Visible Light Photocatalytic Activity Of TiO₂ Nanoparticals And Titanate Nanotubes Loaded With Porphyrins

TiO2 has been proved to have many applications in wastewater treatment, antibacterial, self-cleaning, photocatalytic hydrogen evolution from water reduction and so on due to its high photocatalytic activity, low cost, non-toxic and high chemical stability. However, it is active only in ultraviolet light irradiation because of its wide band gap (3.2eV) so that a large amount of sunlight is unable to be used. In this dissertation, porphyrins are used to sensitize TiO2 nanoparticles to enhance their visible light responses, and to improve their visible light photocatalytic activity for the degradation of organic pollutes and photocatalytic hydrogen evolution form water reduction. In addition, porphyrin molecules with visible light photocatalytic activity are loaded on the titanate nanotubes with a high specific surface area and a large adsorption capacity to improve their visible light photocatalytic activity. The main results are below:Titanate nanotubes (TNTs) with one-dimensional tubular structure were synthesized using TiO2 nanoparticles (Degussa P25) as raw material in a hydrothermal process. The water-soluble porphyrin,5,10,15,20-(tetra(4-(N,N,N-trimethylamino)phenyl) porphyrin iodide (TAPPI) was loaded on the TNTs by electrostatic interactions to form the porphyrin-titanate nanotubes composite (TAPPI-TNTs). The photocatalytic degradation of methyl orange in the presence of TAPPI-TNTs was investigated under visible light irradiation. In addition, a possible visible light photocatalytic degradation mechanism was discussed. The results showed that the TAPPI-TNTs possessed high visible light photocatalytic activity and stability.The effect of center coordinated metals in the porphyrin ring on the photocatalytic properties of porphyrin-sesitized catalysts has been studied. Three porphyrins,5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin (MHTPP),5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin zinc (ZnMHTPP) and trans-2-chlorine-5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin tin (SnCl2MHTPP), were synthesised. These porphyrins were loaded on the surface of TiO2 nanoparticles by refluxing via a dehydration reaction between the phenolic hydroxyl of the porphyrins and the titanium hydroxyl on the surface of TiO2 nanoparticles. The photocatalytic activity of the catalysts was evaluated by degradating methyl orange under visible light in air or in N2. In combination withâ… -â…¤characteristic curves, the photocatalytic degradation mechanism and the difference of photocatalytic activities among the photocatalysts were discussed.Trans-2-hydroxy-5,10,15,20-tetraphenylporphyrin tin (Sn(OH)2TPP) was used as a sensitizer. The co-catalyst Pt was first deposited on the surface of TiO2 nanoparticles by photo electrons of TiO2 under UV excitation. Sn(OH)2TPP was then bound on the surface of TiO2 nanoparticles by refluxing via a dehydration reaction between the axial hydroxys of the porphyrin and titanium hydroxyls on the surface of TiO2 nanoparticles. The photocatalyst loaded with Pt and porphyrin was utilized for the photocatalytic hydrogen evolution from water reduction. In addition, Sn(OH)2TPP was first bound on the surface of TiO2 nanoparticles and H2PtCl6 was in situ reducted under visible light irradiation to form the co-catalysts Pt. The catalyst obtained was used for the photocatalytic hydrogen evolution from water reduction. The effects of pH, loading amount of Pt and amount of the catalyst on the hydrogen evolution were studied. The results showed that the photocatalytic hydrogen evolution activity of the former catalyst was higher than the latter under the same conditions.