Green synthesis of polypyrrole-SnO2 nanocomposites using Foeniculum vulgare extract for crystal violet adsorption and solvent-dependent radical scavenging

Abstract

The development of multifunctional nanomaterials provides new opportunities to address both environmental and biomedical challenges. In this study, SnO₂ nanoparticles were synthesized using Foeniculum vulgare seed extract and subsequently incorporated into independently synthesized polypyrrole (APS-mediated oxidative polymerization) to obtain PPy-SnO₂ nanocomposites. Comprehensive structural, optical and morphological analyses, including FTIR, UV-Vis spectrophotometry, XRD, SEM-EDS, HRTEM, DLS, zeta potential, and BET, confirmed the successful formation of the nanocomposites and the uniform incorporation of SnO₂ within the PPy matrix. The PPy-SnO₂ nanocomposites demonstrated significant adsorption performance for crystal violet, achieving 92% removal under optimized conditions, including pH 7, a dye concentration of 10 ppm, 50 mg adsorbent, and 50 °C for 150 min. Adsorption behaviour followed a pseudo-2nd-order kinetic model, and a maximum capacity of 162.6 mg g⁻¹ estimated from the Langmuir isotherm was achieved. The antioxidant activity assessed by DPPH and ABTS assays in methanol and hexane showed higher radical scavenging efficiency in methanol, achieving 90.8% inhibition at 800 µg mL⁻¹. PPy-SnO₂ consistently outperformed pure polypyrrole, indicating the significant role of SnO₂ in enhancing electron-transfer-based scavenging. Overall, these results highlight the PPy-SnO₂ NCs as an effective dual-application material that combine strong antioxidant properties with high-efficiency dye removal to provide a sustainable approach for environmental remediation.