Ecologically friendly 2D/2D Na+-MXene/LDH for cesium adsorption in salt lakes: A comprehensive study on adsorption performance, mechanisms, and environmental impact

Abstract

Cesium is a rare metal of paramount importance across various domains. Despite abundant cesium resources in Qinghai-Tibet Plateau salt lakes, concentrations remain low, and existing adsorbents generally exhibit limited adsorption capacities. Consequently, there is a pressing need for the development of an adsorbent capable of effectively separating and efficiently extracting cesium ions. This work utilizes the unique functional groups and negative charge characteristics of the two-dimensional (2D) MXene surface to promote the precipitation and crystallization of 2D layered double hydroxides (LDH), thereby enabling the in-situ growth of hydrotalcite on the MXene surface and synthesizing a 2D/2D stacked Na⁺-MXene/LDH composite. The results indicated that Na⁺-MXene/LDH exhibited enhanced specific surface area and interlayer spacing, introducing additional active sites that significantly improved Cs⁺ adsorption capacity, with a maximum recorded uptake of 961.5 mg/g, surpassing previously reported MXene-based adsorbents. Adsorption tests conducted on brines from four hydrochemical types of salt lakes on the Qinghai-Tibet Plateau revealed that Na⁺-MXene/LDH displayed the highest distribution coefficient (K_d^Cs) of 31.92 × 10⁴ mL/g in Dong Taijnar Lake, demonstrating a strong affinity and selectivity for Cs⁺. The mechanisms underlying the enhanced adsorption performance were elucidated. Additionally, ecological safety assessments, along with evaluations of microbial diversity and water quality in Qinghai Lake, confirmed that Na⁺-MXene/LDH preserved microbial diversity and stabilized community structures, thereby underscoring its non-toxic and environmentally friendly characteristics. This research provides a promising adsorbent for cesium extraction from brine, with potential applications in water purification and ecological restoration.