Preparation Of Porphyrin Based Composites And Its Application In Photocatalysis And Electrocatalysis

Porphyrin widely exist in nature, has the attractive optical properties, ultrafast electron transfer and high absorption coefficient to light harvesting, plays an important role in the living body. They are assembled in the living body with other molecules or organs, showing a unique biocatalytic activity. Therefore, the study of porphyrin assembling and developing new porphyrin composites can improve the catalytic activity of porphyrin molecules, which helps us to fiirther developed in the fields of biology, chemistry, optoelectronics, and medicine. For this purpose,a series of porphyrin composites were synthesized by the combination of porphyrin and other excellent nanomaterials. They can be effectively used for oxygen reduction reaction, photocatalytic degradation, electrocatalytic oxidation, sensitive detection, and antibacterial agents. Details were described as below.（1） The oxygen reduction reaction （ORR） plays important role at the cathode of fuel cells in practical application. Herein, the titanium dioxide/graphene supported hemin （TiO₂/Gr/Hem）composite materials with a flower-like superstructure was successfully prepared through a two-step solvothermal reaction. By a further heat-treatment, the electrocatalytic activity of the as-obtained catalysts were examined, and it was found that the pyrolysis at 700 ℃ gave rise to the best catalytic activity for the ORR in alkaline media. This heat-treatment temperature was found to be crucial in determining the activity and stability of catalysts, due to the enhanced structural defects, active sites, geometrical complexity, and larger fraction of the pyridinic nitrogen and pyrrolic nitrogen groups. The titanium dioxide/graphene （TiO₂/Gr） and graphene/hemin （Gr/Hem） were also studied and compared, it was revealed that the catalytic activity of TiO₂/Gr/Hem catalysts for ORR can be further enhanced. In addition, the chemically bonded element iron in the heat-treatment TiO₂/Gr/Hem catalysts showed inhibition effect for ORR and Ti-C-N materials garnered high catalytic activity compared with Ti-C-N-Fe materials in alkaline media. The higher methanol tolerance and durability of the TiO₂/Gr/Hem composite materials during ORR were also confirmed. These results reflect the critical influences of the pyrolysis temperature and the chemically bonded element dopants to be the key factor for ORR.（2） A three-dimensional hemin-functionalized graphene hydrogel （Hem/GH） was prepared by a facile self-assembly approach. The as-prepared Hem/GH showed good mechanical strength with a storage modulus of 609-642 kPa and a high adsorption capacity to organic dye contaminants (341 mg g^-1 for rhodamine B). Moreover, Hem/GH could be used as photosensitizer for photocatalytic degradation of organic dyes, and showed superior photodegradation activity of methylene blue （MB） with respect to the counterparts such as graphene hydrogel （GH） and commercial catalyst P25. The excellent cycling performance of the Hem/GH was well maintained even after multiple cycles on adsorption process and photocatalytic reaction. Interestingly, after the photodegradation of MB, a light-induced pH change of the solution from alkaline pH 8.99 to acidic pH 3.82 was observed and 10 wt%total organic carbon remained. The liquid chromatography/time-of-flight mass spectrometry（LC/TOF-MS） analysis confirmed the generation of acidic degradation products. The photocatalytic mechanism was further investigated by trapping experiments, which revealed that the MB degradation was driven mainly by the participation of superoxide anion radicals in the photocatalytic reaction. As an extended application, visually intuitive observation showed the as-prepared Hem/GH also had strong antibacterial properties. These results suggest that Hem/GH could be potentially used for the practical application due to its high adsorption ability, excellent photocatalytic activity, and strong antibacterial properties.（3） Surface patterns of well-defined nanostructures play important roles in fabrication of optoelectronic devices and applications in catalysis and biology. In this paper, the diporphyrin honeycomb film, composed of titanium dioxide, protoporphyrin Ⅸ and hemin,（TiO₂/PPIX/Hem） was synthesized using dewetting technique with the well-defined polystyrene （PS） monolayer as template. The TiO₂/PPIX/Hem honeycomb film exhibited a higher photoelectrochemical response than that of TiO₂ or TiO₂/PPIX, which implied a high photoelectric conversion efficiency and a synergistic effect between the two kinds of porphyrins. The TiO₂/PPIX/Hem honeycomb film was also a good photosensitizer due to its ability to generate singlet oxygen （¹O₂） under irradiation by visible light. This led to the use of diporphyrin TiO₂/PPIX/Hem honeycomb film for the photocatalytic inactivation of bacteria.In addition, the photocatalytic activities of other metal-diporphyrin-based honeycomb films,such as TiO₂/MnPPIX/Hem,Ti02/CoPPIX/Hem,TiO₂/NiPPIX/Hem,TiO₂/CuPPIX/Hem, and TiO₂/ZnPPIX/Hem, were investigated. The result demonstrated that the photoelectric properties of diporphyrin-based film could be effectively enhanced by further coupling of porphyrin with metal ions. Such enhanced performance of diporphyrin compounds opened a new way for potential applications in various photoelectrochemical devices and medical fields.（4） Novel porphyrin-based two-dimensional （2D） metal-organic framework （MOF）nanodisk was prepared through a bottom-up method. Based on the influences of nucleation modulator 4, 4’-Biphenyldicarboxylic acid （BPDC） and reaction solvent, the size of the prepared Zn-TCPP nanodisk could be effectively regulated and a plausible mechanism was proposed. Morphologies and properties of the prepared Zn-TCPP（BP） nanodisk was analyzed,and the MOF structure of the products was clearly observed. The as-prepared Zn-TCPP（BP）nanodisk exhibited obviously electrocatalytic activity and have the sensitivity of 158.1 μA mM^-1 cm^-2 in the electrochemical detection of nitrite （NO2 ）,which is higher than most reported in the literature. The Zn-TCPP（BP） nanodisk also has a low detection limit of 0.26μM and excellent selectivity on NO2- ions. The independent distribution of the porphyrin molecules in the framework and sandwich structure of the prepared Zn-TCPP（BP） nanodisk may be enhanced the accessible active sites between the materials and NO2- ions,which ultimately make the prepared Zn-TCPP（BP） nanodisk exhibits higher sensitivity and lower detection limit for nitrite.