| The interfacial catalysis of liquid-liquid biphase has been widely applied in various chemical catalytic systems.The immiscibility of reagents in the reaction system,however,commonly caused the high mass transfer resistance,which produces the low reaction effiency.The key point is to increase the contact area of the reactants for highly efficient catalysis.Generally,the simple vigorous agitation and addition of surfactants are used to increase contact area.However the agitation method causes the high energy consumption and the insufficient interfacial contact,which results in limitations of mass transfer and heat transfer.At the same time,the addition of surfactants brings a lots of problems,such as the separation and purification of the products,and recovery of the catalyst.Pickering interface catalysis is an important strategy in greem chemistry because the formation of high emulsion interfacial area sharply increases the contact area of immiscible reactans,realizing the efficient catalysis without solvents and agitation,which can figure out the above-mentioned problems in the interfacial catalysis of liquid-liquid biphase systems.Thereby Pickering interfacial catalysis has been widely applied in refining of fuel oil and cosmetics,and emulsion polymerization.In addition,the strong point of Pickering interfacial catalysis is to realize the multi-step chemical reactions(so-called the cascade reactions)in the same system via optimization of emulsion systems and usage of the difference of solubility between compounds.Equally important,the product can be simply purified by phase transfer depending on the relative solubilities of the chemical substances.Obviously,Pickering interfacial catalysis,acted as green,highly efficient,and lower energy consumption catalytic strategy,has attracted attention in green chemistry.The most critical element of Pickering interfacial catalytic systems is the solid particles acted as the stabilizer for emulsion and the catalyst for reaction systems.In general,the solid stabilizer can be divided into two types of Janus particles and homogeneous particles.Compared to homogeneous particles,Janus particles exhit higher interfacial adsorption energy and better interfacial activity,which result in the Pickering emulsion with the high stability and excellent thermodynamic performance.Therefore,it is very meaningful and challenging to prepare Janus solid particles stabilizer,which possess the high interfacial activity for the stable Pickering emulsion,the efficient loading of catalytic components,and easily recycle and reuse.On the basis of the controllable preparation of porous silica microspheres in our lab,the magnetically responsive Janus Au/SiO2 composited porous microspheres were designed and prepared.Pickering emulsion stabilized by as-synthesized Janus microspheres exhibited the extremely high mechanical stability and good thermodynamic performance.The as-prepared Pickering emuslions could achieve the effective interfacial catalysis in the three catalytic reactions.Specifically,the major work was done in the following two aspects:In the first part of the thesis,the magnetically responsive Janus Au/SiO2 composited porous microspheres were designed and prepared.Based on our previous efforts on preparation of hierarchical porous vinyl silica microspheres,the magnetically responsive hierarchical porous SiO2 microspheres were prepared in one-step multi-phase emulsion templated method.Then,the successful loading of Au NPs in hierarchical porous channels of SiO2 microspheres is achieved by taking advantage of the capture capacity of metal nanoparticles of amino groups on the surface of internal pores.Finally,the magnetically responsive Janus Au/SiO2 composited porous microspheres were prepared through a series of surface grafting chemical reactions.It is confirmed that the porous structure and the overall morphology still remain well after the multi-step modification by using SEM measurements.Besides,it was demonstrated that the magnetically responsive Janus Au/SiO2 composited porous microspheres were successful prepared from the results of TEM,XRD,XPS,AAS,N2 adsorption,contact angle,and magnetic characterization measurements.The as-prepared microspheres will be expected to be used as emulsifier and catalyst to achieve the stable Pickering emulsion and to realize Pickering interfacial catalysis.In the second part of the thesis,we focused on the behaviors and interfacial catalytic properties of the Pickering emulsion stabilized by the as-syntheiszed magnetically responsive Janus Au/SiO2 composited porous microspheres in the first part of the thesis.The interfacial activity of the microspheres was investigated by using the as-syntheiszed microsphere as stabilizer,the different organic solvents(benzene,toluene,p-xylene,ethylbenzene,benzyl alcohol,dichloromethane,trichloromethane,tetrachloromethane and decahydronaphthalene)as the oil phases,and the aqueous solution as the water phase.And then the mechanical property of Pickering emulsion with different organic phases was also investigated,suggesting the good mechanical stability of as-prepared emlsions.Based on this,the interfacial catalytic peropermance of emulsions stabilized by Janus SiO2 microspheres was investigated by selection of the reaction of lauraldehyde and glycol as the model system.The experimental results showed that the sulfonic groups acted as active sites which had a certain catalytic activity on the reaction of lauraldehyde and glycol.At the same time,the activity of sulfonic groups of Janus porous SiO2 microspheres was also used to achieve the dehydration and degradation of fructose in the emulsion interface.Finally,the catalytic oxidation of benzyl alcohol was studied by using the magnetically responsive Janus Au/SiO2 composited porous microspheres as stabilizers and catalysts in the Pickering interfacial catalysis system.The experimental results showed that the magnetically responsive Janus Au/SiO2 composited porous microspheres have a certain catalytic activity in solvent-free Pickering interface catalysis by using the 30%hydrogen peroxide solution as the oxidizing agent. |
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