Pickering Emulsion Stabilized By Magnetic Mesoporous Silica Particles With Surface Roughness And Its Application In Interfacial Catalytic

Pickering emulsion is a thermodynamically stable dispersion system that uses solid micro and nano particles as emulsifier to stabilize two incompatible liquids.This particle emulsion has the characteristics of environmental protection,easy design and good emulsion stability,and is widely used in the fields of interface catalysis,food,cosmetics and biomedicine.Pickering emulsion interfacial catalytic system is based on the high interfacial area provided by micro and nano particles.In this catalytic system,amphiphilic particles are usually selected,which can act as emulsifier,catalyst and catalyst carrier.However,this kind of particle emulsion catalytic system requires strict control of particle amphiphilism,and it is difficult to continue to stabilize Pickering emulsion after catalyst loading.Particles with surface roughness can greatly improve the stability of Pickering emulsion,but it is difficult to accurately control the surface morphology of particles due to the complex interfacial interaction,properties of growing substances and concentration during the preparation process.Therefore,it is an urgent problem to prepare micro-nano particles with adjustable surface roughness easily and in large quantities.In this paper,the research focuses on the control methods of surface roughness of nanoparticles and Pickering interface catalytic applications.Firstly,the magnetic mesoporous silicon particles with adjustable surface roughness were prepared by assembling silane/surfactant composite micelles on the interface of seed particles by heterogeneous nucleation growth mediated by growth substances.Then,the magnetic mesoporous silicon-supported platinum catalyst was prepared using the surface roughness particles as the support,and its near infrared photothermal performance and photothermal catalytic performance of p-nitrophenol were studied.Finally,Pickering emulsion was constructed with different surface roughness catalysts to study the interfacial catalytic hydrogenation reduction of nitroanisole.The main research contents and results of this paper are as follows:（1）Study on controllable preparation and formation mechanism of magnetic mesoporous silica particles with rough surfaceMagnetic mesoporous silica particles with surface roughness were prepared by introducing hydrophobic organosilane 1,2-bis（triethoxysilicyl）ethane（BTEE）into inorganic tetraethyl silansilicate（TEOS）as co-growth material using ferric oxide as seed particle and cetyltrimethylammonium ammonium bromide（CTAB）as pore-causing agent.The effect of the reaction kinetics of growth materials on the morphology of magnetic mesoporous silica particles and its regulation were studied by adjusting the dripping rate of growth materials and the concentration of growth materials.The formation mechanism of magnetic mesoporous silica particles with surface roughness was studied by adjusting the amount of CTAB,the drip-adding sequence of two kinds of silanes and the morphologies of nanoparticles over time.The results showed that increasing the dripping rate and decreasing the seed particle concentration could increase the surface roughness of the particles,and the addition amount of CTAB and the hydrophobic silane can regulate the interaction between the growth substance and seed particles,and control the nucleation mode of the growth substance on the surface of seed particles.Finally,the magnetic mesoporous silica particles with surface roughness can be prepared through the dual control of the interaction between the growth material and seed particles and the reaction kinetics of the growth material.（2）Preparation of magnetic mesoporous silicon-supported platinum catalysts with surface roughness and study on its near-infrared response photothermal catalytic performanceBased on the near-infrared responsiveness of ferric oxide,the photothermal effects of magnetic mesoporous silica particles with different surface roughness were studied.Using particles with high photothermal conversion efficiency as catalyst support,the platinum-supported catalysts prepared by in-situ reduction before and after amino modification were studied.Taking the hydroreduction reaction of p-nitrophenol as the research object,the catalytic performance and comparison of the catalyst under conventional,photothermal and water bath heating conditions were studied,andthe effect of the amount of catalyst on the catalytic reaction rate was investigated.The recyclability of catalyst was investigated.The results show that under near infrared irradiation,with the surface roughness of particles varies from nuclear shell,raspberry-like,multi-legged to tentacle-like,the photothermal conversion efficiency of the particles are 0.085,0.157,0.152 and 0.054,respectively.The raspberry-like particles have the strongest photothermal conversion efficiency.The particle size of loaded platinum decreased and the load increased after amino modification.In the reduction hydrogenation reaction of p-nitrophenol,the photothermal catalysis rate（3 min）was 1.07 min^-1,2.06 times that of conventional catalysis（6 min）,1.17 times that of water bath heating catalysis（4 min）,and the conversion frequency was as high as 101.67 min^-1,1.80 times that of conventional catalysis.It is 3.18 times that of commercial Pt/C catalyst(31.92 min^-1).With the increase of the amount of catalyst,the catalytic efficiency is improved obviously,especially the photothermal catalytic efficiency.After 10 cycles of catalytic reaction,the catalytic efficiency can still reach 96%.（3）Pickering emulsion stabilized by magnetic mesoporous silicon roughness particles and its interfacial catalytic applicationUsing magnetic mesoporous silica particles with roughness surface as solid particle emulsifier and decane as oil phase,after adding water,Pickering emulsion was formed by highspeed shear of homogenizer.The effectiveness of Pickering emulsion constructed by roughness particles was studied.Based on the formation of Pickering emulsion,the regulation of the amount of particle,particle surface charge properties（positive and negative）under different p H on Pickering emulsion was studied,and the magnetic responsiveness and storage stability of Pickering emulsion were investigated.Furthermore,the Pickering emulsion was constructed with magnetic mesoporous silicon-supported platinum catalyst with the same surface roughness,and the catalytic performance of its Pickering interface for reducing hydrogenation of p-nitroanisole was studied.The results showed that the particles with surface roughness will be in Wenzel wet state under the action of capillarity force and surface contact line nailing,and the emulsification performance is greatly improved,which can be used to directly construct emulsion.The particle size of emulsion decreases with the increase of the amount of particle.When the particle charge intensity is maximum（p H=10）,the emulsion formed is the most stable and the particle size is the smallest.The prepared emulsion has good magnetic response and storage stability.It will not break milk under the external magnetic field,and the storage stability can be up to 3 months.The Pickering interface catalyzed the hydrogenation of nitroanisole based on petal-shaped magnetic mesoporous silica-supported nano platinum catalyst,and the conversion rate of 4-nitroanisole reached more than 80%within 15 min,which was 14 times higher than that of the unemulsified catalytic system.In summary,in this paper,CTAB was used as pore-inducing agent,and magnetic mesoporous silicon particles with surface roughness ranging from nuclear shell to multi-foot morphology were prepared by heterogeneous nucleation growth method mediated by TEOS/BTEE mixed silane coupling agent,and platinum-carrying catalysts were prepared by using them as the carrier loaded with nano-platinum.The rate of 4-nitrophenol catalyzed by near infrared photothermal catalysis in aqueous phase is 2.06 times that of conventional catalysis.Meanwhile,the prepared platinum catalyst with rough surface can be used as emulsifying agent to stabilize Pickering emulsion.The interface catalysis of Pickeirng emulsion for 4-nitroanisol is successfully realized,and the conversion efficiency is up to 80%.The above not only provides a new idea for designing new functional nanoparticles,but also broadens the application scenarios of coarse particles.