Fabrication,Performance Of Amphiphilic Janus Nanoparticles And Applications In Catalysis

Janus particles refer to those particles with non-centrosymmetrical particles.In contrast with homogeneous particles,Janus particles would exhibit different properties and potential applications because Janus particles not only exhibit the properties of the components but also some other extending ones.Therefore,researchers pay a lot of attention on this topic.Till now,the researches on Janus particles mainly focus on preparation,especially for organic ones.These particles,however,would undergo deformation or even disintegration,yielding inferior properties.Fabrication of Janus particles which could be applied to harsh conditions is of crucial practical importance.Moreover,the applications of Janus particles are lagging behind relatively,especially for those in catalysis.Herein,spherical and dumbbell-shaped Janus nanoparticles were prepared by Pickering emulsion template and wet-chemical process,respectively.The Pickering emulsion stabilized by this spherical Janus nanoparticle exhibited much better stability than Pickering emulsion from homogeneous nanoparticles based on centrifugation tests.Excellent performance could be obtained in cascade reations if catalytic active species with different properties were loaded onto respective regions of a single dumbbell-shaped Janus nanoparticle regioselectively.The main results are as follows.1.Spherical inorganic Janus nanoparticle NH₂-SiO₂-C8 was prepared by Pickering emulsion template method.NH₂-SiO₂-C8 showed excellent interfacial activity and stable Pickering emulsions can be obtained from many oil-water two phase systems with various interfacial tensions.Phase inversion can be triggered by variation of pH in water phase.This is the first example in Pickering emulsion stabilized with inorganic Janus particles.The stability of Pickering emulsion from Janus particle was investigated via different experimental methods.By centrifugation test,the desorption energy of Janus particles from oi-water interface of Pickering emulsion was 3.2 times higher than that of homogeneous particles,which is in high accordance with theoretical calculation result.To the best of our knowledge,this is the first time to demonstrate this result experimentally.The library of Pickering emulsion was further enhanced.2.On the basis of previous work of our group,dumbbell-like Janus nanoparticle RF@void&PMO with yolk@shell architecture was fabricated by combining wet-chemical method and hydrothermal treatment process.This Janus nanoparticle contained one periodical mesoporous organosilica（PMO）compartment and the other yolk@shell structure with resorcinol formaldehyde as the core and PMO as the shell.The asymmetric property showed not only in its components,but also in wettability,hollow void,and pore size.The formation of void can be attributed to confined hydrothermal treatment in which temperature,time,and ammonia water played important role in the dimension of void.As far as we known,this novel Janus nanoparticle is the first one in literature.3.On the basis of RF@void&PMO,bifunctional hybrid nanoreactor（CALB/RF）@void&[Pd/（PMO-NH₂）]was constructed after loading incompatible active species CALB and Pd regioselectively onto respective compartment.The deactivation of CALB and Pd can be avoided due to spatially isolation.This nanoreactor demonstrated good activity,selectivity,stability,and universality after being applied to dynamic kinetic resolution of primary aromatic amines.4.On the basis of RF@void&PMO,bimetallic hybrid nanoreactor（Pt/RF）@void&[Ni/（PMO-NH₂）]was fabricated after loading Pt and Ni regioselectively onto respective compartment.Pickering emulsion can be obtained by stabilizing oil-water two phase system with this nanoreactor due to its amphiphilicity.Applied this nanoreactor to cascade reaction“hydrogenation of ammonia borane and reduction of nitro-compounds”,substrates can convert to corresponding products in a rapid and high-efficient mode under static condition because Pt and Ni were mainly located at oil phase and water phase,respectively,exhibiting synergistic effect.In this situation,hydrogenation of ammonia borane and reduction of nitro-compounds were catalyzed by Ni and Pt,respectively.The utilization efficiency of active species was enhanced greatly due to their favorable orientation at the oil-water interface.This is an eco-friendly process on account of no additional energy input.Janus nanoparticles fabricated in this research exhibited excellent performance for cascade reactions in catalytic processes,which open up a new avenue for extending applications of Janus nanoparticles.