Adsorptive Removal Of Trace Rare Earth Ions From Water By Graphene Oxide-Based Hydrosols In Dialysis Bags

To further improve adsorption performance of graphene oxide?GO?hydrosol for trace rare earth ions?REs?,aiming at the uncertainty of the adsorption active sites on GO surface,especially the significant issue about these incompletely-exposed inherent adsorption active sites on GO surface due to the spontaneous stacking of GO nanosheets during the adsorptive remediation of REs wastewater,the dissertation was dedicated to the systematical studies from two aspects.In the first part,to ascertain the dominant adsorption active sites on GO surface,the relationship between the content of carboxy groups?-COOH?on GO surface and its adsorption capacity for trace REs was established by comparing the adoption performance of GO for REs before and after carboxylation of GO,which is favorable to pointing out a clear direction for enhancing adsorption properties of GO.In the second part,highly stable carbon nanotubes?CNTs?/GO and WO₃·2H₂O/GO hydrosols were prepared by dispersing CNTs and WO₃·2H₂O into GO hydrosol under ultrasonication,respectively,based on their excellent dispersibility in GO hydrosol.As a result,their adsorption performances were observed to be greatly enhanced after formation of GO-based hydrosols as the space steric hindrance of CNTs and WO₃·2H₂O can effectively expose more adsorption active sites by preventing GO nanosheets from restacking to great extent.In this dissertation,the effects of pH value,contact time?t?,temperature?T?and the initial REs concentration?C₀?on adsorption equilibrium were dealt with systematically,and the kinetics and thermodynamics of adsorption process were analyzed,respectively.In the end,the adsorption-desorption regeneration abilities of GO-based hydrosols were also evaluated.The results demonstrated that under the condition of pH=5.8 and T=303K,the theoretical maximum adsorption capacities of carboxylate GO?GO-COOH?for Nd?III?and Dy?III?were 408.16 mg·g^-1 and 354.61 mg·g^-1,respectively,which were higher than those of GO for Nd?III?(338.98 mg·g^-1)and Dy?III?(316.46 mg·g^-1)by 23.24%and 29.38%,respectively,and suggested that carboxyl groups were the key adsorption activity sites on GO surface.The CNTs/GO hybrid hydrosol with mass ratio between CNTs and GO(M_CNTs:M_GO=1:6 h)exhibited the theoretical maximum adsorption capacity of 534.76 mg·g^-1 for Gd?III??pH=5.9,t=60min,T=303K?with a leap of 86.42%compared to GO(286.86 mg·g^-1).The WO₃·2H₂O/GO hybrid hydrosol with mass ratio between WO₃·2H₂O and GO(M_WO3·2H2O:M_GO=1:2)possessed the enhanced maximum adsorption capacities for Nd?III?(429.18 mg·g^-1)and Dy?III?(400.00 mg·g^-1),higher than those of WO₃·2H₂O for Nd?III?(406.50 mg·g^-1)and Dy?III?(361.01 mg·g^-1),respectively.Thus,it can be concluded that CNTs/GO and WO₃·2H₂O/GO hybrid hydrosols exhibited the remarkable synergistic enhancement effect for REs adsorption.Moreover,the thermodynamic and kinetic studies on adsorption revealed that the adsorption of the above-mentioned REs on the investigated GO-based adsorbents was an endothermic,spontaneous and monolayer adsorption process,which more well fitted the pseudo-second-order model and Langmuir adsorption model.Significantly,the desorption ratios of the REs-saturated GO-COOH,CNTs/GO and WO₃·2H₂O/GO hydrosols in the dilute nitric acid?pH=1.0±0.1?were about 80%,indicating the excellent regeneration performance.In summary,this work investigated a series of GO-based hydrosol adsorbents for highly efficient,regenerable and re-pollution free removal of trace REs from water,which provides some novel facile approaches for improving the adsorption ability of GO hydrosol and promises of extensive application in the treatment of heavy metal ions-containing wastewater.