Mass preparation of multilayer MXene powder

For the small-batch chemical etching, 1 g of the Ti3AlC2 was slowly added over 5 min into a 60 mL polypropylene bottle containing 10 mL solution composed of 1 mL 29 M (49 wt. %) HF , 3mL deionized H2O, and 6 mL 12 M HCl , as described in detail in previous reports.The reaction was allowed to continue for 24 h with stirring at 500 rpm at 35 ℃. Forthe large-batch synthesis, a custom-designed 1 L reactor was used for etching . Prior to addition of the MAX phase, 50 mL of HF, 150 mL H2O, and 300 mL HCl (same 1:3:6 volumeratio as earlier) were added into the reactor. With a screw feeder, 50 g of the Ti3AlC2 powder was uniformly added into the reactor over 5 min. The mixture was stirred at 150 rpm for 24 h, with water continuously flowing through the reactor cooling jacket to maintain the temperature at 35 ℃.Once the reaction was complete, both mixtures were washed with deionized water by centrifugation at 3500 rpm to settle the powders and decant the clear supernatant. The washing cycles were repeated until the supernatants reached neutral pH.