Study On Electrochemical Analysis Method Of Methylmercury Based On Phosphorus And Sulfur Doped Graphite-like Carbon Nitride

Due to the accumulation and persistence of mercury in the ecological environment,mercury ions are highly toxic,carcinogenic,non-biodegradable and widely distributed in the environment,and mercury is easily methylated in the environment.Methylated forms of mercury are more dangerous because of their high solubility in lipids,which enables them to be concentrated through the food chain.Methylmercury is extremely harmful to human body.Because of its small molecular weight and strong fat solubility,methylmercury can easily cross the blood-brain barrier,so it shows strong neurotoxicity.Traditional techniques for detecting methylmercury have high selectivity and sensitivity,but the analysis process is complicated.Therefore,there is an urgent need for a rapid and sensitive technique to detect methylmercury in the environment.Graphite carbon nitride（g-C₃N₄）is a kind of nanometer material with unique energy band structure,excellent stability and good biocompatibility.In this paper,g-C₃N₄ with different proportions of phosphorus and sulfur was prepared by modifying g-C₃N₄ and introducing phosphorus and sulfur elements,which was used as an electrochemical electrode modification material to build an electrochemical sensor on the gold electrode to explore the analysis and detection performance of methylmercury.The details are as follows:（1）An electrochemical sensor was constructed using phosphorus-doped g-C₃N₄（PCN）modified gold electrode for the determination of methylmercury（CH₃Hg⁺）.Under the best experimental conditions,CH₃Hg⁺shows a good differential pulse voltammetric response signal:the peak current has a good linear relationship in the concentration range of 0-25μg·L^-1,and the calculated sensitivity is 0.42μA/（μg·L）^-1 and the lowest detection limit is 0.182μg·L^-1（S/N=3）.The electrochemical response of PCN sensitive interface to CH₃Hg⁺has good anti-interference ability in the presence of Cu²⁺,Cd²⁺,Pb²⁺,Bi³⁺and As³⁺,and has excellent stability and reproducibility.The recovery rate of electrochemical detection of CH₃Hg⁺in actual water samples is 94.7%-111.6%.（2）An electrochemical sensor was constructed using sulfur-doped g-C₃N₄（UT-g CN）modified gold electrode for the determination of methylmercury（CH₃Hg⁺）.Under the deposition potential of-0.80 V,CH₃Hg⁺was rapidly detected by differential pulse voltammetry（DPV）in naac/HAC buffer（p H=5）for 800 s.The calibration curve of CH₃Hg⁺is linear in the concentration range of 0-25μg·L^-1,the sensitivity is 0.52μA/（μg·L）^-1,and the detection limit is 0.175μg·L^-1（S/N=3）.In addition,by adding DTPA and Sn Cl₂,the influence of inorganic mercury on the detection of methylmercury was eliminated.UT-g CN sensitive interface has good stability,reproducibility and anti-interference ability.The recovery rate of CH₃Hg⁺in actual water samples was91.2%-101.2%.（3）The electrochemical response mechanism of PCN and UT-g CN nano-material modified electrode to CH₃Hg⁺was studied by means of series characterization and theoretical calculation.The results show that the doping of phosphorus and sulfur mainly plays the following two roles:on the one hand,the band gap of g-C₃N₄ narrows and the conductivity increases;On the other hand,the adsorption performance of methylmercury can be improved by doping.