Single Particle Imaging Of Aggregation,Deposition And Transformation Of Nanoparticles In Aquantic Environment

Nanoparticles have been widely used for a variety of applications because of their unique physical and chemical properties.The toxicity of nanoparticles to the environment and human health has gained rapidly growing research interest in recent years.It is of great significance to systematically explain the transport and transformation of nanoparticles in the environment,especially to understand the basic principles of the interaction between single nanoparticles and physical,chemical,and biological interface.In this dissertation,aiming at the key processes of aggregation,deposition and transformation of nanoparticles in water environment,a series of research work has been carried out using the single particle imaging method based on surface plasmon resonance(SPR).We have.realized the successful application of this method in environmental analysis,and elucidated the interaction mechanism of nanoparticles.The main research contents and results are as follows:1.The surface plasmon resonance microscopy(SPRM)was used to accurately measure the deposition efficiency of nanoparticles and to study the influence of environmental factors on the deposition of nanoparticles.Benefiting from the real-time imaging ability and high spatial-temporal resolution of SPRM,the deposition dynamics of nanoparticles can be detected in situ.The effects of ion strength,valence,solution pH and surface functional group on the depostion process were further explored by using the modified deposition efficiency.The deposition efficiency obtained by this method avoids the complex procedure of the normalization of the maximum deposition rate,reduces the experimental error caused by external factors such as particle concentration and ionic strength in the experimental process,and provides a promising test platform to predict the fate of nanoparticles in the environment.2.Based on the high sensitivity of SPRM and the linear relationship between image intensity and particle size,a quantitative analysis method for the aggregation of nanoparticles at the level of single nanoparticles was established.By analysing the change of the average size of aggregates with time,the critical coagulation concentration(CCC)of aggregated particles is obtained,proving the validity of this method.By deconvolution of the intensity of aggregated particles,the specific particle number of each aggregates is quantitatively analyzed,and the relationship between the electrolyte concentration and the number of monomers and polymers in solution is established.Compared with the essembled method,this approach can provide more information about the aggregation kinetics of nanoparticles,and help to better understand the aggregation mechanism of nanoparticles.3.The dynamic process of nanoparticles at the solid-liquid interface is tracked at the single nanoparticle level.Taking advantage of the sensitive z-axis resolution(5 nm)and high time resolution(0.67 ms)of SPRM,we track the movement of a single nano particle at the interface,and find that the nanoparticle is obviously hydrodynamicly hindered,which is responsible for the the multicollision process of the nanoparticle at the interface in low ionic strength solution.By chaning the surface functional group of the solid interface,we gain a deeper understanding of the dynamic behavior correlated with surface chemistry.This method focuses on the instantaneously interfacial behaviour of single nanoparticles,which is helpful to elucidate the depositon process of nanoparticles in the environment from microscopic perspective.4.Owing to the refractive index-sensitive features of SPRM,the kinetic process of the oxidation and dissolution of a single silver nanoparticle on the electrode surface was determined.We can not only detect the instantaneous electrochemical oxidation process of single silver nanoparticles,but also monitor the diffusion behavior of dissolved silver ions in real time.Further signal processing and data analysis of the original image through the reference image recognition method ia able to separate the overlapped signal and help us to characterize the oxidation and dissolution process of single nanopartilces more accurately.This method has great potential in the electrochemical reaction and catalytic process of other similar single nanoparticles,which will improve the understanding of the environment behavior of electrically active nanoparticles.