Tunable fluorescent amino-functionalized Ti 3 C 2 T x MXene quantum dots for ultrasensitive Fe 3+ ion sensing.

The development of sensors with high sensitivity, good selectivity and reproducibility are of great importance for the detection of Fe 3+ in contaminated water for environmental monitoring. In this work, a reflux approach has been adopted to synthesize Ti 3 C 2 T x quantum dots (QDs) based on the cutting effect of tetramethylammonium hydroxide (TMAOH) on Ti 3 C 2 T x at high temperature. The surface-functionalized Ti 3 C 2 T x QDs contained abundant amino groups and exhibited tunable pH-dependent emission, which was attributed to the protonation and deprotonation of the surface terminations. The linearity of the radiometric fluorescence intensity versus pH indicates its great potential as a dual-emission ratiometric pH sensor. Additionally, the Ti 3 C 2 T x QDs exhibited tunable excitation-dependent emission behavior, which was related to the degree of passivation by the amino groups on the surface. Furthermore, the fluorescence intensity of the Ti 3 C 2 T x QDs shows a linear response toward Fe 3+ in the nanomolar to micromolar range with a low detection limit of 2 nM, originating from the oxidation and reduction between Fe 3+ and Ti 3 C 2 T x . This ultra-sensitive and selective detection capability demonstrated the environmental application potential for Ti 3 C 2 T x QDs as a nanoprobe to monitor Fe 3+ .