Preparation,Structure And Properties Of Graphene Oxide And Its Separation And Adsorption Materials

Graphene oxide(GO)is a graphene derivative with two-dimensional nano lamellae.Because it contains carboxyl,hydroxyl,epoxy and other groups,GO is easy to form composites with various properties through covalent or non covalent interaction with other substances.Due to the large specific surface area and good adsorption of GO,GO composites have great advantages in the preparation of filter membranes and adsorbents for sewage treatment.At present,GO composite materials used as filtration membrane and adsorption materials have some problems,such as poor filtration and adsorption efficiency,difficult secondary recycling after adsorption and so on.The structure and properties of GO have a great impact on the filtration and adsorption properties of the prepared composites.Therefore,the preparation of GO and the control of its structure and properties are still the focus of research.In this paper,aiming at the problems of filter membrane and adsorbent for sewage treatment,several GO composites were prepared.CGO/PVDF ultrafiltration membrane was prepared by combining GO with degraded collagen and polyvinylidene fluoride.GO/PAPSQ adsorbent was prepared by compounding GO with polyaminophenylsiloxane.GO and amino modified Fe3O4 were used to prepare magnetic adsorbent GO/Fe3O4@SiO2-NH2.The purpose is to improve the separation,recovery and reuse performance of GO based adsorbent and the membrane performance of PVDF composite ultrafiltration membrane.(1)The effects of graphite particle size and the amount of concentrated sulfuric acid,KMnO4 and NaNO3 on the structure and properties of GO prepared by Hummers method were studied.The purpose is to obtain high oxidation degree GO nano flakes and provide GO nano materials with excellent structure and performance for the preparation of filtration membranes and adsorbents for sewage treatment.The structure of GO was characterized by FTIR、XRD、Raman、UV-vis、SEM、XPS、TGA and AFM.The results show that:Increasing the dosage of intercalator concentrated sulfuric acid and oxidant potassium permanganate,and using sodium nitrate is conducive to improve the oxidation degree of GO and prepare high oxidation degree GO.Based on the weight of graphite,when concentrated sulfuric acid was 42:1 and potassium permanganate was 3:1,GO nano flakes with a thickness of 1～4 nm and containing hydroxyl groups,epoxy groups and a small amount of carboxyl groups were prepared.When the concentrated sulfuric acid was 84:1 and potassium permanganate was 6:1,the carbonyl and carboxyl groups in the prepared GO increased,the oxidation degree of GO increased,and the plane size of the lamella decreased.Through the synergistic action of sodium nitrate and concentrated sulfuric acid,the oxidant penetrates into the depth between graphite layers for oxidation.Increasing the spacing of GO layers makes GO form more defects and improve the oxidation degree of GO at the same time.When the dosage of concentrated sulfuric acid is 84:1,potassium permanganate is 6:1 and sodium nitrate is 2:1,the oxidation degree of GO of graphite with particle size of 325 mesh is the highest,and the C/O ratio is 2.724.This highly active GO is suitable for the subsequent preparation of GO composites.(2)GO/PVDF composite ultrafiltration membrane was prepared by degrading collagen and GO,and its structure and properties were studied.The waste leather shavings were degraded by alkali and enzyme to prepare degraded collagen.Then it was combined with GO to prepare collagen modified GO(CGO).Then GO or CGO was compounded with PVDF respectively.With polyvinylpyrrolidone(PVP)as porogen and N-methylpyrrolidone(NMP)as solvent,GO/PVDF and CGO/PVDF composite ultrafiltration membrane were prepared by solution casting method.The structure was characterized by a series of methods.The effects of GO and CGO contents on the membrane properties such as porosity,average pore diameter,water contact angle,pure water flux,BSA rejection and flux recovery were studied.The results show that with the increase of carboxyl content of CGO,the dispersion stability of CGO in water is improved,and the dispersion of CGO in PVDF is better.The porosity and average pore diameter of CGO/PVDF composite membrane are higher than that of GO/PVDF composite membrane.And with the increase of CGO content,it shows the trend of first increasing and then decreasing.When the addition of CGO was 1.0wt.