Study Of Ammonia Nitrogen Detection Method Based On Copper Modified Graphene Electrode

In today’s world,water pollution problems are frequent,and real-time monitoring of water pollution is becoming more and more important.In China’s"12th Five-Year Plan",ammonia nitrogen has become the main water pollution binding control index after COD.At present,the national standard method for ammonia nitrogen detection is mainly nano-reagent spectrophotometry（HJ 535-2009）and salicylic acid spectrophotometry（HJ 536-2009）,these two methods have some reagents toxic（nano-reagent spectrophotometry in the chromogenic agent is mercury salt）,the need for sample pretreatment,reagent stability（only 1 month）requirements are strict（salicylic acid spectrophotometry）,long detection time（3 hours）and other problems.In order to solve the above problems of the national standard method,this thesis is based on copper-modified graphene electrode for ammonia nitrogen detection.The main research contents are as follows:（1）Graphene electrodes were prepared by high-temperature thermal cracking and chemical vapor deposition and characterized by scanning electron microscopy（SEM）and electrochemical workstation.The oxidation potential of ammonia nitrogen was determined as 1.2 V vs.Ag/AgCl.The effect of graphene electrode on the oxidation efficiency of ammonia nitrogen and its reaction products in the presence of chloride ions was analyzed.（2）A three-electrode system was used to prepare copper-modified graphene electrode using electrochemical deposition method.Characterization was performed by scanning electron microscopy（SEM-EDS）and electrochemical workstation.The nitrate detection potential of-1.36 V vs.Ag/AgCl was determined,and the electrochemical response of nitrate on the surface of copper modified graphene electrode was analyzed by constant potential polarization method using potassium nitrate as a standard.（3）To eliminate the interference of metal ions in water samples on the detection of ammonia nitrogen while ensuring high sensitivity,the experimental results showed that the use of carbon rods as working electrodes with cathodic polarization at-0.5 V vs.Ag/AgCl for 5 min pretreatment of water samples to be measured can effectively adsorb and detect the metal ions in water.The effects of p H,reproducibility of experimental results,detection range,and detection limit were also analyzed.（4）Twenty-three actual water samples from different sampling sites were actually tested by the established electrochemical method and compared with salicylic acid spectrophotometric method.The relative error of both comparisons is less than 9%,with a minimum of 0.38%,which is lower than the allowable error of 10%by national regulations.The minimum detection limit of the electrochemical method was 1.3μg·L^-1,and the detection range was 0-100 mg·L^-1without sample pretreatment,and the single detection time was 30 min.In summary,this thesis completed the preparation of copper-modified graphene electrode by electrochemical deposition method and successfully applied to the rapid detection of ammonia nitrogen.This study not only established a rapid detection method,but also provided a solution for realizing online monitoring of ammonia nitrogen in water quality.