Study On Graphene-based Metal Compunds Modified Electrodes For Electrochemical Detection Of Heavy Metal Ions

Although heavy metals are naturally occurring elements,they accumulate in organisms directly or through the food chain through natural and human activities.In the body,metal ions can be converted into more toxic forms,causing various disorders and damage to the human body.Therefore,it is necessary to detect heavy metals in water environment and food.Compared with traditional heavy metal detection methods,electrochemical methods have received extensive attention because of their advantages of environmental friendliness,easy operation,and high efficiency.For electrochemical detection of heavy metals,high-performance electrode modification materials play a vital role in improving the sensitivity of sensor detection.Therefore,this article focused on the preparation and performance of graphene composite transition metal materials.The specific work was as follows:?1?In this study,a rGO/MoS₂/CS nanocomposite modified glassy carbon electrode?GCE?was used to construct a sensitive sensor for detecting lead ions in tobacco leaves.The reduced graphene oxide?rGO?was used to increase the conductivity of the sensor,and the nano-flowered MoS₂ could provide a large reaction specific surface area and a certain active site for heavy metal reaction.Chitosan?CS?was used to improve the enrichment ability of heavy metals and increase the electrocatalytic activity of electrode.Thus,an electrochemical sensor with excellent performance in reproducibility,stability and anti-interference ability was established.The stripping behavior of Pb???and the application conditions of the sensor were studied by square wave anodic stripping voltammetry?SWASV?.The investigation indicated that the sensor had high detection sensitivity in the range of 0.005?0.05?2.0?M,and the limits of detection?LOD?was 1.67 nM.Finally,the experiment detected Pb???in the actual sample?tobacco leaf?and calculated that the Pb???content in the tobacco leaf was about 1.157?g·g^-1.In order to verify the reliability of the experimental results,ICP-MS test was also performed on the samples,and the result was 1.204±0.0542?g·g^-1.The results showed that the sensor had reliable detection results in practical applications.?2?The ZnMn₂O₄/GO nanocomposite was prepared by the one-pot method,and a new sensor for detecting heavy metal ions was designed and manufactured.Combined with SEM,XRD and electrochemical methods,the surface morphology and electrochemical properties of the materials were investigated.The SWASV method was used to investigate the corresponding effect of the ZnMn₂O₄/GO modified electrode on the detection of Pb???and Cd???.The results showed that it had a good response in the range of 0.05?0.7?M;the sensitivity was 69.85 ?A·?M^-1 and 47.32?A·?M^-1;their LODs were 3.98 nM and 9.38 nM,respectively.Finally,this experiment detected Pb???and Cd???in actual water samples.Cd???was not detected in the water at the entrance of Licun river estuary,and the concentration of Pb???was 0.2022?M/L.It was concluded that the water sample complied with the National Surface Water Category IV water quality standard?GB3838-2002?;however,two heavy metals didn't have been detected in the tap water.From the blank addition experiment of actual water samples,the recovery rate of the two ions was between 96.2%and 104.2%,which proved that the scheme was a practical and effective method for detecting heavy metals.?3?The sulfur-nitrogen co-doped graphene?SNGO?was prepared by hydrothermal method,and the nano-composite MnO₂/SNGO was synthesized by a simple liquid phase reaction.SEM,XRD and electrochemical methods were used to explore the properties of the prepared materials;meanwhile,the SWASV method was used to investigate the electrochemical response of the modified electrode to Pb???and Cd???.It had a good response effect in the range of?M,with sensitivities of 58.48?A·?M^-1 and 20.11?A·?M^-1,respectively;their LODs were 4.38 nM and12.74 nM,respectively.Finally,the experiment detected Pb???and Cd???in the actual water sample.The concentration of Cd???in Baisha river estuary was 0.0404?M/L and the concentration of Pb???was 0.2728?M/L,which complies with the National Surface Water Category V water quality standard?GB 3838-2002?;however,two heavy metals didn't have been detected in tap water.From the blank addition experiment of actual water samples,the recovery rate of the addition of the two ions was between 95.4%and 103.9%,which proves that the practical application of the sensor was good.