Beyond carbon dots: Intrinsic reducibility in Ti3C2 MXene quantum dots induces ultrasensitive fluorescence detection and scavenging of Mn(VII)

Recently, cutting two-dimension MXenes into quantum dots (QDs) becomes a hotspot due to the introduction of photoluminescence properties with concomitantly extensive applications. However, it is still a challenge to utilize MXene QDs (MQDs) for the simultaneous detection and scavenging heavy metal ions that may threaten environment safety and human health. Herein, MQDs are prepared by hydrothermal treatment of Ti3C2 MXene in the presence of ethylenediamine and oxidized by H2O2 to obtain carbon dots (CDs). These MQDs and CDs with various functional groups show excellent dispersibility, small size (less than 10 nm), good fluorescence, and high stability. Then, Ti3C2 MQDs are firstly utilized to establish the fluorescent probe towards Mn(VII) with limit of detection (LOD) as low as 5.2 nM. The ultrasensitive selectivity of Ti3C2 MQDs is attributed to their inherent reducibility, which can cause the redox reaction between Ti3C2 MQDs and Mn(VII) with precipitous fluorescence quenching and elimination of Mn(VII). After the lack of reducibility, CDs show selective response to Mn(VII) with LOD of 230 nM based on synergistic inner-filter effect (IFE) and static quenching. Furthermore, the MQDs are successfully applied as a dual functional platform to evaluate the level of Mn (VII) and scavenge it in plant leaves. The comparation of MQDs and CDs for Mn(VII) detection and scavenging will bring more inspiration about intrinsic properties of QDs derived from MXenes for their composite material design and multifunctional use.