Figure 2
From: Synthesis of 2D layered transition metal (Ni, Co) hydroxides via edge-on condensation
2D Ni(OH)2 growth mechanism. (A) 2D growth mechanism of Ni(OH)2 via edge-on condensation after nucleation. I. The buildup of localized negative charge (orange ring) incurred by edge OH− ions on the nucleus attracts approach of Ni2+ ions; II. Ligand exchange at labile Ni2+ centers, undergoing substitution with hanging OH− groups when proximal to an existing crystal, which guides continues substitution of terminal OH− groups at newly bounded Ni2+; III. The unit is locking into the crystal structure; IV. Deprotonation of coordinated H2O or its displacement by OH− to extend the crystal domain (V) or to continue the add-on (II). (B) Schematic of [Ni(NH3)6]2+ blocking the growing nuclei and crystals, the orange ring represents the localized negative charge. (C) Optical image of the obtained 2D Ni(OH)2 without additional NH4OH, where circular flakes are widely observed. (D) Optical image of the obtained 2D Ni(OH)2 with 0.6 ml additional NH4OH, the crystal size are significantly decreased. (E) Absorbance of 2D Ni(OH)2/H2O dispersion without (red curve) and with 0.6 ml additional NH4OH (purple curve), three absorption bands assigned left to right as 3A2g → 3T1g (3F), 3A2g → 3T1g (3F), 3A2g → 3T2g, consistent with homoleptic six-coordinate Ni(II) complexes. Inset: 2D Ni(OH)2/H2O dispersion of (C) (left) and (D) (right).
