Synthesis of zero valent Fe/Mn anchored Alstonia scholaris flower biochar for wastewater treatment and bactericidal application

Abstract

The zerovalent iron- and manganese-embedded NaOH-activated Alstonia scholaris flower biochar composites (ZMNASB and ZFNASB) were prepared using sodium borohydride-assisted metal reduction and strategic intercalation into the biochar matrix for Eriochrome Black T (EBT) and Cr(VI) removal from aqueous solutions, along with simultaneous antibacterial use. Both materials were characterized by FTIR, SEM- EDX, BET surface area, TEM-SAED, VSM, and PXRD. The zero-point charges were found to be 7.20 and 6.81, respectively. A pseudo-second-order model best described the uptake dynamics. EBT adsorption followed the Freundlich model (R2=0.999), while Cr(VI) adsorption followed the Langmuir model (R2=0.999). ZMNASB and ZFNASB displayed maximum uptake capacities of 242.082 and 293.225 mg/g, respectively, for EBT, and 56.376 and 50.566 mg/g, respectively, for Cr(VI) at 328 K and pH 7. Both scavenging processes are endothermic (12.496 to 25.709 kJ/mol) and favorable (–0.109 to –7.419 kJ/mol). Using 50% methanol and diluted NaOH, the adsorbents were successfully regenerated (70-76%), enabling three cycles of reuse. Their practical applicability was demonstrated by their ability to effectively remove contaminants from field wastewater (~73.2-94% efficiency). The column adsorption capacity of both composites was 20.046-272.477mg/g for EBT and Cr(VI). To address disposal concerns, spent materials were pyrolyzed to transform into secondary adsorbents with efficiencies of 50–68%. Furthermore, approximately a ~3 cm inhibitory zone was observed against both Staphylococcus aureus and Escherichia coli bacteria using the composites at a concentration of 100 mg/mL. With a surface area of 56.008 and 101.571 m2/g, the materials exhibit dual advantages and outperform several contemporary materials.