The Research On Revoval Of Organic Dyes And Heavy Metals In Water By Static And Dynamic Adsorption Of Graphene Oxide Nanomaterials

Heavy metal and ionic dyes commonly co-exist and become the most dangerous source of environmental water pollution.Graphene has the potential in the application to remove heavy metal ions and ionic dyes in waste water because of its large surface area,but it can not be dissolved in common solvent.In this paper,graphene oxide(GO)was prepared using the Hummer method and its surface contains oxygen containing functional groups.GO can be dissolved in common solvent but can not be separated from solution after adsorption.Therefore,magnetic graphene oxide(MGO)was prepared by chemical co-precipitation method on the surface of oxidized GO particles.Its saturation magnetization is 31.8 emu/g,the MGO can be easily separated from aqueous solution.By scanning electron microscopy(SEM)and transmission electron microscopy(TEM),the surface of the synthesized MGO is smooth and there are many folds,and the surface was covered with white iron oxide particles.By Fourier infrared spectroscopy analysis,it was proved that the iron oxide was covered on the surface of magnetic GO,and the surface of MGO contained oxygen containing functional groups such as hydroxyl,carbonyl,carboxyl and epoxy groups.X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)was used to detect the lattice composition of the synthesized GO and MGO,thus confirming that the GO and MGO were successfully synthesized.The isoelectric point of the surface of MGO is 3.5.The surface of MGO adsorbent was positively charged when pH is less than 3.5,and was negatively charged when pH is greater than 3.5.Batch experiments on MGO adsorption metal ion Cd(?)and ion dyes including methylene blue(MB),orange G(OG)and Congo red(CR)in ultrapure water..Results showes that with increase of pH value,Cd(?)and MB adsorption quantity increases gradually,OG adsorption quantity adsorption reduces gradually,Congo red adsorption quantity increases to a maximum value and then decreases gradually when the pH value ranging from 3 to 10.The adsorption capacity increases with time,and then increases slowly until the equilibrium was reached when the pH value ranging from 3 to 10.The experimental data is in accordance with the quasi two order kinetic model.The adsorption of Cd(?)and ion dye by MGO in the ultrapure water was better fitted with the Langmuir isotherm model.When pH is 6,the maximum adsorption capacities on Cd(?),MB,OG and Congo red are 91.29mg/g,64.23mg/g,20.85mg/g and 143.62mg/g,respectively and the isothermal adsorption constants in the Langmuir model are 0.0160,4.4344,0.5301,and 0.0452,respectively.In tap water,the adsorption isotherms of both Cd(?)and ion dye by MGO are in accord with the Langmuir model.When pH is 6,the maximum adsorption capacities on Cd(?),MB,OG and CR are 59.69mg/g,58.08mg/g,20.48 mg/g and 287.57 mg/g,and are 65.39%,90.43%,99.23%and 200.23%compared with that in ultrapure water.However,at low concentration,the adsorption amounts of Cd(II)in tap water is much higher than that in ultrapure water.The MGO is suitable for the removal of Cd(?)in the actual water treatment.After reusable desorption for three times,the MGO adsorption capacities on Cd(?),MB,OG and CR are 28.63mg/g,25.15mg/g,11.88mg/g and 72.27mg/g respectivley and the corresponding values are 33.77%,42.25%,47.32%and 82.95%respectively,when compared with the first adsorption,thus demonstrating MGO exhibited a good reusability.To meet the needs of fixed-bed column adsorption,GO-coated sand was prepared.EDAX analysis and Raman spectra can prove that GO was coated the majority of the surface of individual sand granule and its thickness was estimated by TGA.The thickness can be estimated from weight loss data,the sand granules density,and the density of GO.In the experiment of fixed-bed column adsorption on Cd(?)and MB,it was observed that the column filled with clean sand had adsorption property,but the column filled with GO-coated sand exhibites better adsorption capacity.The continuous adsorption capacity of GO was affected by the flow rate of the column.The slower the flow rate is,the stronger the continuous adsorption ability of GO exhibites.In this paper,the adsorption properties of MGO in binary systems including Cd(?)-MB,Cd(?)-OG and Cd(?)-CR for simultaneous removal of heavy metals and ionic dyes were investigated.The adsorption capacity was suppressed for Cd(?)with increasing MB concentration and almost was not affected for MB with increasing Cd(?)concentration in Cd(?)-MB binary system.However,in Cd(?)-OG binary system,the assorption capacity was enhanced for OG with increasing Cd(?)concentration,the assorption capacity of Cd(?)was independent on the OG concentration,but dependent on the initial Cd(?)concentration.In Cd(?)-CR binary system,the experiment results are similar to the results obtained in Cd(?)-OG binary system.The experimental results appear to be closely related to the charge properties of the Cd(?)and the dye ion surface as well as the value of the isothermal adsorption constant B in the Langmuir model.