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 Lcysteine and ammonium citrate was 1:2 (L1 sample), the icorr value exhibited a minimum of 11 & mu;A/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 (& UDelta;E) 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.