Study On The Preparation Of Biomimetically Modified Graphene With Dopamine As An Adsorbent For The Dye Pollutant Removal

With the development of human society,various industries,and civilization,daily human life becomes increasingly more convenient;however,at the same time,the environmental pollution problem is of growing concern.The water pollution accounts for an increasing proportion of the various kinds of environmental contamination,such as water eutrophication,freshwater resource depletion,and water contaminant toxicity against aquatic animals and plants.For the water pollution,organic dyes,including methylene blue,methyl green,etc.,are regarded as highly toxic and hazardous pollutants,thereby making it imperative for the development of the environmental remediation methods and functional materials for the removal of the organic dye pollutants.Among various environmental remediation methods,adsorption processing is one of the most viable and popular ones due to its well-developed theory,low cost,high efficiency,and no secondary pollution that will be generated.The study of this thesis is conducted based on graphene oxide（GO）as the precursor for the biomimetic preparation of different kinds of graphene-based adsorbents.The bio-inspired surface modification of GO with dopamine combined with the further functionalization with Fe₃O₄ nanoparticles or MoS₂ nanosheets leads to the generation of two kinds of graphene-based adsorbents.The facile,cost-effective,and environmentally benign aqueous solution method was employed throughout this study for the preparation of these two kinds of graphene-based adsorbents that were subsequently used for tackling different kinds of organic dyes.The adsorption performance,mechanism,and recycling properties were thoroughly analyzed by various characterization methods such as scanning electron microscopy（SEM）,X-ray diffraction（XRD）analysis,and Fourier transform infrared spectroscopy（FTIR）to obtain highly efficient,environmentally friendly,easily recyclable,and reusable graphene-based adsorbents.The conclusion of the research of this thesis is presented below:（1）GO is plagued with many disadvantages when used as a precursor for the preparation of graphene-based adsorbents.For example,GO has a high tendency to agglomeration and consequent precipitation,and it is also suffered from difficulties in recycling.In this study,the use of dopamine for the biomimetic modification of GO can impede the aggregation of the graphene sheets as caused by the interlayer van der Waals force.Besides,more oxygen-containing functional groups are introduced,such as the reactive catecholamine group,onto the modified graphene surface,and the water dispersibility of the modified graphene sheets is promoted as well.Furthermore,the oxidative self-polymerization of the modifier（i.e.,dopamine）can spontaneously take place,especially under alkaline conditions,yielding the polydopamine coating on the graphene surface.In the meanwhile,the GO is chemically converted to reduced graphene oxide（RGO）to some extent,with the partial restoration of the destructed in-plane network structure of GO.The fascinating adhesion properties of the surface polydopamine layer on the graphene make it easy for the further functionalization of the water-dispersible,modified graphene by a solution route.The incorporation of different kinds of functional compositions onto the surface of the polydopamine-modified graphene,including Fe₃O₄ nanoparticles and MoS₂ nanosheets,results in the generation of two kinds of graphene-based adsorbents,of which the structure and surface properties are thoroughly characterized and analyzed.（2）Both of the Fe₃O₄ nanoparticles-and MoS₂ nanosheets-functionalized graphene after being modified with dopamine are demonstrated to be excellent adsorbents for the uptake of the organic dyes.Based on the systematic study of the adsorption dynamics,isotherm,and thermodynamics,these two kinds of graphene-based adsorbents are demonstrated to possess large adsorption capacity,excellent stability,and durability,e.g.,the magnetic graphene-based adsorbent with Fe₃O₄ nanoparticles shows a maximum adsorption capacity of as high as 151.98 mg/g towards methylene blue,while the MoS₂nanosheets-functionalized graphene-based adsorbent displays the maximum adsorption capacity reaching 235.29 mg/g for methyl green.Such adsorption capacities are superior to many reported adsorbents.Importantly,it is worth mentioning that both of the graphene-based adsorbents possess the advantage of the ease in recycling and reuse since only an exterior magnetic field is needed for the quick recycling of the magnetic Fe₃O₄-functionalized graphene.For the MoS₂-functionalized graphene-based adsorbent,it presents as an aerogel in the bulk form,which makes it even more facile since the adsorbent can be directly picked from the wastewater after processed.