Preparation Of Graphene-based Composite Materials And Its Removal Performance For U(?) And Cr(?) In Water

The current radioactive pollutants and heavy metal pollutants in the wastewater pose a serious threat to human health and living environment,and the adsorption method has been used at home and abroad because of its high selectivity,high selectivity,high removal efficiency,and low cost.Researchers are widely used to remove uranium and chromium pollution in water.As a new type of two-dimensional sheet material,graphene oxide material?GO?has a large specific surface area,a large number of oxygen-containing functional groups,and excellent dispersibility,so that GO has a strong application advantage in the field of removing environmental pollutants.In this dissertation,graphene oxide material is used as a matrix material.Based on its unique properties,a series of environmentally friendly graphene oxide-based composites with easy separation,low cost and high efficiency are designed and prepared.The structure and composition of the prepared graphene oxide-based composite adsorbents were studied.The effects of different influencing factors on the removal of U???and Cr???by graphene oxide-based composite adsorbents were studied,and the experimental data were fitted by means of isotherm models,kinetic models,and thermodynamic formulas.The removal process and the removal types of graphene oxide-based composite adsorbents for U???and Cr???were discussed in theory.At the same time,the mechanism of removing U???and Cr???by graphene oxide-based composite adsorbents was studied using XPS and other characteristics.The main research results of this paper are as follows:?1?Preparation and characterization of graphene oxide?GO?materials:The morphology,structure and composition of the graphene oxide precursor were discussed in depth.The surface of the graphene oxide precursor synthesized in this paper is uneven,has a large number of wrinkles,has a transparent layered structure like a yarn,and has a large number of oxygen-containing functional groups on its surface.?2?Preparation of graphene aerogel?GA?and its adsorption properties for U???:graphene aerogel?GA?was successfully prepared through a simple hydrothermal method.The resulting GA exhibited a porous network structure with a large specific surface area?350.8 m²/g?,ultra-light mass and easy separation from water.The pH_ZPC value of the GA was estimated to be 3.5.The adsorption process and the factors that affect adsorption capacity were studied.The adsorption could be conducted in a wide pH range from 2.0 to 7.0.The maximum adsorption capacity of GA towards U???at pH 4.0 and T=298 K was 238.67 mg/g.The GA has greatly rapid adsorption property for the removal of U???at pH 4.0.Kinetic data showed good correlation with pseudo-second-order equation.Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry characterizations showed that GA adsorbed U???through chemical interaction by oxygen-containing and nitrogen-containing groups functional groups.The results show that GA has excellent application potential as an adsorbent material for removing U???from aqueous solution.?3?Preparation of ATGO-nZVI and its adsorption and reduction properties for Cr???:ammonium thiocyanate functionalized graphene oxide?ATGO?-supported nanoscale zero-valent iron composite?ATGO-nZVI?employed to extract Cr???from aqueous solution,was successfully synthesized by chemical oxidative polymerization and sodium borohydride reduction method.Characteristics of XRD and HR-TEM confirmed the high disperse and activity of nZVI after supported by ATGO.Batch experiments showed that the removal efficiency of ATGO-nZVI was higher than that of bared nZVI and ATGO.Furthermore,the stability of ATGO-nZVI composite was higher than that of nZVI,which was proved by the Tafel polarization curves.Dynamic experiments suggested that the removal process was conformed to be in agreement with not only the pseudo-second-order model for adsorption but also Langmuir-Hinshelwood first-order model for reduction process,which revealed that the removal of Cr???by ATGO-nZVI composite was dominated by chemical surface-limiting step.Considering the experiments and characterization,the removal mechanism containing rapid adsorption of Cr???onto the ATGO-nZVI surface and reduction by nZVI was clarified.The above results suggested that ATGO-nZVI would become a promising remediation material for Cr??? pollution cleanup.