Fabrication Of Mesoporous Silica Spheres Based Nanorectors And Study Of Their Products

Mesoporous silica spheres have opened up many possibilities for applications in absorption and separation, and host-guest assembly, due to their large surface areas, large pore volume, controllable pore size, easy surface-functionalization, good stability and biocompatibility. However, it can’t work without the functionalization of mesoporous silica spheres. An effective way of the functionalization of mesoporous silica spheres is the fabrication of mesoporous silica sphere-based nanorectors to assemble nanomaterials according to the acquirements of properties. It is worth noting that the pore size is one of the important factors to affect the performance of the nanoreactors. Due to the size-selective effect, the charged nanomaterials with different sizes can be assembled on MS spheres with different pore sizes selectively. In addition, layer-by-layer (LbL) assembly technique is also useful for confined reaction. Herein, we fabricated four kinds of mesoporous silica sphere-based nanorectors. With the help of LbL assembly technique, different types of nanoparticles were assembled on the mesoporous silica spheres, forming composite spheres with different properties, such as catalytic, photoelectric, and fluorescent properties. Their properties and applications in different areas were also investigated.1. In Chapter2, MS spheres were firstly prepared with hexadecylamine as surfactant, ammonia as catalyst, and tetraethyl orthosilicate (TEOS) as silica precursor. The size of the resulting MS spheres is ca.1.3μm. In the presence of complex salts, the pores of MS spheres can be controlled by calcination, which retained the spherical morphology. The effect of calcination temperature and atmosphere on the pore size was also investigated. The pores can be enlarged from3.2to46.8nm effectively. This method is simple and feasible, which is the base for the fabrication of nanoreactors.2. In Chapter3, the assembly of Au nanoparticles or urease on MS spheres was carried out through their electrostatic interaction, forming MS/Au composite spheres. The increasing amount of Au nanoparticles assembled on MS sphere lead to their different aggregation. The color of Au colloid was accordingly changed initially from red, then to purple, and finally to violet blue. Similarly, urease with different amount was assembled on MS spheres with different pore sizes. By using MS spheres as nanoreactors, urease loaded on MS spheres can catalyze urea. And the enzymatic activity increased with the increase of the loading amount of urease.3. Considering the excellent catalytic activities of metal oxide nanoparticles, we assembled them on MS spheres using MS spheres as nanorectors with the help of LbL assembly technique in Chapter4. Metal ions absorbed in the pores of MS spheres can react with the product from the hydrolysis of urea. Metal oxides (CuO, NiO, or CO3O4) nanoparticles were then formed in the pores of MS spheres by calcination. The resulting composites are still spherical, monodisperse, and mesoporous, which is favorable to enchance their properties. This method can be expanded to prepare other composites which contain other metal oxides nanoparticles. In addition, the resulting composite spheres have large redox peak area so that they have many catalytic active sites.4. Considering the good photoelectric properties of CuO and FeS2, we assembled them on MS spheres using MS spheres as nanorectors in Chapter5. With the help of LbL assembly technique together with solvothermal method, Cu2+which was absorbed in the pores of MS spheres can react with the product from the hydrolysis of urea, and at the same time Fe3+can react with Na2S2O3, reslting in the successful assembling of CuO and FeS2. The resulting MS@CuO@FeS2composites are spherical, have rough shell with flake-like texture, and can absorb a wide range of light, from UV to near-infrared, making them sensitive to UV light. In addition, they show ferromagnetic properties, which enable them to align in PVA gel. The obtained films were anisotropic and promising for improving the performance of solar cells.5. Considering the excellent biocompatibility and fluorescent properties of CDs, we prepared them on MS spheres using MS spheres as nanorectors in Chapter6. By etching silica with NaOH, CDs can be released. The resulting hydrophilic CDs have good stability, wavelength-dependent and up-converted photoluminescent properties. They are also easily functionalized. The increase of the pore size of MS spheres and the amount of precursor of CDs results in the increase of the size of CDs. CDs were then used as fluorescent probes for the detection of Cu2+and L-cysteine (L-Cys). The addition of Cu2+cations leads to their absorption on the surface of CDs and the significant fluorescence quench of CDs. While the addition of L-Cys reverses the quenching and restore the fluorescence due to its ability to remove Cu2+from the surface of CDs. This method for the detection of Cu2+and L-Cys is facile, rapid, low-cost, environment-friendly, and highly selective and sensitive. The detection limit is2.3×10-8M for Cu2+and3.4×10-10M for L-Cys. In addition, the Au-PAMAM-CDs conjugates were formed by conjugating of Au nanoparticles (Au NPs) and CDs to PAMAM dendrimers through an amidation reaction. This makes Au NPs and CDs in an appropriate distance for the fluorescence enhancementdue to the strong local electric fields created by Au NPs surface plasmon resonance. Varying the amount of Au NPs or CDs in the system can affect the fluorescence enhancement. The results showed a62-fold enhancement for CDs was achieved.