Preparation And Properties Of Titanate Nanotubes Modified By Porphyrin

Compared to P25 TiO2 nanoparticles, titanate nanotubes have great potentials in photocatalysis and solar cell due to larger specific surface area, ion-exchangeable ability and hollow cavity. In order to expand the photoresponse of titanate nanotubes and improve their photocatalytic and photoelectrochemical performance, the effects of the central metal ions of porphyrins, the anchoring modes between titanate nanotubes and porphyrin molecules, and co-sensitized by CdS nanoparticles and porphyrin molecules on visible-light photocatalytic activities and photoelectrochemical properties of TNTs were investigated, respectively. It provided some good ways for preparing one dimensional organic-inorganic nanocomposites with excellent performance. The main researches are as follows.Titanate nanotubes (TNTs) treated by acid were chosen as the substrate because of their extraordinarily performance. TNTs sensitized by four kinds of metallotetraphenylporphyrin were prepared by stirring at room temperature. The effect of the central metal ions of the porphyrin on the photocatalytic degradation of methyl orange (MO) under visible-light irradiation was studied. The results indicated that the TNTs sensitized by tetraphenylporphyrin zinc (TNTs-ZnTPP) exhibited the best photocatalytic activity owing to the extended absorption of TNTs-ZnTPP to visible light and effective transfer of photoelectron in the TNTs-ZnTPP. It provided an evidence for choosing which metal ion was to coordinate with porphyrin ligands in the following studies.In order to study the effects of anchoring modes of porphyrin zinc on the photocatalytic activity of titanate nanotubes, two kinds of porphyrin zinc with different functional groups, 5,10,15,20-tetraphenylporphyrin zinc (ZnTPP) and 5-(4-hydroxyphenyl)10,15,20-triphenyl-porphyrin zinc (ZnMOHPP), were chosen as the sensitizers of TNTs, respectively. The TNTs sensitized by ZnTPP and ZnMOHPP (denoted as TNTs-ZnTPP and TNTs-ZnMOHPP) were prepared by the simple reflux method. According to the different experimental phenomenon during synthesis process, the results of spectral characterization, thermogravimetric analysis, photocatalysis and photoelectrochemistry, it demonstrated that the ZnMOHPP molecules were bonded mainly on the outer surfaces of the TNTs through hydrogen bond, while ZnTPP were physically adsorbed into the pore channels of the TNTs via a capillary process. The different distributions and anchoring modes between two kinds of porphyrins and TNTs resulted in the remarkable distinctions of photocatalytic and photoelectrochemical properties of TNTs-ZnTPP and TNTs-ZnMOHPP. TNTs are with large specific surface area, ion-exchangeable ability and full of hydroxyl groups on their walls, which make them ideal substrates. In this section, the TNTs co-sensitized with CdS nanoparticles and ZnMOHPP molecules were prepared via an in-situ formation of CdS nanoparticles, followed by dipping method in the CH2Cl2 solution of ZnMOHPP. In the co-sensitized composites, there existed a strong coupling between the TNTs and CdS nanoparticles by in-situ ion-exchange reaction, and a hydrogen bond interaction between the hydroxyl groups of TNTs and ZnMOHPP molecules. The intimate contact between two sensitizers and the TNTs contributed to increase absorbance of CdS nanoparticles and ZnMOHPP molecules on the surface of TNTs, extend photoresponse of TNTs to visible light, furthermore, be profitable for transferring electrons of two sensitizers into the conduction band of TNTs. So the photocatalytic and photoelectrochemical properties of the TNTs co-sensitized by CdS nanoparticles and ZnMOHPP molecules can be improved significantly relative to the pure TNTs.