Comprehensive waste‐free utilization of <i>Calendula officinalis</i> <scp>L</scp> . biomass: Cationic ( <scp>Basic Green</scp> 4) and anionic ( <scp>C</scp> ongo <scp>Red</scp> ) dye adsorption capacity and antioxidant activity

Abstract The research aimed to elucidate the multifaceted applications of Calendula officinalis L. in environmental remediation by examining the adsorption efficacy and antioxidant characteristics. This biomass waste was analyzed using FT‐IR, SEM, and pH pzc . Adsorption tests were conducted by varying the concentration (10–50 mg/L), duration (0–180 min), pH (2–10), and dosage (0.01–0.20 g/50 mL). The equilibrium data were utilized in various non‐linear two and three‐parameter isotherms. The findings indicated that the removal process transpired as a monolayer according to Langmuir isotherm, with the value established at 40.06 mg/g for BG4 dye and 25.08 mg/g for CR dye at 298 K. Kinetic analyses indicated that the adsorption of BG4 and CR onto C. officinalis L. conformed to pseudo‐second‐order and Elovich kinetics. Thermodynamic analyses indicated that the process was endothermic ( = 18.96 kJ/mol for BG4 and 16.92 kJ/mol for CR) and spontaneous ( = −28.66 kJ/mol for BG4 and −30.19 kJ/mol for CR). The antioxidant capacity was assessed using multiple methods utilizing the extract of C. officinalis L. in the second section. The study's results demonstrated that C. officinalis L. may serve as an effective and reusable adsorbent for both cationic and anionic dyes in aqueous solutions, as well as a natural source of antioxidants.