The Design,Synthesis And Photocatalytic Performance Of Metal-Porphyrin-Framework/TiO₂

With the increasing concern of the environmental pollution,various contaminants are exerting significant influence on the human health and social development.Recently,a series of organic pollutants were observed lately in water environment,including pharmaceuticals and personal care products?PPCPs?that were commonly applied in the everyday life.Because of widely utilization,continuous release,and reluctance to remove by the traditional treatment,the concentration of PPCPs has been rising and most are beyond the threshold all around the world.Photocatalytic oxidation technology has the advantages of high oxidation efficiency,high reaction rate,and highly effective for a variety of organic pollutants treatment.This technology is environmental friendly and possessed an application prospect since it can utilize the solar energy effectively.Due to the characteristics of low cost,strong oxidation capability and so on,TiO₂ becomes a key research topic in photocatalytic oxidation.However,there were still some drawbacks of TiO₂ itself,such as relatively limited specific surface area,lower light energy utilization ratio,lesser quantum yield and so on.These deficiencies have hindered the application of TiO₂.Thus,it has an important practical significance to design and synthetize novel photo-catalysts with visible light response and highly efficiency,which can be achieved via Mental-Organic-Frameworks?MOFs?.On one hand,most organic ligands had good light response capability and made MOFs possessing optical activity;On the other hand,through the choice of secondary structural unit could result in porous structure and larger specific surface area of MOFs.In this study,the high purity porphyrin ligand was synthesized via modified Lindsey method.Using solvothermal method,the corresponding MOFs crystal based on the manganese porphyrin?MP1?was prepared.Then,MP1-TiO₂ was prepared by co-crystallization method.The composition,crystal structure,morphology,optical properties and pore structure feature of MP1 and MP1-TiO₂ catalysts were characterized respectively by Fourier transform infrared spectrometry?FT-IR?,X-ray diffraction?XRD?,the field emission scanning electron microscopy?SEM?,UV-Vis diffuse reflectance spectrum?UV-Vis DRS?,nitrogen adsorption-desorption.The results showed that MP1 and MP1-TiO₂ had extremely large specific surface area and uniform pore structure;TiO₂ showed anatase crystal in as-prepared catalyst,and dispersed evenly on the surface of MP1.Both MP1 and MP1-TiO₂ were characterized by light adsorption over full-wave band,and compared with MP1,the adsorption intensity of MP1-TiO₂ increased significantly.The photocatalytic activity of MP1 and MP1-TiO₂ had been investigated by photo-catalyticdegradation of Rhodamine B?RhB?,Methyl Orange?MO?and Ofloxacin?OFX?under the visible light radiation.The influencing factors,including initial concentration of the pollutants,catalysts dosage,p H value,were investigated systematically to optimize the degradation conditions and establish the kinetics equations under different conditions.The recycling property of composite catalyst was also investigated.The mechanism of photocatalytic oxidation was studied by radicals capture experiments.The results were shown as following,?1?After 180 min irradiation,the degradation ratio of RhB reached 98.3% under the photocatalytic action of MP1-TiO₂,which was much higher than TiO₂,MP1 and MP1+TiO₂?physical mixing with the same quality proportion?.This is due to the synergistic action between MP1 and TiO₂ in MP1-TiO₂,MP1 which had an excellent light adsorption properties and emitted by visible light.The chemical energy had been transferred to TiO₂ promoting the generation and separation of electron-hole pairs.?2?Under the optimal conditions,after 160 min irradiation,RhB?C0 = 10 mg/L;pH = 6.2?,MO?C0 = 20 mg/L;pH = 5.2?and OFX?C0 = 20 mg/L;pH = 6.2?had been degraded almost completely by MP1-TiO₂?dosage: 20 mg?.All photo-catalytic degradation followed the first order kinetic reaction equation.The kinetic constant of photocatalytic degradation was 13,31,21 times as great as the photolysis and was 7.8,27,10 times as great as TiO₂ P25.?3?The stability of photocatalytic activity of MP1-TiO2 was studied through three times recycle degradation of RhB.With the increase of recycling,the adsorption quantity declined gradually with the rate of 49.3%,32.7% and 29.2%,respectively;the photocatalytic degradation rate of RhB over the MP1-TiO₂ still achieved 98.0% after three recycling,indicating the MP1-TiO₂ was stable.?4?The active groups in MP1-TiO2 react system were tested via radicals capture experiments,the results showed that the hole,hydroxyl radical and superoxide radical took parts into the photo-catalytic degradation of MO and OFX,hole and superoxide radical played key roles in photoreaction.