Research On The Construction And Photocatalytic Performance Of Supported Fiber Aggregates Based On Iron-based Metal Complexes

As a branch of the advanced oxidation process,photocatalysis has become a research hotspot in the field of organic pollutants treatment due to its mild,effective,and green course of reaction.However,several issues still remain for most photocatalysts represented by titanium dioxide,such as strong dependence to ultraviolet light,difficulties in nano-particle recovery and high recombination rate for photocarriers.To solve the problems,a series of PAN fiber aggregates based iron complexes were prepared by using PAN nonwoven fabric(nPAN)and PAN yarns(PAN)as catalyst substrates,and further studied their catalytic activity in organic pullutants degradation.The preparation and photocatalytic degradation ability of the iron complex system in gas-solid phase and liquid-solid phase reaction were investigated.In addition,organic ligands and heterometal ions were employed to enhance the catalytic performance of these complexes systems.On the basis of studying the heme supported PAN complexes,biomimetic functional PAN metal complexes were synthesized,and its catalytic performance was found to be improved compared with the traditional iron complexes.First of all,PAN nonwoven and PAN fibers were modified by hydroxylamine hydrochloride to prepare the amidoximated PAN nonwoven/fiber support(AO-nPAN/AO-PAN).Subsequently,AO-nPAN and AO-PAN were chemically coordinated with Fe(?),iron phthalocyanine(FePc),2,2'-dipyridyl(FeB),hemin to prepare Fe-nPAN,FePc-nPAN,FeB-nPAN,hemin-PAN and FePc-PAN,respectively,and the preparation craft of different metal complexes were optimized through experiments.Scanning electron microscope(SEM),fourier transform infrared spectrometer(FTIR),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),diffuse reflectance UV-Vis spectra(DRS),dynamic thermomechanical analysis(DMA),differential scanning calorimetry(DSC)and thermogravimetric analysis(TG)were employed to characterize the surface morphology,molecular structure,optical and thermodynamic properties of PAN and its metal complexes.Gaseous formaldehyde and aqueous dye solution were chosen as the pollutant model to investigate the photocatalytic activity of AO-nPAN metal complexes and AO-PAN metal complexes correspondingly,then the catalytic properties and mechanism of these catalysts were further studied.The results indicated that prolonging the reaction time,temperature and hydroxylamine hydrochloride concentration could promote the modification degree of AO-nPAN.Enlarging the reaction temperature,Fe ions concentration in solution and weight gain rate of AO-nPAN will contribute to the Fe ion loading on the surface of the complexes.The characterization revealed that Fe(?)supported on AO-nPAN mainly through coordination bond,thus barely ions leakage had been found in the solution.Fe-nPAN was employed in the degradation of gaseous formaldehyde and showed excellent catalytic activity in appropriate conditions,in which the degradation rate could be as high as 95.7%in 60 min.Compared with the PAN fiber based Fe(?)complexes,the degradation activity of Fe-nPAN was enhanced about 28.4%.On the other hand,FePc and FeB were also employed with a dyeing method to prepare the nPAN based metallic complexes for the purpose of replacing the role of Fe(?),which is donated as FePc-nPAN and FeB-nPAN.As a result,the catalytic activity of FeB-nPAN was mainly promoted under visible irradiation,while the FePc-nPAN exhibits better catalytic performance in removing formaldehyde in the dark state.Their catalytic characteristic should be attributed to the metallo-organic compounds which maintain the property of photosensitivity and bionic properties,respectively.It is found that iron ions could activate the molecular oxygen atoms and produce Fe(?)=O species through heterolytic cleavage.Besides,the GC analysis showed that CO2 was the main product during the formaldehyde degradation with the catalytic system of the three complexes.Hemin supported AO-PAN complexes(hemin-PAN)with the biomimetic properties was successfully prepared.The characterization techniques indicated that hemin combined with hydroxyl and amino groups of AO-PAN through coordination effect,thus barely ions leakage had been found in the dyes solution.DRS showed that the light response capability of hemin-PAN covers the entire visible light band.Hemin-PAN/H2O2 system was also introduced in dyes degradation to find its biomimetic catalytic activity under visible irradiation:with the effect from different ligands,the O-O bond will be selectively cleaved through the heterolytic or homolytic cleavage and thus produce Fe(?)=O and hydroxyl species to degrade organic pollutants.The RhB dyes could be completely decolorized by hemin-PAN/H2O2 within 30 min.Besides,hemin/PAN composite nanofiber membrane were also prepared in this study,it is found that hemin and PAN were compounded by ?-?conjugate,and the catalyst showed obvious activity during oxidative degradation of Rhodamine B dye(RhB).Through the mathematical model study,the results indicated that the catalytic activity of this hemin/PAN composite nanofiber membrane is produced by the synergistic effect between adsorption and catalytic reactions.The assisted metal ions Cu(?)were introduced and resulted in the competition between Cu/Fe ions during metal coordination process,thus enabled the two metals close to each other at molecular level to reach the synergistic effect.SEM?FTIR?XPS found that Cu(?)caused a significant difference in the coordination structure of the monometallic complexes:both of the two metal ions could coordinate with one amidoxime unit through hydroxyl and amino group so as to provide the possible synergies.Photoluminescence,ESR,XPS showed that there were interactions between Cu/Fe ions in the bimetallic complexes:visible irradiation promoted the cyclic valence transformation between Fe(?)/Fe(?)and Cu(?)/Cu(?)in the complexes,thus facilitating the decomposition of H2O2 and other oxidants to produce hydroxyl radicals.It is found that CuFePc-PAN presented as a light-driven catalyst and was able to degrade a range of aqueous organics,which is quite different from PAN fiber based FePc complexes(FePc-PAN).Besides,the reaction rate constant of CuFePc-PAN reached 0.046 in degrading RhB dyes which is 2.7 times bigger than that of FePc-PAN catalyst.The catalytic activity of FePc-PAN in activating PMS,PS,H2O2 and O2 found that FePc-PAN/PMS system was of the most efficiency.The catalytic activity order from high to low are:PMS,H2O2,PS,O2,respectively.Besides,the cata.lytic system of FePc-PAN/PMS was further studied with different reaction factors,and the results showed that reaction temperature and light intensity are favorable to enhance its catalytic activity.Of note,PAN/PMS showed better catalytic activity in the acidic environment(pH=3)than the alkaline condition(pH=9),which would provide valuable reference for the optimization and expansion of PAN-based metal complexes.