Adsorption And Dissolution Characteristics Of Copper Oxides Nanoparticles In Typical Agricultural Soils In China

Nanoscale copper oxides（nano-CuOs）,as one of the most important metal oxide nanomaterials,are widely used in industrial,agricultural,and other fields.It will inevitably enter the soil environment in the processes of production,usage,disposal,and so on.The dissolution and adsorption of nano-CuOs are important processes that affect the toxicity and bioavailability in soil media.Therefore,the dissolution and adsorption behavior of nano-CuOs in ten typical agricultural soils of China were studied in this thesis,the main factors controlling the dissolution and adsorption of nano-CuOs were also determined.Besides,we established quantitative models of dissolution and adsorption,which provided a basis for scientific assessment of the environmental risks of nano-CuOs.The primary results were summarized as follows:（1）The effects of nanoparticle morphology,low-molecular-weight organic acids（LMWOAs）,p H,and other factors on the dissolution characteristics of nano-CuO in soil solutions were elucidated.The results showed that the copper ions(Cu²⁺)released from spherical nano-CuO（CuO NPs）,tubular nano-CuO（CuO NTs）,and spherical bulk CuO（CuO BPs）in the ten soil solutions were 26.6-4194.0μg/L,4.90-217.1μg/L,and 10.8-326.0μg/L,respectively.The release of Cu²⁺from CuO NPs is significantly higher than those from CuO NTs and CuO BPs（P<0.05）.The concentration of Cu²⁺was negatively correlated with the p H of the soil solution and positively correlated with the contents of dissolved organic carbon（DOC）,aluminum,and manganese.Furthermore,the dissolution of CuO NPs could be well predicted by p H and DOC contents of the soil solutions.In the Guangdong（GD）soil solution（acidic）,the amendments of LMWOAs at 4 times（low concentration treatment）and 8 times（high concentration treatment）of the DOC content in the initial soil solution significantly promoted the dissolution of CuOs,with the release of Cu²⁺increased by 4.55-11.3 and 5.67-16.2 times,respectively.In the Chongqing（CQ）soil solution（neutral）,only high concentration treatment could significantly promote the dissolution of CuO,increasing the release of Cu²⁺2.13-16.6 times.While in the Shandong（SD）soil solution（alkaline）,the promotion on the dissolution by the two concentration treatments was only observed for nano-CuOs,with Cu²⁺elevated by factors of 1.56-4.64 and 1.38-4.48 times,respectively.The amendments of Al³⁺and Mn²⁺in soil solution increased the release of Cu²⁺1.13-4.80 and 1.02-1.46 times in the GD soil solution.In comparison,no significant promoting effects were observed in CQ and SD soil solutions due to their stronger buffering capacities.（2）It is indicated that the nanoparticle morphology,soil organic matter（SOM）,Ca CO₃,and other factors played important roles in the adsorption of nano-CuOs in soil.The results showed that the apparent single-point distribution coefficients（KD）of CuO NPs,CuO NTs,and Cu²⁺in the ten soils were 338-6631 L/kg,1600-19944 L/kg,and 151-1023 L/kg,respectively.The adsorption of nano-CuOs and Cu²⁺in soil were well fitted by Freundlich isotherm model.There were significant differences in the distribution of different forms of Cu between soil solid and liquid phase.The adsorption capacity,Freundlich affinity coefficient（K_F）,and Freundlich parameter（N）ranked as CuO NTs>CuO NPs>Cu²⁺.The values of KD,KF,and N of CuO NPs and Cu²⁺were positively correlated with soil p H,EC,Ca CO₃,Al,Mn,K,Ca,Na,and Mg,and negatively correlated with free Fe.The adsorption parameters of CuO NTs showed no significant correlation with soil properties due to the high agglomeration.The values of KF(CuO NPs and Cu²⁺)and K_D（CuO NPs）could be well predicted by soil p H,and the value of N(CuO NPs and Cu²⁺)could be predicted by the contents of K,Ca,and Ca CO₃ in soil.The removal of SOM decreased the KD values of CuO NPs,CuO NTs,and Cu²⁺by 15.9-16,3.85-115,and 12.2-70.6 times,respectively.The amendments of Ca（NO₃）₂ in soil showed different effects on the distribution of nano-CuOs and Cu²⁺.For the CuO NPs,the K_D values in different soils were varied with the increase of Ca（NO₃）₂ concentration,and the K_D values in GD,CQ,and SD soils were 0.10-0.32,1.75-2.63,and 0.22-8.59 times of those of the control group,respectively.The adsorption capacity of CuO NTs in soil was increased with the amendments of Ca（NO₃）₂,with K_D values of 1.89-34.1 times that of the control group.For the Cu²⁺,the K_Dgenerally showed a downward trend with increasing Ca（NO₃）₂,which was 0.22-0.81 times that of the control group.The amendments of Na₂CO3 in soil increased the p H of soil.In the GD soil（acidic）,the K_D values of almost all the experimental groups increased,which was 1.14-14.9 times that of the control group.In CQ（neutral）and SD（alkaline）soils,the K_D values of almost all the experimental groups decreased,which was 0.03-0.88 times of that of the control group,except that the medium and low concentration of Na₂CO3 increased the adsorption of Cu²⁺.