Graphene Oxide:Preparation By Plasma Technology,O-/N-/S-Functionalization,and U（Ⅵ） Enrichment

The development of new materials for U（Ⅵ）enrichment with high selectivity is of great significance for the U（Ⅵ）pollution control and uranium extraction from seawater.In order to explore the effect of different functional groups in U（Ⅵ）adsorption,graphene oxide（GO）is prepared by a modified Hummers method.And on GO basis,O-containing（furan）,N-containing（pyrrole and aniline）,N-containing（thiophene）functionalized GO are prepared by plasma grafting technology,naming furan/GO（FGO）,pyrrole/GO（PGO）,aniline/GO（AGO）and thiophene/GO（TGO）composite adsorbents.The mechanism of O-/N-/S-containing functional groups in U（Ⅵ）enrichment are evaluated through comparing the enrichment properties of raw-GO and functionalized GO.The structural properties of the materials are analyzed by XRD,SEM,XPS,FT-IR,BET and other characterization methods.Taking pH value,ion interference,adsorption time and temperature as medium variables,and the adsorption capacity of materials for U（Ⅵ）is studied through adsorption experiments,meanwhile the mechanism of adsorption process is explored by adsorption isotherm model,kinetic adsorption model and thermodynamic parameters.On the basis of the experiment,the AGO has been studied on the toxicity of human liver cells and the toxicity of fish.The specific experimental study and conclusions are as follows:（1）On the basis of GO,furan,pyrrole,aniline and thiophene are grafted onto GO surface by radio frequency plasma technology.SEM,XRD,EDS mapping,XPS,BET and other characterization methods show that plasma can modify the surface of GO,and the modified O-/N-/S-functional groups are uniformly grafted on the surface of the GO material,which proves that FGO,PGO,AGO and TGO are successfully prepared.According to TGA analysis,the functional group grafting rates of FGO,PGO,AGO and TGO are about 12.28%,4.99%,7.53%and 7.72%,respectively.And plasma modification will reduce the specific surface area of the microporous material GO.While the grafted aniline will not only reduce the specific surface area but also increase the pore width of the material,and finally be modified into a mesoporous material.（2）The adsorption experiments show that FGO,PGO,AGO and TGO all have great adsorption performance for U（Ⅵ）.The adsorption process of U（Ⅵ）on FGO,PGO,AGO and TGO all conformed to the pseudo-second-order kinetic equation and Langmuir model,indicating that the adsorption all are monolayer chemisorption..Considering the varietof environmental factors,the selective adsorption capacity of the materials are:AGO>FGO>TGO>PGO.AGO not only has excellent selective adsorption capacity but also good recycling capacity,the AGO still has more than 80%adsorption capacity after 5 cycles of adsorption.Thermodynamics indicates that the adsorption of U（Ⅵ）by AGO is an endothermic reaction.（3）The study on the adsorption mechanism of U（Ⅵ）shows that U（Ⅵ）is weakly physical adsorption on all materials due to the protonation effect at low pH,which is also the reason for the material to desorption.In the weak acid environment,the mechanisms between different functional groups with UO₂²⁺lead to different affinities,resulting in differences in adsorption properties of materials.comparing with PGO,FGO and TGO,AGO has great selective coordination ability with U（Ⅵ）.（4）Toxicity experiments show that all materials have no toxicity or low toxicity at low concentrations,and obvious toxicity at high concentrations.The toxicity of different materials:TGO>PGO>AGO>FGO.After adsorption of U（Ⅵ）with FGO,PGO,AGO and TGO,the toxicity of the materials and U（Ⅵ）could be reduced.Cells imaging profiles also indicate the low toxicity of the AGO material.（5）The excretion-promoting experiment of fish shows that AGO can effectively reduce the content of U（Ⅵ）in fish meat and promote the excretion of U（Ⅵ）from the body.Experiments also proved that U（Ⅵ）is mainly enriched in bones of fish.After comprehensively comparing the adsorption performance and toxicity of four functionalized GO materials,it is found that AGO is a highly efficient,selectively adsorbed and environment-friendly material,and has the potential for practical sewage treatment applications.