Amorphous manganese polyphosphates: preparation,characterization and incorporation of azo dyes

Amorphous Mn²⁺ polyphosphate materials were prepared at room temperature through the coacervation of polyphosphate solutions. These new materials display the typical Mn²⁺ red emission with a broad band centered at 15,290 cm⁻¹ (bandwidth—1,320 cm⁻¹). Excitation spectra display typical Mn²⁺ (d⁵) absorption bands assigned to transitions from the ⁶A_1g ground state to the ⁴T_2g, (⁴A_1g, ⁴E_g), ⁴T_2g, and ⁴T_1g Mn²⁺ excited states. Transition energies allow estimating the Mn²⁺ ligand field strength as intermediate between the one observed in Mn²⁺ aqueous solutions and the one observed in Mn²⁺ phosphate glasses. Azo dyes, methyl red and methyl orange, were incorporated into the manganese polyphosphate coacervates structure. Raman scattering and visible light reflectance results show azo dyes acid forms inside the hydrated polyphosphate structure and sensitivity to the atmosphere pH. Release of azo dyes species was observed from these new solid hybrid materials in aqueous medium.