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The Influence And Mechanism Of Oxidation Debris On Aggregation And Adsorption Properties Of Graphene Oxide

Posted on:2023-03-06Degree:MasterType:Thesis
Country:ChinaCandidate:S Y ZhangFull Text:PDF
GTID:2531306845979659Subject:Municipal engineering
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The excellent properties of graphene oxide(GO)have led to its rapid development and wide application in various fields.GO has shown unique advantages in water treatment,but there is also a risk of release into the natural water environment.Therefore,clarifying the behavior characteristics of GO in water environment will help improve the application efficiency and evaluate potential impact of GO on the water environment.The latest structural model shows that GO consists of two parts: large,lightly oxidized functionalized sheets(FG)and small,highly oxidized oxidation debris(ODs),GO=FG+ODs.ODs are known to be about 1~3nm,attached to the base surface of FG,and can be stripped under alkaline conditions.Such structural changes are bound to change the physical and chemical properties of GO and affect its environmental fate and application efficiency.Based on this,in this study,ODs and FG were prepared and characterized,the aggregation of GO in standard synthetic freshwater and adsorption of different aromatic compounds were studied.The emphasis was on the effect of ODs stripping on GO aggregation and adsorption behavior.The mechanism was revealed by combining experimental methods and molecular dynamics simulations.The research results of material characterization show that the mass ratio of ODs to FG in GO is 1:2,and the carbon/oxygen ratio is 1.59:3.60.The higher the pH value is,the more favorable ODs stripping is.The pH10 is the critical value of obvious ODs stripping,and the maximum amount can be reached about 5~10min.The aggregation kinetics study showed that the GO in the three synthetic freshwaters would significantly aggregate with the increase of pH value under alkaline conditions,which was contrary to the existing theories.By means of experimental determination,calculation and molecular dynamics simulation,the promotion mechanism of GO aggregation at high pH was discussed from three aspects.First,the increase of pH value enhanced the deprotonation of oxygen-containing functional groups on FG and ODs,promoted the separation of ODs,and reduced the electrostatic repulsion between FG.Second,the promoted metal adsorption at high pH can offset the negative charges generated by the deprotonation,and made the residual negative charges decrease with the increase of pH,which reduced the stability of FG and ODs.Third,according to the molecular dynamic simulation,the stripped ODs can recombine to the edge of FG and eventually form FG-water-ODs aggregates by ODs-bridging.Therefore,the aggregation of GO was accompanied by deprotonation of functional groups,metal adsorption,and structural and surface properties transformation triggered by the stripping of ODs.The adsorption isotherm and kinetic studies showed that GO exhibited the same pHdependent adsorption regardless of whether the aromatic compounds carried ionizable functional groups or not: The adsorption capacity decreases gradually when pH < 12,and increases when pH > 12 with the adsorption rate increases significantly.The influence mechanism of ODs was revealed by experimental determination and molecular dynamics simulation.The results show that the adsorption affinity of ODs for aromatic compounds is significantly higher than that of FG.When pH>10,part of adsorbates desorbed with ODs stripping and the adsorption capacity and rate decrease slightly.When pH > 12,a large number of stripped ODs adsorbed aromatic compounds,and then recombine with FG to form large aggregates,thus the adsorption capacity and adsorption rate increase.In general,the increased adsorption capacity upon ODs stripping was mainly mediated by weakened electrostatic repulsion,increased π-π interaction,and increased hydrophobic interaction.And the significant aggregation of GO upon ODs stripping was responsible for the increased adsorption rate.In summary,ODs play a key role in determining the aggregation and adsorption behavior of GO and should be considered in the development of GO related nanomaterials and the evaluation of environmental impact.
Keywords/Search Tags:Graphene Oxide, Oxidation Debris, Aggregation, Adsorption, Molecular Dynamics Simulation
PDF Full Text Request
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