Experimental and molecular simulation studies of N, S-doped Carbon dots as an eco-friendly corrosion inhibitor for protecting Cu in HCl environment

A serious of N, S-doped carbon dots (N, S-CDs) as an eco-friendly corrosion inhibitor with different S/N ratios were synthesized by finely tuning the ratio of L-cysteine and ammonium citrate through a hydrothermal method. The chemical composition and morphology of these N, S-CDs were characterized by FTIR, UV-Vis, TEM and XPS techniques. The N, S-CDs showed good dispersion in aqueous solution with average particle size of about 3–6 nm. An abundant of unsaturated bonds and polar groups were found on the surface of the N, S-CDs. The inhibition performance of the N, S-CDs for copper metal in 1.0 M HCl environment was studied by electrochemical, combining FTIR, XPS and Raman to investigate the corrosion products. The inhibition efficiency of N, S-CDs displayed a first increased and then decreased trend with the increasing of S/N ratio. When the mass ratio of L-cysteine and ammonium citrate was 1:2 (L1 sample), the icorr value exhibited a minimum of 11 μA/cm2 at 160 mg/L after immersing for 24 h and the inhibition efficiency reached up to 94 %. N-Cu and S-Cu bond from XPS implied anchoring interactions between copper and N, S-CDs with multiple heteroatoms as active sites. From DFT calculation, the obtained low energy gap (ΔE) represented a strong physicochemical of N, S-CDs on Cu substrate. With its merits of high corrosion inhibition efficiency and low cost, N, S-CDs inhibitor is a very promising alternative to traditional inhibitors and could significantly extend the service life of copper in corrosive environments.