Preparation And Photosensitive Property Of Azobenzene-functionalized Mesoporous Silica

Stimulus-responsive materials can receive external stimuli and generate response signals.They are attractting more and more attention from researchers because of their wide application and high sensitivity.Photo-responsive materials are regarded as one of the most promising stimulus-responsive materials due to their advantages such as environmental friendly,non-invasive,remote and intensity controllability,high accuracy,and instantaneity.Azobenzene is a typical photosensitive organic molecule,which can realize photo-chemical isomerization between its trans and cis isomers under UV/Vis irradiation because of the presence of N = N.Mesoporous silica nanoparticles(MSNs)have been widely studied in catalysis,adsorption,optics and drug delivery systems,etc.due to their unique properties such as large specific surface area,high porosity,adjustable pore size and good biocompatibility.We can obtain mesoporous silica with photo-responsive properties by introducing the photosensitive molecule azobenzene which as the "switch" of photo-response behavior into mesoporous silica through rational design.The size of the aperture can be controlled by the photo-response performance of azobenzene.It will have broad prospects in the fields of adsorbent and drug release.The contents of this dissertation are as follows:(1)Pendant-type and bridged-type azobenzene-silane precursors(4-[3-(triethoxysilyl)propoxy]azobenzene;4,4'-[3-(triethoxysilyl)propoxy]azoben-zene)were synthesized by connecting the azophenyl group into the organic silane molecules through Si-C covalent bonding.The NMR results proved that the required samples were successfully prepared with high purity.The UV-Vis absorption spectrum analysis results show that the sample has good reversible light response ability and can be used as a precursor of light stimuli-responsive materials.(2)Azobenzene-functionalized mesoporous silica(Azo@MSNs)with a novel core-shell structure was successfully prepared by the sol-gel method using the pendant azobenzene-silane precursor synthesized above,and azophenyl groups were anchored in the mesopores of the shell portion.The results of adsorption and release experiments using rhodamine B(RhB)as a guest molecule show that the trans-cis isomerization of the azobenzene moiety under different light irradiation conditions can cause the mesopore size of Azo@MSNs to change,and achieve controlled adsorption and release.Thus,controlled adsorption and release of guest molecules can be achieved.(3)Hollow mesoporous silica was prepared using selective etching and self-template methods,respectively.The azobenzene-silane precursor was used to modify its surface to obtain azobenzene-functionalized hollow mesoporous silicas(Azo-HMSs).Rhodamine B(RhB)and doxorubicin(Dox)were used as model molecules for loading,and cyclodextrin(?-CD)was used for capping.The results show that Azo-HMSs have higher loading capacity and can release more model molecules under UV light irradiation.