Synthesis, Characterization Of Rhodamine-functionalized Mesoporous Silica Hybrid Materials And Their Applications In Al(Ⅲ) Sensing

Organically functionalized mesoporous silica materials are a kind of organic-inorganic hybrid materials that are obtained through incorporation of organic groups into pure silica matrix in the form of chemical bond. As a novel class of functional materials, they have been widely applied in the fields of catalysis, drug delivery, biological markers, cell imaging, adsorption and detection. Colorimetric and fluorescent molecules used for detecting physiologically and environmentally important analytes, especially heavy and transition metal cation, have attracted great attention due to their simplicity, sensitivity and selectivity. In recent years, fluorescent hybrid solid chemosensors that are obtained through covalent attachment of the organic fluorescent probe molecules to the inorganic materials have been interesting in the research for new methodologies for ion recognition and sensing. Immobilizing probes molecules on the inorganic support can improve photo-stability and avoid the photobleaching of the probes. In addition, the obtained solid chemosensors can be easily recyclable by suitable chemical treatment. Because of the high porosity, tunable pore sizes, large surface area and good thermal stability, ordered mesoporous silica materials are ideally support materials for sensitive probes. The resulting fluorescent hybrid mesoporous silica materials have great potential applications in environmental and biological fields.In this thesis, A series of ordered mesoporous silica hydrid materials with different rhodamine contents were developed through one step co-condensation method, using the hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent. Systematic structural characterization demonstrated that the resulting rhodamine B-based hybrid mesoporous silica materials (RBMSiO2) possessed ordered mesoporous structure. The optical tests indicated RBMSiO2 displayed excellent selectivity and sensitivity towards Al(Ⅲ) over a wide range of tested metal ions on the basis of "Off-On" mechanism. The main contents and results were outlined as follows:(1) Firstly, organosilane precursor (RBSi) was synthesized successfully by a two-step reaction. Then rhodamine B-based mesoporous silica hybrid materials (RBMSiO2) were prepared through co-condensation using RBSi and tetraethoxysilane (TEOS) as mixed silica sources and CTAB as the template. RBMSiO2 materials were characterized by FT-IR,29Si magic angle spinning NMR (29Si MAS NMR), which confirmed the successful incorporation of rhodamine moieties in silica materials. The results of small-angle X-ray scattering (SAXS), high-resolution transmission electron microscopy (HRTEM) proved that RBMSiO2 materials possessed ordered mesoporous structure.(2) UV-vis spectra and fluorescence spectra were used to study the respond of RBMSiO2 materials towards metal ions. The results demonstrated that RBMSiO2 show good recognition ability for Al(Ⅲ) in ethanol on the basis of "Off-On" mechanism. Rhodamine B moieties in RBMSiO2 were in the form of spirolactam before chelating with Al(Ⅲ), so no fluorescent emission of the sensor can be detected. Upon the addition of Al(Ⅲ), fluorescent emission intensity could increase by 110-fold with the color change from colorless to red, and the detection limit of this hybrid chemosensor towards Al(Ⅲ) can be as low as 1.3×10-7 M. Photostability of rhodamine B diethylenetriamine (RBD) could be significantly improved after introducing RBD into the mesoporous silica materials, which could be attributed to the protection of the framework of RBMSiO2.(3) X-ray absorption near-edge structure (XANES) spectroscopy was used to probe the response mechanism of RBMSiO2 to Al(Ⅲ), which demonstrated that Al (Ⅲ) was in the form of six coordination in RBMSiO2.Al(Ⅲ) might be coordinated to the’O’and’N’atoms in rhodamine B moieties, thus triggering a spirolactam ring-opening reaction. The scanning transmission X-ray microscopy (STXM) measurements suggested that rhodamine B moieties in RBMSiO2 could serve as the selective binding sites for Al(Ⅲ), which promoted the adsorption capacity of the hybrid materials towards Al(Ⅲ).