Preparation And Photocatalytic Activity Of MPc/TiO₂ Hybrid Photocatalyst

TiO2 is a kind of semiconductor with wide band gap, it can only absorb the ultraviolet ray of sunlight, the harvest of solar light is low. Another disadvantage of photocatalytic systems upon band gap excitation of the semiconductors is the high degree of recombination between the photogenerated charge carriers. As a result of this recombination the photocatalyst efficient is decreased as well as the quantum yield. To improve the quantum yield and broaden the absorbing spectrum range becomes a very important problem in the research field of photocatalysis.We chose MPc (M=Fe,Mn) as sensitizied materials, which have high stability and catalytic activity. With taking the advantage of the excellent property of both MPc and TiO2, a novel photocatalyst with high photo-quantum yield and responsibility at widened spectrum range was prepared by sol-gel process 1,MPc/TiO2 hybrid photocatalysts with higher catalytic activity were prepared by sol-gel method. A strong action could be formed between MPc and TiO2, thus the transfer of photo-excited electron can be accelerated, and the recombination of photo-induced carriers can be reduced. The photocatalytic activity of these hybrid photocatalysts is greatly improved also. At the same time, the sunlight can be absorbed and excited by MPc, thus it broadens the absorbing spectrum range.Without oxidant introdued to the reaction system, the RhB at the concentration of 1×10－5mol/L by FePc/TiO2 was degradated completely within 10 minutes under ultraviolet ray. The degradation efficient is reach to 99%. While the RhB at same concentration within 60 minutes and the methyl orange (3×10－5 mol/L) within 150 minutes were degraded all by FeClPc/TiO2 under sunlight. The chemical oxygen demand of p－chloroaniline was droped from 500 mg/L to 400mg/L by FeClPc/TiO2 in 12 hours under sunlight.2,The factors for the catalytic activity of MPc/TiO2 hybrid photocatalysts during the preparation were studied. If the content of MPc is too low, the sensitized effect is not obvious, but that of MPc is too high, MPc will become the recombined sites of photogenerated carriers again and absorbing ligh are prevented at the surface of TiO2. The optimal contents for the sensitized MPc are different from MPcs. For FeClPc and FePc, the optimal mol ratio of MPc to TiO2 is 1:400, for MnPc, it is 1:1200. Low calcinations temperature is not advantageous to form strong interaction between MPcs and TiO2, and if the temperature is too high, MPcs is discomposed partially due to MPc oxidated by oxygen. The calcinations temperature at 250℃ is the optimal temperature. The pH could effect the hydrolysis of Ti(C4H9O)4 during the sol-gel process and the growth of particles, but the influence on the activity of catalysts is not obvious.Supercritical fluid drying technology is a process without oxygen, so it can prevent MPc from decomposing or oxidizing at the process.FeClPc is stable and not be decomposed during the preparation process, so FeClPc/TiO2 hybrid photocatalyst has a strong light absorption and high activity in visible light region. 3,Different photocatalytic mechanisms of MPc/TiO2 hybrid photocatalysts under untraviolet ray and visible light are suggested. The photoexcitation with ultraviolet ray yields the electron-hole pair by TiO2. It is MPc at the initial excitation under visible light, so more MPc is in favor of absorbing sunlight. The activity sequence of MPc/TiO2 hybrid photocatalyst under ultraviolet ray varies from that under visible light.