Fabrication Of Titanium Dioxide Based Composites And Investigation Of Their Electrochemical And Photoelectric Properties

As well known, TiO2 existed naturally as n-type semiconductor, which can generate electron and hole pairs under the illumination by ultra violet (UV) light. Due to its good optical transparency, biocompatibility and electrical conductivity, it has been widely used for the application in photocatalysis, super-hydrophilic self-cleaning materials, fuel cells, solar cells, biosensors and so on. However, TiO2 is not perfect for all purposes and performs rather poorly in the application associated with solar light. Generally, the photoresponse of TiO2 in the most active anantase phase is only observed under illumination of UV light, which takes no more than 5% of the total solar light on the earth, due to its wide bandgap (3.2 eV). Besides, it possess high photogenerated carrier recombination rate. Therefore, in order to obtain materials with excellent performance, the modifications are very necessary for TiO2. Herein, we employed there different methods to prepare three dimensional (3D) macroporous structure of TiO2, sulfide semiconductor sensitized TiO2 fibers and TiO2 composite nanoparticles with core-shell structure, respectively. And their applications in biosensors, photocatalysis and photo-anode were also explored.1. Firstly, we prepared the 3D macroporous TiO2 film, derived from a sol-gel procedure using polystyrene colloidal crystals as templates and combining with high temperature calcinations, to modify indium-tin oxide (ITO) electrode. SEM, XRD and EDS results confirmed the formation of 3D macroporous TiO2. Glucose and H2O2 biosensors were constructed by using these modified electrodes. The large specific surface area and cross-linking of the pore structure are beneficial to both the adsorption of enzyme and the electrons transfer between the enzyme and electrode, thereby improve the performance of biosensors. The glucose oxidase (GOx) biosensor constructed by 3D macroporous structure TiO2 modified electrode showed better performances. The sensitivity and the detection limits of glucose were 151μA cm-2 mM-1 and 0.02μM, respectively. The linear range was 0.05 mM-2.5 mM. Besides, a novel photo-enhanced horseradish peroxidase (HRP) biosensor was also investigated. The sensitivity of H2O2 detection was 70.04μA mM-1 in dark, and it increased to 102.97μA mM-1 under UV light. Owing to the efficient photovoltaic effect, the HRP/TiO2 biosensor displayed better electrochemical performance under UV light.2. Sulfide semiconductor sensitized TiO2 fibers were fabricated by directly electrospinning titanium alkoxide precursor containing a cadmium or zinc salt. After being calcined at 500℃. the as prepared fibers were directly exposed to thioacetamide solution. This method avoided the introduction of chemical cross-linking agent and obtained small sulfide semiconductor particles, which were uniformly dispersed in the TiO2 matrix. The doping concentration was also controllable. The UV-Vis absorption spectra indicated that after doped with CdS, the absorption edge of TiO2 fibers expanded from 400 nm to 530 nm. The results also showed that the introduction of P123 template changed the porous structure of TiO2 fibers, and increased the surface area of the fibers. Hence, P123 was added to the electrospinning precursor of ZnS/TiO2 fibers. The as prepared fibers can be used as the modification materials for photo-anode in the enzyme fuel cell application. The addition of ZnS could improve the electrochemical performance of TiO2 fibers.3. Considering the requirements both of environment and particular application, the environment friendly CuInS2/TiO2 composite materials were prepared. Since CuInS2 (CIS) is a ternary semiconductor, the formation mechanisim is much more complicated. Hence we employed electrospinning combined with solvertherml method to prepare CIS/TiO2 composites. The morphology is related to the type of CIS precursors. When Cu+and S powder were used as the precursors, the CIS hierarchical microarchitectures were obtained. Under the condition of higher concentration of CIS precursors, the big CIS hierarchial structure wrapped the TiO2 fibers, and if the concentration of CIS precursors decreased, the fibers twined with the small CIS particles. Such composites can degrade methylene blue very quickly under the illumination of simulated sunlight, and the degradation can reach about 50% within 5 min. When the precursors of CIS were Cu2+ and Na2S,4-bromothiophenol was employed as both reductant and capping agent, thus small CIS particles were prepared. The particles distributed uniformly on the surface of TiO2 fibers, the composites still maintained the one dimentional structure. The density of distribution was related to the concentration of CIS. When the mass ration of CIS:TiO2 was 0.6:1, the corresponding composites showed the best photo-response under the illumination of visible light (λ>400 nm).4. TiO2/ZnS/CIS core shell nanoparticles were prepared via metal organic synthesis. The introduction of ZnS shell could enhance the stability and fluorescence properties of CIS core. The fluorescence intensity was related to the reaction time, after 60 min growth of ZnS shell the quantum dots showed best fluorescence performance. After the introduction of TiO2 shell, the fluorescence quenched quickly, which indicated the electrons transfer from CIS to the conduction band of TiO2. The particles have potential application in solar cells.