Preparation Of Carbon Nanofiber Composites For Electrochemical Sensing Of Hydrogen Peroxide

In recent years,the exploration of new non-enzymatic materials with low detection limit,high sensitivity,wide linear range,fast detection speed and good stability has become an important research subject for electrochemical detection of H2O2.Research indicated that loading metal or metal oxide nanoparticles on the surface of carbon support could significantly improve their properties for H2O2 detection and structural stability.However,which may lead to detachment and aggregation of nanoparticles in the process of application and further affect the stability and properties of the as-prepared nanocomposites.Therefore,how to solve the problem is crucial for application.In the present work,we in situ prepared metal,alloy or metal oxide dispersed in polyporous N-doped carbon nanofibers by pyrolyzing electrospun nanofiber composites from the precursors of polyvinyl pyrrolidone(PVP)and inorganic metal salts.The structure and analytical properties towards H2O2 of as-prepared nanocomposites were systematically investigated.More importantly,we proposed the corresponding structure-active relationship and mechanism of action.And the as-fabricated sensors were applied to the detection of H2O2 in milks and cosmetics.The results indicated that the preparation method could not only realize N doping of carbon nanofibers,embedding different metal or alloy in carbon nanofibers and the preparation of metal or alloy/metal oxide/N-doped carbon nanofibers,but also adjust the size and composition of metal,alloy and metal oxide in composites,which could improve the detection properties of as-prepared nanocomposites towards H2O2.In addition,this embedded structure is important to enhance their stability.Main research contents and conclusions are as follows:(1)Preparation of Ag/NCNFs for electrochemical sensing of H2O2:Ag/NCNFs was in situ prepared by pyrolyzing electrospun nanofiber composites from PVP and AgNO3.The as-prepared Ag/NCNFs were characterized by XRD,SEM,TEM,SAED,HAADF-STEM,EDX,XPS,and so on.Results showed that Ag nanoparticles with average diameter of 14.2 nm were homogeneously embedded in NCNFs porous matrix.Ag/NCNFs displayed good conductivity and obvious characteristic of electrocatalysis for H2O2 reduction.Ag/NCNFs-based sensors exhibited excellent H2O2 analytical performances of low detection limit(0.15 ?M),high sensitivity(142.2 ?A·mM-1·cm-2),wide linear range(0.02-20 mM),high selectivity and anti-interference.In addition,Ag/NCNFs-based sensor had superior reproducibility and excellent stability.The value of kcat for H2O2(1.0 mM)reduction was calculated to be 1.68×104 mol-1·s-1,the Dapp value of H2O2 was 3.0×10-5 cm2·s-1.More interestingly,Ag/NCNFs-based sensor displayed excellent performance for the detection of H2O2 in real samples(milks and cosmetics).Above research results suggested that the preparation method not only improved the properties of Ag/NCNFs by increasing the dispersity of small Ag nanoparticles,but also enhanced its stability by embedding Ag nanoparticles in NCNFs.In the process of Ag/NCNFs electrocatalytic H2O2 reduction,Ag nanoparticles played a major role.The good conductivity,high surface area and porous structure of Ag/NCNFs contributed to its excellent properties.In addition,the introduction of nitrogen atoms in substrate contributed to the side-on adsorption of H2O2,which facilitated the cleavage of O-O bond and thus promoted its reduction.(2)Preparation of Pt/CeO2/NCNFs for electrochemical sensing of H2O2:Pt/CeO2/NCNFs was in situ prepared by pyrolyzing electrospun nanofiber composites from PVP,H2PtCl6·6H2O,and Ce(NO3)3·6H2O.Characterization results indicated that Pt nanoparticles and CeO2 nanoplates were uniformly embedded in the porous matrix of NCNFs.Pt/CeO2/NCNFs displayed good conductivity and electrocatalytic activity for H2O2 reduction.Pt/CeO2/NCNFs-based sensor displayed excellent properties for H2O2 detection with low detection limit(0.049 ?M),high sensitivity(185.6 ?A·mM-1·cm-2),wide linear range(0.5 ?M-15 mM),high selectivity and anti-interference.In addition,the sensor was possessed of superior reproducibility and good stability.The value of kcat for H2O2(1.0 mM)reduction was calculated to be 2.22×104 mol-1·s-1,the Dapp value of H2O2was 3.24×10-5 cm2·s-1.The excellent property of Pt/CeO2/NCNFs-based sensor was found for the detection of H2O2 in real samples.The mechanism of electrocatalytic H2O2 reduction at Pt/CeO2/NCNFs-GCE was proposed based on the synergistic effect of Pt nanoparticles,CeO2 nanoplates and NCNFs.The above results indicated that the introduction of Ce4+(?)Ce3+ redox couple greatly enhanced its electrocatalytic activity for H2O2 reduction.Besides,embedding Pt nanoparticles and CeO2 nanoplates in NCNFs improved their stability.