Tailoring KOH-Activated Hydrochar Derived from Sugarcane Industry By-Products through an Adsorption Study with Fipronil

Rising food demand has intensified pesticide use, notably fipronil, raising concerns over soil and water contamination. Hydrochars (HC) were synthesized from sugarcane bagasse and vinasse via hydrothermal carbonization (HTC) with H3PO4, followed by thermochemical activation with KOH at 500 and 700 °C using HC:KOH ratios of 1:2 and 1:4, yielding four activated hydrochars (AHC-5-2, AHC-5-4, AHC-7-2, AHC-7-4) for fipronil adsorption. HC and AHCs were characterized for composition, structure, morphology, textural properties, and surface functional groups. Activation at 500 °C reduced the carbon content of HC from 77.0% to 52.3% (1:2) and 56.5% (1:4), whereas at 700 °C it decreased to 34.4% (1:2) and 67.6% (1:4). KOH activation removed inorganic matter, decreased the diffraction peaks, and reduced acidic and phenolic groups. AHC-7-4 exhibited the highest surface area (870 m2 g–1) and micropore fraction (71–82%), achieving maximal fipronil adsorption (249 mg g–1 in 300 min), predominantly controlled by diffusion and chemical interactions. Overall, thermochemical activation markedly enhanced HC adsorption, particularly under high-temperature and high-ratio conditions, underscoring the sustainable potential of these materials for pesticide remediation.