Self-assembled monolayer of ammonium pyrrolidine dithiocarbamate on copper detected using electrochemical methods, surface enhanced Raman scattering and quantum chemistry calculations

Ammonium pyrrolidine dithiocarbamate (APDTC) monolayer was self-assembled on fresh copper surface obtained after oxidation–reduction cycle treatment in 0.1 mol L− 1 potassium chloride solution at ambient temperature. The APDTC self-assembled monolayer (SAM) on copper surface was investigated by surface enhanced Raman scattering spectroscopy and the results show that APDTC SAM is chemisorbed on copper surface by its sulfur atoms with perpendicular orientation. The optimum immersing period for SAM formation is 4 h at 0.01 mol L− 1 concentration of APDTC. The impedance results indicate that APDTC SAM has good corrosion inhibition effects for copper in 0.5 mol L− 1 hydrochloric acid solution and its maximum inhibition efficiency could reach 95%. Quantum chemical calculations show that APDTC has relatively small ΔE between the highest occupied molecular orbital and the lowest unoccupied molecular orbital and large negative charge in its two sulfur atoms, which facilitate formation of an insulating Cu/APDTC film on copper surface.