N-doped Graphene-like Carbon Materials Synthesized By Template Method As Peroxidase Mimics

Carbon materials with specific morphology or heterogeneous atom doping possess more abundant electronic structure and surface chemical characteristics than pure products,which exhibited wider applications in energy,bioanalysis,and biomedical fields.Among numerous doping elements,nitrogen has the most extensive use in doping modification because of its similar atomic size with carbon atom and high electron density.Template synthesis of carbon materials can retain the structural characteristics of templates in products,including special morphology or internal microstructures.Therefore,carbon materials with special morphology could be rationally designed and prepared based on templates methods.Nanozymes are functional materials with both the characteristics of nanomaterials and enzymatic properties.They overcome the weaknesses of natural enzymes(e.g.,easy to denaturation and difficult in preparation and extraction).The researches on nanozymes have grown exponentially in the past ten years,making nanozymes a young and vigorous research field.Carbon-based nanozymes with different structures exhibited various enzyme-mimicking activities.For example,zero-dimensional fullerenes possess superoxide dismutase(SOD)-like activity,while one-dimensional carbon nanotubes and two-dimensional graphene exhibit peroxidase(HRP)-like activity.In this work,nitrogen-doped graphene-like carbon materials were synthesized by template method,and their HRP-like activities were studied in detail.Finally,they were successfully used for the detection of hydrogen peroxide,glucose and ascorbic acid.(1)Using natural clay mineral montmorillonite(MMT)as hard template and polyethyleneimine(PEI)with high nitrogen-carbon ratio as carbon and nitrogen source,nitrogen-doped carbon materials with graphene-like morphology were synthesized by assembling MMT and PEI which possessed opposite charged properties.The material was characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),Raman spectra and Fourier transform infrared spectroscopy(FTIR),etc.It was proved that the material was graphene-like,containing carbon,oxygen and nitrogen elements,and had high nitrogen content in the range from 4.65%to 7.53%.By adjusting the molecular weight of PEI and the calcination temperature,it was found that the product obtained by calcination 600 molecular weight PEI at 600 ?(CP600-6)had the highest HRP-like activity.Further detailed studies on other enzymes-mimicking activities(e.g.,oxidase,catalase and SOD)showed that CP600-6 had specific HRP-like activity.The catalytic mechanism was studied,and it was found that the activity arose from producing hydroxyl radicals by catalyzing hydrogen peroxide and further achieved by oxidation of substrates.(2)The HRP-like activity of CP600-6 was further studied.Firstly,it was verified that CP600-6 has intrinsic HRP-like activity,which can catalyze typical substrates such as 3,3',5,5'-Tetramethylbenzidine(TMB),2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)and o-phenylenediamine(OPD).Its catalytic activity depends on the concentration of substrate and catalyst,and varies with the change of pH and temperature.Then,the enzymatic kinetics of CP600-6 was studied.It was found that CP600-6 had a very high vmax value,demonstrating its superior HRP-like activity.Compared with natural HRP,CP600-6 possessed a higher affinity for TMB.Finally,CP600-6 was applied to the detection of hydrogen peroxide,glucose and ascorbic acid with wide detection ranges.The linear detection range for hydrogen peroxide was 20-200 ?M with a detection limit of 15 ?M;the linear detection range for glucose was 10-100 ?M with a detection limit of 10?M;and the linear detection range for ascorbic acid was 8-80 ?M with a detection limit of 8 ?M.