Effect of synthesis conditions on the corrosion inhibition properties of carbon dots

Nitrogen and sulfur co-doped carbon dots (N, S-CDs) are promising corrosion inhibitors, typically synthesized hydrothermally. This study investigates how synthesis conditions, namely reaction time (4–24 h), reaction temperature (170-230 °C), and dialysis duration (12–48 h) affect N, S-CD properties. Nine samples labelled CD-1 (190 °C, 4 h, 24 h dialysis), CD-2 (190 °C, 6 h, 24 h dialysis), CD-3 (190 °C, 12 h, 24 h dialysis), CD-4 (190 °C, 24 h, 24 h dialysis), CD-5 (170 °C, 6 h, 24 h dialysis), CD-6 (210 °C, 6 h, 24 h dialysis), CD-7 (230 °C, 6 h, 24 h dialysis), CD-8 (190 °C, 6 h, 12 h dialysis), and CD-9 (190 °C, 6 h, 48 h dialysis) are synthesized. Results show that optimal conditions maximizing chromophore yield and minimizing particle size distribution were a 6 h reaction, 190 °C temperature, and dialysis ≥24 h. Particle size increased with longer reaction times and higher temperatures. Crucially, inhibition efficiency (η) in 1 M HCl at 150 mg/L directly correlated with these properties, yielding this ranking: CD-2 (94 %) > CD-1 (92 %) > CD-4 (89 %) ≈ CD-3/CD-9 (88 %) > CD-6 (87 %) > CD-7 (82 %) > CD-5 (64 %) > CD-8 (57 %). This confirms that synthesis conditions critically determine CD properties and performance. CD-2, the superior inhibitor, demonstrates temperature and immersion time dependence: η decreased with rising electrolyte temperature but improved with prolonged immersion, suggesting gradual film stabilization.