Sustainable Approach for Eradicating Methylene Blue from Simulated Wastewater by Cost‐Effective and Eco‐Friendly Agricultural Waste

Abstract In this study, marigold ( Calendula officinalis ) leaves, a locally sourced agricultural waste, were used as an alternative and economical adsorbent to remove methylene blue (MB) from both its aqueous solution and simulated textile wastewater. Extensive cultivation of C. officinalis in Asia, Africa, South America, and parts of Europe generates substantial residual biomass. Optimal MB adsorption using marigold leaves powder occurred at pH 7.0, biosorbent dosage 3.0 g L −1 , and 120 min contact time. The maximum dye uptake was found to be 216.10 mg g −1 . The Langmuir isotherm model demonstrated the best fit for the sorbate–sorbent interaction. The kinetic study showed that pseudo‐second‐order and film diffusion model suited the experimental data well, suggesting a chemisorption phenomenon. The MLP biosorbent was comprehensively characterized using zeta potential analyzer, Brunauer–Emmett–Teller (BET) analyzer, Fourier transform infrared (FTIR) spectroscopy, and field emission scanning electron microscopy (FESEM). The proposed dye adsorption mechanism mainly included the interactions such as electrostatic forces, hydrogen bonding, and π–π stacking. Thermodynamically, the dye adsorption process was spontaneous, entropy driven, and endothermic under studied experimental conditions. The encouraging outcomes showed that MLP could be employed as a low‐cost and alternative biosorbent to eradicate MB dye from aqueous solutions.