| Two-dimensional graphene-like materials such as graphene oxide(GO)and transition metal carbide(Ti3C2Tx)have broad application prospects in the field of uranium-containing radioactive wastewater remediation because of their unique layered structure and exceptional physicochemical properties.This application comes along with their presence in the water environment and the potential ecological risks to biological communities and human beings.Currently,how to effectively remove adsorbent materials and trace radioactive elements in water has become the hot problem urgently waiting to be solved,which draws growing attention.Aggregation and photodegradation are two major aspects of the colloidal stability of graphene-like materials entering in the natural environment,controlling their fate and effects.In this paper,GO and Ti3C2Tx were selected as the research objects,and their colloidal properties and photoconversion behaviors under a wide range of conditions relevant to natural environment were investigated by the combination of batch experiments and dynamic light scattering tests.The main research contents were listed as follows:(1)Taking GO as the research object,the colloidal stability and light conversion of GO in water environment were investigated to provide a theoretical basis for reducing the adverse effects of adsorbents and adsorbates exposed to the natural environment.Experimental data showed that GO had excellent dispersion stability and migration ability in an ideal water environment.while GO suspension became unstable in the presence of U(Ⅵ)ions,resulting in the formation of GO aggregates.Under ultraviolet light irradiation,low concentration of U(Ⅵ)promoted the photodegradation of GO nanosheets,while high concentration of U(Ⅵ)induced the aggregation of GO and weakened the photodegradation efficiency of GO.Meanwhile,the UV-excited GO could be used as both adsorbent material and photocatalyst material,thus allowing the effective removal of low concentration U(Ⅵ)from aqueous solution.This work provides an important example of the simultaneous removal of GO(adsorbent)and U(Ⅵ)(adsorbate)in water environment.(2)Taking Ti3C2Tx as the research object,the colloidal properties and stabilities of the purchased Ti3C2Tx were discussed to fully understand its migration and fate in the natural environment.The results showed Ti3C2Tx suspension was electrostatically stable and well dispersed over the pH range from 4.0 to 10.0,and had the strong tendency to form aggregation and agglomeration in real natural water environment(tap water and Chaohu Lake water).In addition,the colloidal stability of Ti3C2Tx in radioactive elements(Cs+、Sr2+、UO22+、Eu3+ and Th4+)solutions followed the classical DLVO theory,and radioactive elements with higher concentrations and higher valences were more effective in destabilizing Ti3C2Tx.(3)Based on the above research,the influence of ultraviolet light irradiation on the environmental behavior of Ti3C2Tx was further discussed,which was of great significance in studying the photoconversion mechanism in a relatively complex environment.Experiments results showed that UV irradiation accelerated the conversion process of Ti3C2Tx to TiO2,and the photodegradation rate increased linearly with the increase of illumination time.For the case conducted in U(Ⅵ)solution,the residual concentration of Ti3C2Tx induced by ultraviolet light was further reduced,especially in the presence of low concentration U(Ⅵ).Meanwhile,the reduction of highly mobile U(Ⅵ)to less soluble U(Ⅳ)co-occurred during the photocatalytic reaction process.These findings showed that ultraviolet light irradiation could simultaneously convert Ti3C2Tx and U(Ⅵ)into the mild toxic components in water environment. |
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