Synthesis Of Core-Shell Nanocomposites And Their Application In Electrochemical Detection Of Heavy Metals

Heavy metal ions are nonbiodegradable toxicants in water,and water is the main source for how these toxic metal ions are taken into the human body.Therefore,it is urgent to propose a fast,economic,sensitive and selective method for monitoring of heavy metal ions in water environment.As a important kind of material,core-shell structured nanocomposites have brought numerous benefits to the field of electrochemical sensing owing to their distinctive geometries and novel properties.This thesis intends to use the core-shell structured nanocomposites to construct electrochemical sensors for Pb²⁺,Cd²⁺or Cu²⁺detection.The main contents and results are as follows:(1)Fe₃O₄@PDA@MnO₂ core-shell magnetic nanocomposites were synthesized,and used to enrich target analyte to construct an electrochemical sensor for sensitive detection of trace Pb(?)in the environmental samples.Given that the constructed sensor is employed under strongly acidic conditions,a dense polydopamine(PDA)coating was firstly formed on the surface of Fe₃O₄ to ensure high stability.Then a high adsorption capacity MnO₂ shell can be simply introduced to the surface of the PDA on the basis of the redox activity between PDA and KMnO₄.Differential pulse voltammetry(DPV)was applied for determining target metal ions.Chemical and electrochemical factors,including quantity of nanocomposites,preconcentration solutions p H,preconcentration time and supporting electrolytes,were optimized.Under excellent conditions,the designed sensor demonstrated a linear response to Pb(?)within the range of 0.1-150?g L^-1 and with a detection limit of 0.03?g L^-1.The proposed methodology exhibits the excellent performance in selectivity,sensitivity and long-term stability,and was also successfully applied to determine Pb(?)in the real water samples.This study suggested that Fe₃O₄@PDA@MnO₂ nanocomposites are a better alternative to Pb(?)analysis resulting from its low cost,low toxicity,strong adsorption,and good reproducibility.(2)PDA with many functional groups can act as the starting points for covalent modification with desired molecules,and DMSA containing abundant sulfhydryl and carboxyl groups can be used as an excellent candidate.Magnetic Fe₃O₄@PDA-DMSA nanocomposites were triumphantly fabricated by covalently modifying dimercaptosuccinic acid(DMSA)around magnetic polydopamine(Fe₃O₄@PDA).This nanocomposite was employed to enrich target analytes to design a novel electrochemical sensor for reliably monitoring of Pb(?)and Cu(?)in environmental samples,based on the specific chelation mechanisms between metal ions and functional groups.X-ray photoelectron spectral data demonstrate the main chelation mechanisms of this preconcentration process.It is shown that the synergistic effect among Fe₃O₄,PDA,and DMSA enhances the electrochemical sensitivity and accelerates the electron transfer.Under optimized conditions,the linear responses to Pb(?)and Cu(?)within the concentration range of 0.5-50?g L^-1 was obtained with the detection limits of 0.1and 0.2?g L^-1,respectively.The little to no interference is generated from common coexisting anions/cations.The proposed sensor shows the prominent performance in selectivity,sensitivity and long-term stability.When it was applied to determine Pb(?)and Cu(?)in the real water samples,the spiked recoveries range from 94.7%to 105.6%and RSDs vary from 1.2%to 3.8%.(3)MnO₂/o-SWCNHs(oxidized Single-wall Carbon Nanohorns)nanocomposites were triumphantly synthesized,and employed to construct an electrochemical sensor for sensitive detection of Cd(?)in the environment sample.When oxidized SWCNHs are modified with manganese dioxide,new materials simultaneously possessing the unique properties of SWCNHs(high conductivity,large surface area and wide electrochemical window)and MnO₂(high adsorption capability and simple synthesis)can be obtained by combining their individual characteristics.The synergistic effect between MnO₂and o-SWCNHs enhances the electrochemical sensitivity and accelerates the electron transfer.Under excellent conditions,the linear concentration ranges of 5-80?g L^-1 for Cd(?)was obtained with a detection limit of 1.5?g L^-1.This research demonstrated that the proposed sensor shows a good performance in selectivity,sensitivity and long-term stability,and a great potential in practical applications.