Exploration of the Novel Adsorptive Remediation of Malachite Green by NaOH‐Activated Chromolaena odorata Stem Biochar Through Performance, Mechanistic Insights, Techno‐Economic Aspects, Toxicity, and Analyses of Regenerability

ABSTRACT The novelty of an adsorptive remediation of an organic cationic malachite green oxalate (MG) dye by modified biochar has been explored. The physisorptive and chemisorptive properties of the NaOH‐activated Chromolaena odorata‐ based biochar (COBB) are investigated for explaining its performance. The physisorptive properties of the bio‐sorbent are investigated using scanning electron microscopy‐energy‐dispersive spectroscopy (SEM‐EDS) and Brunauer‐Emmett‐Teller (BET), while the chemisorptive properties are evaluated using Fourier‐transform infrared (FTIR), x‐ray photoelectron spectroscopy (XPS), and x‐ray diffraction (XRD). The shifting of the C1s, O1s, and N1s peaks of the binding energy in XPS spectra and supplementary evidences from other analytical analyses reveal that the MG adsorption is via electrostatic interaction, H‐bonding, π–π interactions, and pore diffusion. The Langmuir maximum adsorption capacity and % removal of MG are found to be 229.30 mg/g and 96.32%, respectively at an optimum experimental condition. The excellent reusability of COBB is ensured with an adsorption capacity of 168.12 mg/g after five cycles of desorption‐regeneration‐reutilization. Additionally, the toxicity of the treated wastewater is estimated experimentally, and the treated wastewater is found to be toxicologically viable for reuse. Summarily, the explored bio‐sorbent is efficient (capacity of 229.30 mg/g and % removal of 96.32), inexpensive ($5.79/kg) by cost analysis, and reusable.