Nature-inspired compositional control of transition-metal-doped ammoniotinsleyite and spheniscidite particles for design of color hue

Abstract

Leucophosphite-group ammoniotinsleyite [(NH₄)Al₂(PO₄)₂(OH)·2H₂O] and spheniscidite [(NH₄)Fe₂(PO₄)₂(OH)·2H₂O] particles were prepared via a hydrothermal route. The color hues of the particles were controlled by transition-metal doping, i.e., with Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺ ions. Single-phase, non-doped ammoniotinsleyite and spheniscidite particles were obtained from AlCl₃ and FeCl₃ aqueous solutions, respectively, by mixing with (NH₄)₂HPO₄ solutions and subsequent hydrothermal treatment. Transition-metal doping was performed by adding MnCl₂, CoCl₂, NiCl₂, and CuCl₂ to the precursor solutions. The product colors depended on the host materials and dopants. For the ammoniotinsleyite particles, only Cu²⁺ doping was achieved, and the product colors varied from white to light blue. Transition-metal-doped spheniscidite particles were obtained with all the dopants. Brownish spheniscidite powders were obtained by addition of Mn²⁺ and Co²⁺ ions, whereas doping with Ni²⁺ and Cu²⁺ ions resulted in yellow-green and green colors, respectively.