Construction Of An Efficient FePc-TiO₂ Photocatalytic System Based On Fiber Support And Its Visible Light Degradation Performanc

Metal phthalocyanine sensitized TiO₂ represents a promising strategy for constructing visible light driven photocatalytic systems,but this heterostructure still suffers from low photocatalytic oxidation activity and fast recombination of photoinduced carriers,limiting its application for textile wastewater purification.To overcome this limitation,two strategies for improving the visible light driven photocatalytic performance of the iron phthalocyanine（FePc）/TiO₂composite have been proposed in this work,by employing the functional polyacrylonitrile（PAN）fiber and electrospun micro/nanofibers as the support materials,respectively.A series of fibrous photocatalysts with FePc/TiO₂ immobilization has been designed and prepared using the hydrothermal method and electrospinning technology,respectively.The as-prepared photocatalysts were characterized and then used for photodegradation of organic contaminants under visible light irradiation.The photocatalytic mechanism was evaluated and the crucial role of fibrous support in improving the photocatalytic performance of FePc/TiO₂ was also investigated.Firstly,the fibrous photocatalyst was synthesized by simultaneously anchoring FePc/TiO₂ onto an amidoximated PAN fiber,and FePc/TiO₂with a thickness of～400nm was found to be evenly loaded on the fibrous support through coordination bonds.An optimal FePc/TiO₂ ratio with 10.2%in the fibrous photocatalyst was obtained to give the best photocatalytic activity for dye degradation,which delivered an over 30-fold higher reaction kinetics versus a corresponding system with FePc/TiO₂ powder catalysts.The fibrous support could enhance the photoinduced electron injection efficiency from FePc to TiO₂ by changing their microstructures,facilitate the O₂ reduction and contaminants adsorption by creating more oxygen vacancies via affecting their chemical states,and improve the photocatalytic activity of FePc by axial coordination to boost the activation of photoinduced H₂O₂ for ROS production.Subsequently,the catalyst fiber membrane containing FePc/TiO₂ was prepared by electrospinning with PAN/polyvinylpyrrolidone（PVP）as the spinning polymers.Then the obtained catalyst layer was deposited onto a polystyrene（PS）fiber membrane to form a bilayer micro/nanofiber membrane.Although the fibrous membrane support without active groups could not affect the photocatalytic activity of FePc/TiO₂ through strong interaction,the hydrophobic PS layer serves as a gas passage to deliver O₂ from air to the catalytic interface,boosting the photoinduced electrons conversion via O₂ reduction by providing air-liquid-solid triphase contact interfaces,and in turn leading to better visible light driven photocatalytic activity towards contaminants degradation than that of the diphase photocatalytic system.Alveoli-like structure design of the bilayer micro/nanofiber membrane enriched the triphase contact lines by facilitating O₂ transport and further enhanced its photocatalytic activity,which delivered a 10.1-fold higher apparent reaction rate than that for the diphase system.The triphase system also enhanced the H₂O₂generation to trigger efficient Fenton reaction by Fe²⁺/Fe³⁺pair in FePc,producing more reactive oxygen species for contaminants degradation.The fast capture of photoelectrons by gaseous O₂ also restrained their return to FePc holes for charge recombination in triphase system,which allows a superior level of FePc decoration（36%）with high photocatalytic activity and apparent quantum yield under visible light irradiation.Although the bilayer micro/nanofiber membrane could not boost photocatalytic reactions through direct interaction with the photocatalysts,the enhanced O₂ concentration in the photocatalytic interface by the triphase system could also enhance the visible light driven photocatalytic activity of FePc/g-C₃N₄composite,demonstrating its universal application in promoting photocatalytic reactions.