Metal-Nitrogen Co-Doping And Ascorbic Acid Electrodeposition For The Preparation Of Electrochemical Sensor

(1)Using polydopamine as nitrogen-doped carbon precursors,adsorbent and reducing agent of Co Cl₂,nitrogen and Co nanoparticles could be in situ doped and surface modified successively into/onto Si O₂@C spheres,i.e.,Si O₂@C/N-Co,via a facile and one-step calcination under nitrogen protection.The conductivity,electrons transfer ability and electrocatalytic activity of Si O₂@C sphere were improved by the synergistic effect of surface modification with Co nanoparticles and nitrogen doping and then the sensitivity of this electrochemical sensor was enhanced.Compared with Si O₂@C/N,the oxidation peak current of Si O₂@C/N-Co was increased from 39.17μA to 119.4μA for 100μmol/L of catechol（CC）and from 24.0μA to 110.8μA for 100μmol/L of hydroquinone（HQ）,i.e.,the sensitivity of Si O₂@C/N-Co was improved 3.05 and 4.62 times for CC and HQ,respectively.Both CC and HQ could be detected simultaneously by Si O₂@C/N-Co modified electrode with differential pulse voltammetry.This proposed method with wide linear range（1.0-200μmol/L and0.5-400μmol/L for CC and HQ）and low detection limit（0.17 and 0.09μmol/L for CC and HQ）was successfully applied for simultaneous detection of CC and HQ in Jiulong River water.（2）Cobalt,iron and nitrogen co-doped hollow carbon sphere（H-C/N-Co-Fe）with better conductivity,electrons transfer ability and electrocatalytic activity modified electrode is prepared and applied for simultaneous catechol（CC）and hydroquinone（HQ）.The electrochemical performance of H-C/N-Co-Fe/GCE is tested by cyclic voltammetery and different pulse voltammetery.Comapred with bare GCE、H-C/N/GCE、H-C/N-Co/GCE、H-C/N-Fe/GCE,H-C/N-Co-Fe/GCE has better electrocatalytic activity with wide leaner range（0.5-500 and 0.5-1500μmol/L for CC and HQ）and low detection limit（0.075 and 0.080μmol/L for CC and HQ）for detecting CC and HQ,which is due to the synergistic effect of cobalt,iron and nitrogen.Furthermore,the concentrations of CC and HQ in river water have been detected with a recovery of 98.0-104.0%and its relative standard deviation（n=5）is less than 5%.（3）Ascorbic acid was successfully deposited on the bare glass carbon electrode through the method of electrodeposition using cyclic voltammetry.The modified electrodes were characterized by atomic force microscope,infrared spectrometer and cyclic voltammetry.Compared with bare glass carbon electrode,the oxidation peak of AA/GCE was increased from 4.75μA to 11.22μA for detecting 100μmol/L NO₂^-,i.e.,the sensitivity of AA/GCE was improved 2.36 times.NO₂^-could be determined by AA/GCE with differential pulse voltammetry.This method with wide linear range（0.1-1650μmol/L）and low detection limit（0.0797μmol/L）has good stability and anti-interference.