Detection Of Heavy Metal Ions Using Silicon Photoelectrode Modified By Nickel Ferricyanide

In the environment,lots of heavy metal ions such as lead and mercury widely could be found.They can enter the biological body and accumulate.When the content of heavy metal ions is too high,they can cause a variety of serious diseases.In clinical diagnosis,health and environmental protection and other fields,monitoring of the level of nanomole concentration of heavy metal ions is very important significant.Compared withchromatographicanalysisandspectroscopicanalysis,electrochemical measurements have been fast developed for the advantage of cost effective,fast and low demands on sample processing.Meanwhile,electrochemical measurements are high sensitive and good selective with very low detection limit,so electrochemical measurements are widely used.The key role in electrochemical detection lies in the construction of sensitive electrodes.Sensitive electrodes are mostly prepared by modifying specific sensitive material on base electrodes.Noble metal nanoparticles and new developed inorganic materials like ferricyanide are extensively used in some kinds of electrochemical and photochemical studies for their excellent properties.However,single component materials can't always meet the requirements of high selective and high sensitive with low detection limit for an electrode.Therefore,a sensitive electrode for composite modification with various materials have been becoming the main research direction.On the basis of predecessors'research works,we developed a sensitive electrode for electrochemical sensing of Pb?II?by comprehensive utilization of electroactive materials such as noble metal nanoparticles and transition metal ferricyanide.In addition,we also studied the modification methods of silicon photoelectrode.Platinum film coated silicon electrodes were modified with nickel hexacyanoferrate?NiHCF?by three techniques meaning electroplating,transformation of nickel layer and chemical deposition.The detailed contents in this work can be summarized as follows.?1?Photo-electrical effect comparison of three preparations of nickel hexacyanoferrate film modified Pt/n-n⁺-Si electrodesAbout 40 nm Pt layer and 100 nm Ni layer were successively coated on the front surface of n-n⁺-Si wafer by vacuum evaporation.In order to increase the ohmic contact area of the wafer,we coated a layer of high purity aluminum about 300 nm thick on the back of the n-n⁺-Si wafer by vacuum evaporation.First preparation of a stable layer of NiHCF was transformed through the Ni layer into NiHCF on the coated silicon wafer by electrochemical methods.The second and third preparations of NiHCF film were electroplating and chemical deposition,respectively,on the surface of the n-n⁺-Si electrode coated with platinum film.The NiHCF/Pt/Si modified electrodes obtained by the three methods were characterized by X-ray photoelectron spectroscopy?XPS?and fourier transform infrared spectrometer?FTIR?.Photoelectrochemical?PEC?behavior of the NiHCF/Pt/Si electrodes were investigated using cyclic voltammetry?CV?and chronoamperometry under illumination.In this paper,we investigated the photoelectric effect of four probes including hydroquinone?HQ?,catechol?CC?,ascorbic acid?AA?and dopamine?DA?with three NiHCFs modified photoelectrodes on the silicon.Experimental results prove that three Ni HCFs modified electrodes NiHCF/Pt/Si have great detection sensitivity,linearity and response of ascorbic acid?AA?and dopamine?DA?.However,the response of hydroquinone?HQ?and catechol?CC?is not obvious on the three NiHCF/Pt/Si modified electrodes.?2?Detection of heavy metal ions with three nickel hexacyanoferrate film modified Pt/n-n⁺-si electrodesIn this chapter,we conducted photoelectrochemical detection of Pb?II?and Hg?II?with three modified electrodes prepared above.In terms of deionized water,we studied Pb?II?on the catalytic effect of these four photoelectric probes including hydroquinone?HQ?,catechol?CC?,ascorbic acid?AA?and dopamine?DA?.Results prove that the catalytic effect of Pb?II?on catechol and hydroquinone is significant.However,there is almost no catalytic effect of Pb?II?on ascorbic acid and dopamine.Based on the above research,we used reverse thinking.We conducted photoelectric quantitative detection of trace Pb?II?in deionized water.The catechol and hydroquinone are used as photoelectrochemical probes.We also optimized the experimental conditions for Pb?II?detection.It was found that deionized water was the best medium for the experiment.The linear range of Pb?II?detection is 40-560 nM.The detection sensitivity was 1.785nA cm^-2/nM and the detection limit was 7.27 nM?S/N=3?.In addition,we also explored the detection performance of functional electrodes prepared by three methods in actual samples.Under the work of hydroquinone?HQ?and catechol?CC?,we conducted photoelectric effect of trace Pb?II?in drinking water on nickel hexacyanoferrate modified Pt/n-n⁺-Si electrodes.Experimental results prove that in the range of 40-560nM,the linearity of Pb?II?detection is good.The best detection sensitivity of Pb?II?is0.757 nA cm^-2/nM and the detection limit is 32.96 nM.Finally,We conducted photoelectric quantitative detection of trace Hg?II?in deionized drinking water.Experimental results prove that in the range of 40-560 nM,the best detection sensitivity of Hg?II?is 0.05 nA cm^-2/nM and the detection limit is 121.02 nM.