Preparation And Selective Electro-adsorption Of Two-dimensional Layered Nano Titanium Carbide Electrode

Capacitive deionization(electro-sorption)is a simple,energy-saving,and environmentally friendly water treatment technology.The electrode material is the core of electro-sorption.Mxene,a two-dimensional layered nanomaterial,is generally obtained by means of chemical etching.Its surface is often covered by functional groups such as oxygen,fluorine and hydroxyl,with a large specific surface area and good conductivity and hydrophilicity.As the most studied Mxene material,Ti3C2 is a potential electrode material with high volume capacitance,high multiplier performance and cyclic stability.In this paper,titanium carbide aluminum(Ti3AIC2)was etched into Ti3C2 with hydrofluoric acid by liquid etching method.The effect of etching time and temperature on the product was studied.The optimal etching time was 24h and the optimal temperature was 60?.Ti3C2 electrode was prepared by coating method.The morphology,crystal structure and element composition of Ti3C2 electrode were characterized by SEM,XRD and XPS.The cyclic voltammetry and AC impedance of Ti3C2 electrode were measured by electrochemical workstation.Then the effects of CF,NiAl-LMO and Ti3C2 on the selectivity of Ca2+in the mixed solution of Na+,Mg2+,Ca2+were investigated.It was found that when NiAl-LMO was used as the counter electrode,the selectivity of Ti3C2 to Ca2+in the mixed solution was the highest,and the adsorption capacity was 109.76mg/g,2.5 and 9.8 times of Mg2+and Na+,respectively.The adsorption kinetics and isotherm fitting of Ca2+with the highest selectivity and Na+ with the lowest selectivity were carried out.The results showed that the adsorption process was dominated by physical adsorption,the saturated adsorption capacity of Ca2+was 585.29mg/g,and the saturated adsorption capacity of Na+ was 137.19mg/g.The desorption of Ca2+ can be achieved after applying the reverse voltage,and the removal rate of Ca2+ by the Ti3C2 electrode is 39.9%after 5 electro-adsorption-desorption cycles,not significantly different from the initial removal rate of 42.5%.The mechanism of selective adsorption is mainly that Ti3AlC2 is etched by hydrofluoric acid to generate Ti3C2.The ion-exchange sites on the[Ti-O]-H+ group help to adsorb Ca2+,Mg2+and Na+.Compared with the monovalent cation,the divalent cation can provide more negative charge to neutralize the Ti3C2 surface.The divalent cation can be better adsorbed with lower hydration,so the selectivity of Ca2+ is higher than that of Mg2+ and Na+.Finally,the electro-adsorption of Pb2+ on Ti3C2 electrode was studied.The effect of voltage on the adsorption rate of Pb2+was investigated.It was found that the maximum adsorption rate of Ti3C2 to Pb2+was 98.48%when the voltage was 1V.In the mixed solution of Ca2+ and Pb2+,the equilibrium adsorption capacity of Ti3C2 electrode to Pb2+ is 137.47 mg/g,which is 10.5 times of Ca2+equilibrium adsorption capacity(13.11 mg/g).