Promoting the aerobic Baeyer-Villiger oxidation of ketones over carboxylic multi-walled carbon nanotubes

Intensifying Photocatalytic Baeyer-Villiger Oxidation of Ketones with the Introduction of Ru Metalloligands and Bimetallic Units in POM@MOF

The synthesis of visible light-responsive and efficient photocatalysts toward green Baeyer-Villiger oxidation organic synthesis is of extraordinary significance. In this work, we have synthesized two examples of visible light responsive crystalline polyoxometalate@metal-organic framework materials Ru-NiMo and Ru-CoMo by introducing Ru metalloligands and {CdM3O12} bimetallic units (M = Ni or Co). This is the first report of metalloligand-modified polyoxometalate@metal-organic framework materials with bimetallic nodes, and the materials form a three-dimensional framework directly through coordination bonds between {CdM3O12} bimetallic units and metalloligands. In particular, Ru-NiMo can achieve efficient photocatalytic conversion of cyclohexanone to ε-caprolactone in yields as high as 95.5% under visible light excitation in the range of λ > 400 nm, achieving a turnover number and turnover frequency of 955 and 440 h-1, respectively, which are the best known photocatalysts for Baeyer-Villiger oxidation, while apparent quantum yield measured at 485 nm is 4.4%. Moreover, Ru-NiMo exhibited excellent structural stability and recyclability, producing a 90.8% yield after five cycles of recycling.

Additive-Free Baeyer–Villiger Oxidation of Cyclic Ketone Catalyzed by Carboxylic-Functionalized Poly(Ionic Liquids) and Polyoxometalate Ionic Self-Assemblies

Two carboxylic functionalized poly(ionic liquids) and polyoxometalate ionic self-assemblies with tunable amphiphilic and oxidative activity and porous structure were designed and synthesized. They were used as efficient heterogeneous catalysts exhibiting excellent catalytic activity and quite stable reusability in additive–free Baeyer-Villiger oxidation of cyclic ketones, directly using 30% H2O2 solution in liquids–phase. Under optimum conditions, the corresponding lactones were obtained with yields ranging from 59.6 to 90.5%. The unique combination of carboxylic group with polyoxometalate anion, amphiphilic property, and porous structure is revealed to be responsible for their excellent catalytic performances in oxidation.

Electrochemiluminescence Quenching Sensor of a Carboxylic Carbon Nanotubes Modified Glassy Carbon Electrode for Detecting Crystal Violet Based on Nitrogen-doped Graphene Quantum Dots@Peroxydisulfate System

In this work, the electrochemiluminscence system of nitrogen-doped graphene quantum dots (N-GQDs) and K₂S₂O₈ was built for the determination of crystal violet (CV). Meanwhile, a carboxylic carbon nanotubes modified glassy carbon electrode (CCNTs/GCE) was used as an ECL sensor. Thanks to the excellent electron transfer ability and large surface area of CCNTs, the ECL signal of N-GQDs@S₂O₈^2- was remarkablely amplified. With the presence of a low concentration of CV, a distinct decrease of the ECL signal was observed due to a quenching effect of CV on the ECL emission. Moreover, the quenched ECL intensity responded linearly to the logarithm of CV concentration within the range of 0.05 - 5 μmol/L, with a LOD of 45 nmol/L (S/N = 3). The proposed ECL system exhibited high sensitivity and specificity to CV, which was successfully applied in the practical detection of CV in real water samples from a local fishpond farm.