Research On Electrochemical Sensor Of Main Water-soluble Inorganic Ions In PM_2.5

At present,fine particles(PM2.5,aerodynamic diameters<2.5 ?m)pollution in China is becoming increasingly serious and severe PM2.5 pollution events have occurred in many cities successively,bringing extremely adverse effects on people's production,life and physical and mental health.PMi2.5 has extensive sources and complex constituents,among which water-soluble inorganic ions are an important part of PM2.5.Especially,the secondary water-soluble ions(SO42-,NO3-and NH4-,or SNA for short,which do not come from direct emission but are products of photochemical reactions in the atmosphere)have an important influence on the chemical properties of particulate matters,and their concentration size reflects the degree of photochemical reactions in the atmosphere.SNA have strong hygroscopicity,which can affect the chemical composition and optical properties of PM2.5,form cloud condensation nuclei and affect its number and lifetime,and also cause indirect radiation forcing,thus indirectly affecting atmospheric visibility and global climate.SO4-and NO3-have high extinction coefficient and can greatly reduce atmospheric visibility.SNA can affect the acidity of PM2.5 and the toxic substances can be activated with their acidity increasing.At the same time,the hygroscopicity of PM2.5 will also be enhanced,which will increase the toxicity of particulate matters and the impact on the environment,ecology and climate.Although the content of water-soluble heavy metal ions in PM2.5 is very small,they have higher toxicity and biological effectiveness than other existing forms,and are easier to be used by biology.They are also the key component that can cause damage to the cardiopulmonary system through oxidative chemistry.They have a serious negative impact on human health and the ecosystem.In addition,heavy metal ions also play an important catalytic role in the generation of secondary sulfate,heterogeneous generation and elimination of gas hydrogen peroxide,as well as multiphase cloud chemistry.Therefore,the research on the concentration level and formation mechanism of SNA and water soluble heavy metal ion has become a hot topic in the environmental field at home and abroad.It can not only reflect the regional atmospheric pollution status and characteristics to a certain extent,but also provide scientific basis for the analysis of the source of PM2.5,the assessment of the impact on the environment and the formulation of air pollution control policies.The existing detection methods for SNA in PM2.5 mainly include ion chromatography,infrared spectroscopy,capillary electrophoresis,aerosol mass spectrometry,etc.The detection techniques of heavy metal ions include atomic absorption spectrometry,inductively coupled plasma atomic emission spectrometry,inductively coupled plasma mass spectrometry and X-ray fluorescence spectrometry.However,these technologies generally have disadvantages such as large instruments,high technical requirements for experimental operation,expensive equipment,tedious sample pretreatment procedures,time consuming,not suitable for online testing,importability,and the need for multiple instruments to complete quantitative testing.Therefore,it is very necessary to develop a new technology to detect water-soluble inorganic ions in PM2.5 so as to make up for the deficiencies of the above methods and meet people's increasing awareness of environmental protection.Electrochemical sensors are a good choice since they have the advantages of fast detection speed,high sensitivity,strong selectivity,low detection limit,low cost,portability,low power consumption,miniaturization and automation,etc.In particular,they have unique advantages in real-time monitoring complex system.This paper aims to combine the current development trend of electrochemical sensors and utilize nanomaterials such as graphene,gold nanoparticles,ferric oxide nano-microspheres,as well as microelectrode machining to develop new electrochemical sensors that can detect water-soluble inorganic ions in PM2.5 with high efficiency,sensitivity,accuracy,portability and low cost for the first time.The morphology,structure and performance of the electrode modified material and sensor were characterized by the modern analysis methods.The effects of experimental conditions such as concentration of substrate and pH value on the test results were discussed.The selectivity,stability and reproducibility of the sensor were eevaluated.Finally,the concentrations of water-soluble inorganic ions in PM2.5 were analyzed using the prepared electrochemical sensors.The specific research works carried out in this paper and the results obtained are as follows:1.Highly sensitive electrochemical determination of sulfate in PM2.5 based on the formation of heteropoly blue at poly-L-lysine-functionalized graphene modified glassy carbon electrode in the presence of cetyltrimethylammonium bromideUnder the sensitization of cationic surfactant cetyl trimethylammonium bromide(CTAB),a simple and sensitive voltammetric SO42-electrochemical sensor was constructed based on poly-L-lysine(PLL)-functional graphene(GR)modified glass carbon electrode(GR-PLL/GCE).The detection principle of the sensor was that the electrolysis of GR-PLL/GCE generated heteropoly blue in Mo(?I)-HCl-acetone solution containing SO42-,and the oxidation current of hydrolysate was proportional to the concentration of S042-.The structure,morphology and performance of the modified materials and the sensor were characterized by Raman spectroscopy,Fourier infrared spectroscopy,scanning electron microscopy,transmission electron microscopy and cyclic voltammetry.The experiment parameters such as the electrode modified material,the amount of CTAB,substrate concentration,electrolytic potential and electrolytic time were optimized.Under the optimum condition,the sensor measured SO42-by the square wave voltammetry and 0.8-1000 ?M of the linear range and 0.26?M of the detection limit were obtained,showing good sensitivity,selectivity and stability.The new sensor was applied to detect the SO42-in