Construction Of Gas-solid-liquid Three-phase System By Electrospinning Composite Nanofiber Membrane And Its Photocatalytic Performance

TiO₂-based photocatalytic technology is a green,efficient,and low-consumption technology that uses sunlight as a source of energy to catalyze chemical reactions,and the technology plays an important role in the treatment of printing and dyeing wastewater.Due to the large energy band width of TiO₂,it can only use ultraviolet light in sunlight.The dye-sensitized strategy can be used to construct visible-light-responsive TiO₂catalysts,especially for the structurally stable metal phthalocyanine/porphyrin photosensitizers,but the obtained catalysts still suffer from the low photocatalytic activity under visible light irradiation.In this paper,electrospun nanofibers were employed as the catalysts support to tackle such problems.The polyacrylonitrile(PAN)nanofibers anchored TiO₂ catalysts with Fe Pc/hemin as the photosensitizers were synthesized via electrospinning of their composite DMF solution.In addition,polyvinylpyrrolidone(PVP)was introduced into the nanofibers support as a sacrificial agent to improve the porosity and specific surface area of the nanofiber catalysts,and then the obtained catalytic layer was combined with a polystyrene(PS)nanofiber membrane with a porous and hydrophobic structure.The bilayer nanofiber membrane catalyst enables water to wet the catalytic layer,while inhibits water penetration into the PS layer and thus delivers the ambient air from PS layer to the catalytic interface,facilitating an efficient triphase contact of O₂(gas),water(liquid)and catalyst(solid).The as-prepared nanofiber catalyst was characterized by SEM,EDAX,TEM,XRD,FT-IR,XPS,BET,DRS and PL,and its photocatalytic activity was evaluated by degrading organic dyes under visible light and the corresponding photocatalytic reaction mechanism was also proposed.The results show that PAN nanofibers supported Fe Pc/hemin-sensitized TiO₂catalysts have been successfully prepared by electrospinning technology,and the molecular structure and chemical microenvironment of Fe Pc/hemin and TiO₂ did not change significantly after immobilization.The presence of the photosensitizer enables the nanofiber catalyst to show obvious absorption in the visible light region,leading to an effective degradation for organic dye(Rh B)under visible light irradiation,where the dye degradation rate reached more than 80%in 140 minutes.By introducing the sacrificial agent PVP into the PAN spinning solution,the distribution uniformity of the photosensitizer and TiO₂ on the nanofibers could be improved.Moreover,the fiber diameter and pore diameter are also reduced,accompanied by the significant increase in specific surface area,thereby enhancing the photocatalytic activity of the as-prepared Fe Pc-sensitized TiO₂ catalyst.By adjusting the electrospinning parameters,PS nanofiber membranes with a contact angle of 140°can be prepared.Subsequently,the bilayer nanofiber membrane catalyst with both catalytic and hydrophobic layers could be synthesized via combining the PS nanofiber membranes with the nanofiber supported catalyst layer.The high hydrophilicity of the catalytic layer makes the reaction solution easy to penetrate,while the hydrophobic PS layer can prevent the entry of aqueous solution and rapidly transport O₂ from air into the catalytic interface through the porous structure.Therefore,a three-phase photocatalytic system in which gas-solid-liquid coexist was successfully constructed,and the photocatalytic activity was much higher than that of the traditional two-phase system.This may be because O₂ in the three-phase system can be quickly transported to the catalytic interface through the PS hydrophobic membrane,resulting in a high concentration of O₂ participating in the reaction.This not only accelerated the generation of·O^2-but also facilitated the production of H₂O₂,which can react with Fe Pc to generate a large amount of·OH via Fenton-like reactions,thereby significantly promoting the oxidative degradation of the dye.