Design Of Bismuth-based Electrodes And Their Application In Metal Determination In Coastal Waters

Coastal zone,which is the intersection of sea and land,is the unit under the dual influence of high intensitive human activity and global climate change,and has unique properties of land and sea.Coastal waters mainly include coastal seawater and waters derive from off-shore rivers,lakes,reservoirs and so on.Coastal zone is the core of the marine economic zone and the base of marine development activities.The concentrations and distribution of metals in coastal waters are closely related to aquaculture and ecological health.Developing a series of methods for metal detection and exploring the content and distribution of metals in coastal waters are helpful for obtaining the datas of water qulity and effectively monitoring and controlling the water environment.To date,many analytical methods have been used for the determination of metals in waters,such as spectrometry,atomic spectroscopy,mass spectrometry,electrochemical methods,and so on.Each method has its own unique advantages and values,but each also has its own shortcomings.Comparing with other methods,electrochemical methods have a series of merits,such as simpleness,low-cost,fast,sensitive,easy to miniaturization and integration,being used in speciation analysis and suitable for on-line and in-situ determination.Working electrode is the core component of electrochemical sensor,directly determining the analysis performance.Mercury electrode has a positive effect on the detection of metals,but the toxicity of mercury and its inconvenience in storage and transportation limit its further use and development.Bismuth film electrode was first proposed by Wang in 2000.Bismuth was thought to be a promising alternative to mercury and was applied widely and quickly for its lower toxicity,ability to form alloys with metal and considerably sensitive voltammetric detection.Given that the bismuth film electrode has disadvantages of single structure,poor tolerance and poor stability,three kinds of bismuth-based electrodes have been constructed in this paper,and the content and speciation analysis of iron in main rivers of Yantai have been investigated combining simple sample pretreatments and cathodic stripping voltammetry.Through improving properties of bismuth-based electrode,the paper aims to establish a highly efficient and stable method for the analysis of metals in the coastal waters.The main contents of this research are as follows:1.Preparation of bismuth composite film modified electrode and its application in Pb(II)detection.Reduced graphene oxide-bismuth(GR-Bi)composite film modified screen-printed electrode(SPE)was constructed through one-step electrochemical reduction method and used for the determination of Pb(II).Due to the large surface areas and a great deal of sites for particles,GR was used as a support for immobilization of bismuth particles with strong adhesion.Combined the unique structure and electronic properties of GR with the ability to form alloys of Bi,the GR-Bi/SPE had shown excellent electrochemical properties for determination of Pb(II).Under the optimal conditions,a good linear of 0.05~20 μM and a detection limit of 6.8 nM can be obtained based on anodic stripping voltammetry.Additionally,the GR-Bi/SPE was successfully applied to the rapid determination of Pb(II)in real coastal sediment pore water.2.Preparation of bismuth nanosheets modified electrode and its application in Fe(III)detection.The article describes the synthesis of bismuth nanosheets(BiNSs)in the presence of a small quantity of grapheme oxide(GO)which is helpful for the formation of two dimensional BiNSs and improves dispersity.The average thickness and length of the BiNSs were 3~4 nm and 100~200 nm,respectively.Combining the unique nanostructure of the BiNSs,the ability of Bi to form alloys with metal,and the current amplification of the catalytic system,the modified electrode showed an excellent performance for electrochemical determination.Under the optimal conditions,the electrode had a linear response to Fe(III)in 0.01~20 μM concentrations range,with a lower detection limit of 2.3 nM.This method has been successfully applied to determine total dissolved iron in real coastal waters.3.Preparation of bismuth microrods modified electrode and its application in Fe(III)detection.Bismuth-based microrods(BiMRs)were synthesized through a single reductant-controlled chemical reduction method.With the various quantity of reductant,different morphologies of bismuth-based materials were obtained.Characters of BiMRs were investigated by using scanning electron microscope(SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The results showed that the product was uniform rods with a smooth surface and neat edges.Furthermore,BiMRs consisted of bismuth and bismuth oxide which made the material possess both advantages of metal and metal oxide.BiMRs had shown excellent electrochemical performance for Fe(III)determination and was successfully used for the determination of total dissolved iron in real water samples.4.Speciation determination of iron and its spatial distribution analysis based on bismuth microrods modified electrode.In this work,different species of iron in coastal river water including total iron(TFe),total dissolved iron(TDFe)and particulate iron(PFe)had been determined through combining simple sample pretreatments and cathodic stripping voltammetry based on BiMRs modified electrode.Results showed that the main species of iron in three rivers was PFe,which accounts for 84.5%,87.6% and 92.4%,respectively.The concentrations of iron from the estuary to the upstream regions increased firstly and then decreased.The iron concentration was negatively correlated with conductivity and salinity(SA),positively correlated with dissolved oxygen(DO)and had no obvious relations with pH values.5.Voltammetric analysis of different species of copper in seawater based on gold film modified electrode.For comparison with bismuth-based electrodes mentioned above,this study investigated a gold film modified glassy carbon electrode(Au/GCE).Au/GCE can be continuously re-used following simple electrolytic cleaning with good measurement stability and reproducibility.Combined with simple sample pretreatment,Au/GCE was employed for the speciation analysis of copper in seawater by using a voltammetric method.This method was simple and effective for speciation analysis with no complicated pre-treatment or separation steps required,allowing for direct speciation analysis in real water samples with confirmed accuracy.The sensor was used for the fixed-point detection of electroactive copper,acid dissolved copper,inert copper and total copper for 15 days.The results showed that the modified electrode was sensitive,stable and had good practicability in the continuous analysis.6.Preparation of gold-bismuth modified electrode based on etched ITO and its application in speciation analysis of iron.Commercial ITO electrodes were used as working electrodes,and rough surfaces were formed by electrochemical etching of ITO.Modify materials on the rough surface of ITO will result in working electrode with high stability.In this work,gold-bismuth modified ITO was employed as working electrode,and 1-(2-piridylazo)-2-naphthol(PAN)was introduced as complexing agent for Fe(III)to improve the sensitivity and selectivity.An analytical method for sensitive detection of Fe(III)was established based on electrochemical adsorption cathodic stripping voltammetry.Combined this method with sample pretreatment process,the determination of total iron,total dissolved iron and innert iron in the coastal waters have been successfully realized.