| Energy is an important focus of social development,with the rapid development of nuclear power industry,a large amount of uranium-containing wastewater was discharged into ecosystem and caused serious problems on environmental and living organisms.Therefore,the development of economical and efficient uranium removal technology is of great significance for ecological environmental protection.Adsorption has become one of the mostly adopted technolog for pollutant control because of its cheapness,high efficiency and ease operation.In recent years,two-dimensional transition metal carbon/nitride MXenes have gradually emerged in the field of environmental remediation.Especially,MXene has broad application prospects in the field of radioactive wastewater treatment owing to its unique structural properties,large specific surface area and controllability of components.However,as a single adsorbent,Mxene has a relatively limited efficiency capacity for uranium U（Ⅵ）removal,owing to its lack of active adsorption sites.Therefore,surface functionalization of MXene to its improve their adsorption performance is desirable to be investigated.In this thesis,MXene（Ti3AlC2）was used as the substrate to prepare amino,amineoxime and hypophosphite functionalized Mxene（MX-HCCP-PEI,MX-AO and MX-HAP）.The se functionalized MXene composites were used as adsorbents for removal of U（Ⅵ）from aqueous solution.These adsorbents as well as related samples were characterized by Fourier transform infrared（FTIR）,X-ray diffractometer（XRD）,thermogravimetric analysis（TGA）,X-ray photoelectron spectroscopy（XPS）and cold-field emission scanning electron microscopy（SEM）.The characterization results demonstrated that we have successfully prepared the target adsorbents.The adsorption behaviors of U（Ⅵ）by the three adsorbents and the adsorption performance of U（Ⅵ）under different adsorption factors were further explored.Based on the experimental adsorption data,the adsorption kinetics and isotherm thermodynamic model were fitted and related parameters were calculated,and the adsorption mechanism was also analyzed and discussed.The main research contents are as follows:（1）The Al element in Ti3AlC2 was removed by HF etching,and accordion-like MXene was obtained.MXene was further stripped with TBAOH,and the amino groups were subsequently introduced on the surface of MXene via reaction with aminopropyl triethoxysilane（APTES）aminopropyl triethoxysilane（APTES）.The final adsorbent（MX-HCCP-PEI）was prepared via conjugation of APTES functionalized MXene and polyethyleneimine（PEI）by using,hexachlorocyclotriphosphazene（HCCP）as the linker.The adsorption performance of U（Ⅵ）was studied by intermittent adsorption experiment.The adsorption results show that the adsorption capacity of MX-HCCP-PEI is increased by 6 times as compared with unmodified MX.What’s more,the effects of time,p H,U（Ⅵ）concentration and temperature on adsorption performance were further explored,and the optimal conditions for adsorption were defined.Under the conditions of p H=5.0,C0=60 mg/L and T=298 K,the maximum adsorption capacity of MX-HCCP-PEI for U（Ⅵ）reached 216.9 mg/g.The adsorption process of U（Ⅵ）is well fitted by the quasi-secondary kinetic model and the Freundlich isotherm model.The adsorption behavior belongs to chemical adsorption,and the adsorption process is a spontaneous endothermic entropy increase process.The recycle adsorption results demonstrated that MX-HCCP-PEI has good reusability.Al l the above results demonstrated that,MX-HCCP-PEI is a promising adsorbent for removing U（Ⅵ）from wastewater.（2）LiF and hydrochloric acid etching was used to remove the Al element in Ti3AlC2.And a few-layer MXene was obtained via ultrasonical dispersion peeling with deionized water.Then amino groups functionalized MXene was obtained via immobilizationN-Aminoethyl-γ-aminopropyltrimethoxysilane（N-[3-（Trimethoxysilyl）propyl]ethylenediamine,AEAPTMS）on the surface of MXene,which was further reacted with the cyanation reagents,such as diaminomaleonitrile（DAMN）or 4,5-diaminophthalonitrile（4,5-Diaminophthalonitrile）using（HCCP）as the linker.The cyan groups functionalized MXene was further reacted with hydroxylamine hydrochloride（NH2OH·HCl）to botain carboxime functionalized MXene MX-AO（MX-AO（Ⅰ）,MX-AO（Ⅱ））.The adsorption kinetic experiments showed that the adsorption process of the two adsorbents could reach equilibrium within 1 h.At the same time,the effects of time,p H,U（Ⅵ）concentration and temperature on the adsorption effect of MX-AO U（Ⅵ）were also investigated.It was found that the adsorption effect of MX-AO（Ⅱ）was better than that of MX-AO（Ⅰ）,the maximum adsorption capacities of MX-AO（Ⅰ）and MX-AO（Ⅱ）were 129.1 mg/g and247.7 mg/g,which were 2.61 times and 5.02 times as compared with that of original MX（49.34 mg/g）,respectively.MX-AO shows better adsorption performance under acidic conditions.MX-AO can efficiently pounce U（Ⅵ）by the amidoxime groups.The fitting results of adsorption data show that the adsorption process of U（Ⅵ）by MX-AO is a spontaneous endothermic entropy increase process,and follows the quasi-secondary kinetic model and Langmuir model.（3）The hypophosphorus（HPA）modified MXene provides a new research idea for the development of green,environmentally friendly and efficient synthesis strategies.In this chapter,we synthesized hypophosphorus（HPA）functionalized MXene（MX-HPA）and inverstigated its the adsorption behavior for removal of U（Ⅵ）from aqueous solution.The suspension stability of MX-HPA was obviously improved as compared with that of MX-NH2 and original MX.The adsorption experimental results showed that the maximum adsorption capacity of MX-HPA to U（Ⅵ）could reach 160.3 mg/g,which was 3.46 times that of MX（46.39 mg/g）.The fitting results of the adsorption data show that the adsorption process of U（Ⅵ）by MX-HPA follows the quasi-second-order kinetic model and the Langmuir model adsorption,indicating that the adsorption sites on the surface of the adsorbent MX-HPA is non-uniformly distributed.Additionaly,the adsorption process is a chemical process and its adsorption performance is better under acidic conditions.What’s more,the adsorption process is a spontaneous endothermic entropy increase process. |
