Peganum Harmala seeds extract: A green synthesis route for Mn-doped ZnO nanoparticles as an adsorbent for crystal violet dye removal

The employment of green synthesized nanomaterials for water pollution prevention is increasing nowadays. Herein, Mn-doped ZnO nanoparticles were synthesized using Peganum Harmala seed extract and subsequently used for crystal violet (CV) dye removal from aqueous solutions. The first part of the study describes the preparation of the adsorbent (Mn-ZnO NPs) using a simple coprecipitation method. The surface properties of the material were characterized by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The second part investigates the adsorption of CV dye onto the surface of the prepared Mn-ZnO NPs. Additionally, the isotherm, kinetics, and thermodynamics of the adsorption process were studied in detail. Batch adsorption analysis was carried out by evaluating different parameters, such as the amount of the adsorbent (0.01g to 0.04 g), CV concentration (20 to 80 mg/L), adsorption time (30 to 120 min), and temperature (35 to 65 ⁰C). The maximum CV dye adsorption capacity of the Mn-ZnO NPs was 45.60 mg/g. The thermodynamic study revealed the spontaneous, exothermic, and feasible nature of the adsorption process, primarily driven by physical forces. Kinetic and isotherm analyses indicated that the adsorption of the dye best fit the Freundlich isotherm and pseudo-second-order models, respectively. Mn-doped ZnO is considered an effective adsorbent for CV, benefiting from its rapid and easy preparation, non-toxic nature, and 94% adsorption efficiency. The material holds potential for future applications in the removal of organic dyes from wastewater.