Self-assembled monolayers of p-toluene and p-hydroxymethylbenzene moieties adsorbed on iron by the formation of covalent bonds between carbon and iron atoms for protection of iron from corrosion

Abstract

An iron electrode was modified by electrolytic reduction in deaerated acetonitrile solution of p -toluenediazonium tetrafluoroborate CH 3 C 6 H 4 N 2 BF 4 (TDFB) or p -hydroxymethylbenzenediazonium tetrafluoroborate HOCH 2 C 6 H 4 N 2 BF 4 (HOTDFB) below 10 °C to form a self-assembled monolayer (SAM) of toluene CH 3 C 6 H 4 – or hydroxymethylbenzene HOCH 2 C 6 H 4 – (HOMB) moiety, probably adsorbed on the electrode by the formation of a covalent bond between carbon and iron atoms, as shown in references. The protective ability of the layer was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution. The protective efficiencies of these two SAMs were not high, around 30%, a little higher than that of the toluenethiol CH 3 C 6 H 4 SH SAM which was anchored on iron via a coordinate bond between sulfur and iron atoms. The iron surfaces modified with TDFB and HOTDFB were characterized by contact angle measurement, FTIR reflection spectroscopy and X-ray photoelectron spectroscopy. The persistence in protection of iron against corrosion by coverage with the HOMB SAM was confirmed by polarization measurements after immersion in 0.5 M NaCl for a long period of the time.