| Graphene, which is consist of sp2hybridized carbon atoms in a two-dimensionalmaterial. The superior performance of graphene has caused a great stir in the scientificcommunity after the announcement of Nobel Prize in Physics at2010. Grapheneoxide (GO), the derivatives of graphene, it contains a large number ofoxygen-containing functional groups on its surface and edges, such as carboxyl,carbonyl, hydroxyl and epoxy groups, which provide the reaction sites for themodification of graphene. Currently, graphene and graphene-based materials havebeen widely used in many fields of electrochemistry, optoelectronics, biomedicine,catalysts, water purification and others. In order to take full advantage of the excellentproperties of graphene, and broad the scope of its application at the same time, weprepared polynorbornene/graphene composites by using ring-opening metathesispolymerization (ROMP) and the composites were applied in hexavalent chromiumremoval form waste water, the main contents are as follows:In this paper, we demonstrate a functionalization approach to grow polymersfrom GO sheets by SI-ROMP for thefirst time. Considering the oxygen-containingfunctional groups on GO sheets, we use highly efficient Grubbs catalyst for ROMPbecause of its excellent functional group tolerance and remarkable selectivity ofolefins. For the current study, norbornene has been chosen as a model monomer forpolymerization because of its commercial availability and high ring strain for drivingthe polymerization process. Herein, we first prepared GO by modified Hummers’mrthod. Subsequently, norbornenyl initiator ligands were covalently attached ontoGO surfaces by esterification, and the Grubbs catalyst was then employed onto GO,followed by ROMP from the effective catalyst sites on GO with norbornenemonomers at room temperature, resulting in GO-PNb. Finally, GO-PNb was furthermodified by epoxidation of carbon double bonds along PNb chains. The structure, composition, morphology and solubility in organic solvents of GO and GO-PNbwere characterized by infrared spectroscopy (FTIR), Raman spectroscopy (Raman),ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), elementalanalysis and X-ray photoelectron spectroscopy (XPS), transmission electronmicroscopy (TEM), scanning electron microscopy (SEM) and thermogravimetricanalysis (TGA). And then the effect of polymerization conditions on the polymergrafting ratio was preliminary explored. The structure of the GO-PNb and the chaintransfer which existed in polymerization process were speculated. It was found thatSI-ROMP which occurred on GO was uncontrollable under our experimentalconditions, and the grafting ratio of PNb is low, the higest grafting ratio of PNb wasup to50.99%. And the chain transfer reaction in polymerization process includesintramolecular and intermolecular chain-transfer reactions, which made the lowergrafting density of PNb on GO. However, the solubility of GO-PNb in organicsolvents has been improved effectively at the low grafting ratio. We also found thatthe as-prepared GO-PNb materials were still remained ordered layered structure i.e.intercalated structure under our experimental conditions. Finally, the FTIRspectroscopy of GO-ePNb verified the feasibility of experiment routes to theepoxidation of GO-PNb, which provides a chance for further introducing functionalgroups on GO surface. It is worth noting that the polymers synthesized by ROMPcould be further functionalized to generate more novel polymers.Subsequently, in order to achieve the controllability of SI-ROMP on graphene,we further study the polymerization on chemical reduced graphene oxide (RGO).Firstly, we synthesized a new-type hydrophobic RGO-OH by reduction and surfacemodification of GO with2-azidoethanol via nitrene addition reaction at hightemperature. Through subsequent characterization by FTIR, Raman, XRD, elementalanalysis, the resulting RGO-OH was successfully prepared and exhibited acontrollable manner in the content of nitrogen-atoms in RGO-OH. Then, accordingto the basic of SI-ROMP from GO, norbornenyl initiator ligands were covalentlyattached onto RGO-OH surfaces by esterification, and the Grubbs catalyst was thenemployed onto RGO, followed by ROMP from the effective catalyst sites with norbornene monomers at room temperature, resulting in RGO-PNb. The feasibilityof the synthetic route to RGO-PNb was confirmed by FTIR and it showed successfulpreparation of RGO-PNb. We also preliminarily explored the effect of monomerconcentration and polymerization time on the grafting ratio of PNb on RGO byweighing method. It was found that SI-ROMP which occurred on RGO wasuncontrollable under our experimental conditions, and the grafting ratio of PNb isvery low, the higest grafting ratio of PNb was9.302%.Finally, since the as-prepared graphene-based material exhibits a certainhydrophobic character, which bring a great advantage for the process of wastewatertreatment. Additionally, graphene-based materials with large specific surface areaalso bring a new chance for the adsorption of heavy metal ions in wastewater.Accroding to the current application of graphene-based materials in wastewatertreatment, we explored the adsorption capacity of Cr (VI) in acidic solution.Unsurprisingly, the as-prepared graphene-based materials could not dispersed inwater, allowing for easy separation in real applications. We studied the adsorptioncapacity of Cr (VI) at different conditions by GO, GO-PNb and RGO-OH. Theintroduction of nitrogen-atoms onto graphene sheets make the RGO-OH adsorbentshow higher Cr(VI) removal capacity (157.73mg/g) than GO, GO-PNb and activatecarbon. And the content of nitrogen-atoms in RGO-OH can be controlled byadjusting reaction conditions accurately. It is found that the value of Cr(VI) removalcapacity is result from the joint effects of electrostatic adsorption and reductionreaction, which all mainly depend on solution pH. This work not only shows a novelpreparation strategy of graphene-based adsorbent by simply refluxing of GO withazide at high temperature, but also provides a fresh idea for further synthesis ofgraphene-based adsorbent. |
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