| Nuclear energy,as a new clean energy source,was one of the viable options to replace traditional energy sources.However,the radionuclide uranium from nuclear fuel leaks,etc.,posed a significant risk to human health and environmental safety once it enterred water bodies.Therefore,the removal of uranium from wastewater was a research topic of great interest in the environmental field.In addition,the uranium resources on land were very limited,while they were inexhaustible from ocean.At the same time,seawater uranium extraction process was environmentally friendly,so it was imperative to carry out seawater uranium extraction.Adsorption had proven to be one of the most effective water treatment methods because of its low cost,simple operation,practicality and environmental friendliness.It played a non-negligible role in the field of radionuclide removal and seawater uranium extraction.MXenes,as transition metal carbides or nitrides,were inherently radiation resistant and can be ideal materials for nuclide processing.However,MXenes were chemically unstable and had limited ion selectivity.Therefore,in this study,MXenes were modified by amidoxime groups(AO),polyamides(PA)and covalent organic frameworks(COF-LZU1)based on the chemical grafting of aryl diazonium salts to address their inherent disadvantages.The morphological characteristics of MXenes and the modified materials were analyzed by various characterization techniques.The removal of uranium and the application in uranium extraction from seawater were explored by batch adsorption experiments.The possible reaction mechanism was further analyzed by spectral analysis and theoretical calculations.The study could provide a feasible idea for the modification of MXenes,the removal of uranium from wastewater and uranium extraction from seawater.The main findings of this thesis were as follows:(1)Chemical grafting of aryl diazonium salts and further grafting of AO onto the MXene surface were adopted to prepare amidoxime Ti3C2Tx nanomaterials(TC-AO).Various characterization techniques demonstrated that TC-AO contained abundant functional groups.Adsorption batch experiments verified the superior adsorption capacity of TC-AO(279.6 mg·g-1),as well as the fast kinetic performance(～20 min).The adsorption capacity of TC-AO was almost independent of the coexisting competing ions and the background ion concentration(pH=5.0).The results of XPS analysis presumed the existence of complexation between U(VI)and TC-AO.(2)By using diazonium salt grafting and introducing AO to Ti3C2 surface,then PA with a large amount of-NH2 was grafted by a simple one-step hydrothermal method on this basis,a highly efficient uranium adsorbent Ti3C2-AO-PA with anti-bio-contamination properties was produced.It was confirmed that Ti3C2-AO-PA contained-NH2 and AO functional groups by characterization experiments.Ti3C2-AO-PA had the best adsorption capacity for[UO2(CO3)3]4-when the mass ratio of Ti3C2-AO to PA was 1:1.Ti3C2-AO-PA exhibited fast adsorption kinetics(-120 min)and ideal adsorption capacity(81.1 mg·g-1).The removal amount reached 4.9 mg·g-1 in the simulated seawater.In addition,Ti3C2-AO-PA was highly selective for uranium and showed excellent bacterial inhibition(92.9%inhibition rate).It was known from XPS and theoretical calculations that the removal of[UO2(CO3)3]4-benefited from the ideal spatial structure and the presence of AO and-NH2.(3)By electrostatic self-assembly of MXene with LZU1,the structurally stable composite MXene-AO@LZU1 was prepared.Numerous characterization experiments proved that the material had good stability and ideal specific surface area.The results of adsorption experiments showed that MXene-AO@LZU1 had the best adsorption capacity(88.8 mg·g-1)for[UO2(CO3)3]4-when the mass ratio of MXene-AO to LZU1 was 1:2.The removal amount reached 6.8 mg·g-1 in the simulated seawater.MXene-AO@LZU1 remained structurally stable under a variety of extreme conditions and had high selectivity for uranium.XPS showed that the elimination of MXene-AO@LZU 1 on uranium relied mainly on the complexation of nitrogen-containing functional groups,oxygen-containing functional groups with[U02(C03)3]4-. |
