| Since Fujishima and Honda’s pioneering work in the photo-electrocatalytic oxidation of water in 1970, TiO2 nanomaterials have been widely studied for photocatalytic degradation of organic compounds, water splitting, dye-sensitized solar cells, photoreduction of heavy metal ions and other applications. Based on the photocatalytic oxidation of organics of TiO2 nanomaterials, the photoelectrochemical sensor is constructed for organics determination. Nobel metal nanoparticles and Bi-compounds nanostructures are deposited on TiO2 nanotube arrays (NTAs) for enhancing the photoelectrochemical performances and the detection performances.The mian works are listed as following:1. TiO2 NTAs modified with Ag and Pt nanoparticles are fabricated by anodic oxidation combined with photoreduction and hydrothermal method respectively. Structures, element components, morphologies, photoelectrochemical properties of Ag/TiO2 NTAs and Pt/TiO2 NTAs were measured by X-ray diffraction diffractometer, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope and electrochemical workstation. Ag and Pt nanoparticles with size of 4-20 nm are dispersed evenly on the surface of TiO2 nanotubes. The different metals play different roles on the photoelectrochemical performances of TiO2 NTAs. Ag nanoparticles decrease the photocurrent in buffer solution, but increase the photocurrent response to organcis, both of which are benefit for electrochemical detection of organics. Ag/TiO2 NTAs achieve the best detection performance with sensitivity of 0.152 μA/μM and detection limit of 0.53 μM to glucose. On the contrary, Pt nanoparticles can enhance the photocurrent of TiO2 NTAs in buffer solution but decrease the photocurrent response to organic compounds, which are benefit for photocatalytic water splitting but not for photoelectrochemical detection.2. BiOC1 nanosheets are deposited on TiO2 NTAs by sequential chemical bath deposition method in ethylene glycol solution, and the photoelectrochemical performances of the composites are studied. The depositing temperature and water content in the solution are adjusted for controlling the amount and distribution of BiOC1 nanosheets on TiO2 NTAs. Structures, element components, morphologies, photoelectrochemical properties of Ag/TiO2 NTAs and Pt/TiO2 NTAs were measured by X-ray diffraction diffractometer, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope and electrochemical workstation. The synthesis parameters are optimized to be temperature of 60℃ and water content of 5%, which can achieve the best photoelectrochemical determination performances with the determination sensitivity of 0.277 μA/μM, linear range from 0 to 1900 μM, and the calculated detection limit of 12.24 μM.3. BiOC1 nanosheets are deposited by sequential chemical bath deposition method in 1.3 M HNO3 solution. Structures, element components and morphologies are characterized, and the photoelectrochemical properties of BiOCl/TiO2 NTAs are measured. Compared with TiO2 NTAs, the BiOCl/TiO2 NTAs possess low background photocurrent and higher current response to the organics, both of which are benefit for enhancing the photoelectrochemical determination of organics. BiOCl/TiO2 NTAs achieve a sensitivity of 0.327 μA/μM, linear range from 0 to 1300 μM and calculated detection limit of 5.7 μM. The mechanisms of the photoelectrochemical determination are discussed from the optical absorption, charges transfer and surface electrochemical reactions. The photogenerated holes transfer from valence band of TiO2 to that of BiOCl, and oxidize the organics in a direct manner, which produce low background photocurrent and high current response to organics.4. Bi2WO6/TiO2 NTAs are achieved by sequential chemical bath deposition method. Structures, element components and morphologies are characterized, and the photoelectrochemical properties of Bi2WO6/TiO2 NTAs are measured by cyclic voltammetry and chronoamperometry. B12WO6 modification can decrease the background photocurrent and increase the current response to the organics at the same time. The optimized Bi2WO6/TiO2 NTAs possess a sensitivity of 0.244 μA/μM, linear range from 0 to 2500 μM, which possess wider linear range than that of Bi2WO6/TiO2 NTAs. Terephthalic acid oxidation method is applied for comparing the ·OH concentrations of TiO2 and Bi2WO6/TiO2 TNAs in the solution during photocatalytic process, indicating that low·OH radicals are produced on Bi2WO6/TiO2 TNAs during the photocatalytic process. Trapping agents, such as NaI for h+ and isopropyl alcohol (IPA) for ·OH, are added in the solution, and the photocurrents of TiO2 and Bi2WO6/TiO2 NTAs in the different solutions are measured, confirming the direct oxidation of organics by holes plays key roles in enhancing the determination performances. |
PDF Full Text Request