Preparation And Uranium Adsorption Performance Of Functionalized Hierarchical Nanocarbon Materials

With the continuous growth of our country energy consumption and the extensive use oftraditional fossil fuels,environmental pollution has become increasingly serious.Therefore,the development of new energy is an important and arduous research task.Nuclear energy has attracted widespread attention as an ideal low-carbon clean energy source.Uranium is an important nuclear fuel.However,the uranium mine reserve is low and unevenly distributed.Therefore,the researchers pay attention to the vast ocean,which contains about 4.5 billion tons of uranium resources.China is a big country of ocean with vast ocean territory.The research on extraction uranium from seawater has important and long-term strategic significance for exploiting marine resources,achieving sustainable development of our country nuclear energy and ensuring the safety of energy resources.However,the concentration of uranium in seawater is only 3.3?g·L^-1.Simultaneously,a large number of interfering ions make it difficult to extract uranium from seawater.Therefore,it is a huge challenge for designing adsorbent materials with great selective adsorption ability for uranium.The hierarchical nanocarbon precursor materials with large specific surface area were prepared in this paper by hydrothermal method,high temperature carbonization and alkaline activation.The carbon precursor was functionally modified by manganese dioxide,dopamine,Ni-Mn layered double hydroxides and zero-valent iron to increase the adsorption selectivity of the material for uranyl ion.The micro-morphology and structure of as-prepared composites were characterized by SEM,TEM,XRD,FT-IR,XPS and BET.The adsorption experiments were designed to investigate the effects of different p H,initial uranium concentration,adsorption temperature and adsorption time on the adsorption performance.Finally,the materials before and after adsorption were analyzed and the adsorption mechanism was reasonably speculated,which provided theoretical guidance for the following design of adsorption materials.To prepare the adsorption material with high specific area and rich active site,pomelo peel,a universal biomass waste,has been used as raw material.The honeycomb-like porous carbon material?HLPC?with a large specific surface area was synthesized by alkaline activation and high temperature carbonization.In order to further improve the adsorption capacity for uranylion,manganese dioxide nanowires were grown in situ on the surface of the substrate?HLPC/Mn O₂?.The surface area of the HLPC reached 1147.41 m²·g^-1.When the p H was 5 and initial uranium concentration was 100 mg·L^-1,the results of the adsorption experiments showed that the highest adsorption value of the HLPC and HLPC/Mn O₂composite was 140.80 mg·g^-1and 180.29 mg·g^-1,which proved that the modification of Mn O₂effectively improved the adsorption capacity of the materials for uranyl ion.The maximum absorption capacity to uranyl ion of HLPC/Mn O₂ composites was 238.09 mg·g^-1.The waste A4 paper was chose as the raw materials and KOH as the porogen to synthsis the hierarchically porous carbon precursor material by high temperature carbonization?WPC?.Due to the many competing metal ions in seawater,dopamine was employed for surface modification by in situ polymerization to form the polydopamine layer?WPC@PDA?to improve the selectivity of the adsorbent material for uranyl ion.The abundant amine groups in the dopamine can adsorb uranyl ion by surface complexation.The thermodynamic analysis was fitted by the Langmuir model with highest adsorption capacity of WPC@PDA composites as 384.62 mg·g^-1.The adsorbent WPC@PDA showed significant selectivity for removing uranyl ion from simulated seawater.To separate adsorbent from aqueous solutions easily and improve recycling performance,N-doped and Fe-inserted 3D carbon nanosheet frameworks were prepared at high temperatures?Fe-NCNF?,based on the polymer-blowing process and top-down strategy.Zero-valent iron nanoparticles made Fe-NCNF can be easily separated from aqueous solutions with a common magnet.More importantly,it acted as an agent for uranyl ion immobilization by chemical reduction.In order to improve the adsorption capacity for uranyl ion,the Fe-NCNF were decorated with nickel–manganese layered double hydroxide?Ni-Mn LDH?.Finally,Fe-NCNF-LDH composites were synthesized with the maximum adsorption capacity of 598.50 mg·g^-1.The results of adsorption-desorption cycles experiments showed that 0.1 mol·L^-1 HCl was the optimum elution.After five adsorption-desorption cycles,the adsorption capacity of Fe-NCNF-LDH composites for uranyl ion still maintained 417.63mg·g^-1.The suaeda glauca plant growing on the beach was chose as the research object to easily immobilize the adsorbent on the dynamic adsorption bed and keep the high adsorption selectivity for uranyl ion in simulated seawater.The hyperaccumulation effect of the plant and ion-imprinted technology were combined to prepare the uranium ion-imprinted hierarchically porous carbon material?II-HPC?with macroscopic columnar structure.From the adsorption experimental data in simulated seawater,the distribution coefficient?K_d?of II-HPC for uranyl ion was 1.02×10⁴ m L·g^-1.On a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater.The results showed that the amount of adsorbed uranyl ion after 35 days was 0.38 mg·g^-1.The suaeda glauca plant growing on the beach was chose as the research object.The hyperaccumulation effect of the plant and ion-imprinted technology were combined to prepare the uranium ion-imprinted hierarchically porous carbon material?II-HPC?.From the adsorption experimental data in simulated seawater,the distribution coefficient?K_d?of II-HPC for uranyl ion was 1.02×10⁴ m L·g^-1.It exhibited the high selectivity due to the memory effect of the imprinted materials for the uranyl ion.II-HPC material with macroscopic columnar structure was easily to immobilize the adsorbent on the dynamic adsorption bed.On a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater.The results showed that the amount of adsorbed uranyl ion after 35 days was 0.38 mg·g^-1.