Preparation Of Titanium Carbide-based Composites And Their Adsorption Properties And Mechanism Of Anionic Iodine And Chromium

MXenes,a new family of two-dimensional materials,has large specific surface areas,abundant functional groups,easily functionalized,strongly radiation-proof and high conductivity of metals,which make it an ideal material with great application prospects.It is extensively studied in environmental remediation,energy storage,sensors,catalysis,etc.However,with its vigorous development,MXenes material can no longer satisfy market needs.By modifying its functions,the author obtained MXenes-based layered composites with an open structure and effectively improved physical and chemical properties.For example,the increase of specific surface area helps expose more active sites;the expansion of layer-to-layer spacing facilitates ion transport between layers.In addition,the author fixed some substances on the surface or between layers of MXenes via the effect of two-dimensional confinement,which produced a synergistic effect with MXenes and improved the properties of MXenes,thereby greatly expanding the scope of application of MXenes.In this paper,the author synthesized two kinds of composite materials based on Ti₃C₂T_X,the most representative monolayer-layer material in the MXenes family,studied the adsorption properties and mechanism of anionic iodine and chromium in water.The synthesized materials were characterized by SEM-EDS,BET,XRD,FT-IR,and XPS,and analyzed the effects of pH value,adsorption time,initial concentration,temperature and coexisting anions on their adsorption properties through static adsorption experiments.The main results achieved are as follows:(1)Based on silver nitrate,the author prepared nano silver-supported monolayer Ti₃C₂T_x(AgNPs-Ti₃C₂T_X),a new composite material,by surface active connection,and systematically studied its morphology,structure,chemical composition,and adsorption properties through characterization and experiments.AgNPs-Ti₃C₂T_X has a lamellar structure,a large specific surface area,and uniformly distributed nano silver on the surface.At a pH of 2,the removal rate of iodide ion solution with a concentration of 150 mg/L was close to 100%.The adsorption reached equilibrium within 90 minutes,the process of which conformed to pseudo-second-order model.The maximum adsorption capacity for iodide ions reached 415.87 mg/g,whose adsorption isotherm well fitted the Langmuir model.The removal rate in the high-concentration coexisting anion mixed solution was more than 99%,which showed excellent selectivity to iodide ions.Related characterization tests showed that the nano silver active component loaded on Ti₃C₂T_X is the key to achieve efficient removal of iodide ions.(2)Composite material PEI-Ti₃C₂T_X was obtained by combining polyethyleneimine(PEI)with monolayer-layer Ti₃C₂T_X through layer-by-layer self-assembly.It has an irregular porous three-dimensional network structure.Surface-bound PEI could effectively adjust surface charge,amino groups carried by which had a strong affinity for heavy metal ions such as Cr(?).Adsorption experiments showed that the adsorption data of Cr(?)conformed to the Langmuir adsorption isotherm model.The maximum adsorption capacity was186.5 mg/g at 25?.The adsorption reached equilibrium within 100 minutes,data about which conformed to the pseudo-second-order model.The different concentration of anions had little effect on Cr(?)adsorption.The desorption experiments showed that 1 mol/L Na OH solution had a certain effect on the desorption regeneration of the materials.The electrostatic adsorption of Cr(?)on the surface of composite materials and the reduction of Cr(?)by Ti₃C₂T_X made the adsorption of PEI-Ti₃C₂T_X on Cr(?)show obvious advantages.In summary,the successful preparation of two kinds of Ti₃C₂T_X-based composite materials and their outstanding performance in anion adsorption make possible the wide application of Ti₃C₂T_X in adsorption as a carrier.