Preparation Of Three-dimensional Reduced Graphene And Its Adsorptive Properties

Graphene refers to a single layer of sp~2-bonded carbon atoms densely packed into a 2D structural materials.Its special properties of optics,electricity,thermology,mechanics and chemistry have caused wide concern and research.These properties make graphene a promising candidate for a broad range of applications in many fields.However,the irreversible restacking or aggomeration of graphene sheets,because of the strong ?-? and van der Waals interactions limits the scope of its application.While three-dimensional graphene with certain structure strength,enormous specific surface area and high porosity can avoid re-stacking of individual graphene sheets and has broader range of promising applications.Especially,graphene materials used as adsorbent play a notable role in the field of sewage treatment.The study in this paper successfully prepared three-dimensional reduced graphene oxide(3DrGO),adopting hydrothermal reaction combined with freeze-drying method.Then the research regarding to effect of proceesing parameters on 3DrGO and its adsorption properties was also carried out.In addition,the form of three-dimensional crosslinked sructure was analyzed and modification on the 3DrGO was explored.The main contents and conclusions of this paper were:(1)The GO and 3DrGO was successfully prepared through the improved Hummers method and hydrothermal reaction combined with freeze-drying method respectively.Research regarding to processing parameters and its optimization was also carried out.A variety of analytical techniques were used to characterize the structural morphology,composition and hydrophilic-hydrophobic property of 3DrGO.The results suggested the moderate length of time during the medium-temperature reaction was about four hours.Short reaction time would lead to low utilization of artificial graphite,while long reaction time would cause reaction liquid so adhesive that the further reaction was hindered.The formation of the three-dimensional structure was affected by hydrothermal reaction and freeze-drying process.GO solution of different concentrations was used to carry out the hydrothermal reaction.Its results indicated that the concentration increased accompanied with the shorterning of the critical forming time and increasing of the strength of the hydrogel.The method of freeze-drying has more advantages in maintenance of three-dimensional structure of hydrogels.The freeze-drying method could eliminate the damage of the three-dimensional structure caused by surface tension,prevent the phenomena of reunion among the layers and maitain the three-dimensional network structure.(2)The three-dimensional crosslinked sructure formed in the process of hydrothermal reaction was investigated in the experiment.The results suggested that the relative-order crosslinking structrue of 3DrGO was formed during the process of the hydrothermal reaction and the integral relatively ordered crosslinked structrue of the 3DrGO was retained during freeze-drying process.(3)The adsorption characteristics of methyl orange(MO)on the rGO were investigated in the laboratory.The relationship between conditions,namely concentration,temperature,contact time,pH and the adsorption performance is further studied.The adsorption isotherm curve and dynamic curve were drawing and used to fit model in order to explore the adsorption mechanism.The results suggested 3DrGO has good adsorption performance to MO.The maximum adsorption capacity of MO was respectively?165mg/g,?179mg/g and?204mg/g at 293K,313K and 333K.The adsorption isotherm could be described well by Langmuir isotherm,indicating that the adsorption was monalayer adsorption.With the temperature increasing,the maximum adsorption capacity rised,suggesting that the increasing of temperature was beneficial to the process of adsorption.The experiment involving the effect of contact time on the adsorption indicated that the adsoption arrived equilibrium in 400-800min.The experimental data of kinetic fit models showed better complicance with pseudo-second-order kinetic model.The increasing of the pH caused the decreasing of the maximum adsorption capacity finally.Then,the vacuum electric furnace was used for the reduction of the 3DrGO though the treatment in condition of high temperature and vacuum to gain the sample of 3DGN and explore the influence of high temperature heat treatment on the adsorption performance.The results indicated that high temperature influenced the adsorption properties though the change of hydrophilic and hydrophobic properties of the sample.After high temperature treatment,the 3DGN was gained,which displayed hydrophobic property and was reduced.The 3DGN has little adsorption capacity to MO due to the decreasing of hydrophilic property.But its saturation adsorption amount of oil is about 138.44g/g,comparative with the adsorption amount of the carbon nanotube sponge.