Adsorption of Cr(VI) ions onto fluorine-free niobium carbide (MXene) and machine learning prediction with high precision

Abstract

Due to the unique surface microstructure, abundant active sites, and rich functional groups, two-dimensional MXene is increasingly gaining attention in the field of environmental purification. Herein, novel fluorine-free niobium carbide (Nb2CTx) was successfully synthesized using hydrothermal technique and applied towards the Cr(VI) ions elimination from wastewater. The structure and surface properties of the Nb2CTx were analyzed by various characterization techniques. Based on the findings of batch adsorption, the maximum Cr(VI) ions was removed at solution pH 5 with adsorbent loading of 1 g/L and Cr(VI) initial concentration of 10 mg/L just after 20 min of stirring. Besides, the characteristic information of Nb2CTx and their adsorption data was used to build a machine learning CatBoost model with high precision (R2 = 1, RMSE = 0.145, MAE = 0.08). Cr(VI) removal by MXenes displayed rapid kinetics governed by pseudo-second-order reactions, with adsorption isotherm aligning well with Langmuir isotherms (R2 = 0.998), achieving an adsorption capacity of 93.6 mg/g. The removal mechanism investigation proposed that the electrostatic interactions, chemical reduction and hydrogen bonding were the key driving forces. The hydrothermal route proposed in this study enabled the fabrication of environmental friendly Nb2CTx, which can pave the way for their widespread applications in environmental purification.