PM-2.5 samples,and the results were consistent with those of ion chromatography.2.Sensitive detection of sulfate in PM2.5 via gold nanoparticles/poly-L-lysine/graphene composite film based arylsulfatase-inhibition biosensorA novel enzyme-inhibited SO42-electrochemical biosensor was fabricated by crosslinking arylsulfatase(AS)with glutaraldehyde and bovine serum albumin matrix to gold nanoparticles(AuNPs)/poly-L-lysine(PL.L)/graphene(GR)/glass carbon electrode(GCE).AS can catalyze 4-nitrocatechol sulfate(NCS)to hydrolyze to 4-nitrocatcchol(NC)and SO42-.NC has electrochemical activity and can be electrochemically oxidized to obtain an anodic current.However,the production of NC would decrease in the presence of SO42-due to its inhibition effect on the enzymatic hydrolysis reaction,thus leading to a decrease in the oxidation current.The quantitative detection of SO42-was achieved based on the linear relationship between the logarithm of the concentration of inhibitor(SO42-)and this current decrease.Transmission electron microscopy,scanning electron microscopy,Fourier infrared spectroscopy,Raman spectroscopy and cyclic voltammetry were employed to characterize the structure,morphology and performance of the modified materials and biosensor.The experimental conditions such as the dosage of PLL/GE,the electrodeposition time of AuNPs,the concentration of enzyme AS,the buffer concentration,pH and the substrate concentration were optimized.The inhibition experiments were carried out by differential pulse voltammetry and at optimal conditions,the inhibition rate was linear to-log[SO42-]in the concentration range from 1.0×10-7 to 1.0×10-5 M with the detection limit of 4.0 ×10-8 M.The introduced biosensor was further applied successfully to assay S042-constituent in PM2.5.3.Electrochemical detection of nitrate in PM2.5 with a copper-modified carbon fiber micro-disk electrodeA voltammetric NO3-microelectrode electrochemical sensor was developed by the self-made carbon-fiber micro-disk electrode(CFMDE)and the copper layer being in situ electrodeposited on its surface.The CFMDE was prepared as follows:The carbon fiber and copper wire were firstly connected by silver conductive adhesive.Then they were placed in a polypropylene micropipette,and followed by encapsulating,fixing and polishing.The obtained micro-electrode was electrochemically characterized by cyclic voltammetry.The CFMDE was placed in an acidic solution containing copper ions and the fresh copper layer was modified in situ on the electrode surface by electrodeposition,and then NO3-was determined using square wave voltammetry.The change of surface topography before and after electrode modification was observed by scanning electron microscopy.The deposition potential,accumulation time,pH,the concentration of copper ions and chlorine ions were studied in detail.Under optimal experimental conditions,the peak current increased linearly with NO3-concentration over a range of 0.003-2.0 mM,and the detection limit was 1.10 ?M.The sensor was not only simple,easy to prepare,fast,portable,but also low cost and disposable.The electrochemical method and ion chromatography were utilized to detect NO3-in PM2.5,and the results were consistent.4.A promising voltammetric biosensor based on glutamate dehydrogenase/Fe3O4/graphene/chitosan nanobiocomposite for sensitive ammonium determination in PM2.5A voltammetric electrochemical biosensor for the determination of NH4-was developed by GLDH/Fe3O4/GR/CS/GCE,which was constructed by using ferroferric oxide nanosphere(Fe3O4 NSs),graphene(GR)and chitosan(CS)nanocomposite materials to immobilize glutamate dehydrogenase(GLDH).In the analysis system,GLDH catalyzed the reversible reaction,i.e.,the reductive amination of a-ketoglutaric acid and the oxidative deamination of L-glutamate.The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the[Fe(CN)6]3-4-couple,which helped for the amplification of the electrochemical signal.The detection principle of the biosensor was based on the fact that the enhanced response current was proportional to the NH4+ concentration.X-ray diffraction,transmission electron microscopy,scanning electron microscopy,Fourier infrared spectroscopy,and other methods were used to characterize the structure,morphology and composition of the materials.The electrochemical behavior of NH4+ on the sensor was studied by differential pulse voltammetry,and the experimental conditions such as pH and enzyme amount were optimized.Under the optimum conditions,the introduced biosensor had a linear range of 0.4-2.0 ?M for NH4-with the detection limit of 0.08 ?M.The biosensor had simple detection method,low detection limit,good selectivity and reproducibility,and had successfully detected the NH4-component in PM2.5.5.Determination of cadmium in PM2.5 by an electrochemical sensor based on lignosulfonate functionalized three-dimensional porous grapheneUsing the excellent properties of porous graphene(PGR),calcium lignosulfonate(CLS)and Nafion,an electrochemical sensor platform for the sensitive determination of Cd2+ by differential pulse anodic dissolution voltammetry was developed.The Nafion/CLS/PGR composite integrated the high specific surface area and strong adsorption capacity of PGR and the strong cation exchange capacity of CLS and Nation,which could effectively improve the sensitivity and selectivity of the electrode.The structure,morphology and properties of the materials were characterized by scanning electron microscopy,transmission electron microscopy,Fourier infrared spectroscopy and electrochemical impedance spectroscopy.The electrochemical characteristics and experimental parameters of the Nafion/CLS/PGR based sensor were studied and optimized(including the pH value of buffer solution,Nafion concentration,deposition potential and deposition time).Under the best experimental conditions,the linear range for the determination of Cd2+ was 0.05-5.00 ?M and the detection limit was calculated to be 0.003 ?M.This sensor had a simple preparation,low detection limit,good selectivity and reproducibility,and had been successfully applied to the assay of Cd2+ in PM2.5.