Mass Transfer Mechanism In Binary System Of Graphene Oxide-polyethylene Glycol

Graphene oxide(GO)has attracted more and more attention as a new material in the field of membrane separation due to its special physical and chemical properties,but its role and mechanism in membrane separation is not clear yet.In this paper,in order to overcome the firmness of the GO membrane,the desalted separation membrane was prepared by blending with the graphene-macromolecule polymer.In the experiment,the desalination effect of the binary composite membrane with different ratio of GO and PEG were compared with GO membrane and PEG membrane.And the mass transfer mechanism of water and salt in membrane separation process was analyzed.Through experiments,the mass transfer mechanism of the GO-PEG Composite membranes was explored whether the dominance of dissolution-diffusion mechanism or pore-size screening mechanism.In the experiment,GO membrane and GO-PEG composite membrane were prepared by pressure filtration method,while PEG membrane was prepared by UV cross-linking method.The properties of membrane materials were analyzed and characterized by the important parameters such as salt flux,permeability coefficient,water flux and salt rejection of different composite membrane materials.First,the membranes were characterized by characterization test.The membranes were characterized by contact angle(CA),Fourier transform infrared spectroscopy(ATR-FTIR),transmission electron microscopy(TEM),Raman spectroscopy,environmental scanning electron microscopy(SEM)and X-ray diffraction(XRD).The relationship between the hydrophobic,microscopic morphology,crystal form and surface functional groups of the composite membrane was established,and the preparation conditions were optimized by the method of mathematical statistics.The results showed that the graphene oxide exhibits a pleat-like lamellar structure and PEG can crosslink with graphene oxide.With the increase of PEG content,the interplanar spacing,membrane surface wrinkles and membrane roughness of GO-PEG composite membrane showed an increasing trend,but the crystal defects of carbon atoms in the membrane showed a decreasing trend.On the other hand,with the increase of PEG content,the thickness of the composite film gradually increased and the stability increased to some extent.Second,the membranes were tested for performance.During the experiment,four typical salt solutions of sodium chloride,magnesium chloride,copper sulfate and aluminum chloride were used for the performance test.The results showed that the salt flux of the composite membrane is much higher than that of the other three ions.Because the sodium ion hydrate ion radius is less than the other three ions and sodium ions and the weak force with functional groups on the GO.For the GO membrane,the salt flux in the 0.1 mol sodium chloride solution can reach 49.25 g MH,which is 9.68 times,11.17 Times and 3.85 times higher than that of the magnesium chloride,copper sulfate and aluminum chloride solution,respectively,under the same conditions.For GO-PEG composite membranes,the salt flux decreased gradually with the increase of PEG content.When the composite membrane PEG: GO = 5: 1,the salt flux of the four salt solutions decreased by 91.45%,60.18%,75.5% and 89.74% respectively compared with GO membrane.During the experiment,the salt flux of sodium chloride ion was higher than that of the other three ions when the concentration of salt solution was increased.In addition,the salt flux of the four kinds of salt ions decreased to a certain extent after removal of the base film,which indicated that the internal concentration polarization of the membrane material was effectively alleviated to a certain extent after removal of the base film.The results showed that the pure water flux of GO-PEG composite membrane showed a decreasing trend with the increase of PEG content.For example,the water flux of the composite membrane of PEG: GO = 5: 1 decreases from 32.82 LMH to 16.55 LMH compare to GO membrane.For the four kinds of salt solution,the composite membrane for the magnesium chloride,copper sulfate,aluminum chloride solution of the rejection is much higher than sodium chloride.This is because the sodium ion has a smaller radius of hydration than the distance between the GO nanosheets,so that it can pass through the composite membrane quickly.During the experiment,with the operating pressure increasing,the rejection of the membrane showed an increasing trend,and then became stable again,indicating that the membrane had an optimum trapping pressure.Increasing the concentration of the test solution will result in a downward trend in the rejection of the membrane,due to the effect of the Daonan effect between the ions and the membrane.It was found that the permeation volume flux of the four kinds of salt solution was higher than that of the pure water flux,but the permeation volume flux of the sodium chloride solution was smaller than that of the other three ions.The reason is that the Daonan effect of sodium ion between membranes was weaker than other salt ion.The composite membrane gradually decreases with the increase of PEG content and the change of flux volume.From the analysis of the permeability coefficient,the permeability coefficient of the composite membrane was closed to PEG membrane as the PEG content increases.It could conclude that the mass transfer model in the composite membrane is gradually approached to the dissolution-diffusion model.