A one-step ultrasound-assisted synthesis of erbium-substituted nanocrystalline Mn₂O₃ and sonocatalytic degradation of azo dye

In this work, the effective degradation of methyl orange as a model of azo dyes which are the common industrial pollutants by Er-doped Mn₂O₃ nanomaterials was introduced. Erbium (Er³⁺)-substituted nanocrystalline Mn₂O₃ (Mn_2−xEr_xO₃) was obtained by oxidation of Mn(NO₃)₂ at ambient conditions under ultrasound sonication in basic solution. Er³⁺ substitution into the structure of Mn₂O₃ resulted in a material with new physical properties, composition and morphology. The SEM, XRD, EDX, TEM, HRTEM, XPS techniques were used for characterization of prepared material. Increasing the amount of Er³⁺ ions during synthesis did not increase significantly the percent substitution in the final product beyond 6%. The influence of substitution of Er³⁺ ions into Mn₂O₃ caused a red shift in the absorbance and a decrease in the band gap from 2.01 to 1.92 eV in the case of 6% Er-doped Mn₂O₃. The as-synthesized compounds were used for sonocatalytic degradation of Methyl Orange (MO). 6% Er-doped Mn₂O₃ displayed the elevated sonocatalytic activity considering various amounts of erbium. Considering radical scavengers, the sequence of inhibitory effect was 1, 4 Benzoquinone > I⁻ > SO₃²⁻ > t-BuOH > C₂O₄²⁻. The influence of various specifications like catalyst amount, primary dye concentration, and ultrasonic power was explored. Furthermore, 92% degradation of the dye in 70 min under ultrasonic irradiation suggests that 6% Er-doped Mn₂O₃ is a promising sonocatalyst for environmental remediation.