Preparation Of Graphene And Iron Oxide Adsorbent Materials And The Removal Of Cr(?) From Groundwater

In recent years,the pollution of heavy metals in groundwater has been one of the concerned problems.Due to its high toxicity,easy mobility and difficult treatment,hexavalent chromium contamination has been an important problem in groundwater.Adsorption is an effective technology for removing hexavalent chromium from groundwater because of its simple operation,high treatment efficiency and less secondary pollution.However,one of the key problems for this technology is to develop efficient and easily recoverable adsorbents.The excellent physical and chemical properties of graphene oxide make it popular in the water treatment field,but the adsorption capacity of graphene oxide for hexavalent chromium is small,and the separation after treatment is difficult.Both of the problems needs to be solved.This study aims at developing graphene and iron oxide materials to enhance the removal capacity and separation performance of graphene oxide.Using graphene oxide as the base material,Fe₂O₃/RGO was prepared by loading Fe₂O₃ onto graphene oxide surface through hydrothermal method.The best material was selected by comparing the chromium removal performance of Fe₂O₃/RGO made at different preparation conditions.In order to make the separation and recovery of materials more convenient,the modified preparation was carried out to obtain the magnetic graphene.The effects of initial chromium concentrations,solution pH and the treatment time on the chromium removal performance of graphene composites were investigated.The mechanisms of the chromium removal were discussed by means of SEM,FTIR and XPS characterization.The main results are as follows:The hexavalent chromium capacity capacity of Fe₂O₃/RGO increaseed with the increasing of initial chromium concentrations and decreaseed with the increasing of pH.The increasing of temperature could promote the chromium removal capacity of Fe₂O₃/RGO.The results of kinetic fitting showed that the pseudo-second-order kinetic model described the adsorption process better than the pseudo-first-order kinetic model;the Langmuir model had a higher fitting degree to the experimental data.When temperatures were at 288 and 298 K,the maximum Langmuir removal capacity of Fe₂O₃/RGO was 41.67 and 51.81 mg/g,respectively;the removal of hexavalent chromium by Fe₂O₃/RGO was a spontaneous endothermic process.XPS and FTIR analysis showed that the hexavalent chromium removal of Fe₂O₃/RGO was a process of electrostatic adsorption and chemical reduction.In the process of removing hexavalent chromium using magnetic graphene,the removal capacity also increaseed with the increasing of initial chromium concentrations and decreased with the increasing of pH;the coexisting ions HCO₃^2-and CO₃^2-reduced the removal capacity of magnetic graphene.The removal process fitted the pseudo-second-order kinetic model better;the theoretical maximum removal capacities of the magnetic graphene?prepared for 8 and 16 h?were 23.25 and 25.22mg/g,respectively.Similarly,the hexavalent chromium removal of magnetic graphene is a process of electrostatic adsorption and chemical reduction.