Chemical and Microwave Modification of Corn Stalk Biochar: Physicochemical Characterization and Functional Insight

Corn stalk, a globally abundant agricultural residue, presents significant waste management challenges while offering a promising feedstock for biochar production. However, pristine corn stalk biochar is constrained by limited surface functionality and underdeveloped porosity, which impede its performance in environmental and agricultural applications. While acid- or alkali-modified biochar has been extensively applied, the mechanistic basis for the synergistic improvement achieved through microwave modification remains inadequately understood. This study comprehensively compared the structural characteristics and performance relationship of microwave-chemical synergistic modified corn straw biochar. In this study, corn stalk biochar prepared at 500 °C was chemically modified using KOH, H₂O₂, and Chitosan, followed by microwave treatment to systematically evaluate the synergistic effects on physicochemical properties. This study demonstrated that the modified biochars exhibited substantially increased surface functionality and developed rough, densely structured surface morphologies, despite a concurrent decrease in specific surface area and porosity. FTIR and XPS analyses confirmed structural modifications, while elemental analysis revealed nonmonotonic, reagent-dependent element enrichment patterns. The modified biochars showed enhanced electron transfer mediation capabilities and improved chemical functionality, suggesting superior potential for chemisorption-driven contaminant removal and redox-active environmental applications. This study underscores the combined importance of microwave treatment, biomass properties, and chemical modification in optimizing biochar functionality, providing a theoretical framework for understanding synergistic effects in biochar applications for environmental management and soil applications. Future work will evaluate the application-specific performance and long-term stability of the most promising modified biochars in realistic soil and water systems, together with process-scale and techno-economic assessment.