One-pot eutectic molten salt synthesis of MXene-supported nanoscale zero-valent iron composites for efficient adsorption and reduction of uranium

The environmental remediation potential of nanoscale zero-valent iron (nZVI) is generally hindered by severe particle agglomeration or poor stability. A straightforward approach to overcome these challenges is to uniformly and firmly disperse nZVI onto high surface area substrates such as two-dimensional materials. Herein, we propose a novel method for one-pot synthesis of MXene-nZVI composites based on the eutectic molten salt (MS) etching of MAX phase materials. The utilization of ferrous ions with high redox potential in chloride MS enables efficient removal of weakly bonded Al atoms from MAX phases, leading to the formation of MXenes and concomitant in situ reduction of Fe2+ to nZVI on MXene surface. Batch adsorption experiments showed that the effective synergy between nano-lamellar MXene and nZVI played a pivotal role in boosting U(VI) elimination performance of the composites. The optimized MS-MXene-nZVI could rapidly and completely eliminate 291 mg/L U(VI) at an adsorbent dosage of 0.2 g/L, and the maximum removal capacity reached 1750 mg/g. Further environmental application assessment indicated an excellent potential of MS-MXene-nZVI for U(VI) sequestration from complex acid mine drainage. Advanced spectroscopic analyses provided clear evidence of the conversion of Fe0 to structural Fe2+ during the reaction and established that the removal mechanism of U(VI) was primarily reductive immobilization, concomitantly with surface chemisorption and hydrolysis precipitation. This study offers new insights into the green and facile preparation of MXene-based nZVI composites via MS strategy, as well as their environmental remediation application in the highly efficient separation of radionuclides and other contaminants.