The Adsorption Performance And Aggregation Behavior Of 2D MXene Material In Water Environment

Due to its unique structure and excellent physical and chemical properties,two-dimensional transition metal carbon/nitride(MXene)has become one of the research hotspots in many fields such as energy storage,sensing,catalysis,biological applications and environmental pollution control.During the continuous production and application of MXene materials,they will be inevitably discharged into the water environment.However,whether the MXene will cause harm to the ecological environment after entering the water environment has not been known.Therefore,the study of MXene’s behavior in the water environment is of great significance for predicting the migration and fate of MXene and assessing its environmental risks.This article explores the adsorption behavior of MXene materials to pollutants in water environment and its aggregation behavior and stability in real water environment.The main contents of this article are as follows:(1)The adsorption properties of U(Ⅵ)and Co(Ⅱ)in water by two-dimensional few-layer Ti3C2Tx nanosheets were studied.The results of macroscopic adsorption experiments showed that the adsorption of U(Ⅵ)/Co(Ⅱ)on Ti3C2Tx nanosheets was significantly affected by environmental conditions such as pH,ionic strength,and temperature.The maximum adsorption capacities of Ti3C2Tx nanosheets for U(Ⅵ)and Co(Ⅱ)can reach 120.82 and 93.82 mg·g-1 at pH 5.5 and 298 K,respectively.The adsorption equilibrium of U(Ⅵ)can be reached within 5 minutes,and the adsorption of Co(Ⅱ)reached equilibrium within 30 minutes.The adsorption kinetic data all conformed to the pseudo-second-order kinetic model.Microscopic experimental results demonstrated that the oxygen-containing functional groups on the surface of Ti3C2Tx participated in the adsorption reaction of U(Ⅵ)and Co(Ⅱ),thereby achieving the purpose of efficient adsorption.(2)The colloidal behavior and stability of the dispersed Ti3C2Tx MXene suspension in aqueous solution were studied.It was found that in the common pH range(5.0-9.0)of the environment,the pH value had no effect on the stability of Ti3C2Tx,while the ionic valence and ionic strength had a significant effect on the stability of Ti3C2Tx.The critical agglomeration concentrations(CCC)of Ti3C2Tx nanosheets in NaCl,CaCl2 and MgCl2 solutions were determined to be 12,0.3 and 0.4 mmol·L-1,respectively,by dynamic light scattering(DLS).In addition,the aggregation kinetics of Ti3C2Tx in different water systems was closely related to the concentration of cations and the content of organic matter in the solution.Long-term stability experiments indicated that even in natural waters rich in natural organic matter,Ti3C2Tx was unlikely to be transported over long distances.