Interaction Of Natural Organic Matter And Iron Nanoparticles:A Study On Preferential Adsorption And Aggregation Behavior

Natural and engineered nanoparticles are ubiquitous in the environments,and will interact with natural organic matter(NOM),which is also ubiquitous in the environments,thus affect the transport and fate of itself and the associated contaminants.In this study,the effects of NOM on iron-based nanoparticles adsorption and aggregation were discussed in detail by using various advanced techniques,and the control factors of aggregation were determined by quantification of the physico-chemical properties(adsorbed mass,molecular weight,layer thickness,aromaticity and functional groups,ects)of adsorbed NOM components.This study will be critical to understand the transport,stability and fate of iron-based nanoparticles in natural environments.The first part of this study was combined with part of data in my Master's thesis to study the interaction of two kinds of NOM(SRHA and SRFA)with nano zero valent iron(nano-Fe0),which is widely used in groundwater pollution treatment.The results showed that although the total adsorbed mass of different NOM onto nano-Fe0 was similar,the preferential adsorption behavior was different.However,the difference in the preferential adsorption won't affect the inhibition degree of nano-Fe0 by NOM.This might because the adsorbed molecular weight of NOM was similar or the adsorbed mass was the key factor which control the aggregation.The second part of this research studied the effects of different types and concentrations of NOM on ferrihydrite nanoparticles(Fh NPs)aggregation behavior.The results indicated that NOM could inhibit the aggregation of Fh NPs in NaCl by steric repulsion,but accelerate the aggregation in CaCl2 by bridging effect.Besides,the concentration of NOM could also largely affect Fh NPs' aggregation behavior.In the condition of low concentration NOM,the aggregation of Fh NPs in NaCl solution could be largely promoted due to the patch-charge attraction,contrariwise,it would be inhibited by steric repulsion while the concentration was high.Finally,we used a bottom-up molecular weight(MW)cut-off membrane to separate NOM to different MW fractions,to study the controlling mechanisms and factors of Fh NPs aggregation by NOM.The results proves that the SRNOM fractions which MW>3kDa could inhibit Fh NPs aggregation by steric repulsion,and the inhibition effect could increase with the increasing of MW.However,the<3kDa fraction could accelerate the aggregation because of the patch-charge effect which caused by the insufficient adsorption of the<3 kDa fraction which negatively charged forms heterogeneous "patchy" coatings on the surface of positively charged Fh NPs.Furthermore,different character methods prove that the adsorbed mass and molecular weight of adsorbed NOM components were the key factor of the Fh NPs aggregation.