Turning Sugarcane Field Residues into High-Value Adsorbents: CO₂ Activation, PAH Removal Efficiency, and Implications for Low-Carbon Resource Cycles.

Valorizing agricultural residues into engineered carbon materials offers a promising pathway toward both sustainable pollutant remediation and climate-aligned negative emission strategies. This study develops high-performance CO₂-activated biochars derived from sugarcane leaves (SLAB) and bagasse (SBAB), as well as their various blend ratios, to address persistent polycyclic aromatic hydrocarbons (PAHs) in contaminated wastewater. To develop a scalable, low-carbon treatment solution grounded in circular bioresource utilization, the work integrates thermochemical valorization, material optimization, and adsorption modeling. CO₂ activation of sugarcane residues produced biochars with markedly enhanced physicochemical properties, including increased specific surface area, structured pore development, and enriched aromatic carbon domains, which are favorable for the uptake of hydrophobic organic pollutants. Process optimization using Central Composite Design (CCD) and Response Surface Methodology (RSM) generated highly robust quadratic models for naphthalene (NAP) and phenanthrene (PHE) removal (adjusted R² ≈ 0.96; predicted R² > 0.87), evidencing the statistical reliability of the adsorption system. Optimal performance was achieved at acidic conditions, with a pH of 2-3, a contact time of ~ 120 minutes, and a low adsorbent dosage of ~ 0.2 g/L. Among all the blends, the 2:3 SL:SB blend exhibited the highest adsorption capacity. Mechanistic interpretation showed that the removal of PAHs is driven by a synergistic combination of pore-filling, electrostatic attraction, hydrophobic partitioning, and π-π electron donor-acceptor interactions with the aromatized carbon matrix formed upon CO₂ activation. Regeneration studies further confirmed that the material exhibits strong reusability without performance loss in successive adsorption cycles, underscoring its stability and practical viability. The work contributes to technologies aligned with negative emissions by transforming abundant agro-industrial waste into a regenerative, high-efficiency adsorbent that reduces environmental contamination, offering a low-carbon alternative to conventionally produced activated carbons. These findings highlight the potential of CO₂-activated sugarcane biochars to support a circular economy model in water treatment, offering a scalable approach for integrating biomass valorization with broader carbon mitigation efforts.