This study investigates the corrosion inhibition efficacy of a green-synthesized zinc acetate–reduced graphene oxide composite, prepared using aqueous Helianthus annuus (sunflower) seed extract as a reducing and stabilizing agent, for mild steel in aggressive corrosive environments. The composite was synthesized through sequential green reduction of graphene oxide in the plant extract, followed by incorporation of zinc-based nanoparticles derived from zinc acetate under alkaline conditions, yielding a black powdered material with a final mass of 1.42 g. Gravimetric weight loss measurements were conducted on machined mild steel coupons (40 mm × 20 mm × 5 mm) immersed in 1 M HCl (acidic), 1 M KOH (alkaline), and 1 M K₂SO₄ (neutral salt) solutions at ambient temperature (30 ± 2 °C) for durations of 1, 2, 4, and 8 hours. Inhibitor concentrations ranged from 0.050 to 0.125 g/L, with a commercial paint coating and uninhibited blanks serving as benchmarks. In 1 M HCl, the composite exhibited moderate, concentration- and time-dependent inhibition, achieving maximum efficiencies of 20–24% at 0.125 g/L over longer immersions, though significantly inferior to the paint coating (57–80%). In contrast, the composite demonstrated excellent performance in 1 M KOH, particularly at low concentrations (0.050–0.075 g/L), reaching efficiencies up to 95–98% by stabilizing passive films, often surpassing the paint. In 1 M K₂SO₄, the inhibitor effectively reduced weight loss compared to the blank, confirming its versatility. These findings highlight the composite's promising eco-friendly potential, especially in alkaline and neutral saline media, due to synergistic barrier and adsorptive effects from reduced graphene oxide and zinc species. Recommendations include optimization of synthesis parameters and inhibitor dosage for enhanced acidic performance, supplementation with electrochemical and surface characterization studies (e.g., EIS, SEM, XPS) to elucidate mechanisms, and exploration of longer immersion periods or real-world industrial simulations to advance its application in sustainable corrosion protection strategies.
