Study On Detection Of Harmful Organic Small Molecules Applied Electrochemical Analysis

At present,small-molecule organic materials are widely used in coatings,fertilizers,medicine and other fields,which have had a huge change and impact on human life.However,small-molecule organics not only cause serious pollution to the environment,but also continue to affect human health.Therefore,it is necessary to develop sensor materials that can accurately and quickly detect traces of harmful small-molecule organics.The thesis mainly developed three different metal-based nano-sensing materials and prepared them into electrochemical sensors to analyze and detect 4-NP and formaldehyde respectively.The main work done in this paper is as follows:（1）The Au-Ag NPs/graphene nanocomposites with different gold content were prepared by hydrothermal synthesis,and then the morphology of the nanocomposites was characterized and analyzed by field emission scanning electron microscope（FE-SEM）and transmission electron microscope（TEM）.Then the composite nanomaterials were modified on the surface of the working electrode,and the electrochemical behavior was tested by cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）in electrochemical analysis methods.It is found that the gold-rich Au-Ag NPs/graphene nanocomposite has a higher response peak current,and then the differential pulse voltammetry（DPV）is used to study 4-NP detection performance of the electrochemical sensor prepared by Au-Ag NPs/graphene nanocomposite.Studies have shown that when the pH of the buffer solution is 6.13 and the concentration range of 4-NP is 0μmol L^-1 to 10μmol L^-1,the sensitivity is 6261μAμM^-1 cm^-2and the detection limit is at least 0.48μmol L^-1.In terms of stability,the prepared electrochemical sensor has little fluctuation in current response value within 28 days and is relatively stable.（2）When detecting formaldehyde,NiO nanofibers（NFs）are mainly prepared by electrospinning.Analyzed by FE-SEM,X-diffractometer（XRD）and specific surface area test（BET）,it is found that the diameter of NiO NFs is between 200 nm and 220 nm,and has a specific surface area of 29.12 m² g^-1.Then CV and EIS were used to characterize the electrochemical properties of the material.At the same time,the chronoamperometry is used to detect the concentration of formaldehyde.It can be found that when the concentration of formaldehyde is from 0 mmol L^-1 to 84 mmol L^-1,the sensitivity of the NiO NFs electrochemical sensor is 6656μAμM^-1 cm^-2,and the detection limit is 0.45μmol L^-1,which meets the basic requirements for detecting trace amounts of liquid formaldehyde.（3）In order to further improve the sensitivity and detection limit performance of the NiO NFs formaldehyde sensor,this work uses the electrospinning process to prepare SnO₂/NiO NFs,and proposes the mechanism of using a semiconductor PN junction structure to improve the detection performance of the sensor.First,the changes of NiO NFs and SnO₂/NiO NFs in morphology,composition and specific surface area can be obtained through FE-SEM,XRD and BET analysis.Among them,the specific surface area of SnO₂/NiO NFs is twice that of NiO NFs.Then,SnO₂/NiO NFs was tested and analyzed by CV and EIS,and it was found that the electrochemical sensor modified by SnO₂/NiO NFs had higher response current to formaldehyde than NiO NFs 40%,this kind of PN junction structure nano-sensing material does increase the electron transfer rate and the specific surface area of the material,and then use chronoamperometry to detect and analyze liquid formaldehyde,and the highest sensitivity obtained is 12020μAμM^-1 cm^-2.The lowest detection limit is 0.25μmol L^-1.Finally,anti-interference and stability experiments were carried out,and it showed good selection specificity in the face of interference substances such as ethanol（C₂H₅OH）,isopropanol（C₃H₈O）and acetic acid（CH₃COOH）.Moreover,within 30 days,the SnO₂/NiO NFs modified electrochemical sensor still maintained a response of 99.51%.Finally,this thesis uses different nanomaterials to detect and analyze the two different small-molecule organics,4-NP and formaldehyde.Among them,the gold-silver nanocomposite material has a lower detection value(0.48μmol L^-1)for detecting the concentration of 4-NP,which provides a new material composite method for detecting trace amounts of 4-NP nanomaterials.In addition,the use of semiconductor nanomaterials and its PN junction characteristics to achieve a low concentration of formaldehyde detection(0.25μmol L^-1),and at the same time has a higher detection limit(12020μAμM^-1 cm^-2),which is the actual formaldehyde detection and application provides a certain reference value.