Study On Adsorption/Desorption Behavior Of Graphene Hydrogel On Pb²⁺

With the increasing discharge of potentially toxic heavy metal ions from manufacturing and industrial facilities to the aquatic environment,it is urgent to develop stable adsorbents with high adsorption capacity and recovery.Graphene was used as adsorbent to treat toxic heavy metal ions wastewater,we are committed to improving the adsorption performance,including adsorption capacity,adsorption rate and preferential adsorption.Graphene hydrogels were prepared by chemical reduction method.The electrochemical properties of hydrogel were characterized by SEM,TEM,XRD,BET and Wetting Contact Angle.The adsorption behavior,adsorption mechanism and cycling stability of graphene gel on static adsorption and electrical adsorption of Pb²⁺were studied.The specific results were as follows.（1）The precursor GO was prepared by Hummers method using 2000 and 5000natural graphite powders as raw materials.When the mass ratio of GO2000 to GO5000was 1:1,1:0 and 0:1,the graphene hydrogel was prepared in mild temperature system at90℃,and was named MGH,GH2000 and GH5000.The results showed that:all three kinds of GH have hierarchical mesoporous structure,MGH had obvious hierarchical porous 3D structure,the maximum pore diameter was 10μm,and the pore structure was similar to GH5000,while the pore size of GH2000 is uneven.The contents of C and O in MGH,GH2000 and GH5000 were 5.26,5.44 and 4.21,The above statement was a good explanation that the contact angles are 105.9°,119.0°and 113.2°respectively.It showed that MGH had better wettability and hydrophilicity Under the current density of 0.5 A/g,the specific capacitance of MGH,GH2000 and GH5000 in the mixed solution of HCl and Na Cl was 170.00 F/g,148.03 F/g and 144.88 F/g,respectively.Under 10 A/g for 1000cycles,the retention was 97.08%.（2）Static adsorption/electro-desorption of MGH for Pb²⁺in solution.The static adsorption results showed that:when the MGH electrode loading was 10 mg,the initial concentration of Pb²⁺was 10 mg/L,the experiment was carried out for 240 min,the experimental temperature was 25℃,the p H of the solution environment was 5,the removal effect of Pb²⁺was the best,and the adsorption capacity of MGH was 182.47mg/g.The adsorption process was mainly physical adsorption.The adsorption isotherms fit the Langmuir model,the saturated amount was 188.75mg/g,and the surface of MGH was monolayer adsorption.Electro-desorption showed that the highest desorption rate was98.10%at the given voltage+1.2 V,30 min,25℃.The results showed that the adsorption removal rate was still 85.57%of the first adsorption removal rate after 8 cycles of adsorption and electrical-desorption.However,when the power was not supplied,the performance of the adsorption decreased seriously after the fourth cycle of adsorption.（3）Study on the electro-adsorption/electro-desorption performance of MGH for low concentration Pb²⁺in simulated real water samples.The results showed that:when the MGH electrode load was 10 mg,The initial concentration of Pb²⁺was 100μm/L,time was25 min,temperature was 25℃,p H was 5,and the given voltage increases from-0.4 V to-1.2 V,the process of MGH electro adsorption of lead ion was more in line with the quasi first-order kinetics,the physical adsorption is dominant,it′s rate is positively linear with given voltage The adsorption isotherm was suit the Langmuir model,it was monolayer adsorption.The adsorption-capacity was 456.97mg/g at-1.2 V.The results showed that the desorption rate of eluent was 97.78%under the given polarization voltage+1.2 V,desorption time 20 min and desorption temperature 25℃.After 15 cycles of electro-adsorption and electro desorption,the regeneration removal rate did not decrease significantly,and the adsorption removal rate remained above 90%of the first adsorption removal rate.