The Adsorption Of Dye Molecule By Graphene Oxide-based Composites:a Combined Experimental And Molecular Simulation Study

Dyes are widely used in the manufacturing process of plastics,rubber,cosmetics,paints and so on.However,most dyes are toxic and have the possibility of carcinogenesis,which seriously threatened human health and ecological security.Therefore,before dyes discharging into the natural environment,it has become very urgent to use economically feasible and environmentally friendly methods to treat dye wastewater.In recent years,the technology for purification and repair of dye wastewater has attracted extensive attention and has been vigorously developed.Among them,based on the advantages of convenience,ease of operation,wide applicability,and insensitivity to toxic substances,the adsorption method is recognized as a green and environmentally friendly technology and a highly competitive treatment method.In dye adsorption technology,the choice of adsorbent is very important.Graphene oxide(GO)has been widely used as an adsorbent to remove dyes from water because of its super high specific surface area,excellent water dispersion and various oxygen-containing functional groups.Although GO has many advantages,the separation of suspended GO after adsorption and the inevitable secondary pollution in wastewater treatment hinder its industrial application,so there is an urgent need to develop a new GO-based adsorption material that can be used repeatedly.Magnetic separation technology is considered to be a promising,recyclable and high economic adsorption method for the organic pollutants removal in wastewater.Correspondingly,cobalt ferrite(CoFe2O4)has been applied in the field of environmental protection because of its moderate magnetism and good chemical stability.In this paper,magnetic CoFe2O4/GO adsorption materials with high adsorption capacity and reusability after treatment were prepared through experiments firstly.Then,combined with molecular simulation methods,the theoretical mechanism of adsorption was revealed from a microscopic perspective,which provided the basis for the modification of GO-based adsorption composites.The main research contents include the following two parts:(1)In the experiment,the magnetic CoFe2O4/GO adsorbent was prepared by an easy-to-operate and environmentally friendly hydrothermal method.The cationic dyes methylene blue(MB),rhodamine B(RhB)and anionic dye methyl orange(MO)were selected for the measurement of adsorption effect.The experimental results show that CoFe2O4/GO composite material shows selective adsorption characteristics,the equilibrium adsorption capacities of MB,RhB and MO are 230.95,197.46 and 33.85 mg/g,respectively.The equilibrium adsorption capacities of GO are 211.1,106.7 and 33.88 mg/g,respectively,while the synthesized pure CoFe2O4 nanoparticles have almost no adsorption effect,and the adsorption capacities of the three dyes are about 2-3 mg/g.It shows that the adsorption of the three dyes in the CoFe2O4/GO composite mainly comes from GO.The addition of CoFe2O4 can enhance the absorption effect of cationic dyes.At the same time,the reusability of CoFe2O4/GO adsorbent was explored.The removal efficiency of CoFe2O4/GO composite materials can be maintained at about 96.8%,87.2%and 73.3%after two,three,and four adsorption-desorption cycles,which has good reuse performance.(2)In theory,the adsorption mechanism of MB,RhB and MO dyes on GO was studied by molecular simulation.Molecular dynamics(MD)simulation was used to study the conformational change and the adsorption energy(Eads)value of GO adsorption dye molecules.The order of interaction with the dye was MB>RhB>MO,which was in agreement with the experimental results.The modeling analysis shows that the GO surface interacts electrostatically with the dye molecules,and the negatively charged oxygen-containing functional groups on the surface exhibits better adsorption for cationic dyes;The,π-π interaction between the dye molecule and GO is also beneficial to its adsorption;The vacancy defects on the GO surface and oxygen-containing functional groups will also affect the adsorption effect.According to the Eads,the presence of defects will slightly increase its adsorption effect;Among three oxygen-containing functional groups of carboxyl(-COOH),hydroxyl(-OH),and epoxy(-CH(O)CH-),-COOH has the best adsorption effect on dyes.At the same time,quantum mechanical simulation analysis was used to predict the activity of the dye molecules and the sites where the dye molecules adsorbed,which further revealed the reason for the adsorption effect and provided a theoretical basis for the modification of GO-based adsorbent materials.