The Preparation Method Of Porphyrin-TiO₂ Composite Photocatalyst And Its Effect On Photocatalytic Activities

In recent years, the pollution of the environment problem is an important challenge for the human, especially the organic dyes in wastewater treatment. The photocatalysis semiconductor TiO₂ as a kind of green technology has been considered to solve the problem, which have attraced extensively people's attention. The wide band-gap of TiO₂ ?Eg=3.2 eV for anatase? and high rates of electron-hole recombination seriously restrict its application as photocatalyst. A variety of ways has been devoted to solve this problem at present. However, the method to dye sensitization is considered to be cheap, convenient and effective. Porphyrin have a delocalized macrocyclic structure, very strong absorption ?Soret band:400-450 nm, Q band:500-700nm? in the visible region. Besides, it is relatively stable to light and heat, and energy level well match with TiO₂ Therefore, porphyrin molecule as sensitizer are applied to improve the photocatalytic activity of the TiO₂ constantly and the research on the composite photocatalyst will have a profound significance.Based on the study above, we synthesized four kinds of porphyrins. The 5,10,15,20-tetrakis?3-carboethoxymethyleneoxy? phenyl porphyrin ?H₂TEPp?was synthesized according to 3-hydroxybenzaldehyde as the raw material, and then prepared the copper-porphyrin:5,10,15,20-tetrakis?3-carboethoxy-methyleneoxy? phenyl copper-porphyrin ?CuTEPp?. After hydrolyzation of porphyrin with ester group, we can obtain the corresponding porphyrin with carboxyl group:5,10,15,20-tetrakis?3-carboxylmethyleneoxy? phenyl porphyrin ?H₂TCPp?,5,10,15,20-tetrakis?3-carboxylmethyleneoxy? phenyl copper-oporphyrin ?CuTCPp?. All these compounds were characterized by UV-vis, FT-IR, elemental analyses, MS and 1H NMR and their molecular structure were determined.The composite photocatalysts MPp/TiO₂ and MPp-TiO₂ were prepared by two kinds of different ways in the paper. On the one hand, the MPp/TiO₂ were fabricated obtained by porphyrin compounds sensitization TiO₂ nanorods which was gained by P25 as a raw material. On the other hand, the MPp-TiO₂ were obtained by hydrolyzation of the butyl titanate as Ti source, using the porphyrin as the template agent and sensitizers. All the composite photocatalysts were characterized by SEM, TEM, UV-vis, DRS, FT-IR, XRD, PL, N2 adsorption-desorption and their photocatalysis activities were evaluated by the photodegradation of 4-NP solution under UV-vis light irradiation.Based on the analysis above, We can arrive at the following conclusions:?1? These porphyrins can sensitize TiO₂ successfully for all composites in the paper. TiO₂ and porphyrin molecules were connected by Ti-O-C=O action, and their composite photocatalysts have large surface areas, which offers more active sites, accordingly improving photocatalytic activity.?2? The composite photocatalysts MPp/TiO₂ were prepared by two-steps method and their were higher than P25 and TiO₂ nanorod. The CuTCPp/TiO₂ display the best and stability photocatalytic activity in all composites.?3? According to select the best conditions in the experiment, the MPp-TiO₂ mesoporous composites with heterojunction were prepared by one-step method and were formed by particle accumulation, which reveal the interactions between porphyrin molecules and TiO₂ as well as the accumulated pattern of sensitized porphyrin on the surface of TiO₂ play an important role in photocatalytic activity. The composites CuTCPp-TiO₂ reflect the most understanding photocatalytic activity and stability.