Effects Of Tannic Acid Adsorption On The Dissolution Of Copper Oxide Nanoparticles In Aqueous Phase

As one of the most common materials in metal nanoparticles(MNPs),copper oxide nanoparticles(CuO NPs)are increasingly added to products in the fields of electronics,chemistry,medicine,biology and agriculture.The extensive application of these products in industrial production,urban activities and agricultural cultivation makes CuO NPs inevitable released into the environment by means of atmospheric deposition,surface runoff,underground infiltration and so on,which eventually threatens the ecosystem balance and human health.Dissolved Organic Matters(DOMs)is widely distributed in the environment,with carboxyl group,aldehyde group,phenolic hydroxyl group,benzoquinone group and other functional groups on its surface.It is easy to react with CuO NPs and copper ions released into the aqueous phase(such as complexation and adsorption),reduces the effective exposure area of particles in the aqueous phase,and change the dissolution balance of CuO NPs.The above reactions may occur at the same time,affecting the dissolution behavior and dispersion of CuO NPs in aqueous phase,thus controlling the bioavailability of CuO NPsIn this study,the adsorption effect of Tannic Acid(TA),a typical representative of DOMs,on the dissolution process of CuO NPs was systematically studied.The key to understanding this complex process is to quantitatively identify the effective exposed surfaces of CuO NPs in the aqueous phase.Therefore,in this paper,the adsorption behavior of TA on the CuO NPs surface was quantitatively analyzed with the help of adsorption kinetics and adsorption isotherm,and the following hypothesis was proposed:The amount of CuO NPs dissolved in the aqueous phase will decrease with the increase of TA adsorption on its surface.When the CuO NPs surface reaches adsorption saturation,it is believed that the CuO NPs surface is completely covered by TA,preventing the dissolution of copper ions.On the basis of the assumption,the simulation solution pH 5,under the different mass concentration ratio of CuO NPs to TA(solid-liquid ratio)conditions,explored the mechanism of interaction between TA and CuO NPs.And the change of the concentration of total copper ions released by CuO NPs,dissolution release rate and dispersion under TA adsorption(adsorption equilibrium and adsorption saturation)were analyzed.The main results obtained are as follows:(1)TA can be adsorbed on the CuO NPs surface by ligand exchange,and the adsorption amount increases with the increase of TA concentration.The adsorption of TA(10.51 mgC·L-1?55.40 mgC·L-1)on the CuO NPs with the concentration of 13.01 mg·L-1 and 37.91 mg·L-1 reached an equilibrium after 120 h,while the adsorption amount of CuO NPs with the concentration of 82.50 mg·L-1 on 55.40 mgC·L-1 TA continued to increase over time,indicating that the adsorption equilibrium has not yet been reached.Through adsorption isotherm fitting,it was found that the adsorption of TA on the CuO NPs surfaces of 13.01 mg·L-1 and 37.91 mg·L-1 reached the saturation,indicating that the CuO NPs surfaces of these two concentrations were almost completely covered by TA after 120 h,which may hinder the dissolution of copper ions from CuO NPs.(2)The adsorption of TA prevents the dissolution of CuO NPs.When there is no TA in the solution,the copper released into the solution by CuO NPs is mainly in form of free and inorganic complexation(10.56%).However,in the presence of TA,copper ions in inorganic complexation account for only 1%of the total copper ions released by CuO NPs(negligible),so dissolved copper mainly exists in form of free and organic complexation.With the increase of TA concentration,the amount of TA adsorbed on the CuO NPs surface increases,and the total copper ion concentration dissolved by CuO NPs decreases.This indicates that with the increase of TA adsorption on the CuO NPs surface,the larger the surface area of CuO NPs is covered and the smaller the effective exposed area is,which reduces the contact probability between CuO NPs and solute in water(such as H+)and hinds the dissolution of copper ions in CuO NPs.(3)The adsorption of TA promotes the dispersion of CuO NPs in suspension.Under the condition of same concentration of CuO NPs,the?-potential and hydraulic diameter decreases with the increase of the concentration of TA.Since TA dissociates in the solution and the surface is negatively charged,the charge density on the CuO NPs surface can be increased when it is adsorbed on the CuO NPs surface.This increases the electrostatic repulsion and steric hindrance between particles.Therefore,TA adsorption on CuO NPs increased the dispersion of CuO NPs in suspension and inhibited the aggregation of CuO NPs(4)The solid-liquid ratio of CuO NPs to TA determines the contribution of adsorption and dispersion to the dissolution of CuO NPs The hydraulic diameter of CuO NPs and the total copper ion concentration released by the particles increased with the increase of the solid-liquid ratio,while the adsorption capacity of TA on the CuO NPs surface(120 h)decreased with the increase of the solid-liquid ratio.When the solid-liquid ratio is less than 0.84,the surface adsorption of TA is the main driving force affecting the dissolution process of CuO NPs.When the solid-liquid ratio is greater than 1.29,Although the small adsorption amount on the particle surface makes the dispersibility of CuO NPs worse,it also reduces the CuO NPs surface coverage by TA,which increases the effective exposure area of CuO NPs in water phase,and promotes CuO NPs to react with H+ and TA-in the solution.The conclusion of this study is helpful to better identify the migration and transformation mechanism of CuO NPs under the environmental conditions of DOMs,and also provides a theoretical basis for more accurate assessment of the biological toxicity of CuO NPs and reduction of its ecological risks in the future.