Effect of Ti₃AlC₂ MAX Phase on Structure and Properties of Resultant Ti₃C₂T_<i>x</i> MXene

Ti3C2Tx MXene is an attractive two-dimensional (2D) material for a wide variety of applications; however, measured properties vary widely from study to study. A potential factor to the property differences relates to variability in the MAX phase precursors. To illustrate this, Ti3AlC2, the precursor for Ti3C2Tx MXene, was synthesized using three carbon sources (graphite, carbon lampblack, and titanium carbide (TiC)) at 1650 °C for 2 h. Thermal analysis was utilized to examine the reaction mechanism, indicating that the three carbon sources experience different reaction pathways. The Ti3AlC2 MAX powders were then converted into Ti3C2Tx MXene and delaminated. The products revealed differences with respect to the lateral flake size, chemical composition, chemical stability in deionized water, and electrical conductivity. Graphite-produced Ti3C2Tx showed the highest conductivity (∼4400 S/cm) and is the most stable (time constant of 10.1 days), while TiC-produced MXene has comparable conductivity (∼3480 S/cm), but the lowest colloidal stability (4.8 days), and carbon lampblack has the lowest conductivity (∼1020 S/cm) and low chemical stability (5.1 days). Furthermore, gas sensors were fabricated from all three MXenes to probe differences in their performance. The TiC-produced Ti3C2Tx showed the highest response, followed by graphite-produced, and last Ti3C2Tx produced from carbon lampblack. This illustrates that synthesis of the MAX precursor material leads to significant difference within the resultant MXene and provides another pathway for further control over their properties.