Amine Functionalized Graphene Oxide Stabilized Pickering Emulsion for Highly Efficient Knoevenagel Condensation in Aqueous Medium

Particle shape anisotropy in pickering interfacial catalysis for Knoevenagel condensation

Dispersions of two immiscible liquids stabilized by solid particles are termed as Pickering emulsions. Stability of such emulsions is affected by various parameters such as amount of solid particle, method of emulsification, size, and shape of particles, etc. In this study, MgO samples prepared by different methods and characterized by XRD, FESEM, HRTEM, DLS, and CO2-TPD techniques were utilized for stabilizing o/w Pickering emulsions. The effect of particle shape on Pickering Interfacial Catalysis (PIC) for Knoevenagel condensation was investigated. It was found that in the case of rod and plate shaped particles, emulsion stability and catalytic activity were higher as compared to those obtained with other MgO samples prepared. The applicability of the MgO-PIC system is also successfully demonstrated for gram scale synthesis (85 % yield in 30 min). The MgO-PIC system was found to be reusable for at least five cycles without substantial loss in activity.

High-Performance Heterogeneous Thermocatalysis Caused by Catalyst Wettability Regulation

Catalyst wettability regulation has emerged as an attractive approach for high catalytic performance for the past few years. By introducing appropriate wettability, the molecule diffusion of reactants and products can be enhanced, leading to high activity. Besides this, undesired molecules are isolated for high selectivity of target products and long-term stability of catalyst. Herein, we summarize wettability-induced high-performance heterogeneous thermocatalysis in recent years, including hydrophilicity, hydrophobicity, hybrid hydrophilicity-hydrophobicity, amphiphilicity, and superaerophilicity. Relevant reactions are further classified and described according to the reason for the performance improvement. It should be pointed out that studies of utilizing superaerophilicity to improve heterogeneous thermocatalytic performance have been included for the first time, so this is a comparatively comprehensive review in this field as yet.

Pickering emulsions stabilized by metal-organic frameworks, graphitic carbon nitride and graphene oxide

Pickering emulsion is a heterogeneous system consisting of at least two immiscible liquids, which are stabilized by solid particles, in which organic solvent or water is dispersed into other phase in form of micrometre-sized droplets. Compared to traditional emulsions stabilized by surfactant, solids are cheap and can be easily separated and recycled by centrifugation or filtration after use. Moreover, the properties of Pickering emulsions can be adjusted by using different types of solid particles. Up to now, Pickering emulsions have been applied in a wide range of areas such as material science and catalysis. Here we review recent studies on Pickering emulsions stabilized by metal-organic framework, graphitic carbon nitride and graphene oxide.

The behavior of graphene oxide trapped at the air water interface

Graphene oxide is a derivate of graphene obtained by oxidation of graphite and other carbonaceous materials. The more accepted structure consists in carbonyl and carboxyl groups located at the edge of the graphene network and hydroxyl and epoxy groups attached to the basal plane. The percentage of O-groups depends on the synthesis route and the material used as carbon source. In addition, highly oxidized fragments, called oxidative debris, OD, are produced during the oxidation process. These fragments are adsorbed onto the graphene oxide network and can be removed by alkaline washing. The purified material has lower O/C ratio than graphene oxide and its properties are also quite different. Due to its structure, graphene oxide can be adsorbed at the air-water interface of the aqueous solution by diffusion, Gibbs monolayers, or by spreading on a clean water subphase resulting in a Langmuir film. This review is intended to provide information on the importance of controlling the chemical composition, structure, size, and oxidative debris, on the manufacture of graphene oxide films. To this end the review shows the influence of the synthesis route and the starting material on the structure of graphene oxide and analyzes several examples of the behavior and properties of films prepared with different types of graphene oxides. The great variability of behaviors of graphene oxide films caused by the different structure of this material provides a great opportunity to fine-tune the properties of films according to the needs of different applications.

Catalytically active coordination polymer with a tiny Zn2Se2 ring bridged by bis-selone

The unprecedented architecture of a one-dimensional coordination polymer with a tiny Zn₂Se₂ ring system incorporated in the hydrogen-bonded array has been prepared, where the di-selone ligand functions as a unique neutral bridging ligand. The coordination polymer shows excellent catalytic activity in substituted 8-hydroxy-2-quinolinyl synthesis through Knoevenagel condensation reaction.