Construction of MXene-loaded nanoscale zero-valent iron for the sequestration of ReO₄^-/TcO₄^-: Reduction enhancement behavior and remediation mechanism

Radioactive pertechnetate (TcO4-) has been widely reported to impose significant hazardous effect on the soil and groundwater, Yet, efficient purification of TcO4- in nuclear wastes remains challenging. To address this critical need, we proposed and constructed five kinds of MXene/NZVI composites with different structures, namely Ti2AlC/NZVI, Ta4AlC/NZVI, V2AlC/NZVI, Ti2AlN/NZVI and Nb4AlC3/NZVI, for TcO4- sequestration. We applied perrhenate (ReO4-) as a non-radioactive surrogate of TcO4-, and evaluated the effectiveness of ReO4- sequestered onto these MXene/NZVI. The as-constructed MXene/NZVI composites were proved to be better sequestrator in sequestering ReO4- than NZVI alone. This reduction enhancement behavior was mainly due to the synergistic effect of MXene and NZVI, which was attributed to combined factors, including the improved enrichment capacity, facilitation of electron transfer, and boosted reactivity towards ReO4-. The remediation mechanism was revealed by the X-ray diffraction (XRD) and/or X-ray photoelectron spectroscopy (XPS) analyses, which confirmed formation of ReO2 as the major reduction products. Results of this work foreshadow the potential applications of the as-constructed MXene/NZVI including Ti2AlC/NZVI, Ta4AlC/NZVI, V2AlC/NZVI, Ti2AlN/NZVI and Nb4AlC3/NZVI, to purify and sequester ReO4-/TcO4- from contaminated environments, which hold great promise in nuclear waste management.