Visible Detection Of Heavy Metal Ions Based On Nanocomposite

In recent years,with the development of social industrialization,the environmental problems caused by industrial wastewater discharge have become increasingly serious,especially heavy metal pollution.Heavy metal ions can accumulate in organisms and are difficult to decompose.When they reach a certain concentration in the human body,they will cause diseases in the kidney,heart,nervous system and blood system and even death.At present,the detection methods of heavy metal ions in aqueous solution include atomic absorption spectrometry（AAS）,electrochemical analysis,inductively coupled plasma mass spectrometry（ICP-MS）,laser induced breakdown spectroscopy（LIBS）and atomic fluorescence spectrometry（AFS）.These methods all require large instruments and higher requirements for samples,so the visual detection of heavy metal ions in water has attracted our attention.The mechanism of visual detection of heavy metal ions is mainly divided into inhibition of catalytic activity mechanism and on or off mechanism.Like hydrogen peroxide（H₂O₂）,peroxymonosulfate（PMS）can be catalyzed to generate active radicals including hydroxyl radical（·OH）and sulfate radical(SO₄^·-),which can oxidize 3,3’,5,5’-tetramethylbenzidine（TMB）into ox TMB.In this paper,PMS was used as an alternative substrate of H₂O₂ to design two different catalytic visual detection methods for heavy metal ions in water.Compared with other ion detection methods,the two methods are relatively simple,effective and fast.The main experimental contents and results are as follows:1.Ag@Cu₂O nanocomposite was prepared by trisodium citrate reduction method.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to characterize the morphology of the materials.The structure of the nanocomposite is nano core-shell structure（Ag@Cu₂O NPs）,that is,the silver element is basically distributed in the Ag core,copper and oxygen elements are homogeneously distributed in the shell.In addition,X-ray photoelectron spectroscopy（XPS）was used to analyze the element valence states on the surface of the material,and the results show that only Cu⁺exists in the materials before the reaction.At the same time,the electrochemical workstation was used to compare the electrochemical impedance spectroscopy of the materials before and after detection.It was shown that the introduction of Au³⁺to be detected reduced the electrochemical impedance spectroscopy of the materials and accelerated the electron transmission.2.As the synergistic effect between Au and Cu O accelerates electron transport,the catalytic ability of PMS is enhanced.Therefore,a simple and efficient visual detection method for Au³⁺in water is established.The electron paramagnetic resonance spectroscopy（EPR）data showed that the catalytic capacity of PMS was enhanced with the introduction of Au³⁺,and the production of·OH and SO₄^·-increased.As more·OH and SO₄^·-were generated in the system,the oxidation degree of TMB was considerably enhanced.The method has high selectivity for 22 interfering ions,and the detection limit is as low as 290 nmol·L^-1 based on the standard deviation of 3 times blank solution.And only 300 nmol·L^-1 Au³⁺existed in system,the RSD of this method was about 0.1%.3.PMS is often used in advanced oxygen process for the degradation of pollutants.The methods of catalyzing PMS can be divided into homogeneous catalysis and heterogeneous catalysis.A certain concentration of Co²⁺can catalyze the activation of PMS to produce active free radicals,but low concentration of Co²⁺has a weak catalytic ability to PMS.While Na Ac introduced into low concentration of Co²⁺,since Co²⁺reacts with Ac^-to produce[Co²⁺-Ac^-]⁺,the newly generated[Co²⁺-Ac^-]⁺can catalytically activate HSO₅^–to produce[Co³⁺-Ac^-]²⁺.Since Co³⁺has a strong oxidation capacity,the[Co³⁺-Ac^-]²⁺generated is unstable.In the presence of excess excess Ac^-,it immediately decomposes into Co²⁺and Ac^-,which promotes the cycle of Co²⁺and Co³⁺.4.Based on the homogeneous catalytic activation capacity of Co²⁺on PMS and the ligand enhancement effect of Ac^-,a novel,catalyst free,green and efficient Co²⁺colorimetric detection method was designed.The method is specific for the detection of Co²⁺,and has good anti-interference ability against 20 kinds of interfering ions.The detection limit of Co²⁺in this visual detection is about 29 nmol·L^-1.Compared with other Co²⁺detection methods,this method can establish a fast,efficient and green Co²⁺detection platform without the need of synthetic materials,large instruments and complex operation procedures.5.It was found that SO₄^·-played a major role in Ag@Cu₂O NPS/PMS/Au³⁺ system and Co²⁺/PMS/Na Ac system by exploring the sacrificial agent experiments in the two experiments respectively.