Study On Removal Of Ions In Water By Graphene Materials

Recnetly,with the increased population,the fresh water on earth has become less and less.In addition,a large amount of sewage has been discharged desolately because of the rapid development of industrialization,and the sewage contains lots of heavy metal ions,which not only pollute the environment but also be harmful to humans,animals and plants.Therefore,how to remove the heavy metal ions in waste water and obtain more freshwater have become the focus.Adsorption and membrane separation have been gradually used for the dispose of heavy metal ions and seawater desalination because of the simple operation and high efficiency.Graphene has great application potential in the fields of sewage treatment and desalination due to its special two-dimensional structure,high specific surface area and other excellent physicochemical properties.In this paper,graphene was prepared by an improved chemical reduction method and characterized by a series of characterizations?SEM?XRD?Raman?FTIR?.It was used for the adsorption of chromium ions?zinc ions and manganese ions in solution and the adsorption mechanism was discussed.Then the graphene oxide/titania?GO/TiO₂?composite film and polyvinylidene fluoride-graphene/titania-polyvinylidene fluoride composite film?PGTP?were prepared by vacuum suction filtration and ultraviolet photocatalytic reduction.The morphology and structure of the composite membranes were characterized and they were used for the screening of salt ions?sodium ions?calcium ions?potassium ions?magnesium ions?in solution.The separation mechanism of the two composite membranes were discussed and the following conclusions were drawn:?1?The surface of graphene is irregularities and has a large number of wrinkles.Compared with graphene oxide,the graphene has smaller sheets.In addition,some functional groups?hydroxyl group?carboxyl group?epoxy group?still remain on the graphene.?2?At room temperature,the maximum adsorption capacity of chromium ions for graphene?10 mg?is 4.45 mg/g,and the removal rate is 8.9%;the maximum adsorption capacity of zinc ions is 55 mg/g,and the removal rate is 55%;the maximum adsorption capacity of manganese ions is 24.05mg/g,and the removal rate is 80.17%.Compared with the pseudo-first-order kinetic model,the pseudo-second-order kinetic model can better explain the adsorption process of these three heavy metal ions,and the adsorption is chemical adsorption.The theoretical saturated adsorption capacities of graphene to chromium ions,zinc ions,and manganese ions in solution are 4.42 mg/g,55.23 mg/g,and22.42 mg/g respectively.?3?Through the SEM of the composite membranes,it can be found that the protonated titania particles have been successfully inserted into the interlayers of two composite membranes,which are still intact after the experiments.The thickness of the GO/TiO₂composite film and the functional layer of PGTP composite film are 148?m and 129?m,respectively.?4?The removal rates of GO/TiO₂ composite membrane for sodium?calcium?potassium ions in solution are more than 99%.The removal rates of PGTP composite film for sodium?calcium?potassium?magnesium ions in the solution are as high as 99%.