Green synthesis of MnO nanoparticles using Costus woodsonii flowers extract for effective removal of malachite green dye.

The pollution of organic dyes such as malachite green is one of the globally critical issues, calling for efficient mitigation methods. Herein, we developed green MnO nanoparticles synthesized using natural compounds extracted from Costus woodsonii flowers under an ultrasound-assisted mode. The materials were characterized using several physicochemical techniques such as Fourier-transform infrared spectroscopy, X-ray diffraction, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, Raman spectroscopy, and N adsorption desorption isotherm measurement. The X-ray diffraction and N isotherm plots confirmed the presence of tetragonal γ-MnO phase and mesoporous structure, respectively. Carbonyl groups derived from flavonoids or carboxylic compounds were found in the surface of green MnO nanoparticles. The effect of pH, contact time, dose, and concentration on the adsorption of malachite green over green MnO was carried out. The maximum malachite green adsorption capacity for green MnO nanoparticles was 101-162 mg g. Moreover, kinetic and isotherm adsorption of malachite green obeyed Langmuir (R = 0.980-0.995) and pseudo first-order models (R = 0.996-1.00), respectively. Adsorption of malachite green over green MnO was a thermodynamically spontaneous process due to negative Gibbs free energy values (ΔG < 0). Green MnO nanoparticles offered a high stability through the FR-IR spectra analysis. With a good recyclability of 4 cycles, green MnO nanoparticles can be used as potential adsorbent for removing malachite green dye from water.