Analysis Of Environmental Arsenic Pollutants By Surface-Enhanced Raman Spectroscopy

With the continuous transformation of the natural environment by human beings and the rapid development of industrial production,a series of environmental issues produced by mining and excessive use of heavy metals have seriously affected the ecological environment on which human beings depend for survival and threatened human health.To better assess the source of heavy metal pollution and its impact on human and environmental health,it is necessary to accurately grasp information such as distribution,concentration,and properties of heavy metals in the environment and establish a rapid and reliable analysis method.At present,many methodologies for analyzing heavy metal pollutants have been developed.Those lab technologies provide excellent accuracy and precision in analyzing heavy metals,but those methods suffer from time-consuming sample pretreatment,which limits their application in onsite and rapid speciation analysis.Surface-enhanced Raman spectroscopy（SERS）,a rapid and in-situ analytical method,is supposed to be a promising detection technology for arsenic species owing to unique fingerprints.Based on the above research progress,we proposed a robust,reliable,and quantitative method by SERS to solve the problem that it is difficult to accurately analyze different forms of heavy metal arsenic（As）in complex environments.The specific research contents are shown as follows:1.Speciation analysis of arsenic species in aquatic environment by spontaneous enrichment and SERSIn this work,we proposed a method of spontaneous enrichment and SERS to analyse inorganic As in water.At first,this method was based on silver nanoparticles（Ag NPs）as SERS substrates and inorganic salt induced silver sol aggregations to create SERS "hotspots".Then,we examined the effects of pH and inorganic salt on SERS enhancements in the Ag NPs system.The results show that As species were sensed by the SERS "hot spot" generated from the coaggregation of Ag NPs and the different forms of As.Meanwhile,this method also takes advantage of the selective adsorption of As species by Ag NPs,so it can in-situ enhance the Raman signal of As（Ⅲ）and As（V）,which can quickly and accurately achieve the analysis of low concentrations of arsenite（As（Ⅲ））and arsenate（As（Ⅴ））.The detection limit（LOD）of As（Ⅲ）was as low as 6.2 × 10^-11 mol·L^-1,and the analysis enhancement factor was as high as 2.9 × 107.Finally,the method of As（Ⅲ）and As（Ⅴ）in drinking and environment water verify the practical application performance of the method.Overall,this method based on spontaneous enrichment and SERS has great potential in the rapid detection of hazardous materials.2.Inquiry of the crucial role of surface silver ions in the SERS species analysis of arsenic species in aquatic environmentBased on the first study,the SERS substrate with high SERS "hotspots" and activity was constructed by modifying external silver ions（Ag+）on the Ag NPs surface（AgNPs@Ag+）.The role of Ag+on colloidal Ag in the SERS analysis of arsenic species was revealed.Arsenic species were adsorbed on Ag NPs driven by Ag+ and were simultaneously sensed by the SERS"hot spots" generated from the aggregation of Ag NPs.The specific binding affinity of Ag+to arsenic species generated higher sensitivity,wider linear range,faster response（The adsorption equilibrium time of As（Ⅴ）is only 0.7 min,"mixing and reading"）,cleaner spectra background,and better reproducibility.This method can also significantly improve the inconsistent SERS activity of Ag NPs synthesized in different batches or laboratories.Batch-to-batch reproducibility was significantly improved with a variation below 3.1%.The method was also demonstrated with As in drinking and environmental water with adequate recovery and high interference resistance.In summary,the more abundant SERS "hotspots" in the AgNPs@Ag+substrate made arsenic signals further enhanced,providing a reliable monitoring method for rapid and in-situ analysis of trace As contaminants in complex water samples.3.Detection of arsenite in atmospheric aerosol particles by SERSBased on the study of As species analysis by SERS,the relationship between arsenic（As（Ⅲ））and atmospheric aerosol particles was investigated.Silver nanowires（Ag NWs）were prepared by polyol method,and we proposed an analysis method for As（Ⅲ）in atmospheric aerosol particles.The results showed that Ag NWs film had excellent SERS "activity",and sodium borohydride（NaBH4）could remove the interference signal generated by polyethylpyrrolidone on the surface of Ag NWs prepared by polyol method,realizing the accurate identification of target object.The method can also enhance the Raman signal of the object under test in situ.The minimum concentration of As（Ⅲ）aerosol particles can be measured to 3 × 10^-3 mg·m³,the minimum size is less than 2 μm,and the analysis enhancement factor（EF）is up to 48 for As（Ⅲ）aerosol particles with a size of 10 μm.The method combined with Raman imaging technology can also obtain the distribution information of the particles on the basement surface.Through the analysis of airborne particles in real environment,the practical application performance of this method is verified,which provides a reliable method support for the multi-component analysis of aerosol particles in environment.