Study On Adsorption Performance Of Magnetic Graphene Composites For Organic Pollutants

Graphene(G)is two-dimensional monolayer with a honeycomb-like aromatic structure.G possesses a great specificsurface area and a huge π-π conjugated system,which makes G an efficient adsorbent in many fields.However,the stable chemical property,indissolubility with solvents and the strong π-π interaction between the layers,lead to the irreversible agglomerates of G in aqueous solution and restrict the further application.G can be composited with some other materials,which not only can improve dispersion of G in solution,but also gives some novel characteristics to composites.In this paper,three G composites were systhesized and the adsorption performance of composites for environmental pollutants as adsorbents were investigated.Graphite oxide(GO)was prepared via the modified Hummer method,and subsequently attached onto Fe2+ sheets by the electrostatic interaction between Fe2+ and GO.Three dimensional Fe3O4-graphene composite(3D-G-Fe3O4)was obtained after reduction and coprecipitation,and characterized by Fourier Transform infrared spectroscopy,thermogravimetric analysis and transmission electron microscope.According to the adsorption ability of G and the magnetic separation property of Fe3O4,3D-G-Fe3O4 can effectively be used as magneticadsorbent for aniline.The results showed that different analytes had different adsorption behaviors.p-nitroaniline,N,N-dimethylaniline and 2,6-diisopropylaniline were fitted to Langmuir isotherm model,while 1-naphthylamine and diphenylamine were fitted to Freundlich isotherm model,and the maximum adsorption capacity were 23.23 mg/g and 97.84 mg/g.The adsorption processes of 5 aniline compounds were followed preudo-second order kinetics model.In order to further verify the adsorption mechanism of G,three dyes(methylene blue,methyl orange and rhodamine B)with negative or cationic charges and four antibiotics(norfloxacin,enrofloxacin,sulfamethazine and tetracycline)were selected as the target analytes.The adsorption efficiency of dyes can reach more than 90% and the adsorption efficiencies of norfloxacin,enrofloxacin,sulfamethazine and tetracycline were close to 100%.The results showed that adsorption mechanism for aniline of 3D-G-Fe3O4 were π-π conjugation between the adsorbent and the adsorbate.PIL-G-Fe3O4@SiO2composites were synthesized and characterized by FT-IR,SEM,VSM and Zeta potential.Anionic dye(methyl orange)and cationic dyes(methylene blue and rhodamine B)were selected as analytes to investigate the adsorption mechanism between PIL-G-Fe3O4@SiO2 and analytes.The results showed the structure and charged property of analytes had a significant influence on the adsorption.Because of the load of PIL,the adsorption efficiencyof PIL-G-Fe3O4@SiO2 for anionic dyes was enhanced and higher than that of 3D-G-Fe3O4,which indicated the electrostatic attraction between PIL and analytes,the π-π interaction between G and analyte were all studied.Under optimized conditions,the adsorption of acid red,allura red and sunset yellow was fitted to Langmuir adsorption model and secondary kinetic adsorption model.(PIL/GO)n-Fe3O4@SiO2composites were prepared by layer-by-layer assembling of PIL and GO on Fe3O4@SiO2 surface,and characterized by FT-IR.Using five dyes(methylene blue,neutral red,tempting red,orange G and amaranth)as modelanalytes,the adsorption performance of(PIL/GO)n-Fe3O4@SiO2 was studied.The results indicated that the layer number had anevident effect on the adsorption and that(PIL/GO)n-Fe3O4@SiO2 adsorbent with four bilayer of PIL and GO prorided high adsorption for both anionic dyes and cationic dyes.The good adsorption performance for anionic dyes was ascribed to the electrostatic interaction between PIL and analytes,while the π-π interaction between GO and analytes was responsible for the good adsorption of cationic dyes.