Preparation Of Graphite Phase Carbon Nitride Functionalized Materials And Study On Uranium Adsorption Properties

In order to solve the problem of energy shortage worldwide,the development and rational use of clean new energy has become a major concern of people.Nuclear energy is considered to be the most potential emerging energy because of its low carbon emissions,clean,low consumption and small footprint.Uranium is widely used in nuclear fuel due to its fission phenomenon.Therefore,the ocean with 4.5 billion tons of uranium reserves has become the main target for obtaining uranium resources.Graphite carbon nitride(g-C₃N₄)nanomaterials are widely used in the fields of adsorption material preparation and water treatment due to their graphene-like sheet structure and rich N-containing functional groups.However,the functional group on the surface of g-C₃N₄is relatively single,which makes it have certain limitations when applied to the field of adsorption.Therefore,the introduction of groups with higher selectivity to uranium through different modification methods has become an effective method to improve the adsorption performance of g-C₃N₄.In this thesis,g-C₃N₄was used as the substrate,and three kinds of adsorption materials were designed and prepared by modification methods such as loading and deposition,Arg/PDA@g-C₃N₄composite adsorption material,Ag₃PO₄/P-C₃N₄composite adsorption material and Pm AP-MFCN sponge.And through the test of its adsorption performance,analysis and evaluation of its possibility of extracting and enriching U(VI)in simulated seawater.g-C₃N₄was used as the substrate,dopamine was autooxidized to the surface of g-C₃N₄.Subsequently,the final product Arg/PDA@g-C₃N₄composite adsorption material was prepared by hydrothermally modifying L-arginine on a stable substrate formed by polymerization of dopamine.The abundant-NH-and-NH₂in dopamine and arginine provide more active sites for the adsorption of uranium.The adsorption performance test showed that when p H=7.0,the Arg/PDA@g-C₃N₄-2 adsorbent prepared when the mass ratio of dopamine to g-C₃N₄was 1:1reached the maximum removal efficiency of uranyl ions in the solution.Combining the kinetic model,adsorption isotherm model and the results of adsorption thermodynamics,it can be concluded that the adsorption of uranyl ions on the Arg/PDA@g-C₃N₄-2 adsorption material is an endothermic and spontaneous monolayer chemical adsorption,at room temperature the theoretical maximum adsorption capacity can reach 869.6 mg·g^-1.The simulated seawater experiment results show that the Arg/PDA@g-C₃N₄-2 adsorbent has the potential to adsorb uranium in real seawater.According to the analysis of the XPS spectra before and after adsorption,the capture of U(?)by the Arg/PDA@g-C₃N₄-2 adsorption material may be due to the difference between-NH₂/-NH-in the surface-modified polydopamine and L-arginine coordination between carboxyl group and U(VI).Compared with the original g-C₃N₄,the Arg/PDA@g-C₃N₄composite adsorbent modified with dopamine and arginine has a larger saturated adsorption capacity.In order to improve the selectivity of the adsorbent to U(?)in the solution with competing ions,in Chapter 4,(NH₄)₂HPO₄is used as the phosphorus source,and g-C₃N₄is thermally copolymerized doping P into it to prepare P-C₃N₄.Subsequently,Ag NO₃and Na H₂PO₄were co-precipitated on P-C₃N₄to prepare Ag₃PO₄/P-C₃N₄composite adsorption material.When phosphorus is doped onto graphene,the lower negative potential displayed on the surface of the phosphorus atom is very suitable as the binding site of the electrophilic group,and the phosphorus-related functional group has a strong relationship with U(VI).The static adsorption test shows that it has a high removal efficiency for uranyl ions in a wide p H range(p H=3.0?9.0),and the adsorption of uranyl ions in the solution on the Ag₃PO₄/P-C₃N₄composite adsorption material is A spontaneous endothermic monolayer chemical adsorption process.Due to the introduction of phosphate in the Ag₃PO₄/P-C₃N₄composite adsorption material,the selectivity of the material to uranyl ions is greatly improved compared to the original g-C₃N₄.Through XPS analysis of Ag₃PO₄/P-C₃N₄composite adsorbent before and after the adsorption of uranyl ions,it is found that the binding energy of N-containing and P-containing functional groups in Ag₃PO₄/P-C₃N₄-U composite adsorbent has increased,which may caused by its coordination with uranyl ions.Compared with the original g-C₃N₄,the Ag₃PO₄/P-C₃N₄composite adsorbent has more significant selectivity to U(VI).Powder materials have great drawbacks in recycling and reuse.In order to improve the cyclic absorption and desorption capacity and reproducibility of adsorbent materials,Chapter 5Carbonizes melamine sponge(MF)at high temperature under N₂atmosphere to prepare graphite phase carbon nitride sponge(MFCN),and then use(NH₄)₂S₂O₈as a polymerization initiator to polymerize m AP monomer on MFCN and deposit to prepare poly-m-aminophenol deposited graphite phase carbon nitride sponge.The prepared Pm AP-MFCN sponge has a certain load-bearing capacity and is not easily deformed.The adsorption performance was tested,and it was found that the material had the greatest removal efficiency at p H=8.0.The adsorption of uranyl ions in the solution on the Pm AP-MFCN adsorption material is an adsorption process in which the physical adsorption and chemical adsorption of the multi-molecular layer spontaneously endothermic.Pm AP-MFCN shows excellent regeneration and antibacterial properties.XPS analysis can infer that the abundant-NH⁺in the poly-m-aminophenol introduced after modification is the most important functional group that may coordinate with the uranyl ion in the solution.Compared with g-C₃N₄powder,Pm AP-MFCN sponge has stronger cyclic absorption and desorption performance.