A Pickering foam is a complex system where gas bubbles are entrapped in a continuous liquid phase by the adsorption of particles at the gas-liquid interface. In this thesis, we first unveiled the surface-active properties of Aquivion® D98 for producing stable foams in a variety of organic solvents and water. The foaming properties were studied after handshaking and high-speed homogenization. The foam volume fraction generated by Ultra-Turrax was as high as 94% using 5 wt% Aquivion® D98 loading in benzyl alcohol. Both the foamability and foam stability were drastically with Aquivion® D98 compared to polytetrafluoroethylene and fluorinated. The effect of the solvent properties on foam formation was systematically investigated using Aquivion® D98 as stabilizer. The presence of hydrogen bonds formed between the sulfonic acid groups of Aquivion® D98 and the solvent was found as key driver for enhancing the foaming properties.
Taking advantage of the excellent foaming properties of Aquivion® D98, we designed a foaming system for one-pot cascade deacetalization and hydrogenation in water. The combination of Aquivion® D98 and homemade Pd/SiO2 particles achieved a remarkable catalytic performance, with a yield of alcohol 2 times higher than that of a conventional multiphase reaction system. This is attributed to the pronounced increase in reaction interface area and preferential adsorption of particles at the air-water interface. Indeed, cooperation between sulfonic acid centers and palladium active sites was an essential prerequisite for improving the catalytic activity in the foaming system.
Next, we developed a new type of surface-active, non-halogenated particles stabilizing foams in organic solvents. Biphenyl-bridged particles could adsorb at the air-oil interface, lowering the solvent surface tension and hence facilitating the generation of high-volume foams in benzyl alcohol. The particle structure was directly related to the foamability, and both the presence of biphenyl rings (mimicking the structure of the aromatic solvent) and ethoxy groups (well wetted by the gas phase) were essential to ensure good foaming. In addition, the contact angle was a key parameter controlling foaming. Foams were generated in the contact angle range between 32° and 53°. At the same time, the surface tension of the solvent should lie in the range 35-44 mN·m-1.
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