Electrochemistry And Laser-Induced Breakdown Spectroscopy For Detection Of Heavy Metal Ions In Complex Environments

In the face of increasingly severe heavy metal ions(HMIs)pollution and its huge toxic effects on the human body,it is very necessary to detect HMIs in the environment.It is worth noting that the composition of the environment(water,soil or food)is complex,including small ions and organic matter.Compared with the concentration of other substances,the concentration of HMIs is too low.How to overcome the severe interference of other substances and achieve highly sensitive,rapid and stable detection of HMIs in the environment is very important.The electrochemical(EC)method and the electrochemical-laser induced breakdown spectroscopy(EC-LIBS)method areconsidered to be effective methods for detecting HMIs.However,they still need to overcome some difficulties that need to be solved in the detection of HMIs in the environment(especially in complex environments),such as poor anti-interference performance of EC and poor detection stability of EC-LIBS.Based on the above problems,this thesis studies the functionalized nano-material-modified working electrode to improve the anti-interference performance of EC,and improves the detection stability of EC-LIBS by constructing a stable substrate and assisting active controllable spark discharge device.The main research contents are as follows:(1)A sensitive and anti-interference sensing interface for detection of Pb2+in rice phloem sap is fabricated based on the glutathione-functionalized gold/multi-walled carbon nanotubes(MWCNTs-GSH-Au-GSH).The high adsorption capacity and selectivity toward Pb2+caused by the surface functional groups(-COOH,-CONH-and-NH2)on MWCNTs-GSH-Au-GSH,which are strongly proved by XPS and EXAFS,enhances anti-interference electrochemical detection of Pb2+ in rice phloem sap.The excellent electrocatalytic ability of uniform,dense,small-sized Au NPs leads to high electrode current and low LOD.Additionally,the good stability and high reproducibility of MWCNTs-GSH-Au-GSH electrode toward Pb2+ have shown that such an electrode can be well applied to long-term detection of Pb2+ in rice phloem sap.This research may be able to offer a simple and effective approach for further investigation on the migration and transformation of HMIs in rice plants.(2)Self-organizing,highly ordered manganese doped titanium dioxide nanotube arrays(Mn-TiO2 NTAs)is fabricatedfor detecting Cd2+.The Mn-TiO2 NTAs are evenly arranged and have the same height on the electrode,which is favorable for uniformity of ablation spots after Gaussian laser irradiation.Both the depth of the ablation spots and matrix effect(i.e.,the effect of chemical composition,physical and chemical state changes on the signal intensity,etc.)were reduced compared to the pure titanium foil and the Mn-TiO2 electrode which was modified through traditional method.The uniformity of the shallow ablation spots results in a uniform plasma,which ultimately leads to a stable signal.The ECP-LIBS intensities obtained at six locations on a Mn-TiO2 NTAs electrode and six different Mn-TiO2 NTAs electrodes arecompared with Mn-TiO2 electrode modified through drip coating method.The proposed method perfectly realized accurate detection of Cd2+ in water,soil and tea.This work may provide a new opportunity for stable analysis of trace heavy metal contaminants in environment.(3)A new approach,low-pulse-energy LIBS supported by active controllable spark discharge and electrochemical enrichment is proposed to detect As3+.The pulse energy was reduced from the previously reported about 100 mJ to 15 mJ for reducing the volatilization of arsenic and mercury.But at the same time,lowing pulse energy brings the problem that the excited plasma is insufficient.Active controllable spark discharge makes up for the insufficiency in plasma content,and overcomes the instability of traditional spark discharge assist LIBS through control the delay time between spark discharge and laser.Preconcentration prior to detection is a critical step in enhancing the LIBS signal.Electrochemical enrichment assisted LIBS can significantly enhance LIBS signal by efficiently concentrate analyte in the electrochemical enrichment stage.Highly efficient and rapid preconcentration of As3+was achieved by electrochemical enrichment on flower-like NiCo2O4-x-NH2 nanosheets with adjustable oxygen vacancies.As a result,a high sensitivity of 3.35 counts ppb-1,low LOD of 8.69 ppb,excellent stability(relative standard deviation is lower than 5%)for arsenic(?)were achieved.The important role of active controllable spark discharge,oxygen vacancies and amino groups are studied in detail.This method expectedly enhances the detection signal of HMIs.