Study On Adsorption Of The First Category Metal Pollutants From Aqueous Solution By Magnetic Graphene Nano Material

The treatment of the first heavy category metal pollutants in water is of great concern now.Adsorption has been widely used in the removal of pollutants, but the traditional adsorbent isdifficult to recover. In this study, efficient adsorption of the first category metal pollutants wereperformed based on magnetic graphene nanocomposites. Magnetic graphene compositesmaterials were prepared by compositing graphene with magnetic material. We have preparedCoFe2O4-reduced graphene oxide (CoFe2O4-rGO), CoFe2O4-chitosan/reduced graphene oxide(MCGS) successfully, and used them to study the adsorption of the first category metalpollutants. The main research contents and results are as follows:(1) Magnetic graphene composites materials were prepared by compositing graphenewith magnetic material and characterized by SEM, FTIR, XRD, BET, Zeta potential andmagnetic separation effect characterization. The results indicate that the magnetic material wasattached to the surface of the graphene, and the CoFe2O4-rGO and MCGS were successfullyprepared.(2) The CoFe2O4-rGO was used for the study of metal ions in the aqueous solution, Pb(II)and Hg(II) were selected as the representative to consider the optimum adsorption conditions(such as pH value, adsorption time, adsorbent dose). Adsorption mechanism was investigatedby adsorption kinetic, adsorption isotherm and adsorption thermodynamics. The resultsshowed:(i) Pb(II), the best amount of sorbent was8mg, the best adsorption time was80min,and the best pH value was5.3. Removal efficiency could reach above80%.(ii) Hg(II), thebest amount of sorbent was7mg, the best adsorption time was60min, and the best pH valuewas4.6. Removal efficiency could reach above80%. The adsorption kinetics data well fit thepseudo-second-order equation, which indicated the adsorption process was mainlychemisorption. The theoretical maximum adsorption capacity was123.3mg/g and27.91mg/g,respectively. At different temperatures, adsorption of Pb(II) and Hg(II) onto CoFe2O4-rGO allagreed well to the Langmuir isotherm models, which illustrated the adsorption process wasmonomolecular layer and uniform on the surface. Thermodynamic studies illustrated theadsorption process was exothermic. The temperature increasing was not favorable to theadsorption reaction.(iii) We also study the adsorption of CoFe2O4-rGO on the other heavy metals, like Cd(II), Cr(III). However, the adsorption efficiency is very poor.(3) The MCGS was used for the study of metal ions, Hg(II) was selected as therepresentative to consider the optimum adsorption conditions (such as pH value, adsorptiontime, adsorbent dose). The optimum adsorption conditions were considered, and theadsorption mechanism was investigated by adsorption kinetic, adsorption isotherm andadsorption thermodynamics. The results showed: the best amounts of sorbent were6mg, thebest adsorption time was240min, and the best pH value was7.0, and removal efficiencycould reach above80%. The adsorption kinetics data of Hg(II) fitted the pseudo-second-orderequation well, which indicated the adsorption process was mainly chemisorption. Thetheoretical saturation adsorption capacity of Hg(II) adsorption onto MCGS calculated by thepseudo-second-order equation was182.8mg/g. Under different temperatures, adsorption ofHg(II) onto MCGS was agreed well to the Langmuir isotherm models, which illustrated theadsorption process was monomolecular layer and uniform on the surface. Thermodynamicstudies of Hg(II) was showed: G <0, H>0. Which illustrated the adsorption process wasendothermic and spontaneous, and higher temperature was beneficial to the phosphateadsorption. The positive values of S suggested that the entropy turned larger and thedisturbance degree was higher during the adsorption process.The MCGS was also used for the study of other metal ions, such as Pb(II), Cd(II),Cr(III). However, the adsorption efficiency of such metal cations were very low, so we had nostudy about them next.(4) The effect of different types of desorption agent with the desorption of metal ionsfrom two magnetic graphene composites materials were studied. Under the adsorption-desorption experiment of CoFe2O4-rGO,0.01mol/L HCl solution was selected as thedesorption of Hg(II), with five recycling experiment, the adsorption efficiency was also veryhigh.