%,the porosity of CGO/PVDF composite membrane reached 64.6%and the average pore diameter was 25.1 nm.CGO has better hydrophilicity than GO.The water contact angle of CGO/PVDF composite membrane is about 15°and 20°lower than that of pure PVDF membrane and GO/PVDF composite membrane,respectively.The pure water flux and flux recovery rate of CGO/PVDF composite membrane are larger than those of pure PVDF membrane and GO/PVDF composite membrane,and show a trend of first increasing and then decreasing with the increase of CGO addition.When the addition amount of CGO is 1.0wt.%,the pure water flux and flux recovery rate reach the maximum,which are 92 L·m-2·h-1 and 67.0%respectively.The antifouling property of CGO/PVDF composite membrane is higher than that of pure PVDF membrane and GO/PVDF composite membrane.(3)In order to improve the separation and recovery of GO composite adsorbent and improve the reuse efficiency,GO/PAPSQ composite was successfully prepared by acylation of organosilane micro powder PAPSQ and GO.The structure and morphology of GO/PAPSQ were characterized by a series of methods.The effects of pH,GO/PAPSQ dosage,adsorption time,initial concentration of methylene blue(MB)and temperature on the adsorption of MB in water by GO/PAPSQ were investigated,and the adsorption kinetics and thermodynamics were analyzed.The results showed that the adsorption capacity of GO/PAPSQ for MB increased with the increase of pH at 25℃.When the dosage of GO/PAPSQ is 500 mg·L-1 and the initial concentration of MB is 50 mg·L-1,the adsorption capacity is 90.53 mg·g-1.The experimental data of MB adsorption by GO/PAPSQ were fitted by isothermal equation.It was found that the linear correlation of Langmuir isothermal model was much higher than Freundlich model,indicating that the adsorption process of MB by GO/PAPSQ was monolayer adsorption.The adsorption kinetics accorded with the quasi second order kinetics.The adsorption of MB by GO/PAPSQ is an endothermic process,and the adsorption capacity can be improved by increasing the temperature.The adsorption-desorption cycle test showed that after 4 times of adsorption-desorption,the desorption rate of MB by GO/PAPSQ remained above 93%and the adsorption rate remained above 88%.It shows that GO/PAPSQ can be reused as MB adsorbent.GO/PAPSQ is easier to separate and recover from water than GO,which provides convenience for industrial application.(4)In order to further improve the separation and recovery of GO composite adsorbent,magnetic GO composite material GO/Fe3O4@SiO2-NH2 was prepared by amidation reaction between amino functionalized Fe3O4 and GO.The structure and morphology of GO/Fe3O4@SiO2-NH2 were characterized by a series of methods.The effects of pH,GO/Fe3O4@SiO2-NH2 dosage,adsorption time,MB initial concentration and temperature on the adsorption performance of MB in water were investigated,and the adsorption kinetics and thermodynamics were analyzed.The results show that the adsorption capacity of GO/Fe3O4@SiO2-NH2 to MB increases with the increase of pH at 25℃.When the dosage of GO/Fe3O4@SiO2-NH2 is 500 mg·L-1 and the initial concentration of MB is 50 mg·L-1,the maximum adsorption capacity is 74.62 mg·g-1.The adsorption data of MB adsorbed by GO/Fe3O4@SiO2-NH2 were fitted by isothermal equation.It was found that it was consistent with Langmuir isothermal model,indicating that the adsorption of MB by GO/Fe3O4@SiO2-NH2 was monolayer.The adsorption kinetics accorded with the quasi second order kinetics.The adsorption of MB by GO/Fe3O4@SiO2-NH2 is an endothermic process,and increasing the temperature is conducive to the adsorption.After 4 times of adsorption-desorption,the desorption rate of GO/Fe3O4@SiO2-NH2 to MB remained above 90%and the adsorption rate remained above 89%.It shows that GO/Fe3O4@SiO2-NH2 has good reusability.GO/Fe3O4@SiO2-NH2 has the advantages of easy filtration and magnetic field separation than GO,so it is more convenient for application.