Study On Separation Performance Of Graphene Oxide Membrane For Removal Of Heavy Metals And Other Contaminants From Drinking Water

Nanofiltration（NF）membrane has a good application prospect in water supply systems.Graphene oxide（GO）is expected to be used to prepare new types of NF membranes.Focusing on the core problem of GO membrane separation for heavy metals and other pollutants,researches were carried out from two different views.Firstly,the effects and mechanisms of geometric parameters,edge modification,number and size of nanosheet on the performance of GO membrane were explored by molecular dynamics（MD）.Then,on the basis,experimental researches were carried out,and the preparation method was continuously improved to enhance the performance.The main results are as follows:（1）The effects of layer spacing and offset on the rejection rate of heavy metal ions were more significant than that on water permeability,while the influences of pore width on water permeability were also notable.The internal mechanism can be explained from the perspectives of the effective channel width of water molecules and ions as well as the changes of free energy barrier of particle migration.（2）The effects of different kinds of amino-compounds on the membrane performance were investigated.The negatively charged alanine and glycine groups could most effectively improve the rejection rate at the cost of water permeability.The effect of Ethylenediamine（EDA）on the rejection rate was better than that of non charged amino acid groups,and had little adverse effect on the water permeability.（3）MD studies showed that constructing membranes with small-sized GO nanosheets could increase the water molecular channel within certain limits.Because the energy barrier for water molecules to pass through the membrane was small,it could still maintain high water permeability.Due to the large energy barrier for Cd²⁺to pass through the membrane,the adverse effect on the rejection rate is relatively small.（4）The preparation method of the composite GO NF membrane was improved,that is,microfiltration membrane was used as the substrate,polydopamine was deposited as the adhesive layer,EDA was used for edge modification and chemical crosslinking,and polyethyleneimine（PEI）was loaded to strengthen the Donnan effect.The experimental study verified that the membrane constructed with small-sized SGO（small graphene oixde）nanosheets had better performance.When the loading amount of SGO was 7.5 mg/m²,the specific flux was 12.8 L/（m²·h·bar）,and the rejection rates for Pb²⁺or Cd²⁺were both more than 97%.（5）The partial reduction of SGO with NaOH under 70℃could remove more epoxy and hydroxyl groups without damaging carboxyl groups,which is conducive to controlling the layer spacing and improving the rejection performance.The membrane with only one layer of PEI on the outer surface had a good antifouling performance to bovine serum albumin（BSA）.However,its antifouling performance to humic acid（HA）and sodium alginate（SA）was poor.Nevertheless,the membrane PEI10-PSS10 covered with PEI and poly sodium styrene sulfonate（PSS）could simultaneously strengthen the Donnan effect for cations and anions,and improve the hydrophilicity so as to enhance the rejection rate and antifouling performance.If fouled by HA the specific flux of PEI10-PSS10 only reduced by 9.3%,and the specific Specific Flux Recovery Ratio was as high as 98.6%after being hydraulic cleaned.SA and BSA could hardly cause fouling for this kind of membrane.The results of this study have a great application potential in ensuring the safety of drinking water quality.