Maize Straw-Derived Biochar- Nanobiochar for Sustainable Wastewater Treatment: Mechanistic Insights into Heavy Metal and Nutrient Adsorption

The conversion of agricultural byproducts into advanced nanomaterials offers an ecologically sound strategy for addressing wastewater contamination. This study investigates biochar derived from maize straw, assessing its effectiveness as an adsorbent for the simultaneous removal of heavy metals and nutrient pollutants. The synthesis involved pyrolyzing maize straw under oxygen-limited conditions, followed by ball-milling and mortar pestle to create nanoscale particles, which significantly enhanced its surface properties for chemical reactivity. Extensive characterization using techniques such as XRD, FTIR, BET, SEM–EDS, and zeta potential measurements revealed a material with a highly porous structure, abundant oxygenated functional groups, and disordered graphitic domains. Leveraging these structural insights, batch adsorption experiments were conducted, demonstrating substantial removal capacities for lead, cadmium, copper, ammonium, and phosphate ions. Subsequent kinetic and isotherm modeling indicated that the adsorption mechanism aligned with pseudo-second-order kinetics and Langmuir–Freundlich models, suggesting a chemisorption process and monolayer adsorption onto diverse active sites. Thermodynamic analysis further characterized the process as spontaneous and endothermic. Furthermore, the synthesized biochar exhibited remarkable reusability, maintaining over contaminant removal efficiency across five regeneration cycles, thereby confirming its structural integrity and operational resilience. Collectively, these findings highlight MSB's potential to integrate waste valorization with efficient contaminant sequestration, positioning it as an environmentally engineered solution for advanced wastewater purification. This research makes a significant contribution to the development of cost-effective, renewable, and high-performance adsorbent materials, supporting the broader transition towards circular bioeconomy principles and sustainable environmental innovations.