Preparation Of Carbon-based Nanomaterials For Enzyme-like Performances

Nano-enzymes have the advantages of low cost,good stability and easy storage,but as a substitute for natural enzymes,their active centers are not clear and there is a lot of room for improvement in catalytic activity and selectivity.In recent years,carbon-based nanozymes,due to its enzyme-like catalytic activity and unique physical and chemical properties,has shown great potential in the diagnosis and treatment of physiological diseases,catalysis,sensing and other fields.Therefore,carbon-based single atom nanomaterials with natural enzyme-like active center structure and maximum atomic efficiency have become a research hotspot.However,there are few studies on the internal relationship between the activity and the structure factors such as coordination environment and surface defects,so it is difficult to provide guidance for the synthesis and large-scale application of carbon-based singleatom nanomaterials.Based on the construction of nitrogen-doped carbon-supported Fe single-atom nanomaterials,this paper studied the effects of coordination structure and surface defects on peroxidase activity by regulating the loading capacity of metal precursors,types of carbon and nitrogen sources,reaction atmosphere and temperature,and revealed its catalytic mechanism,and applied the synthesized carbon-based single-atom nanomaterials to colorimetric biosensing.The main research contents are as follows:1.Four kinds of g-C₃N₄-supported Fe single-atom nanomaterials were prepared by annealing at high temperature in different atmospheres using urea,melamine and thiourea as carbon and nitrogen sources mixed with metal precursors.Among them,Fe monatomic enzyme（Fe-CN-U-H₂）prepared in Ar/H₂ atmosphere with urea as precursor showed the highest peroxide-like activity.The results of XAFS and XPS indicate that Fe-CN-U-H₂ has the lowest Fe-N coordination number（CN=3）and the highest pyridine nitrogen content.Therefore,the synergistic effect of high-unsaturated coordination Fe N₃ site and pyridine nitrogen may be the main reason for the highest catalytic activity of Fe-CN-U-H₂.In addition,based on the peroxide-like properties of Fe-CN-U-H₂ nanomaterial,a colorimetric biosensor was constructed for the detection of ascorbic acid.The detection limit was 0.034μM,and it showed strong anti-interference against amino acids,carbohydrates and common ions.The design method of regulating the coordination environment of active center by changing the type of synthetic precursor proposed in this work has certain guiding significance for the preparation of carbon-based nanomaterials with high enzyme activity.2.On the basis of using urea as carbon and nitrogen source,nitrogen doped carbon supported Fe single-atom nanozymes（Fe-NC）with different metal loads were prepared by introducing additional carbon sources and increasing the reaction temperature.The results of enzyme-like activity test and enzymatic reaction kinetics study showed that0.1%Fe-NC showed higher peroxide-like activity,substrate affinity and catalytic efficiency compared with 1%and 4%Fe-NC.XAFS results showed that 0.1%Fe-NC had smaller Fe-N coordination number than 1%Fe-NC,and XPS and Raman spectroscopy showed that 0.1%Fe-NC had more pyridine nitrogen and surface defects（I_D/I_G=1.49）.Therefore,the synergistic effect of unsaturated coordination environment,large number of surface defects,and high content of pyridine nitrogen may be the main reason why 0.1%Fe-NC has the highest peroxide-like activity.Subsequently,0.1%Fe-NC ascorbic acid colorimetric sensor was established,which also showed strong anti-interference ability and lower detection limit（0.024μM）.This work provides a new way to design high performance single atom enzyme catalysts.