The Preparation Of Janus Nanoparticles Stabilized Pickering Emulsions For Enzyme Immobilization

Encapsulation of enzymes during the creation of an emulsion via micro/nanoparticles is a simple and efficient route for enhancing enzyme catalysis in organic media. In this thesis, we prepared three kinds of SiO2 Janus particles(JPs), namely amphiphilic JPs, aldehydes modified JPs, and mesoporous JPs, via the wax/water emulsion method. The Pickering emulsions were formed using these JPs as stabilizers for the encapsulation of enzyme molecules for catalysis purposes in organic media. Furthermore, the lipase from Candida sp. was chosen as a model enzyme for encapsulation within the JPs capsules during their formation, then we evaluated the catalytic performance of enzymes immobilized in three different JPs capsules according to the esterification of 1-hexanol with hexanoic acid.(1) Amphiphilic SiO2 JPs: We demonstrated that the JP capsules had a monolayer shell consisting of closely packed silica JPs. The capsules were on average 5-50 μm in diameter. The results showed that the Pickering emulsion stabilized via amphiphilic silica JPs presented no obvious changes in physical appearance after 15 days, indicating the high stability of the emulsions and JP capsules. It was found that the specific activity of the encapsulated enzymes(28.7 U mL-1) was more than 5.6 times higher than that of free enzymes in a biphasic system(5.1 U mL-1). The enzyme-loaded capsule also exhibited high stability during the reaction process and good recyclability. In particular, the jellification of agarose in the JP capsules further enhanced their operating stability. The enzyme fractions in the jellified capsules retained 65% of their initial specific activity after eight cycles.(2) Aldehydes modified SiO2 JPs: We developed an enzyme immobilization method via the encapsulation of enzyme within aldehydes modified SiO2 JPs assembled microcapsules in Pickering emulsion. It was found that the specific activity of the encapsulated enzymes was 156.4 U mL-1, which was much higher than that of free enzymes in a biphasic system(8.6 U mL-1). After 24 h incubation, the specific activity of the encapsulated enzymes increased to 172.5 U mL-1. This increased activity should be attributed to binding of enzyme positioned in the capsule core onto the JPs via the aldehydes-amide reaction.(3) Mesoporous SiO2 JPs: The mesoporous SiO2 nanoparticles with pore size of 2.5 nm and specific surface area of 862.044 m2 g-1 were synthesized. Using these mesoporous SiO2 as starting materials, we prepared mesoporous SiO2 JPs via the selective modification in the wax/water emulsion. We demonstrated the formation of a Pickering emulsion containing the encapsulated enzyme with mesoporous SiO2 JPs as stabilizer in heptane/enzyme solutions. The results showed that the specific activity of the encapsulated lipase was 65.9 U mL-1, which was 16 times higher than that of the free lipase. This excellent catalytic activity should be attributed to the large interfacial area of Pickering emulsion and the porous structure of SiO2 JPs.