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    Unraveling Particle Size and Roughness Effects on the Interfacial Catalytic Properties of Pickering Emulsions

    Year: 2020

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 599, AUG 20

    Authors: Li, Yao; Zhao, Guolin; Hong, Bing; Zhao, Shuangliang; Han, Xia; Pera-Titus, Marc

    Organizations: CNRSCentre National de la Recherche Scientifique (CNRS)European Commission; Solvay; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21808056, 21878078]; 111 Project of ChinaMinistry of Education, China - 111 Project [B08021]

    Keywords: Pickering Interfacial Catalysis; emulsion; amphiphilic silica; acetalization; particle size; surface roughness

    Pickering Interfacial Catalysts (PIC) has emerged as a powerful concept for designing multiphasic reactions between immiscible reagents using heterogeneous catalysts. Nonetheless, systematic studies addressing the influence of the particle self-assembly on the catalytic properties are scarce. To fill this gap, here we studied the effect of the particle size and surface roughness of catalytic nanoparticles on the reactivity of non-aqueous immiscible systems in the presence of Pickering emulsions. To this aim, we prepared a library of amphiphilic silica nanoparticles with the same surface properties and bearing catalytically active acid centers, but showing variable particle sizes in the range 90-460 nm and surface roughness. The nanoparticles were characterized in detail using different techniques, including acid-base titration, TGA, TEM and DLS. The silicas were tested in the biphasic acetalization reaction of dodecanal and ethylene glycol. The catalyst productivity was enhanced for smaller sized nanoparticles ( < 210 nm) as a result of the formation of more stable ethyleneglycol-in-dodecanal emulsions along with larger interfacial surface areas and a more compact interfacial self-assembly of particles. By contrasting the experimental emulsification results with dissipative particle dynamics simulations combined with the generalized Young equation, the particle-size dependence of ethyleneglycol-in-dodecanal emulsions could be explained by a stabilizing role of the line tension. The surface roughness of the particles was found to be detrimental for emulsion stability, but its negative effect was largely compensated by the stabilizing role of the line tension, especially for smaller particles. Overall, the particle size exerts a more prominent effect than the surface roughness on emulsion stability and interfacial catalysis for the ethyleneglycol/dodecanal system.
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