| In recent years,environmental pollution has aroused serious public concern.Photocatalytic oxidation process,as an environmental-friendly technology,has the potential for oxidative degradation and mineralization of many organic pollutants under the light irradiation without the addition of chemicals.Titanium dioxide(TiO2)is the most commonly used semiconductor photocatalyst due to its chemical stability,mechanical robustness and low cost.TiO2 nanoparticles are typically used as a suspended slurry by intensively mixing with pollutants which can maximize the light absorption and mass transfer.However,this requires an energy-intensive separation process for catalyst recovery with the risk of secondary pollution of the powder.If TiO2 can be immobilized on a solid substrate,the costly separation step can be largely eliminated.On the other hand,TiO2 in general has low adsorption capacity toward organic pollutants.Using an appropriate support material can also offer an opportunity to adsorb the pollutants to the near photocatalytic sites,resulting in more efficient utilization of the short-lived reactive oxygen species(ROS)by combining the adsorption and photocatalytic degradation for effective removal of contaminants.In order to develop photocatalysts with low cost,high reactivity and easy recovery,polyacrylonitrile(PAN)nanofibers containing TiO2 nanoparticles were successfully prepared using a facile fibre processing technique-electrospinning-in this study.SEM,BET,CA,XRD,FTIR and nano-indentation were used to characterize the microstructure,morphology,composition and mechanical properties of the electro-spun fibers.The effects of TiO2 content,PAN concentration and thermal treatment on the adsorption,photocatalytic and mechanical properties of PAN-TiO2 nanofibers have been investigated.Additionally,porous PAN-based TiO2 nanofiber membrane was prepared by selectively dissolving Polyvinyl Pyrrolidone(PVP),and the effects of different PVP weight ratio on its adsorption and photocatalytic properties were studied.The main results include:(1)The embedded TiO2 nanofibers possess the property to effectively decompose Rhodamine B(RhB)under simulated sunlight irradiation.The photocatalytic reaction fits well in pseudo first-order kinetics,and RhB was degraded through gradual decolorization under the tested conditions.The increasing TiO2 nanoparticle dispersity could improve the photocatalytic performance.Besides the adsorption active sites,light penetration and mass transfer of polymer matrix influence the photocatalytic property of TiO2 nanoparticles.(2)TiO2 content,PAN concentration and thermal treatment process affect the hardness and reduced modulus of as-prepared fibers.This is related to the particles agglomeration and formation of voids in the fiber,diameter variation,and the relaxation,un-entanglement,as well as composition changes of the fiber during heating.(3)The size of porous fibers was uniform with high hydrophilicity,and the TiO2 nanoparticles evenly distribute on the fiber surface.XRD results showed that the ratio of TiO2 anatase phase to rutile was 9:1.FTIR data revealed that a part of PVP still remained in the membrane.(4)The electro-spun fibers have good adsorption performance in removing cationic dyes such as Methylene blue(MB),while there is almost no removal of anionic dye like Methylene orange(MO).The adsorption process of MB is more in accordance with the pseudo-first-order kinetic model and Langmuir-Freundlich isotherm model.The results of fitting the multi-stage internal particle diffusion model show that the internal mass transfer process is not the rate-limiting step of the adsorption process.The organic dyes are adsorbed on the membrane which can be removed by UVA irradiation for in-situ photoregeneration and membranes recycling.(5)PVP may act as both pore-forming agent and film-forming agent in preparation of porous fiber membranes.Prolonged soaking would backfill the dissolved PVP,thus reducing the porosity.By improving the elution conditions,the BET specific surface area of fiber membranes can be increased from 12.6 m2/g to 27.6 m2/g,and the pore volume from 0.045 cm3/g increased to 0.085 cm3/g.The loading of TiO2 can be increased to 45%by changing the composition of the electrospinning solution.Through coupled adsorption and photocatalytic processes,the porous fiber membranes can degrade MB by more than 90%in 30 minutes.(6)Modifying the fiber membrane by noble metal deposition on the surface has been carried out.Controlling the time,deposition power and argon gas pressure of the magnetron sputtering can adjust the thickness of Ag nanoparticles.The sputtering time is the most important factor,while the sputtering power and argon gas pressure have minor effect.Therefore,the sputtering power and argon gas pressure were fixed at 50 w and 4.2 m torr,respectively.The deposition of Ag nanoparticles can increase the hydrophobicity of the membrane surface and improve the photocatalytic property to certain extent.This study highlights the potential applications of electrospinning technique to fabricate supporting materials for cooperating functional nanoparticles in environmental remediation,which can be widely used in the fields of wastewater treatment and air purification technology. |
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