The Stability Of Adsorbed Cu(Ⅱ) On Graphene Oxide Under The Water Environment

With the rapid growth of population and the continuous development of industrialization,the threat of heavy metals in water to human beings is gradually increasing.How to deal with heavy metal pollution has become the focus of the current society.Graphene oxide（GO）,as a highly efficient new adsorption material,has a huge specific surface area and a unique network structure.It has excellent adsorption capacity for heavy metals in water and has a great prospect in the field of environmental treatment.As for the structural model of GO,the two-component structure model is generally recognized at present,which consists of two parts:low-degree oxidized bw GO（base-washed Graphene oxide）and high-degree oxidized OD（Oxidation Debris）.Based on the binary structure model of GO,the relationship between the total acidity of GO and the acidity of bw GO and OD was obtained by titration method.At the same time,the adsorbed Cu（Ⅱ）on GO surface can undergo desorption under alkaline or reductive conditions,and the stability of adsorbed Cu（Ⅱ）on GO surface in aqueous environment is less studied.The main results of this study are as follows:（1）The total acidity of GO bw GO and OD aqueous solutions were 9.72,2.74 and26.45 mmol·g^-1,respectively,and the total acidity of GO was about the sum of 70.56%bw GO and 29.44%OD.This relationship is consistent with thermogravimetric analysis,indicating that the acidity of GO in aqueous solution is due to the sum of the acidity of its different components.（2）The adsorption capacity of GO and OD on Cu（Ⅱ）is affected by the pH of the solution,and the adsorption capacity changes greatly under different pH conditions.The adsorption capacities of GO and OD were 72.20 mg·g^-1 and 362.32 mg·g^-1,respectively,when the solution pH value was about 5.0.The pseudo-second-order adsorption kinetics and Langmuir adsorption isotherm model can well fit the adsorption process of Cu（Ⅱ）by GO and OD,indicating that the adsorption of Cu（Ⅱ）by Go and OD belongs to monolith chemisorption.（3）Under the action of soil Eh and pH,GO is reduced to r-GO,which leads to the decrease of its adsorption capacity.In the soil environment,GO-Cu（Ⅱ）desorption occurs.When the desorption reaches equilibrium,the concentration of Cu（Ⅱ）in leachate is1.2 mg·L^-1,the desorption rate is 45.6 mg·mg^-1·d^-1,and the desorption rate is about 8.41%.（4）Under the alkaline condition provided by Na HCO₃,GO-Cu（Ⅱ）desorption occurs.The greater the alkalinity in the solution,the more Cu（Ⅱ）is desorbed.The desorption process of GO-Cu（Ⅱ）is slow,and the desorption equilibrium is reached after 6 h of reaction.After 0.01～1.00 mol·L^-1 Na HCO₃ solution for 48 h,the desorption rates of GO-Cu（Ⅱ）were 3.2%11.4%and 27.5%,respectively.（5）The migration of OD in saturated porous soil is affected by the ionic strength of the solution in the soil.When the ionic strength of the solution increased from0.001 mol·L^-1 to 0.1 mol·L^-1,the OD recovery decreased from 87.2%to 52.6%.At the same time,the particle size of OD is smaller than that of GO,and its migration performance is also better than that of GO.Therefore,under alkaline conditions,the shedding of OD from GO can promote the transport efficiency of Cu（Ⅱ）in the soil layer.As the concentration of Na HCO₃ increases,the penetration rate of Cu（Ⅱ）also increases.