Non-thermal Plasma Modified Nanomaterials And Their Adsorption On Uranium Containing Wastewater

Uranium(VI)has been a key element of nuclear industry development,which is also one of the main sources of radioactive pollution in wastewater.Thus,it is imperative to eliminate the toxic radioactive U(VI)from the wastewater before being discharged into the environment,which is not only beneficial to the sustainable development of nuclear power,but also beneficial to resource recycling,environmental protection and human health.Adsorption has been confirmed to be the most effective method for radionuclides removal due to its large amount of advantages,including high efficiency,ease of operation,low-cost and wide range of material sources.The development and utilization of new efficient adsorbents is closely related to adsorption method whether it is successful in practical application or not.Materials functionalized by amine groups have been attracted great interests in the removal of U(VI)from aqueous solutions.Plasma treatment is regarded as a promising and an environmental friendly method technique,which can be utilized as a novel alternative to traditional modification methods since no solvent is involved in this modification process,almost no waste is produced and virtually all solid materials can be modified via this plasma treatment.In this work,several common nano-materials were selected as the substrates and plasma treatment was applied to modify the-NH2 groups onto their surface.Moreover,a new kind of 2D MOFs nano-sheets was successfully prepared by a one-step synthesis method using a mixing solution of methanol(MeOH)and H2O at ambient temperature.The obtained products were tested for the immobilization of U(VI)to evaluate their removal performance and their adsorption mechanism:(1)Modification of carbon materials by non-thermal plasma treatmentThe carbon materials of flake graphite(FG)and MWCNTs were selected as the substrates and non-thermal plasma treatment was applied to modify the amine groups onto their surface.In this process,O-phosphorylethanolamine(O-PEA)was selected as the-NH2 groups sources.The plasma treatment time,the adsorption contact time,solution acidity,ionic strength,and reacting temperature were also studied to characterize the adsorption performance of the plasma treated carbon materials.The results indicate that the modified carbon materials have higher high U(VI)entrapment efficiency than others,and longer treatment time results in higher efficiency.Additionally,the adsorption process is dependent on the solution pH values rather than ionic strength.The macroscopic experiments can be satisfactorily simulated by pseudo-second-order model.The maximum adsorption capacities of modified FG and MWCNTs based on Langmuir isotherm model are 140.68 and 80.4 mg·g-1,respectively.Thermodynamic studies reveal that the U(VI)entrapment process onto modified FG is endothermic while that onto modified MWCNTs is exothermic.The fast and efficient adsorption performance of the modified carbon materials suggests that non-thermal plasma treatment can be applied as an effective method for modifying adsorbents with great adsorption performance for U(VI)entrapment.(2)Modification of Fe304 by non-thermal plasma treatmentAlthough the modified carbon materials exhibited enhanced U(VI)removal performance,their solid-liquid phase separation process must be fulfilled by centrifuge method,which is complicated.Hence,in this study,Fe3O4 nanoparticles(MNP)were synthesized by a one-pot hydrothermal method,which was also selected as the substrate and non-thermal plasma treatment was applied to modify the-NH2 groups onto their surface.In this process,O-phosphorylethanolamine(O-PEA)was also selected as the-NH2 groups sources.The effects of plasma treatment time on the surface properties of Fe3O4 were investigated.Simultaneously,a series of batch adsorption experiments were carried out under various physicochemical conditions,such as reaction time,solution pH,ionic strength,and temperature.Longer treatment time results in more agglomeration and higher adsorption capacity and efficiency.Additionally,the adsorption process is dependent on the solution pH values rather than ionic strength.The macroscopic experiments can be satisfactorily simulated by pseudo-second-order model.The highest adsorption capacity of modified Fe3O4 nanoparticles based on Langmuir isotherm model is 228.17 mg·g-1 at 333 K,pH = 6.0 ± 0.1.Thermodynamic studies reveal that the adsorption process of U(VI)is endothermic and spontaneous.XPS studies indicate that the U(VI)removal is fulfilled through the binding interactions between U(VI)and-NH2,-OH and phosphate groups on the modified MNP surface.The environmental-friendly modification method,fast and efficient adsorption performance and much more convenient magnetic separarion method suggest that modified Fe304 nanoparticles can be utilized as great adsorbents for U(VI)removal in practical application.(3)One-step preparation of 2D MOFs nanosheetsAlthough both the modified carbon materials and magnetic Fe3O4 nanoparticels exhibited enhanced U(VI)removal performance,their adsorption capacities for U(VI)removal are always in the middle position.Hence,it is significant to explore new kind of efficient adsorbents.In this study,a new kind of 2D MOFs nano-sheets was successfully prepared by a one-step,and cost-effective chemical synthetic route.This synthesis method allows for the high-yield and large-scale production of thin 2D MOFs nano-sheets.The effect of the solvents ratios on 2D MOFs nano-sheets structure,morphology and U(VI)removal performance were also investigated in this study.The results indicate that nano-sheets became larger with decreasing the volume ratios of MeOH/H2O.The 2D MOFs exhibited great U(VI)removal performance.The macroscopic experiments can be satisfactorily simulated by pseudo-second-order model.The highest adsorption capacity of 2D MOFs based on Langmuir isotherm model is 591.77 mg·g-1 at 293 K,pH = 6.0 ± 0.1.The U(VI)adsorption by the obtained MOFs samples can at least compete with if not better than the previously reported MOFs adsorbents for U(VI)removal,indicating the obtained MOFs samples can be applied as potential candidates for the sequestering of U(VI)from an aqueous solution with its cost-effective and environmental-friendly synthetic method.Furthermore,thermodynamic studies reveal that the adsorption process of U(VI)onto MNS materials is exothermic and spontaneous.XPS studies indicate that the U(VI)removal is fulfilled through the binding interactions between U(VI)and-OH groups,and C-N(H).