The Detection Of Pb²⁺ Based On The Mesoporous Silica As Controlled-released System And The Study Of Photoelectrochemical Properties On The Mesoporous Titania Thin Film

Mesoporous silica nanoparticles （MSN） have been extensively studied for drugdelivery because of their uniform tunable, narrow pore size distribution, highporosity, big pore size, large surface area, well-defined surface properties,amorphous hole wall whose surface is rich in active hydroxyl, which can be easyselectively functionlized the internal and the external surface with desired organicfunctional groups, along with the high chemical and thermal stability and themorphology to be easy controlled and good biological compatibility. This study haspresented a metal ions-responsive system, which used mesoporous silicananoparticles as support, the biotin-avidin complex as a biomolecule-based “cap”and the metal ions as stimuli. On the basis of the controlled-release delivery system,metal ion was detected with fluorescence analysis of the guest.Mesoporous titanium dioxide was applied widely in the photocatalysis and solarcells because of excellent optical, electrical properties and chemical stability.Because of the high porosity and abundant porous structure, mesoporous TiO₂showed higher photoelectric capability compared with the traditional one.Mesoporous TiO₂can be easy selectively functionlized the surface with sensitized agent, redox coupling agent, and other nano-structured semiconductor. Compared tothe mesoporous powder, the mesoporous TiO₂film more easily integrated into thedevice that make it commonly used as the semiconductor film materials. But thewide band gap of TiO₂（3.2eV） limits its absorption to the ultraviolet region, whichtakes only a little of the solar spectrum. Nanocrystalline CdS is a direct band-gapsemiconductor material with a reasonable band-gap of2.43eV at room temperaturewhich matches the solar visible spectrum very well. Sensibilization of mesoporousTiO₂film with CdS quantum dots can tune the response of the photoelectrode in thevisible region. In addition, the conduction band position of CdS quantum dots ishigher than that of TiO₂, once incident photons are absorbed by the CdSnanoparticles, photoexcited electrons in the conduction band of CdS will quicklytransfer into that of the TiO₂to decrease its energy level and accelerate the chargeseparation and finally improve the photoelectric performance of TiO₂film electrodes.This thesis mainly consists of the following issues:1. Mesoporous silica nanoparticle （MSN） with large average pore size and highcapacity was synthesized by sol-gel method. It was selected as support and loadedwith dye fluorescein. Then, the external surface was functionalized with epoxy group.8-17DNAzyme was chosed to construct the biosensor for Pb²⁺because of its veryhigh activity by a fast rate. The substrate strand5’-end labeled with-NH2group wasanchored on the outer surface of the MSN. The immobiled17DS were thenhybridized with enzyme strand carrying a biotin moiety at the5’-end. Finally, thepores were cappede with biotin-avidin complex after the addition of avidin, owing tothe specific reaction between biotin and avidin. In the presence of Pb²⁺, the substratestrand was cleaved by the17E DNAzyme, and the realease of cleaved flagmentresulted in the uncapping of the pores, and release of the entrapped cargo. This studypresented a biomolecule-based metal ions-responsive cap system for mesoporoussilica. The linear range for Pb²⁺was1.0×10^-8mol/L².0×10^-6mol/L. The detectionlimit for Pb²⁺was8.0×10-9mol/L.2. Mesoporous TiO₂with good crystallinity was prepared by sol-gel method usingtriblock-copolymer as templated and1,3,5-trimethylbenzene （TMB） as a swellingagent. ITO/TiO₂/CdS composite thin films were successfully prepared byelectrodeposition of CdS on ITO/TiO₂substrate. The aggregation structure of thefilms was investigated by SEM, UV-vis spectroscopy, Raman and X-ray diffraction（XRD）. The transient photocurrent action spectra of ITO/TiO₂/CdS composites thin film demonstrated that CdS was successfully deposited in the channel and on thesurface of mesoporous TiO₂film and the modification of CdS for ITO/TiO₂couldstrongly ameliorate the photoelectric capability of ITO/TiO₂thin film. By optimizingthe deposition time, the optimum time of deposition CdS on the mesoporous TiO₂electrode is25min.3. Mesoporous TiO₂with good crystallinity was prepared by sol-gel method usingtriblock-copolymer as templated and tetrabutyl titanate as the inorganic precursor.Spectroelectrochemical experiments were done by immersed the mesoporous TiO₂thin film electrode in PBS buffer solution containing triethanolamine. The electrondonor of triethanolamine for ITO/TiO₂could strongly ameliorate the photoelectriccapability of ITO/TiO₂thin film.