Photocatalytic Properties Of PAN Fiber Reinforced TiO₂ And MOFs

Photocatalytic oxidation technology is considered as a solar-driven environmental remediation method,which plays an important role in the treatment of dye wastewater.TiO₂ is well-known to be the most attractive semiconductor photocatalyst due to its stable chemical properties,light corrosion resistance and excellent photocatalytic properties.Recently,MIL-53(Fe)with unsaturated metal active sites and semiconductor-like properties has been used as a novel photocatalyst in wastewater treatment.However,TiO₂ shows low visible light utilization due to its wide band gap,and MIL-53(Fe)suffers from weak stability in water environment and high recombination rate of photo-generated carriers.Moreover,these powder photocatalysts also suffer from the difficult recycling,severely limiting their practical application in the treatment of dye wastewater.In this paper,the low-cost and easy-to-recover amidoximated polyacrylonitrile fiber(AO-PAN)was used as support material to immobilize TiO₂ and MIL-53(Fe)through coordination bonds,respectively,to synthesize the LMCT sensitized TiO₂ catalyst(TiO₂-PAN)and irregular MIL-53(Fe)catalyst(MIL-53(Fe)-PAN).In addition,a carbon fiber-based photocatalyst(MIL-Fe-ACF)containing highly active Fe atoms was also obtained through further treatment of MIL-53(Fe)-PAN by carbonization and acidification.SEM,EDAX,XRD,FT-IR,XPS,DRS and PL were used to characterize these fibrous photocatalysts,and the oxidative degradation of organic dyes were carried out to evaluate their photocatalytic activity under visible light irradiation.Furthermore,the corresponding photocatalytic mechanism was also investigated.The results show that the fiber ligand can combine with TiO₂ through coordination bonds to prepare TiO₂-PAN,and the light response range of TiO₂ can be extended to800 nm through LMCT effect.This photocatalytic system can produce a large amount of�O^2-upon visible light,and completely oxidize and degrade Rh B dye within 60 min.The excellent photocatalytic activity of TiO₂-PAN is mainly attributed to the LMCT sensitization between fiber ligand and TiO₂ as well as the interaction of N atom of-NH₂doped in TiO₂ lattice.In addition,TiO₂-PAN also shows versatility for a variety of dyes,good durability and the feasibility of repeated recycling.On the other hand,the irregular structure of MIL-53(Fe)can be constructed on the surface of AO-PAN by in-situ synthesis with the aid of the synergistic effect between fiber ligand and terephthalic acid ligand.This new MOFs photocatalyst MIL-53(Fe)-PAN shows much better activity than that of MIL-53(Fe)powder and its directly loaded AO-PAN catalyst.The decolorization rate of Rh B dye solution is close to 90%in 100 min,and the main active species are h⁺and�O^2-.In addition,this method can also be used to enhance the photocatalytic activity of MIL-100(Fe),which shows a certain universality in improving the photocatalytic performance of MOFs.Furthermore,the MIL-Fe-ACF obtained by pre-oxidation,carbonization and acidification treatment of MIL-53(Fe)-PAN can maintain excellent light absorption performance,and its Fe atom activity is significantly improved compared with MIL-53(Fe)-PAN.The MIL-Fe-ACF/H₂O₂system can completely degrade the Rh B dye solution when exposed to visible light for20 minutes,mainly originating from the high-efficiency Fenton system constructed by H₂O₂ and Fe in MIL-Fe-ACF.This system can produce a large amount of�O^2-and�OH that induce the oxidative degradation of the dye.