Negative role of triphenylphosphine in the inhibition of benzotriazole at the Cu surface studied by surface-enhanced Raman spectroscopy

The adsorption behaviour and the formation of a surface complex film of benzotriazole (BTAH) on Cu electrodes have been studied by in situ surface enhanced Raman spectroscopy in acetonitrile solution. A potential-dependent Raman study revealed that the adsorption and film formation process of BTAH involves the formation of a chemisorbed adlayer and a compact polymer film in two different potential regions in the acetonitrile solution. The results showed that BTA− ion can interact with the Cu surface through the two N atoms of the triazole ring to form a surface polymer complex of [Cu(BTA)]n, which suppressed the dissolution and oxidation of Cu effectively. When triphenylphosphine (pph3) was introduced into the solution, the formation of the surface polymer complex film was suppressed due to the formation of soluble Cu ( pph 3 ) n + . In solution, a complex of Cu with BTA− and pph3 was formed leading to a significant decrease of the surface inhibition efficiency. These two kinds of surface complexes were prepared by the direct electrochemical synthesis technique in similar solutions, and characterized by normal Raman spectroscopy and elemental analysis. The results showed that the final complexes were insoluble [Cu(BTA)]n polymer and CunBTAm(pph3)p complex with low solubility in the acetonitrile solution.