Hyphenated Method Of Membrane Filtration And SERS For Preconcentration And Analysis Of Nanoparticle Pollutants

With the development of nanotechnology and industrial production,a large number of particulate pollutants are discharged into the environment,which poses threats to the environment and organisms.To better evaluate and deal with the environmental problems caused by particulate pollutants,it is necessary to obtain accurate information on the abundance,distribution and behaviour of particulate pollutants in the environment.A key prerequisite for obtaining this information is the development of a reliable and feasible analytical method.Although many analytical methods for micron particle pollutants have been developed,these methods cannot be directly applied to the analysis of nanoparticle pollutants.Therefore,it is of great significance to improve and optimize these methods to make them suitable for analysing nanoparticle pollutants.When analysing nanoparticle pollutants,the preconcentration step is inevitable to obtain a certain number of particles that can be detected,because the environmental concentration of nanoparticle pollutants is below the detection limit of routine analytical instruments.Among the commonly used preconcentration methods,membrane filtration has been widely used in separating and preconcentrating particulate pollutants due to its advantages of simple operation,high enrichment efficiency,non-destructive and wide applicability.After enriching,the concentrated sample needs to be transferred to proceed with the following analysis,but the nano-sized particles tend to be adsorbed on the membrane,which makes the particles difficult to be eluted and causes sample loss.Therefore,it is urgent to develop an in-situ analytical technique that can be coupled with the membrane filtration technique.Surface-enhanced Raman spectroscopy(SERS),as an in-situ and sensitive analytical technique,has the advantages of non-destructive,low water interference,and characteristic fingerprint features.It is expected to be used as an in-situ analytical technique for nanoparticle pollutants enriched on the membrane.Based on the above research progress,we proposed the hyphened method of membrane filtration and SERS in this thesis to solve the problem that the enrichment step and the characterization step are difficult to connect in the routine analysis process of particulate pollutants.The main research contents are shown as follows:1.Identification of nanoplastics in water by the hyphenated method of membrane filtration and SERSIn this work,we proposed a hyphenated method of membrane filtration and SERS to analyse trace nanoplastics in water.This method was developed based on the construction of the silver nanowires(AgNWs)membrane.At first,one-dimensional AgNWs were synthesised by the polyol process,and the AgNWs membrane was prepared by the flow-through method.Then,the filtration performance and SERS performance of the AgNWs membrane were investigated.The results show that the AgNWs membrane can efficiently enrich nanoplastics with sizes in the range of 50-1000 nm and the retention rate for 50 nm nanoplastics reached 86.5%.Meanwhile,the AgNWs can in-situ enhance the Raman signal of nanoplastics.The detection limit of the proposed method for 50 nm polystyrene nanoplastics was 10-7 mg/mL,and the enhancement factor reached 230000.The distribution information of nanoplastics on the membrane can be obtained in situ via SERS with Raman mapping.Furthermore,the proposed method has been successfully applied in detecting micro-and nanoplastics in leftover water samples of the seafood market.Overall,the hyphened method not only keeps the superiorities of membrane filtration and SERS but also avoids sample loss caused by the additional sample transfer step,providing methodological support for the analysis of trace nanoplastics in the aquatic environment.2.Identification of silver nanoparticles in antibacterial products by the hyphenated method of membrane filtration and SERSBased on the first study,a hyphened method for silver nanoparticles(AgNPs)without Raman signal was developed in this work.At first,Raman probe molecules that can be adsorbed on the surface of AgNPs were added to the water sample,which allows using signals of the probe to reflect the presence of AgNPs.Then,the iodide modified AgNWs membrane was used to separate and enrich trace AgNPs,in which the iodide modified layer can be used as a barrier to avoid the adsorption of excess probe molecules on AgNWs,so as to ensure the accurate identification of AgNPs.At the same time,the electromagnetic coupling effect between AgNWs and AgNPs can in-situ enhance the Raman signal of probe-AgNPs complexes,which allows the sensitive detection of AgNPs.The results show that the proposed method can enrich more than 84.0%of different types of AgNPs.The detection limit of the proposed method for AgNPs reduced by sodium citrate was 10-6 mg/mL.The distribution information of AgNPs can also be obtained in situ by SERS with Raman mapping.Furthermore,AgNPs in antibacterial products were successfully detected by the proposed method.Overall,the enrichment and in-situ detection of AgNPs without Raman signal are realized by borrowing the signal of Raman probe molecules and combining the hyphened method of membrane filtration and SERS,which provides a new solution for the detection of AgNPs.