Environmental Behaviors Of Copper Oxide Particles With Different Particle Sizes In The Presence Of Tannic Acid

With the rapid development of science and technology,Metallic Nanoparticles(MNPs)have been widely used in various fields such as agriculture,chemical industry and aerospace due to their unique physical and chemical properties.In the process of use,these MNPs can enter the environmental media through atmospheric circulation,surface runoff and other ways,thus posing a potential threat to the health of organisms and human beings.With the decrease of particle size,the specific surface area,surface charge density and surface energy of MNPs increase,which affect the interface reaction and biological effect of MNPs to a large extent.Therefore,the relationship between the change of physical and chemical properties of MNPs and its environmental behavior and biological effect has received more and more attention.On the surface of Dissolved Organic Matter(DOM),there are a large number of oxygen-containing functional groups,such as hydroxyl and carboxyl groups,which can undergo adsorption and complexation reactions with MNPs,thus changing the bioavailability of MNPs.At the same time,the size of MNPs will also change under the influence of DOM,thus affecting their environmental behavior and even biological effects.How to quantify and clarify the relationship between them has become the focus of this study.Therefore,CuO particles,a widely used MNPs,were selected as the research object in this paper,and TA(Tannic Acid),as a typical DOM,was applied in this study.In this paper,the relationship between adsorption,dissolution and dispersion of CuO particles with different particle sizes in different concentrations of TA solution was explored through adsorption kinetics,dissolution kinetics,dispersion and various characterization experiments.Through previous literature reading,it was found that due to the decrease of particle size,the specific surface area of CuO particles increased,and the number of vacant active sites available increased.As a result,the surface has many structural defects and is extremely unstable,which makes it easy to react with other substances.Therefore,it is hypothesized that the CuO particles with small particle size may adsorb more on the surface of CuO particles due to their unique physical and chemical properties in the reaction with TA,which reduces the effective exposure area and thus inhibits the dissolution of CuO particles.On the basis of this hypothesis,we designed and completed the above experiments and reached the following conclusions:(1)When p H=5 and ionic strength is 0.1 M,TA can be adsorbed on the surface of CuO particles through ligand exchange.With the increase of TA concentration,the adsorption capacity of 5 nm,40 nm and 150 nm CuO particles on TA increases.When the CuO particle size was 5 nm and 150 nm and TA concentration was 30.46 mg C·L^-1and 55.40 mg C·L^-1,the adsorption tended to increase with the increase of TA concentration.This indicates that the adsorption at 5 nm and 150 nm may not reach adsorption saturation at 120 h,possibly due to the large specific surface area at 5 nm and large total surface area at 150 nm,resulting in too many vacant sites.(2)Dissolution kinetics test data show that with the increase of TA concentration,the adsorption of CuO particles on TA increases,which reduces the effective surface exposed area of CuO particles but inhibits the dissolution of CuO particles,and the higher the concentration,the greater the degree of inhibition.When CuO particles were 37.91 mg·L^-1,the concentration of total copper ions and the dissolution release rate of CuO particles with different particle sizes of 5 nm,40 nm and 150 nm decreased with the increase of TA concentration,and the decrease rate was up to 71%.This indicates that CuO particle dissolution is inhibited with the increase of TA concentration,which may be independent of the particle size but related to the concentration of TA.(3)By measuring the dispersion degree in the reaction process of TA-CuO particle system,it is found that the increase of CuO particle adsorption amount to TA has different effects on the dispersion degree of CuO particles with different particle sizes.TA is adsorbed on the CuO particles at 40 nm,so that the surface of the particles is negatively charged and the electrostatic repulsion reaction occurs,which increases the dispersion degree of the CuO particles at 40 nm in the system and inhibits the aggregation.However,the dispersion of 5 nm and 150 nm CuO particles in the system does not increase with the increase of TA concentration.This may be due to the fact that the surface free energy of particles with small particle size is too large for self-aggregation,while the adsorption of particles with large particle size cannot overcome the gravity effect due to its large gravity.(4)TA adsorption on the surface of CuO particles has an important effect on the Zeta potential,hydrodynamic diameter and ion release of CuO particles.Although the dissolution of the three types of CuO particles was inhibited by the increase of TA concentration,the addition of TA dispersed 40 nm CuO particles,but increased the aggregation of 5 nm and 150 nm CuO particles,so that the reduction of total dissolved Cu in 40 nm CuO particles at a certain mass concentration was relatively small.The dissolution of CuO particles is affected by the action of H⁺,the complexation of TA-Cu,the dispersion of TA and the coating of TA.Among them,the dispersion of TA is less than the encapsulation of TA,which will lead to a gradual decrease in the ion release of CuO particles at different TA levels.These findings will further deepen our understanding of the behavior of CuO particles of different sizes in the environment and help us to conduct risk assessment and control for related products in the near future.