Efficient Removal of Paraquat Pollutants Using Magnetic Biochar Derived from Corn Husk Waste: A Sustainable Approach for Water Remediation

Due to the widespread production of maize, the waste created by this crop has become a serious concern. This study applied the concept of waste circulation to the production of magnetic biochar from corn husk waste to remediate paraquat-contaminated water. Magnetic biochar (MB) was produced by impregnating maize husks with iron and carbonizing the residue in a nitrogen environment. Carbonized MB at the temperature of 850°C (MB-01-850) exhibited a combination of microporous and mesoporous structures ( $V_{\text{meso}}=0.30\text{c}{\text{m}}^3/\text{g}$ , $V_{\text{micro}}=0.12\text{c}{\text{m}}^3/\text{g}$ ), while biochar created only a microporous structure ( $V_{\text{micro}}=0.11\text{c}{\text{m}}^3/\text{g}$ ). According to the findings, Fe(NO3)3 significantly affected the increase in mesopore formation after carbonization. In addition, biochar exhibits excellent magnetic responsiveness. MB-01-850 reached equilibrium within approximately 20 min in synthetic water. Batch adsorption studies showed that MB-01-850 had maximum adsorption capacities ( $Q_0$ ) of 34.97 mg/g and 31.63 mg/g for synthetic and natural water, respectively. The unmodified biochar (without mesopores) had a $Q_0$ of 4.08 mg/g. This indicates that the presence of mesopores improves the effectiveness of paraquat adsorption. Additionally, the adsorption performance of magnetic biochar exhibited no statistically significant variance when tested under natural water conditions. Furthermore, magnetic biochar demonstrates impressive regeneration capacity, allowing it to be regenerated almost entirely for a minimum of four cycles using a sodium hydroxide (NaOH) solution with a concentration equal to or greater than 0.5 M.