Carbon Nanotubes Enhanced The Catalytic Activity Of Metalloporphyrin

Persistent Free Radicals?PFRs?,a kind of new environmental hazardous substances,have received extensive attention due to its long life and high toxicity,but the international research on the environmental damage mechanism of PFRs keep relatively scarce.In this work,iron porphyrin?hemin?is supported on carbon nanotubes?MWCNTs?containing persistent free radicals?PFRs?through covalent bond due to the excellent performance of carbon nanotubes and metalloporphyrin,obtaining a novel catalyst?hemin-MWCNTs?.We investigated the catalytic performance of hemin-MWCNTs with H₂O₂ as oxidant and dyes as model pollutants.Compared whith single hemin,the results of experiments showed that the introduction of PFRs significantly improved the catalytic performance,pH tolerant of iron porphyrin.In addition,we introduced ascorbic acid into this system and compared with another catalytic system that actived carbon fiber?ACF?also containing PFRs as support for hemin,and we found that MWCNTs as support has more excellent catalytic performance than that of hemin-ACF/H₂O₂/AA.This article provide novel view about the application of metalloporphyrin as a catalyst for degradation of organic pollutants,and pave a solid foundation for PFRs to apply in environmental catalysis field.The main research contents are as follows:hemin was anchored on MWCNTs covalently,obtaining hemin-MWCNTs catalyst,and it was characterized by XPS.Using dye MB as model pollutant and H₂O₂ as oxidant to investigate the catalytic activity of hemin-MWCNTs.The results indicated that the introduction of MWCNTs significantly improved the catalytic performance of hemin compared with hemin/H₂O₂,and 98% of MB could be degraded by hemin-MWCNTs/AA/H₂O₂ system in 60 min,meanwhile,the MB decomposition rate constant was calculated to be 0.04195 min-1 in the hemin-MWCNTs/H₂O₂ system,which was almost 61 times than that?0.00068 min-1?in the hemin/H₂O₂ system.Except MB,this system could degrade other different structure dyes,such as AO7,AR 1,BG,etc.In addition,this system has good pH tolerant?3-11?and temperature adaptability.Scavenger?IPA?and electron paramagnetic resonance?EPR?spectroscopy method have identified that ·OH and?Fe?IV??were generated during the degradation process,and ·OH played dominant role for dye degradation.In order to construct higher efficiency of hemin system,AA was added into the hemin-MWCNTs/H₂O₂ system.Using dye RR M-3BE as model pollutant,and compared with hemin-ACF/AA/ H₂O₂ catalytic system.The results showed that hemin-MWCNTs/AA/H₂O₂ presented higher catalytic activity than that of hemin-ACF/AA/ H₂O₂,and hemin-MWCNTs/AA/H₂O₂ could completely degrade RR M-3BE in 6 min,meanwhile the reaction rate constant?k1=0.022 min-1?was 2-fold than that of hemin-ACF/AA/H₂O₂?k1=0.011 min-1?.This system showed good pH tolerant and temperature adaptability.After being utilized 7 times,of which performance showed no obvious change.Different scavengers,such as ethanol,triethanolamine,combined with electron paramagnetic resonance?EPR?spectroscopy and electrochemical experimental were used to explore the mechanism of dye degradation.The results suggested that the dye degradation in hemin-MWCNTs/AA/H₂O₂ was attributed to hole generation,which was different from that of hemin-ACF/AA/H₂O₂?free radical mechanism?.Moreover,EPR analyses were performed to investigate the PFRs in MWCNTs and ACF at room temperature,and the results indicated that different electronic state of MWCNTs and ACF resulted in two different catalytic mechanism.