Adsorption/Electrochemical Assistant Adsorption Of Pollutants On Graphene

Graphene belongs to a new class of carbon nanomaterials-2-D materials made up entirely of conjugated sp2 carbons arranged in a honeycomb structure.All atoms were surface atoms that provided graphene with a large specific surface area and rich pore structure which made it widely used in the study of pollutant adsorption.Domestic and foreign studies were proved that graphene had a good adsorption effect on several pollutants,however,limited production scales and recycling technology limited it's application in environmental pollution control.Consequently,improving the adsorption capacity and adsorption rate of graphene could accelerate it's application process in the environmental field.In this dissertation,adsorption of methylene blue(MB)on graphene under electrochemical assistance was explored.The graphene/Ti electrodes and graphene/polyaniline/Ti electrodes were prepared by electrophoretic deposition(EPD)as well as their ability of adsorption of typical pollutants were systemically investigated.The influence of the oxygen content of graphene,the applied potential,the pH of the contaminant and the concentration of the electrolyte on adsorption were also discussed.This study expected to develop an efficient,low energy consumption and environment-friendly method to expand the application of graphene in water pollution control.Correspondingly,several studies were conducted as follows:(1)By using graphene oxide(GO)as the precursor which were made by the improved Hummers' method,RGO and GR were prepared by hydrothermal reduction method and chemical method(hydrazine hydrate),respectively.EPD were used to fabricate three kinds of electrodes which based on graphene with different oxygen content.XRD,SEM,FT-IR,EDS,BET and Zeta potential were employed to analyzed the crystal form,the morphology,the type of functional groups,the type of element,the specific surface area and the colloidal stability of the samples,respectively.It was found that initial adsorption rate(?0)and equilibrium adsorption capacity(Qe)of adsorption of MB on graphene under electrochemical assistance could be improved.The oxygen content of the graphene,the applied potential,the pH value and the concentration of the electrolyte may effect the electrosorption properties.The Qe of MB at different voltages is shown as follows:-0.6 V>OC>0.6 V>no voltage;Among the three electrodes,the RGO/Ti electrode exhibits the best adsorption performance:When the pH was 7.5,the concentration of the Na2SO4 was 10 mM,the value of Qe and ?0 at-0.6V of the RGO to the MB were 150.67 mg/g and 44.17 mg/h/g,respectively.It was found that adsorption kinetics of MB on RGO under electrochemical assistance was fitted with pseudo-second-order model,and the adsorption isotherm was well fitted with Langmuir model.(2)The composite(RGP)of RGO and polyaniline(PANI)has been fabricated in a single step by hydrothermal method,EPD technology were employed to fabricate RGP/Ti electrodes.The characterize results of XRD,FT-IR,SEM,BET and C-V indicated that the RGP had a rich network structure and a large specific surface area,the RGP/Ti electrodes had a higher specific capacitance and better electrochemical stability than the RGO/Ti electrode.The adsorption/electrosorption properties of the RGP were evaluated with the cationic dye MB and the reactive cyanide(KN-R)as the target pollutants.The effects of the mass ratio of PANI and GO,the applied potential,the initial pH of the solution and the chargeability of the pollutants on the pollutant removal rate were investigated.The experiment results showed that the RGP1(PANI and GO was 1:1)has the best adsorption capacity.The relationship between the adsorption capacity and the applied for MB was-0.6V>OC>0.6>no voltage;The optimal adsorption conditions of RGP1 for MB were including:MB concentration was 5 mg/L,solution pH was 7.5,electrolyte concentration was 10 mM,applied potential was-0.6 V;The adsorption rate of RGP1 to MB reached equilibrium at 7 h,When the adsorption reached equilibrium,the Qe of RGP1 to MB was 164.34mg/g and the ?0 was 86.43mg/h/g at-0.6 V.The value of Qe at-0.6 V were found to be 2.38 times than RGP1 at no voltage.Especially,the value of ?0 at-0.6 V was found to be 1.95 times for RGO under the same conditions and2.15 times for RGP1 at no voltage,respectively.It was found that adsorption kinetics of MB on RGP1 under electrochemical assistance was well fitted with pseudo-second-order model,and the adsorption isotherm was well fitted with Langmuir model.The relationship between the adsorption capacity and the applied potential of RGP1 on KN-R was:0.6 V>OC>-0.6 V>no voltage;The results also showed that the improved adsorption properties of RGP was mainly due to the enhanced electrostatic adsorption by applied voltage.Consequently,the adsorption/electrosorption performance of RGP was better than RGO,which indicated that the combination of PANI and RGO could improve the adsorption performance of RGO;RGP was an efficient,low-energy,environmentally friendly adsorbent with good adsorption properties for different ionic types of dyes.In this work,MB and KN-R were removal effectively on RGO and RGP under electrochemically assistant adsorption,which provided theoretical guidance for pollutants adsorption by graphene and also facilitated application and development of graphene in the field of water pollution control.