Preparation Of GO And Co/rGO Magnetic Composites And Their Ion Adsorption Properties

After in-depth research on the preparation technology of graphene oxide and its composite materials,as well as the application of graphene oxide and its composite materials in the field of adsorption,this paper firstly and systematically studies the adsorption characteristics of graphene oxide for the alkali metal ions,proposes and successfully uses the adsorption-in-situ reduction method to prepare metal/rGO composite materials,which has excellent adsorption properties for Cu2+.First,this paper uses modified Hummers method to prepare graphite oxide,which is ultrasonically stripped in aqueous solution to obtain graphene oxide dispersion.The graphene oxide material is characterized by various means,and the adsorption characteristics of graphene oxide to different alkali metal ions are investigated.Then,this paper uses adsorption-in-situ reduction method to prepare Co/rGO magnetic composites with different morphologies,and studies the adsorption performance,reusability,adsorption thermodynamics,kinetics and adsorption mechanism of Co/rGO composites for Cu2+.(1)Using flake graphite as the raw material,this paper uses the modifiedHummers method to prepare graphite oxide,and then disperses and peels it into graphene oxide nanosheets under ultrasound.The structure and thermal stability of graphene oxide were characterized by SEM,FT-IR,Raman,XRD and TG-MS.Studies have shown that graphene oxide is a layered structure with a large number of folds on the surface;the oxygen,content is as high as 42.66%,and—COOH has the highest content of oxygen-containing groups,which is conducive to ion exchange reactions(2)Aiming at the adsorption mechanism of graphene oxide for alkali metal ions,this paper adopts the modified Hummers method to prepare graphene oxide nanosheet and it is used as an adsorbent to adsorb Li+,Na+,K+,Rb+ and Cs+ in the solution.The experimental results show that the adsorption of graphene oxide to alkali metal ionsstrongly depends on the initial pH of the solution and the rich oxygen-containing groups on the graphene oxide surface.The adsorption process of graphene oxide to Li+,Na+,K+,Rb+ and Cs+ conforms to the Langmuir isotherm model,and the adsorption of graphene oxide to K+conforms to the Freundlich isotherm model and they all conform to the pseudo-second-order kinetics.The thermodynamic parameters show ?G<0,?H>0,which shows adsorption is a spontaneous endothermic process and is a chemically controlled process.In this paper,in single or mixed alkali metal solutions,graphene oxide has higher adsorption capacity and ratio of K+.The separation factor of graphene oxide for K/Na is 2.11 and the separation factor of K/Rb is 2.53.(3)At room temperature,this paper prepared Co/rGO composites from graphene oxide.Using propanol as a solvent,the cobalt nanoparticles have been further functionalized to prepare magnetic Co/rGO composite materials.Co/rGO composites have superparamagnetic properties,which can be easily separated using magnets,and oscillate and disperse Co/rGO composites without magnetic field.This paper systematically investigated the influence of key factors including the amount of NaOH added,the type of complexing agent,and the type of solvent on the morphology and distribution characteristics of Co particles on the rGO.The Co/rGO composites prepared under the optimal conditions are characterized by FT-IR,XRD,and SEM.The results show that for the Co/rGO composite material prepared by in-situ reduction method,the particle size of cobalt particles is mainly affected by the amount of NaOH added,the added citric acid is beneficial to disperse the cobalt nanoparticles,while in the propanol solution,the cobalt nanoparticles are petal-shaped spherical,which significantly increases the adsorption performance of the composite Research on the adsorption effect of Co/rGO composites synthesized by different conditions on Cu2+ in solution,the optimal reaction condition is OH-/Co2+=8,the solvent is propanol,and the complexing agent is citric acid.The Co/rGO composites prepared under optimal conditions are fold-shaped planes,and the graphene C=C structure has been obviously restored,but due to the protective effect of Co,more oxygen-containing active groups such as C—OH remain group are remaining Cauliflower-like metallic cobalt particles smaller than 100 nm are more uniformly dispersed on the surface.(4)This paper also explores the effects of initial pH value,adsorption time,initial Cu2+ concentration and reaction temperature on the adsorption performance of the solution,as well as adsorption thermodynamics and the reuse of compound materials.The results show that the Co/rGO composite has stable adsorption/desorption performance for Cu2+.Under the experimental conditions,its maximum adsorption capacity for Cu2+ reaches 117.5 mg/g and the adsorption equilibrium can be achieved within 5 minutes,which is far superior to that of the raw material graphene oxide(the adsorption capacity of graphene oxide is 27.5 mg/g within 60 min).The adsorption process of nano-Co/rGO magnetic materials for Cu2+is in line with the Freundlich model and belongs to the multilayer adsorption.At room temperature,the enthalpy of adsorption is ?H=17.81 kJ/mol,and the equilibrium constant of adsorption is K0=3.65.When the initial concentration of Cu2+ is 10 mg/L,the desorption rate exceeds 93%.After five adsorption/desorption cycles,the adsorption capacity remains at 94%of the initial value,and the residual Cu2+concentration in the solution after each adsorption meets the cobalt electrolyte's requirement for the concentration of impurity copper ions(5 mg/L)and meets the level 3 of GB 8978—1996 comprehensive sewage discharge standard(2 mg/L),and it is expected to play a important role in related fields.