Three-dimensional porous MXene-cellulose aerogel: An efficient adsorbent for sequential capture of Hg(II) and decolorization of methylene blue

A 3D porous MXene/cellulose aerogel is fabricated by sol-gel and freeze-drying technique. • It achieves a high Hg(II) uptake of 877.19 mg/g at 318 K via chemisorption and redox. • The aerogel also removes methylene blue efficiently by electrostatic attraction. • It shows good reusability, easy separation, and structural stability. Aqueous contamination by heavy metal ions and organic dyes represents two major categories of water pollutants. Developing adsorbents that can efficiently remove both types is highly desirable. Here, multilayered MXene (Ti 3 C 2 T x ) was prepared by selective etching of Ti 3 AlC 2 using LiF/HCl and combined with cellulose to construct a three-dimensional porous MX@Cell composite aerogel via sol-gel and freeze-drying. The materials were characterized by SEM, XRD, FTIR, nitrogen adsorption-desorption, and XPS. Batch adsorption tests for Hg(II) and MB were conducted separately. MX@Cell-25 (25 wt% MXene) achieved a maximum theoretical Hg(II) capacity of 877.19 mg/g at 318 K, outperforming numerous previously reported adsorbents. It followed pseudo-second-order kinetics and the Freundlich isotherm, indicating chemisorption-dominated multilayer adsorption on a heterogeneous surface. Thermodynamic analysis indicated that the adsorption of Hg(II) on MX@Cell-25 was a spontaneous process accompanied by an entropy increase and an endothermic reaction ( ΔH  > 0), confirming that higher temperatures favored the adsorption process. XPS revealed a synergistic mechanism of electrostatic attraction, surface coordination, and redox reactions. For MB, the maximum capacity was 104.93 mg/g at 318 K, with pseudo-second-order kinetics and Langmuir isotherm fitting, suggesting monolayer adsorption driven by electrostatic attraction. The composite showed good reusability (about 85% Hg(II) capacity retention after seven cycles), as well as easy separability and environmental friendliness. This work demonstrates that MXene/cellulose composite aerogel is a promising candidate for removing both heavy metal ions and organic dyes from water. Download: Download high-res image (274KB) Download: Download full-size image