Synthesis of Zn-doped MnO2 nanoparticles using Echinops Kebericho root extracts for photocatalytic application

The discharge of effluents from industries containing persistent organic dyes such as methylene blue (MB) and methyl orange (MO) poses a significant environmental concern. Addressing this challenge requires sustainable, eco-friendly, highly efficient, and cost-effective treatment technologies. In this study, the Zn-doped MnO 2 NPs (Zn = 1 %, 3 %, 5 %M) were synthesized by a green route using Echinops Kebericho root extract, to evaluate photocatalytic degradation of methylene blue (MB) and methyl orange (MO). UV–Vis, SEM, XRD, FT-IR, and TGA characterized materials. Comparisons between undoped MnO 2 and 3 % Zn-doped MnO 2 NPs were used to assess optical and structural changes. The undoped MnO 2 (3.10 eV) and the 3 % Zn-doped sample (2.62 eV) showed a bandgap reduction, along with a slight crystallite-size decrease from 24.64 to 23.76 nm. SEM revealed irregular morphologies. In photocatalysis, MB degraded (95 %) at a catalyst dose (0.596 g), MB concentration (105 mg/L), and contact time (95 min); MO degraded (93 %) at a catalyst dose (0.557 g), MO concentration (48.3 mg/L), and contact time (142.6 min). Pseudo-first-order kinetics yielded R 2 = 0.996 for MB and 0.995 for MO. Isotherm modeling favored Langmuir adsorption (R 2 = 0.997 for MB and 0.996 for MO). Thermodynamics indicated ΔH° ≈ 30.283 kJ mol −1 (MB) and 30.38 kJ mol −1 (MO); ΔS° ≈ 45.54 J mol −1 K −1 for both dyes; ΔG° ≈ 30.24–30.34 kJ mol −1 K −1 T over the studied temperatures. The 3 % Zn-doped MnO 2 NPs demonstrated excellent stability and recyclability, retaining about 78 % MB and 76 % MO degradation after six cycles over six months. This study, green-synthesized Zn-doped MnO 2 NPs, especially at 3 % Zn, exhibit enhanced optical and catalytic properties and show strong potential as recyclable photocatalysts for degrading industrial dyes and other organic contaminants in wastewater.