighted the recent progress in the field of CO2 reduction, hydrogen evolution, organic synthesis, organic pollutant removal, and nitrogen fixation. The intrinsic relationships between the structure and the property of porphyrin-based MOFs received special attention, especially the relationships between the arrangements of porphyrin ligands and metal nods and the charge transfer mechanism. We attempted to provide more valuable information for the design and construction of advanced photocatalysts in the future. Finally, the challenges and future perspectives of the porphyrin-based MOFs are also discussed.

Selective oxidation of amines powered with green light and oxygen over an anthraquinone covalent organic framework

The exploration of emerging photocatalysts like covalent organic frameworks (COFs) is an essential but challenging endeavor to find sustainable solutions for selective organic transformations. Anthraquinones are envisaged to construct COFs for visible light photocatalysis because their derivatives are employed industrially as oxidation catalysts or organic dyes. Herein, an anthraquinone COF, TpAQ-COF, is successfully constructed with 1,3,5-triformylphloroglucinol (Tp) and 2,6-diaminoanthraquinone (AQ). Then, the selective oxidation of amines over TpAQ-COF is implemented. Amines can be effectively converted into corresponding imines over TpAQ-COF powered with green light and oxygen, during which superoxide radical anion is discerned as the pivotal reactive oxygen species. This work suggests that COFs could inherit the advantages of molecular building blocks for selective reactions powered with broad visible light.

Salt-templated porous melamine-based conjugated polymers for selective oxidation of amines into imines under visible light

Conjugated polymers have a broad application foreground in the field of photocatalytic organic synthesis to produce value-added chemicals due to their functional diversity, broad light responsive ability, high thermal and chemical stability, and tunable band structure. Herein, using mixed chloride salts (i.e., NaCl/LiCl) as building template, a series of porous conjugated polymers constructed by melamine and terephthalaldehyde monomers were obtained through a Schiff-base reaction in the absence of any external solvent. Melamine-terephthalaldehyde polymer (i.e., PMTPA-x, x represents the mass ratio of salt-mixture to mixed precursors of PMTPA) materials displayed porous morphologies and possessed different energy band structures via regulating the mass ratio of mixed-salt to monomers. Specifically, PMTPA-20 has a larger specific surface area and more suitable redox potential towards the photocatalytic oxidative coupling of amines to imines. Under visible light, with molecular oxygen as oxidant, PMTPA-20 achieves 97% conversion of benzylamine in 8 h which is 3.9 times higher than that of pristine PMTPA (25% conversion in 8 h). In addition, PMTPA-20 catalyst has good structure stability and reusability performance for photocatalytic reactions.