more recently, also 2D pnictogen compounds have come into focus because of their combination of unusual, potentially useful properties in electronics, energy, and catalysis. [6][7][8][9][10][11][12][13] For the case of bismuth, this includes recent work on binary 2D bismuth oxides, [10][11][12][13] and 2D ternary and multinary oxygen-containing bismuth compound phases, including 2D Bi-oxyhalides, 2D Bi 2 WO 6 , 2D Bi 2 MoO 6 , or 2D BiVO 4 . [2,3,9,14,15] Amongst the ternary bismuth compound phases, the bismuth oxycarbonate (BOC) Bi 2 O 2 CO 3 phase, also called bismutite and bismuth subcarbonate (BiO) 2 CO 3 , is of particular interest. [16] Bi 2 O 2 CO 3 has an intrinsically layered structure composed of alternating Bi 2 O 2 2+ and CO 3 2− sub-layers and is a semiconductor with a band gap of ≈3.1-3.5 eV. [16] In nanostructured form Bi 2 O 2 CO 3 has been shown to have useful properties in particular toward energy, catalysis, and photocatalysis. [16] In particular for photocatalysis, 2D morphology can offer benefits over other morphologies including intrinsically high specific surface areas and short migration lengths of photogenerated charge carriers to the reaction fronts on the 2D materials' surfaces. This can reduce recombination losses and thus lead Laterally large (≈3 µm), atomically thin 2D Bi 2 O 2 CO 3 nanosheets (2D bismuth oxycarbonate, 2D bismutite) are fabricated via sonochemically assisted, template-free synthesis. Keys to the synthesis of the freestanding, laterally large 2D Bi 2 O 2 CO 3 nanosheets from bulk Bi powder are choice of suspension medium, controlled reaction temperatures, and several hours processing time. Lateral sizes of 2D Bi 2 O 2 CO 3 can be controlled between µm-sized nanosheets and tens of nm sized nanoflakes solely based on the choice of suspension medium.
