| Graphene oxide?GO?is an intermediate product formed during the extraction of graphene from graphite film via chemical oxidation.GO has similar hexagonal carbon rings to those in graphene,but many oxygen-containing functional groups,such as carboxyl?O=C-O?,hydroxyl?C-O?,and epoxy?C-O=C?groups,have been detected at the edges and surfaces of GO nanosheets.Under certain conditions?thermal reduction,chemical and electrochemical reduction,etc.?,GO can be reduced to reduced graphene oxide?r-GO?.Compared with GO,the adsorption performance of r-GO on heavy metal ions in water was significantly reduced.The availability of GO electrochemical reduction suggests that the oxidation-reduction potential?ORP?play important roles in GO structure and composition transformation.Based on the characteristics of the changes in the redox potential domain that are common in the natural water environment and water treatment process,it is necessary to study the stability of the adsorbed heavy metal pollutants adsorbed on the GO surface into the water.In this study,an electrochemical method was applied to provide an adjustable redox potential.The characteristics of the reduction and conversion of oxygen-containing functional groups on GO surface under the simulated ORP conditions were studied.Pb???was selected as the target heavy metal pollutant,and studies of the GO reduction characteristics and the Pb???adsorption kinetics on the GO/r-GO surface were performed.The characteristics of Pb???desorption from GO-Pb???under different reducing potential were also investigated.The results will help us help us understand the potential ecological risks when GO is applied as an adsorption material and the treatment of heavy metal pollutants in water environment.The main research results are as follows:?1?GO has acidic characteristics in aqueous solution,and can maintain good dispersibility in water environment with pH of 3-7.Thermogravimetric and transmission electron microscopy analysis shows that OCGs are unevenly distributed on the surface of GO,and the particle size is about 30 nm,the mass percentage of OCGs on GO was?33%..?2?The adsorption site for Pb???on the GO surface was related to the OCGs.The pseudo-secondary adsorption kinetics and the Langmuir adsorption isotherm model can better fit the adsorption process of GO on lead,indicating that the adsorption belongs to monolayer adsorption.After GO is electrochemically reduced to r-GO,the content of surface OCGs is significantly reduced.and the maximum adsorption capacity of GO for lead ions decreased from 931.66 mg·g-1 to 714.78 mg·g-1.?3?The concentration of lead ions in the GO-Pb???solution changes with the potential.The release of adsorbed Pb???from GO-Pb???increased gradually when the potential dropped from 0 to-600?mV.The content of released Pb???decreased when the potential reached-700?mV because of the reduction of Pb???to insoluble Pb?0?.?4?Cyclic voltammetry?CV?analysis demonstrated that there are three reductive potentials,e.g.-760,-400,and-120?mV,related to the reduction of OCGs.X-ray photoelectron spectroscopy indicated that the reducing sequence of three OCGs,namely C-O,C=O and O-C=O groups,depended on the applied potential. |
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