The effect of etching solution on adsorption properties of Ti3CNTx for chlortetracycline removal†

2D MXenes are highly promising for adsorption due to their hydrophilicity, large surface area, multilayer structure, and surface functionalities. This study synthesizes a new MXene, titanium carbonitride (Ti₃CNT_x), using HF and LiF + HCl etching solutions, resulting in two types: M-HF30 and M-LiF + HCl. The adsorption capacities of these MXenes were evaluated for chlortetracycline hydrochloride (CTC). Characterization techniques, including X-ray powder diffraction, scanning electron microscopy, the pH of the point of zero charge, and Fourier-transform infrared spectroscopy were employed to assess the material properties and structural changes post-CTC contact. Both MXenes demonstrated significant CTC adsorption, with M-LiF + HCl achieving a higher removal capacity of 290 mg g⁻¹ compared to 105 mg g⁻¹ for M-HF30. This enhanced performance is attributed to LiF intercalation and improved surface functional groups, even if it has a lower surface area than M-HF30. Adsorption kinetics and isotherms indicated that CTC adsorption followed a pseudo-second-order kinetic model and the Langmuir model, suggesting monolayer adsorption dominated by chemisorption. Additionally, M-LiF + HCl showed good reusability over three adsorption cycles. Overall, Ti₃CNT_x MXene, particularly M-LiF + HCl, presents a promising new adsorbent for water treatment applications.