The Stability Of Natural Soil Nanoparticles And Their Changes In Paddy Soil During Pedogenic Process

Nanotechnology is a rapidly growing science.It is widely applied for use in each corner of modern scientific research.Nanoparticles are usually defined as materials with one or more dimension smaller than 100 nm.Because of its small size,nanoparticles?<100 nm?usually have some unique characteristics.The behavior and fate of ENPs under different environmental conditions,especially in soil and aquatic environments,have been widely discussed.And Research into natural clays and iron oxide colloids in the range of 200-2000 nm has been carried out for much longer than that into ENPs.Although there has been considerable research on various aspects of ENPs and colloids,little has been carried out on the behavior and fate of natural colloids less than 100 nm,or natural nanoparticles?NNPs?.We extracted natural nanoparticles from four typical zonal soils of China and conducted a series of research on their characteristics,stability and environment behaviors.And our main results were as follows:?1?By ultrasonic dispersion and centrifugation,soil natural nanoparticles could be extracted from four typical zonal soils of China?Liaoning,Jilin,Jiangxi and Hainan?.The results of dynamic light scattering?DLS?showed that the sizes of nanoparticles were 90.0 nm?LN?,90.9 nm?JL?,82.8 nm?JX?and 95.8 nm?HN?,respectively.The extracted NNPs remained stable in a long period?100 days?.The extract contents of natural nanoparticles increased as the ultrasonic energy as logarithmic function.And their extract rates were 0.51%?LN?,2.49%?JL?,0.44%?JX?and 0.42%?HN?,respectively.The extracted soil natural nanoparticles were then characterized by TEM,BET and FTIR.?2?The aggregation of soil natural nanoparticles in electrolytes could reflect its stability directly.And the critical coagulation concentrations?CCC?of particles reflected the aggregation of particles.CCC values of JL NNPs were 76.5 mM for NaCl,1.15 mM for CaCl2,and 0.050 mM for LaCl3;CCC values of LN NNPs were 140 mM for NaCl,1.79 mM for CaCl2,and 0.055 mM for LaCl3;CCC values of JX NNPs were 29.5 mM for NaCl,0.744 mM for CaCl2,and 0.024 mM for LaCl3;CCC values of HN NNPs were 103 mM for NaCl,1.89 mM for CaCl2,and 0.082 mM for LaCl3.The aggregation of soil natural nanoparticles became obvious as the ionic strength of electrolytes increased.And when the concentration of certain electrolyte reached the critical coagulation concentrations,the aggregation of nanoparticles reached the top.And di-and trivalent ions had a stronger tendency for coagulation than monovalent ions.Based on the DLVO theory,the electrostatic repulsive forces and the van der Waals forces between particles determined the aggregation of particles.The aggregation of soil natural nanoparticles and their stability rank could be well explained by DLVO theory.The Hamaker constant was 6.99×10-20 J?JL?,5.16×10-20 J?LN?,4.47×10-20 J?HN?and 10.40×1020 J?JX?,respectively.?3?The H₂O₂-treatment and the hematite-addition could largely make the soil natural nanoparticles unstable.After the H₂O₂-treatment,the CCC values of JL NNPs decreased to 51.7 mM for NaCl,0.7 mM for CaCl2,and 0.72 mM for MgCl2;he CCC values of HN NNPs decreased to 40.6 mM for NaCl,0.31 mM for CaCl2,and 0.33 mM for M9Cl2.And after the hematite-addition,the CCC values of JL NNPs decreased to 55.0 mM for NaCl.By DLVO simulation,both the H₂O₂-treatment and the hematite-addition could weaken the electrostatic repulsive forces between particles and enlarge their van der Waals forces,which led to the decrease of their stability.?4?The soil natural nanoparticles were apt to aggregate and deposit in the saturated porous media.Their sizes increased to 110.2 nm?JL?and 118.5 nm?HN?.And their recovery rates were 79%?JL?and 89%?HN?.The recovery rates and the shapes of breakthrough curves were related to NNPs stability.The aggregation and deposition of natural nanoparticles was enhanced in the electrolytes.In the electrolytes,their recovery rates became 42%?JL?and 49%?HN?.After the H₂O₂-treatment,the tailing and delay in the breakthrough became more obvious,and their recovery rates became 76%?JL?and 60%?HN?.These results of mobility could be corresponding to the results of stability analysis.And the destabilization of NNPs hampered the breakthrough.?5?The natural nanoparticles fraction was isolated and characterized along with bulk soils?<2-mm fraction?for selected physical,chemical and mineralogical properties from CIxi area.The natural nanoparticles content increased with increasing cultivation age and accumulated in the deep layers of soil,which was due to the desalination of soil.Tendency and regulation was showed in the changes of these properties.The changes in several NNP properties of natural nanoparticles were consistent with the bulk soil fraction across the chronosequence.Based on changes in NNP and bulk soil properties,the dominant pedogenic processes were inferred.The cluster analysis based on the NNP properties divided the pedogenesis into three periods?0-50 years,50-700 years and 700-1000 years?in all soil layers,which followed the trend of soil properties.The categorization of pedogenic processes based on NNPs offers us an alternative and enhances interpretation of long-term soil management research.