Owing to the functionalities and broad utilization of these materials in different fields, the PEs stabilized by them have unique properties and largely expanded applications. Recently, many efforts have been devoted to the construction of PEs stabilized by metal–organic frameworks (MOFs), graphitic carbon nitride (g-C 3N 4) and graphene oxide (GO). In earlier work, silica (SiO 2), 13,14 polymers, 15,16 metal oxides 17 and carbon black 18 are the mostly adopted emulsifiers to stabilize PEs. Oil-in-water emulsions are usually produced by solid particles with more hydrophilic surfaces, while particles with more hydrophobic surfaces are conducive to the formation of water-in-oil emulsions. Only particles with intermediate hydrophilicity can readily accumulate at the oil–water interface and stabilize emulsions. 9–12 Generally, stabilization of solid particles at the interface is considered to be directed by particle wettability. ![]() The inherent properties of solid particles can affect the preparation, characteristics and application of PEs. 4–6 Therefore, PEs have broad applications in the fields of food, cosmetics, petroleum, pharmacy, and biomedicine, interfacial catalysis, fabrication of superstructures, 4,7,8 etc. 2,3 Compared with the traditional emulsions stabilized by a surfactant, PEs have many advantages, such as low cost, easy separation and recycling of solid, good stability and biocompatibility. Alternatively, colloid particles could be used to stabilize two immiscible fluids to form macro-emulsions, which are called Pickering emulsions (PEs). Generally, macro-emulsions are stabilized by amphiphilic materials like surfactants. 1 Different from the thermodynamically stable micro-emulsions, of which the droplets are smaller than 100 nm, macro-emulsions are thermodynamically unstable and have larger droplets in the range of 0.1–10 μm. 1 Introduction Macro-emulsions are mixtures of two immiscible liquids (usually water and an organic solvent). Here we review recent studies on Pickering emulsions stabilized by metal–organic framework, graphitic carbon nitride and graphene oxide. Up to now, Pickering emulsions have been applied in a wide range of areas such as material science and catalysis. Moreover, the properties of Pickering emulsions can be adjusted by using different types of solid particles. ![]() Compared to traditional emulsions stabilized by surfactant, solids are cheap and can be easily separated and recycled by centrifugation or filtration after use. 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.
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