One-step synthesized cottonseed hull-derived magnetic biochar for efficient extraction and determination of benzotriazole-based UV stabilizers

In this study, a novel magnetic biochar (Fe₃O₄/CHBB) derived from cottonseed hulls was synthesized via a simple one-step pyrolysis method and applied as a magnetic solid-phase extraction (MSPE) sorbent for the efficient enrichment and determination of Benzotriazole-based Ultraviolet Stabilizers (BUVSs). The synthesis conditions, including FeCl₃·6H₂O concentration and pyrolysis temperature, were systematically optimized to enhance the material's adsorption performance. Comprehensive characterization using SEM, XPS, FT-IR, BET, and VSM revealed that the optimized Fe₃O₄/CHBB exhibited favorable magnetic properties, abundant surface functional groups, and a porous structure suitable for BUVS adsorption. The MSPE procedure was further optimized in terms of sample pH, sorbent dosage, extraction/desorption time, and solvent type and volume. Under optimal conditions, the method showed good linearity (R² ≥ 0.9939), low limits of detection (6.6–14.1 ng/mL), and satisfactory precision (intra-day RSDs: 0.98–8.36 %; inter-day RSDs: 2.45–13.26 %). Application to commercial beverage and herbal samples demonstrated the method's practical applicability, although no BUVSs were detected above the method’s LOD. Overall, the proposed Fe₃O₄/CHBB-MSPE method is simple and cost-effective, offering a promising analytical platform for trace-level detection of BUVSs in complex aqueous environments while promoting the sustainable utilization of agricultural waste.