Green Synthesis of Nano-Sized Multiflower-like Fe₃O₄@SiO₂/_L-Tryptophan from Natural Resources and Agricultural Waste: A Photo-Switchable Oxidation Catalyst

This study presents a novel, eco-friendly, and cost-effective magnetic hybrid photocatalyst, Fe₃O₄@SiO₂/_L-tryptophan, synthesized through a scalable three-step green approach using natural and agricultural waste. The Fe₃O₄@SiO₂/_L-tryptophan nanoparticle features a core-shell structure with a high surface area (63.14 m²/g), strong visible-light absorption (λ > 448 nm), a narrow band gap (1.84 eV), and superparamagnetic properties (22 emu/g), enabling efficient separation and reusability. Characterization techniques (XRD, XPS, FT-IR, FE-SEM, HR-TEM, UV-vis DRS, TGA, BET, and EIS) confirmed its structural stability, charge separation, and interfacial charge transport. The photocatalyst achieved 82.1% oxidative desulfurization of dibenzothiophene (DBT) and high conversion rates for toluene (85%) and styrene (90%) under visible light using O₂ as an oxidant. It retained over 85% activity after five cycles, demonstrating excellent durability. For the first time, all components are derived from natural sources: Fe₃O₄ from sorghum seed extract, SiO₂ from rice husk, and _L-tryptophan for enhanced light absorption and charge separation. This sustainable synthesis reduces chemical waste and energy consumption, setting a new benchmark for environmentally friendly photocatalysts.