(3)Preparation of PtNi/NCNFs for electrochemical sensing of H2O2:PtNi/NCNFs were in situ prepared by pyrolyzing electrospun nanofiber composites from PVP,H2PtCl6·6H2O and NiCl2·6H2O.Characterization results indicated that PtNi alloy nanoparticles were in situ synthesized in the process of thermal treatment and uniformly embedded in NCNFs porous matrix.It is feasible to control the size and composition of PtNi alloy nanoparticles by adjusting the ratio of Pt and Ni.Among the as-prepared composites,PtNi/NCNFs(3:1)showed the smallest particle size and highest dispersity,and the average diameter was 9.0 nm,which would contribute to the excellent properties.PtNi/NCNFs(3:1)-based sensor showed excellent analytical properties towards H2O2 with low detection limit(0.038 ?M),high sensitivity(248.5 ?A·mM-1·cm-2),wide linear range(0.5 ?M-8 mM),high selectivity and anti-interference.PtNi/NCNFs-based sensor had superior reproducibility and good stability.The value of kcat for H2O2(1.0 mM)reduction was calculated to be 3.13×104 mol-1·s-1,the Dapp value of H2O2 was 3.62×10-5 cm2·s-1.The analysis results of H2O2 in real samples suggested that PtNi/NCNFs(3:1)was an ideal materials for H2O2 sensing.The mechanism of electrocatalytic H2O2 reduction at PtNi/NCNFs-GCE was proposed based on the synergistic effect of PtNi alloy nanoparticles and NCNFs.These results manifested that the introduction of the second metal Ni improved the electrocatalytic analysis properties of Pt nanoparticles towards H2O2 and increased its resistance to interference.Embedding PtNi alloy nanoparticles in NCNFs indeed improved their stability.(4)Preparation of PtNi/CeO2/NCNFs for electrochemical sensing of H2O2:PtNi/CeO2/NCNFs were in situ prepared by pyrolyzing electrospun nanofiber composites from PVP,H2PtCl6 6H2O,NiCl2·6H2O and Ce(NO3)3 6H2O.Characterization results indicated that PtNi alloy nanoparticles and CeO2 nanoplates were in situ synthesized in the process of thermal treatment.More interestingly,most of PtNi alloy nanoparticles were dispersed on CeO2 nanoplates due to the electrostatic interaction of Ce3+,PtCl62-and Ni2+,and PtNi alloy/CeO2 plates were uniformly embedded in the porous matrix of NCNFs.The special structure of PtNi/CeO2/NCNFs would enhence the synergistic effect of PtNi alloy and CeO2 nanoplates.PtNi/CeO2/NCNFs-based sensor displayed excellent properties for H2O2 detection with low detection limit(0.025?M),high sensitivity(345.0?A·mM-1·cm-2),wide linear range(0.5 ?M-15 mM),high selectivity and anti-interference.In addition,the sensor was possessed of superior reproducibility and good stability.The value of kcat for H2O2(1.0 mM)reduction was calculated to be 3.52×104 mol-1·s-1,the Dapp value of H2O2 was 4.94x10-5 cm2·s-1.The analysis results of H2O2 in real samples indicated that PtNi/CeO2/NCNFs-based sensor held the potential applications toward actual measurement.The mechanism of PtNi/CeO2/NCNFs electrocatalytic H2O2 reduction was proposed base on the synergistic effect of PtNi alloy,CeO2 nanoplates and NCNFs.PtNi/CeO2/NCNFs showed the best properties for H2O2 detection in comparison to Pt/CeO2/NCNFs and PtNi/NCNFs,because PtNi/CeO2/NCNFs possessed the advantages of PtNi alloy,meanwhile it gave full play to the synergistic effect between PtNi alloy and CeO2 plates due to the special structure.In summary,we successfully prepared new carbon nanofiber composites with embedded structure by electrospinning and subsequent thermal treatment.The properties for H2O2 detection was gradually improved by adjusting the size and composition of metal,alloy and CeO2,and PtNi/CeO2/NCNFs displayed the best detection properties towards H2O2 with detection limit of 0.025?M and sensitivity of 345.0 ?A·mM-1·cm-2.The stability of composites was also enhanced by embedding metal,alloy and CeO2 in NCNFs.The carbon nanofiber composites possessed of a certain application in fabricating effective non-enzymatic H2O2 sensors.In addition,we proposed the corresponding structure-active relationship and mechanism of action for as-prepared nanocomposites.This work provided novel idea and method for the design and preparation of new materials.