The Adsorption And Aggregation Of Graphene Oxide On Environmental Media

Graphene oxide(GO)was the most important type of graphene because of its unique physical and chemical properties.With the widespread application of GO and GO-based materials,it would be released into the environment easily in the production,use and disposal process.Strong reactive sites,high surface area,and abundant oxygen-containing functional groups made GO interact with environmental media easily.The interaction between GO and environmental media,such as minerals and oxides,would affect its fate and toxicity in the environment.In this work,we investigated the adsorption and heteroaggregation of GO with environmental media ssystematacially.The main conclusions show as follows:(1)We have studied the influnce of size on U(?)adsorption and desorption on GO.Batch experiment was conducted to study the adsorption and desorption of U(?)on GO with two different size(2-5 ?m and 100-300 nm)at different solution chemistry(pH,coexisting ions,humic acid and temperature).Faster adsorption rate and better adsorption capacity were displayed on smaller size GO.Additionally,U(?)desorption is hysteretic,more so with the smaller size GO.These results showed that GO size played a significant role in determining its adsorption and desorption behavior.(2)We have given a focus on functional group of GO impact on adsorption capacity,include types and content of functional groups.Phosphate-functionalized graphene oxide(PGO)was prepared by grafting triethyl phosphite onto the surface of GO using Arbuzov reaction.The application of the PGO to remove U(?)from aqueous solution was investigated with a maximum adsorption capacity of 251.7 mg·g-1 at pH 4.0 ± 0.1 and 303 K.Moreover,experimental results gave a better removal efficiency toward U(?)on PGO surface than other heavy metal ions at acidic solution,indicating the selective extraction of U(?)from environmental pollutants.Furthermore,we have paied attention to the content of GO functional group effected its adsorption capacity.GOs with different oxidation degrees were synthesized by ozone treatment.The ozonized GOs were further applied as Co(?)adsorbents from aqueous solutions.The adsorption results showed that this adsorption processes were endothermic and spontaneous,and followed the pseudo-second-order kinetics and the Langmuir adsorption models.As expected,increased adsorption capacities were observed by GOs with higher oxidation degrees.(3)We have investigated the interaction between GO and minerals.Aluminum oxide(Al2O3)was selected as a natural solid particle representative to mimic the interaction between GO and environmental media.Batch experiments were conducted in solution with different pH and ionic strength.Results indicated that the attachment capacity of large GO onto Al2O3 particles was greater than that of small GO.Besides,kaolinite and goethite were choosen as a representative of environmental media.Adsorption and desorption were used to study the reversibility of interaction between GO and goethite/kaolinite.The electrostatic attraction and hydrogen-bonding interaction dominated the interaction process between GO and minerals.These findings are important for better understanding in the environmental fate and transport of GO.(4)Attapulgite(ATP)as a typical fibrillar mineral was chosen to investigate the impact of interaction between ATP and GO on the adsorption of U(?).The adsorption capacity order was GO>ATP-GO>ATP,which achieved from adsorption isotherms,indicating adsorption capacity was related with interaction between ATP and GO.Then systematical investigation on U(?)adsorption at various environment factors(time,pH,and ionic strength)was employed on single adsorbent(ATP)and heterogeneous aggregate(ATP+GO).Adsorption kinetics displayed both U(?)adsorption on ATP and ATP+GO were better fitted with pseudo-second-order kinetic model than the first-order kinetic model.The solution pH and ionic strength had a great influence on interaction between ATP and GO.This study provided new insights into the impact of interaction between minerals and GO on the adsorption of pollutant.