Study On The Preparation Of Carbonaceous Nanomaterials Enhanced Iron-based Nanozymes And Its Mechanism Of Adsorption And Degradation Of Dyes

Nanozyme is a kind of nanomaterials with natural enzyme catalytic performence.Its appearance overturns the inherent cognition that inorganic nanomaterials are biologically inert substances.Compared with natural enzymes,nanozymes have been widely studied in the fields of medical treatment,sensing,and environment due to their advantages such as low price,easy accessibility,tuneable activity,and strong environmental tolerance.However,because of their relatively lower catalytic activity compared with natural enzymes,its practical application is still greatly restricted.Therefore,exploitation of nanozymes with excellent catalytic activity is of great significance.In this paper,we selected Fe₃O₄nanoparticles(Fe₃O₄NPs)with both enzyme-like activity and magnetic response characteristics as research object,and Fe₃O₄NPs is composited with different loading amount of single-walled carbon nanotubes(SWCNT)and graphene oxide(GO)which possess different spatial structures and surface chemical properties.The peroxidase-like activities of prepared nanozymes are examined.After that,we further explored the efficiency and mechanism of carbon nanomaterials enhanced Fe₃O₄nanozymes when applied in the adsorption and enzyme-like degradation of methylene blue(MB)dye.The main research content and results of the paper are as follows:(1)The co-precipitation method is adopted to quickly synthesize Fe₃O₄nanozymes compositedw ith 1%,5%,10%and 15%loading anmount of SWCNT and GO,respectively.The analysis results of scanning electron microscope(SEM),X-ray diffraction(XRD)and Fourier infrared spectroscopy(FT-IR)all comfirmed the successful attachment of Fe₃O₄NPs on the surface of SWCNT and GO.As SEM shows,the introduction of carbon nanomaterials(CNMs)can effectively improve the agglomeration of nanoparticles in Fe₃O₄NPs,and the higher amount of CNMs is loaded,the more“fluffy”the Fe₃O₄NPs are.However,at 15%GO loading situation,due to the strong attraction of excessive oxygen-containing groups on the surface,Fe₃O₄NPs reappeared in an aggregated state,showing a limitation or even inhibition effect of dispersing Fe₃O₄NPs by GO.Conprehensive analysis results of XRD and FT-IR indicate the coverage of Fe₃O₄NPs in the surface of CNMs,and that although SWCNT/Fe₃O₄ has high particle crystallinity,they may be peroxided during the preparation or storage and thus doped by maghemite(?-Fe₂O₃),leading to a damaged purity.In contrast,GO/Fe₃O₄ nanomateials have excellent purity,but as the loading amount of GO increased,the crystallinity of Fe₃O₄NPs gradually decreases,which is closely related to the re-aggregation of nanoparticles under high GO loading.(2)The detection results of peroxidase-like activities of prepared nanozymes show that all of the 9 nanozymes have catalytic performance similar to peroxidase(POD).With the introduction of CNMs and its increasing loading amount,the catalytic activities of composited nanozymes have been enhanced to varying degrees.Ultimately,peroxidase-like activities of Fe₃O₄ nanozyme withr 15%SWCNT and GO loading are7.283×10^-4 U and 9.870×10^-4U,which are 2.68 and 3.63 times that of pure Fe₃O₄nanozyme.(3)By applying nanozymes to the adsorption removal of MB dye,we find that the composition of CNMs can significantly improve the adsorption capacity and adsorption efficiency of nanozymes to MB,which show a significant positive correlation with the loaded CNMs amount.Whith the MB concentration range between 5 mg/L?30 mg/L,the maximum adsorption capacity of 15%SWCNT/Fe₃O₄ and 15%GO/Fe₃O₄composited nanozymes to MB are 4.931 mg/g and 4.656 mg/g respectively,compared with pure Fe₃O₄ nanozyme(0.998 mg/g),they significantly increased by 3.941 and3.665 folds,respectively.In an overall view,the adsorption performance of SWCNT/Fe₃O₄ nanozymes are all slightly stronger than that of GO/Fe₃O₄ nanozymes with the same loading amount,which is attributed to the difference in physical and chemical properties of the two carbon nanomaterials.The adsorption kinetics and the isotherm adsorption fitting results showed that the adsorption of MB by synthetic nanozymes were better fitted to the quasi-second-order kinetic adsorption process with the Langmuir isotherm adsorption model,indicating the adsorption behavior of nanozyme adsorbents to MB molecules belongs to monolayer adsorption and chemisorption are their important adsorption mechanisms.Electrostatic attraction andp-pstacking may be the main chemical effects.(4)Based on the enhanced catalytic performance of iron-based nanozymes by CNMs,the difference in catalytic removal efficiency of MB by all synthetic nanozymes is compared at 20 m M?200 m M H₂O₂concentrations and 5 mg/L?30 mg/L initial MB concentrations.Contrary to the results we got about the adsorption capacity,GO composited nanozymes show a higher catalytic performance than that of SWCNT/Fe₃O₄nanozymes,and also exhibit a lower dependence on H₂O₂concentration.According to the monolayer adsorption behavior of the nanozymes,it is inferred that there may be competitive adsorption between H₂O₂ and MB on the surface of composited nanozymes during the enzyme-like catalysis,and GO/Fe₃O₄nanozymes have a higher affinity towards H₂O₂,while SWCNT/Fe₃O₄ nanozymes have a stronger affinity to MB.(5)Active oxygen quenching experiments show that the enzyme-like catalytic activity of nanozymes comes from the Fenton-like reaction process,and hydroxyl radical(·OH)is the main active intermediate substance in the catalytic system.A comprehensive analysis of the full text suggests that the mechanism of enhanced catalytic properties of iron-based nanozymes by CNMs mainly stems from the overall structure and properties changes of nanozymes caused by CNMs.Structurally,the introduction of CNMs has improved the dispersion of Fe₃O₄ NPs and increased its catalytic contact area.In terms of performance,firstly,as CNMs are also a kind of nanozymes,the compistion of CNMs and Fe₃O₄ nanozymes may exhibit a synergistic effect of enzyme-like catalytic activities;secondly,Fe₃O₄ nanozymes composited with CNMs is beneficial for enhancing their affinity to substrates;last one,electrochemical analysis show that CNMs can also act as electron conductor between iron-based nanozymes and H₂O₂ and thus accelerate the electron exchange and transfer during the redox reaction process,leading to the improved the catalytic efficiency.(6)After 5 times of recycle use,the composited nanoenzymes show a lower catalytic stability than that of Fe₃O₄ nanozymes.The reason may be that Fe3O₄ NPs dispersed on the surface of CNMs are more unstable than they are in aggregated state,and are prone to cause decrease and passivation of the active sites during repeated extraction.