Modification Of MXene Ti₃C₂ And Its Adsorptive Removal Of Radioactive Cesium

To a large extent,the industrial use of nuclear resources depends on the efficient disposal of nuclear waste.Therefore,the use of different adsorbents to effectively remove radionuclides from liquid effluents becomes critical.Selective removal of ¹³⁷Cs from nuclear wastewater remains a challenge due to the development of highly efficient adsorbents and the presence of high concentrations of competitive ions.MXene Ti₃C₂ is a two-dimensional transition metal carbide,which has been applied in the field of radionuclide removal by adsorption because of its layered structure and heterogeneous sites（hydroxyl,oxygen and fluorine）.However,the adsorption activity of MXene cannot reach the optimal state due to the key limitation of agglomeration,narrow layer spacing,reduced long-term stability and recyclability,etc.Therefore,modification of MXene Ti₃C₂ to improve its adsorption efficiency for radionuclides can expand its application field and has economic and social value in practical application.In this paper,MXene Ti₃C₂ was modified by Na OH and MXene Ti₃C₂ was doped by zif67 in order to improve the adsorption rate of ¹³⁷Cs.The adsorption rates of Ti₃C₂ modified by KOH and zif67 doped by Ti₃C₂ on radionuclide Cs⁺were studied.The influences of different factors on the adsorption rates of Ti₃C₂ modified by KOH and zif67 doped by Ti₃C₂on radionuclide Cs⁺were investigated.MXene Ti₃C₂ was first surface hydroxylated with KOH.Ti₃C₂ nanosheets treated with KOH were prepared by alkali solution agitation.After surface hydroxylation modification,the delamination morphology and surface structure of hydroxy-modified Ti₃C₂ are improved compared with the original Ti₃C₂.The spacing between Ti₃C₂ layers is larger and the fluorine group in Ti₃C₂ is converted to hydroxyl group as the adsorption site of Cs⁺.The adsorption efficiency of hydroxy-modified Ti₃C₂ for Cs⁺is significantly improved.The optimum ratio of Ti₃C₂ modified by Na OH was optimized,and the adsorption rate of Cs⁺whenthe initial concentration of 5 mg·L^-1 and 50 m L of the model wastewater was removed by 0.05 g of the optimum adsorbent within 5 minutes to reach 90%.Hydroxy-modified Ti₃C₂ also showed high adsorption selectivity for Cs⁺in the presence of competing metal ions such as K⁺,Na⁺,Mg²⁺and Ca²⁺.The mechanism of Cs⁺removal by adsorption of Ti₃C₂ modified by Na OH is proposed.The mechanism study shows that the ion exchange between[Ti-O]^-H⁺/Cs⁺mainly promotes the adsorption of Cs⁺,and the complexation between the oxygen-containing group[Ti-O]and Cs in the modified Ti₃C₂ is also involved.Hydroxy-modified Ti₃C₂ is easy to regenerate and has good Cs⁺adsorption recyclability.The imidazoli-zeolite imidazole framework zif67 was self-assembled in a two-dimensional MXene layer by in-situ synthesis.The high surface area,porosity,multiple functions,pore-limiting effect,and adjustable coordination space of MOF provided a favorable environment to prevent the aggregation of MXene.Hybridization of MOF with functional layered MXene materials may be beneficial if the main structure provides appropriate interactions to stabilize and improve the desired properties,combining the advantages of MOF and MXene to improve the adsorption rate of radionuclide Cs⁺.The structure and morphology of the nano-sheet were characterized.The introduction of zif67 did not interfere with the Ti₃C₂ crystal phase,which confirmed that zif67 was successfully doped between the MXene Ti₃C₂ layers.The optimal ratio of doping Ti₃C₂ with zif67 was optimized to obtain the best adsorption and removal efficiency of radionuclide Cs⁺.The introduction of zif67 on Ti₃C₂ improves the adsorption capacity of Ti₃C₂to radionuclide Cs⁺.The adsorption rate of Cs⁺of 50 m L and initial concentration of 5 mg·L^-1 in model wastewater can reach97.2%in 1440 minutes with the optimal adsorbent of 0.05 g.The mechanism of adsorption removal of Cs⁺by zif67 doped Ti₃C₂ is proposed.The mechanism study shows that the complexation between Ti₃C₂ oxygen-containing group[Ti-O]and Cs and Co-OH may change into Co-O-Cs after adsorption reaction,partly because zif67 inserted into Ti₃C₂ layer increases the specific surface area of the material,the active site was added.Compared with pure Ti₃C₂,KOH hydroxy-functionalized MXene Ti₃C₂ and zif67 doped Ti₃C₂ significantly improved the adsorption rate of radionuclide Cs⁺,which also provided a simple and feasible scheme for the preparation of materials with high adsorption activity of radionuclide.