Construction of Microreactor Based on Pickering Emulsion and Its Catalytic Performance

Author:Qi Liang

Supervisor:luo zhi gang


Degree Year:2019





Pickering emulsion is a kind of emulsion which solid particles adsorbs and stabilizes at the oil-water interface.In chemical catalysis,as a stabilizer,solid catalyst can effectively adsorb at the oil-water interface,and the reactants and products can complete the whole catalytic process through dissolution,diffusion,transmission and migration between water phase and oil phase.In biocatalysis,Pickering emulsion protects water-soluble enzyme molecules in the water phase to avoid contact with organic reagents.Due to its clear structure and minimalist preparation process,researchers have been analyzing and exploring Pickering emulsion microreactors in many aspects for a long time.In this thesis,the natural polymer starch,gold nanoparticles(AuNP),metal organic framworks(MOFs),enzymes and dopamine were used to achieve the greeniztion,sustainablility and biochemical alteration of Pickering emulsion microreactor.Through the learning from materials in different fields,it is believed to broaden the research direction and enrich the research content of Pickering emulsion microreactor.The main research is as follows:(1)The pH responsive starch nanoparticles prepared by grafting of dimethylaminoethyl methacrylate(DMAEMA)and gelatinization-alcohol precipitation method were used to stabilize Pickering emulsion.By adjusting pH value,the changing rule of emulsion was explored.Meanwhile,the pH responsiveness mechanism of emulsion was summarized by the surface characteristics and size of nanoparticles.Then D-g-SNP/AuNP stabilized Pickering emulsion microreactor was constructed using pH-responsive starch nanoparticles as the stabilizers,and was used for catalytic hydrogenation of p-nitroanisole.Compared with the single phase system and the planar system,it is confirmed that the emulsion system has higher yield,and its recyclable catalytic performance could maintain at least 8 reaction cycles.(2)Through optimizing the rational adjustments of anhydride and phthalic anhydride substitution degree and cooperation with the gelatinization-precipitation method,we synthesized two starch nanoparticles with the similar regular spheres but distinct surface characteristics.In the esterification of 1-butanol and vinyl acetate,the specific activity of CALB in the o/w or w/o Pickering emulsion microreactor was much higher than that of free enzymes in the monophasic and biphasic system.By contrast,a higher catalysis efficiency was achieved in o/w Pickering emulsion microreactor because of less substrate transfer distance in phase and higher enzyme affinity on the interface.Impressively,the products could be isolated from both Pickering emulsion microreactors and their high effectiveness was highlighted by at least 10 reaction cycles.(3)A highly porous lipase-loaded MOF composite was synthesized via biomimetic mineralization of ZIF-8 around lipase from Candida rugosa(CRL).For deep understanding of mineralization process,the role of CRL in modulating size,crystallinity and morphology of composite was clarified in detail.More importantly,in this process,we discovered that surface-embedded CRL of crystal was responsible for surface chemical characteristics of CRL-loaded ZIF-8 that directly affected its ability to stabilize oil-in-water emulsion.Furthermore,through the comparison of hydrolyses involving small substrate(p-nitrophenyl butyrate)and a larger one(p-nitrophenyl palmitate),we have confirmed that size selectivity of ZIF-8 shell could lead to different locations of substrates in contact with enzymes,thus resulted in the discrepancies in catalysis efficiency.Impressively,we could employ this system for transesterification by only changing the encapsulated enzyme and optimizing the ratio of oil/water.The excellent catalytic performance highlighted the versatility of this Pickering emulsion microreactors.(4)Through the combination of MOF biomimetic mineralization and dopamine bioviscosity,a composite nanomaterial PDA@ZIF-8,which could locate and assemble the positions of glucose oxidase and lipase,was synthesized and its formation mechanism was revealed.Four different Pickering microbioreactors with double enzymes were constructed using enzyme loaded PDA@ZIF-8 for glucose-pyridine biphase reaction.By analyzing the difference in the utilization degree of intermediate product H2O2 in the four bioreactors,the relationship between double enzymes assembly and reaction efficiency was established.