Preparation Of Functionalized Graphene Oxide And Their Adsorption Properties Study

As a novel two dimension carbon nanomaterials, graphene oxide(GO) composed of a single layer of sp2 and sp3 network of covalently bonded carbon atoms bearing various oxygen functional groups on their basal planes and edges,and owning a large delocalized π-electron system. Besides, GO have much larger specific surface areas and high mechanical stability. The unique structures and properties of GO make it available to bind heavy metals and organic compounds, as well as to keep high stability in acid or alkali solution.Therefore,GO is considered to be a super absorbent. However, GO sheets tend to aggregate during removing organic compounds and metal ions due to the decreased electrostatic repulsion between oxygen-containing groups, leading to the sharp decline of specific surface area, and thus resulting to the decrease of the adsorption performance. In addition, separating and recycling GO sheets after adsorption is very difficult due to its nanometer-sized volume, which greatly limits its application. Therefore, it is of great significance to improve the adsorption performance and the recycling ability of GO based materials by the functional modification of GO. However, the preparation of GO based materials still faces several challenges that are needed to be solved. For example,the synthesis process is quite complex; a large number of organic solvents and toxic substances are used; the adsorptive groups functionalizing on the surface of the GO are less,which result in the decrease of adsorption capacity. To solve these problems, GO based materials as high efficiency adsorbents for heavy metal ions were synthesized by a simple and green self-assembly method. For organic pollutants adsorption material, supermolecule material were introduced to the surface of GO through covalent modification to improve the adsorption performance for organic pollutants in waste water. The main contents of this dissertation lie as follows:(1)Novel graphene oxide(GO) membranes were prepared by induced directional flow, their structure were characterized by SEM、TEM、XRD、FT-IR、Raman. The results indicated that GO membranes have highly ordered layered structure. The interlayer spacing of GO membranes is larger than that of GO due to the support of PVA. The effects of pH, ionic strength, contact time and metal ion concentration on Cu2+, Cd2+ and Ni2+ sorption as well as regeneration of the adsorbents were investigated. The results indicated that the adsorption of Cu2+, Cd2+ and Ni2+ onto GO membranes was greatly influenced by the pH and weakly affected by the ionic strength. The adsorption isotherms for Cu2+, Cd2+ and Ni2+ were well fitted by the Langmuir model. The maximum adsorption capacities of the GO membranes for Cu2+, Cd2+ and Ni2+ were approximately 72.6, 83.8 and 62.3 mg/g, respectively. The adsorption kinetics of Cu2+, Cd2+ and Ni2+ onto GO membranes followed the pseudo-second-order model. The adsorption equilibrium was reached within 15 min. the adsorption capability for Cu2+, Cd2+ and Ni2+ decreased only after the 6th cycle to approximately 10%, 12% and 21%, respectively.(2)On the basis of adsorption of Cu2+, Cd2+ and Ni2+ from aqueous single metal solutions onto GO membranes, the adsorption behavior and mechanism of Cu2+, Cd2+ and Ni2+ onto GO membranes were systematically investigated in binary and ternary solutions using batch experiments. The results indicated that all of the isotherms results for Cu2+ indicated that GO membranes exhibited good selectivity in the adsorption of Cu2+ over Cd2+ and Ni2+. The uptakes followed the order of Cu2+ > Ni2+ > Cd2+ in binary systems. For the ternary system, the order of the amount adsorbed was Cu2+ > Cd2+ > Ni2+. Previously adsorbed metal ions on GO membranes could be displaced by subsequently adsorbed metal ions from the solution. The difference in the hard and soft acids and bases of Cu2+, Cd2+ and Ni2+ was identified as the main reason for GO membranes to be able to selectively adsorb favorable metal ions during competitive adsorption in a binary system. This interaction mechanism between the favorable component and other metal ions could be the primary cause of the direct displacement.(3)Novel poly(vinyl alcohol)/graphene oxide(PVA/GO) nanofibers were prepared by electrospinning and used as adsorbents for the removal of aqueous Cu2+ and Cd2+. Their structures were characterized by SEM、TEM、XRD、FT-IR、Raman. The results showed that PVA/GO nanofibers contain abundant oxygen functional groups and its surface are smooth, continuous and no beads. GO(up to 20 wt%) could be uniformly dispersed in PVA nanofibers and that PVA/GO nanofibers possess good adsorption ability for Cu2+ and Cd2+. The factors influencing their adsorption behavior, such as pH, ionic strength, temperature, contact time and metal ion concentration, as well as their regenerability, were investigated. The adsorption isotherms for Cu2+ and Cd2+ were well fitted by the Langmuir model. It is found that the carboxyl and the carbonyl groups, as well as the π-electron systems, of GO on the surface of the nanofibers mainly participated in the adsorption of Cu2+ and Cd2+. Adsorption equilibria were reached in a short time, and the adsorption processes followed the pseudo-second-order kinetic model. The desorption efficiency for Cu2+ and Cd2+ decreased only after the 8th cycle to approximately 15.5% and 13.8%, respectively.(4)A beta-cyclodextrin-functionalized graphene oxide(GO-β-CD) hybrid was prepared by two-step reaction. From XPS and FT-IR analysis, β-CD was successfully grafted onto the surface of GO. The adsorption performance of GO-β-CD for phenolphthalein, a model organic compound, from aqueous solution was investigated using batch experiments. The result showed that adsorption of Php by GO-β-CD was insensitive to ionic strength variation. The sorption kinetic experiments revealed that the adsorption equilibrium was achieved within 20 min and the adsorption system fitted well to the pseudo-second-order model. The adsorption isotherms are well by the Langmuir model and the maximum adsorption capacities of Php on GO-β-CD were approximately 94.6, 72.3 and 65.8 mg/g at 298 K, 308 and 318 K, respectively. The adsorption mechanism was also proposed to clathration, π-π interaction and hydrogen bond. The regeneration study showed that GO-β-CD have good stability and can be recycled several times with no significant loss in its adsorption capacity.