| Hierarchical porous microspheres,especially the hierarchical porous materials with micrometer-sized macropores,have always attracted much attention due to their wide applications not only in the tranditional fields of adsorption/separation,catalysis/degradation,bio-medicine and so on,but also in the emerging fields of batteries,supercapacitors and sensors.This is mainly because the hierarchical porous materials combine the advantages of nanometer-sized pores(micropores and mesopores)including good selectivity and confinement performance,high specific surface area,large pore volume and high embedding load rate,and the superiority of fast mass transfer rate via the micrometer-sized pores.So far,several interesting methods have been developed for preparing hierarchical porous microspheres materials with micrometer-sized pores,including multi-emulsions template,hard template,spray drying process,seed swelling and so on.Wherein the multi-emulsion droplet can serve as the ideal template to prepare the interconnected multi-compartment hierarchical porous microspheres with micrometer-sized pores because of their low-cost,environment-friendly,intrinsic multi-compartment structure,easiness in control of pores structure and simple removal of template by evaporation of liquid materials.However,there is a huge challenge because of the inherent metastable of emulsion systems and a strong tendency to destroy the interfacial film with the process of reaction in emulsion phase.This is not only difficult to maintain the multi-compartment structure of multi-emulsions but also more difficult to fine control the porous structure of the corresponding porous microspheres.While the key point to solve the above-mentioned problem is to obtain and keep the super-stable emulsion interface films and to understand the evolution mechanism of the interfacial films with changing micro-environment due to chemical reaction in emulsion phase.Thus,it is essential to design the special stabilizer moleculers for constrcuting stable interfacial films.This is the fundamental ways to understand and obtain the super-stable emulsion interfaces,and also effectively prepare the hierarchical porous materials by using the multi-emulsions template.Base on the above research background,and combining the previous efforts for effectivly preparing the silica aerogels through a HIPE template in our group,a strategy for the super-stable multi-emulsion-templated method coupled with formation of the rigid film was developed to achieve the hierarchical porous microspheres.By using a special stabilizer with strong aggregation property,which can form the super-stable and rigid interfacial film by self-assembled at the O/W interface.This interface film can be used to resist coalescence,demulsification and inversion in multi-emulsions caused by the changes of micro-environment,and finally achieving the controllable and effective preparation of the hierarchical porous microspheres.Specifically,the major work was done by the following two aspects:In the first part of the thesis,a W/O/W emulsion was first formed by one-step homogenization of the acidified deionized water and VTEO solution containing a certain amount of stabilizer,Chol-OH.And a super-hydrophobic multi-compartment vinyl organosilica microsphere with highly interconnected macro-mesopores(HIMC-vinyl SMs)was successfully developed after the reaction in oil phase of the multi-emulsions under the NH3 atmosphere.These multi-emulsion droplets with complex structure show a marvelous stability,efficiently resisting the coalescence of inner droplets during the sol-gel process.The highly stable interface makes the multi-emulsion droplets transfer their intrinsic structures into the multi-compartment organosilica microspheres with highly interconnected macro-mesopores,rather than single compartment microspheres.It is demonstrated that as-prepared HIMC-vinyl SMs exhibit the coexistence of micrometer-sized macro-,meso-and micro-pores.Furthermore,the synergistic effects of the existence of vinyl groups on the surface and the geometrically rough surface lead to the super-hydrophobic property of HIMC-vinyl SMs(water contact angle is up to 163.9°).And the loading of Ag nanoparticles did not attenuate their super-hydrophobicity,which also show a high water contact angle(151.0°).The excellent high hydrophobicity makes them to form liquid marbles and catalytic liquid marbles with excellent stability and high mechanical robustness,and the catalytic liquid marbles stabilized by the composite hierarchical porous microspheres can act as a highly efficiently catalytic micro-reactor,in which can realize the degradation of MB to leuco methylene blue by NaBH4 in 10 min.The result of this part in the thesis could provide some guidance for easy,low-cost and benign preparation of multi-compartment and highly interconnected macro-mesoporous microspheres,especially for the inorganic oxide hierarchical porous microsoheres.In the second part of the thesis,inspired by the specific structure of Chol-OH in the first part of the work and its successful application in the preparation of hierarchical porous organosilica microsphere maerials.Three amphiphilic azobenzene-containing compounds,denoted as CF3-Azo-N-OH,CF3-Azo-N-(OH)2 and Azo-N-OH,were designed and synthesized.Their structures are similar to the Chol-OH,but the structures of their aggregates are more regular and more rigid.It is demonstrated that these compounds show faster response to the trans-cis isomerization in 31 s after UV irradiation with the wavelength of 365 nm and quick recovery performance of cis-trans isomerization in 120 s after visible light irradiation.In addition,the amphiphilic properties of the three amphiphilic molecules were studied by using the CF3-Azo-N-OH,CF3-Azo-N-(OH)2 and Azo-N-OH as stabilizers,the aqueous solution of K2CO3 as aqueous phase,and the solution of toluene containing 4,7-dibromobenzo[c]-1,2,5-thiadiazole,1,3,5-phenyltriboronic acid and tetrakis(triphenylphosphine)palladium(0)as the oil phase.It is found that the compound CF3-Azo-N-OH is an effective stabilizer for the above-mentioned emulsion system.Moreover,the covalent organic hierarchical porous polymer materials prepared by using the CF3-Azo-N-OH as the special stabilizer show a novel micro-nano composite structure with micrometer-sized macropores,ordered micropores and fiber-interweaved substructure.Therefore,the results of this study have some reference value for the design and synthesis of amphiphilic molecules and the preparation of novel covalent organic hierarchical porous polymer materials. |
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