The Studies On Encapsulation Of Mesoporous Materials And The Preparation Of Hierarchical Porous Materials

In the past decades, mesoporous silica has attracted much research attention due totheir high surface area and adjustable pore size. The wall surface of mesoporous silicacan be modified with proper organic functional groups and provide accessibility foranchoring other substrates. The encapsulation of guest molecules in these hosts leadsto composite materials with novel properties, which enable possible applications asmaterials for catalysis, adsorption, and electronic devices.Tris (8-hydroxyquinoline) aluminium is presently considered as one of the mostreliable emitting materials because of its excellent stability and luminescent properties.Alq₃ is a green emitter with PL peak wavelength in the range of 500 nm. In our work,Alq₃ has been encapsulated in the channels of SBA-15 with NH₂ group and significantblue shift and red shift respectively in PL spectra of about 90 nm and 30 nm wasobserved.The NH₂ functional group plays an important role on the photoluminescenceproperties of Alq₃. The possible mechanism is related to the interaction between theelectron donating NH₂ group and the Alq₃ molecule. For the phenomenon of blue shift,as a donor group, NH₂ on the pore surface may attack the Al atom of Alq₃ and formweak Al-Ns (Ns represent the N atom on the surface of SBA-15) bond. The staticeffect and the steric hindrance provided by the NH₂ group weakened or prohibited theformation of Al-Np (Np represent the N atom of pyridyl ring) bond. Because theluminescent property of Alq₃ is related to the covalent nature of Al-N bond, the PLemission shifts to shorter wavelength subsequently. For the phenomenon of red shift,as a donor group, NH₂ on the pore surface connect with hydroxybenzene by -CH₂group, heightened the energy of the HOMO and form strong Al-Ns (Ns represent the Natom on the surface of SBA-15) bond. Proved the formation of Al-Np (Np representthe N atom of pyridyl ring) bond. Because the luminescent property of Alq₃ is relatedto the covalent nature of Al-N bond, the PL emission shifts to longer wavelengthsubsequently.Owing the respective unique structure characteristics, microporous,mesoporousand macroporous applied in corresponding application areas. Recently, hierarchicalporous materials with two or more levels of porosities have attracted much attentionfor their applications in separation, catalysis and ion-exchang. Such materials improvethe diffusion of the guest molecules through the inorganic network of pores andchannels, because smaller pores provide higher surface areas and larger pore volumeswhile the larger pores allow for better molecular accessibility. The hierarchical poroussilica materials with the structure of ordered hexagonal mesoporous and macroporoushave been prepared using block copolymer P123(EO20PO70EO20 ) and PLA as dualtemplates. The presence of hierarchical meso/macroporous systems was confirmed bythe results from scanning electron microscopy, powder X-ray diffraction studies.