| In recent years,the nuclear power industry in various countries has developed rapidly.However,nuclear power plants will produce a large amount of radioactive wastewater.Radioactive cesium and iodine have high radioactivity and a long half-life.Therefore,it is of great significance to research and develop high-efficiency radioactive wastewater adsorption materials and effectively remove radioactive ions from wastewater.In this paper,a series of composite adsorbent materials were prepared by using biomass-based high specific surface area nitrogen-doped hierarchical porous carbon material as a carrier,loading metal compound nanoparticles on its surface,and used it in wastewater containing Cs+and I-treatment,the effect of corresponding parameters on the adsorption performance was studied,the thermodynamic and kinetic mechanisms of the adsorption process were clarified,and the adsorption mechanism was revealed.The main findings are as follows:1.We adopt cattle bone as a precursor and KOH as an activator.Through pre-carbonization and carbonization activation methods,three-dimensional nitrogen doping hierarchical porous carbon(NHPC)with high specific surface area and micropore-mesoporous-macropore hierarchical porous structure was synthesized.The specific surface area and nitrogen content of NHPC were effectively controlled by changing the activation temperature and the amount of KOH.The results indicated that the best mass ratio of KOH to the pre-carbonized product is 0.6 and the activation temperature is 750?,the specific surface area of NHPC is as high as 2098.9 m2 g-1,the pore volume is 1.43 cm3 g-1,and the nitrogen content is 3.14%under this condition.2.We utilize the high surface area NHPC as the support where the Prussian blue(PB)nanoparticles is in-situ grew due to the rich heteroatoms on the surface.Oxalic acid is used as a complexing agent to control the release of metallic Fe3+and the generation rate of PB.Therefore,highly dispersed Prussian blue/nitrogen-doped hierarchical porous carbon composites(PB/NHPC)is prepared.The results show that PB/NHPC inherits the three-dimensional hierarchical porous structure of NHPC,with a specific surface area of up to 1884.0 m2 g-1 and micropores accounting for 72.4%;PB nanoparticles are dispersed uniformly on the surface of NHPC with an average particle size of 53 nm.The adsorption tests showed that PB/NHPC exhibits a remarkable adsorption performance with a capacity of 125.31 mg g-1,a superior recyclability with 87%of initial capacity retained after 5 cycles,and an outstanding adsorption selectivity for Cs+,which was better than PB under the same conditions.X-ray diffraction,X-ray photoelectron spectroscopy combined with 57Fe Mossbauer spectroscopy results reveal that cesium ions are inserted into the crystal channels of PB to generate a new phase(CsFe2(CN)6·3H2O)after adsorption.Moreover,the adsorption process is spontaneous and endothermic which can be described by the Langmuir isotherm and pseudo-second-order kinetic models.3.Analogously,we also use the high surface area NHPC as the support where silver/silver oxide nanoparticles were distributed to prepare silver-silver oxide/nitrogen-doped graded porous carbon composite adsorbent(Ag-Ag2O/NHPC).NHPC high surface area and surface heteroatoms can effectively improve the dispersion of Ag and Ag2O nanoparticles,and its rich pore structure can effectively promote the mass transfer of adsorption.The adsorption results show that when the pH of the I-solution is 4,the maximum adsorption capacity of Ag-Ag2O/NHPC is 442.48 mg g-1 under 30?,and adsorption reached equilibrium adout 4 h.The adsorption process can be described by the Langmuir isotherm.The adsorption kinetics results show that the adsorption process of I-on Ag-Ag2O/NHPC conforms to the pseudo-second-order kinetic models. |
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