Structural Regulation,emulsifying Performance And Application Of Ultrathin SiO₂ Two-dimensional Nanoporous Materials

Pickering emulsions have been widely used in various fields,but the construction of Pickering emulsions under extreme conditions such as special liquid-phase systems and high temperatures still faces the problem of insufficient stability,which limits their wider and deeper applications.At present,the research on improving the stability of Pickering emulsions starting from particle emulsifiers mainly focuses on the material selection and morphology regulation of particles,and the influence of the micro and nano structure of particles on the emulsification performance has not received the due attention.In this thesis,ultrathin two-dimensional nanoporous materials with theoretical advantages in emulsification performance were selected as the target of study,and the correlation between their micro and nano structures and emulsification performance was investigated to develop particle emulsifiers with super emulsification performance which can be prepared on a large scale.Three types of ultrathin SiO₂ nanoporous materials with different pore sizes and morphological structures were prepared by using the method of emulsion interface-induced self-assembly combined with pore-making technology.The super emulsification performance of asymmetric ultrathin SiO₂ nanonets was found to achieve stable emulsification of eight different types of liquid systems at high temperatures,including those difficult to be emulsified by conventional particle emulsifiers.The Pickering emulsion constructed with asymmetric ultrathin SiO₂ nanonets achieved efficient interfacial catalytic degradation of PET and higher reaction efficiency at lower temperatures compared with the homogeneous reaction system.The results of this thesis show that the micro and nano structure of the particles has a significant influence on their emulsification performance and it is one of the key factors to be considered in the development of high performance particle emulsifiers.The specific studies and results of this thesis are as follows:1.Preparation and structural regulation of ultrathin SiO₂ two-dimensional nanoporous materials.Using an emulsion interfacially induced self-assembly method incorporating micelle soft template pore-making technology,ultrathin SiO₂two-dimensional nanomaterials were prepared and open pore structures were constructed in them.Three types of ultrathin SiO₂ nanoporous materials including mesoporous nanosheets（MNSs）,meso/macroporous topology-nanosheets（TNSs）and asymmetric nanonets（ANNs）were prepared by tuning the open pore size and microstructure.By studying the effects of surfactant/silane ratio and the ratio of different types of silane reagents on their micro and nano structures,the continuous regulation of the open pore size and microstructure among the above three materials was achieved.By studying the evolution process between the structures of the three materials,the formation and evolution mechanism of ultrathin SiO₂ two-dimensional nanoporous materials were elucidated.The preparation method and regulation developed in this paper are universal that provides a reference for the preparation of other two-dimensional nanoporous materials.2.Influence of micro and nano structures of ultrathin SiO₂ two-dimensional nanoporous materials on their emulsification properties.Using octyltrimethoxysilane to hydrophobically modulate three ultrathin SiO₂ two-dimensional nanoporous materials,M-MNSs,M-TNSs and M-ANNs were obtained.By investigating the effect of the modification degree on their emulsification performance,it was found that M-ANNs with a contact angle of 120°as a particle emulsifier were able to stabilize the emulsification of special liquids such as concentrated hydrochloric acid,concentrated ammonia,saturated brine and decane liquid systems.The differences in emulsification performance between SiO₂ nanospheres,M-MNSs,M-TNSs and M-ANNs with the same contact angle were investigated.The results of emulsifying eight different liquid-liquid systems at room temperature and high temperature proved that M-ANNs have excellent emulsification universality and stability.In addition,M-ANNs also showed good emulsion stability performance for liquid metals.The micro-nano structural differences between the three materials were investigated,and theoretical calculations showed that M-ANNs have extremely high interfacial detachment energy and surface roughness,revealing the underlying reasons for their superb emulsification performance.The results show that M-ANNs as a high performance particle emulsifier can significantly improve the stability of Pickering emulsions and broaden the range of Pickering emulsion systems.3.Asymmetric ultrathin SiO₂ nanonets constructed emulsion interfacial catalytic degradation of PET.The efficient degradation of waste polymers has practical significance for resource recovery,alleviating environmental pollution and energy crisis,and helping to achieve the goal of carbon neutral society.By precisely modulating the micro and nano structures of M-ANNs,a stable Pickering emulsion interfacial catalytic system of biphenyl/ethylene glycol was constructed by using M-ANNs at high temperature for the glycolysis reaction of PET.PET dissolved in biphenyl was subjected to alcoholysis reaction with ethylene glycol at the emulsion interface under the action of catalyst zinc acetate（dissolved in ethylene glycol）to form monomers.The effects of reaction temperature,reaction time,M-ANNs content and catalyst amount on the reaction efficiency were investigated,and it was confirmed that the Pickering emulsion interfacial catalytic system could achieve higher alcoholysis efficiency at lower reaction temperature and shorter reaction time than the homogeneous system,and the alcoholysis efficiency and product yield remained high after several cycles.Pickering emulsion interfacial catalytic system has the advantages of designable solubility characteristics and interfacial reaction,which can improve the reaction efficiency and enable the production under relatively mild conditions,and has the potential of industrial application.