Graphene Sensors And Its Application In The Detection Of Heavy Metals

In recent years, with the rapid development of China’s economy and industry,heavy metal and theirs compounds have become one of the most harmful pollutants inwater environment. Heavy metals pose a serious threat to human health andecological systems due to their toxicity and enrichment. In fact, heavy metalcontamination has being become one of factors for seriously threatening human health.Therefore, it is very important to develop a rapid, sensitive and simple analyticalmethod for detecting and monitoring these environmental pollutants in water. Thisthesis will eventually prepare a disposable electrochemical sensor with low-cost andexcellent performance using graphene modified screen-printed electrode byelectrochemical techniques. The sensors we prepared enrich the application of thesystem of portable and on-line analysis of heavy metals in industry and everyday life.Graphene is ideal material for implementation in electrochemical applicationsdue to its high electrical conductivity, large surface area and unique heterogeneouselectron transfer rate. In addition, most of the graphene used in electrochemistry isproduced from the reduction of graphene oxide and usually has defective areas andfunctional groups such as hydroxyl and carboxyl, which are advantageous foradsorbing heavy metal ions. Poly(sodium4-styrenesulfonate)(PSS) is acation-exchange polymer and can improve the sensitivity of the voltammetric signalof Cd2+and Pb2+due to its less compact structure with more sulfonate groups (pergram) available for interaction with cations. What’s more, graphene is dispersed intothe PSS solution to form a homogeneous suspension. Prepared the modifiedscreen-printed electrodes (SPE) with PSS and GR composite in situ plated bismuthfilm. The testing conditions and performances of the GR/PSS/Bi/SPE were optimizedby differential pulse anode stripping voltammetry (DPASV) and the simultaneousdetection Cd2+and Pb2+based on GR/PSS/Bi/SPE was established. The linearity wasfound to be0.5-120μg L1for Cd2+and Pb2+. The calibration curves was y=0.012x-0.03982and y=0.00702x–0.02311for Cd2+and Pb2+. Based on three times of thebackground noise (S/N=3), the limits of detection were0.042μg L1for Cd2+and 0.089μg L1for Pb2+. In addition, it was also successfully applied to thedetermination of trace heavy metal ions in real samples.To achieve better performance, various chemical and physical methods havebeen used to modify graphene. One alternative is nitrogen-doped grapheme (NGR)which has high electrical conductivity, large surface area and unique heterogeneouselectron transfer rate. In addition, most of the nitrogen-doped graphene used inelectrochemistry is produced from the reduction of graphene oxide and usually hasdefective areas and functional groups such as hydroxyl and carboxyl, which areadvantageous for adsorbing heavy metal ions. The testing conditions andperformances of the NGR/Bi/SPE were optimized by DPASV and the simultaneousdetection Cd2+and Pb2+based on NGR/Bi/SPE was established. The linearity wasfound to be0.5-100μg L1for Cd2+and Pb2+. The calibration curves was y=0.01189x-0.02982and y=0.006802x-0.02328for Cd2+and Pb2+. Based on three times ofthe background noise (S/N=3), the limits of detection were0.21μg L1for Cd2+and0.16μg L1for Pb2+. In addition, it was also successfully applied to the determinationof trace heavy metal ions in real samples.