New insight into electropolymerization of melamine. I: Chloride promoted growth of polymelamine in different pH medium

Highlights: • Polymelamine is first synthesized in neutral and alkaline besides acidic solution. • Cl⁻ ions as the necessarty condition rather than H⁺ is first recognized. • Electrodeposition of polymelamine film can be efficiently promoted by Cl⁻ addition. • New electropolymerization mechanism involving active chlorine is proposed. Electropolymerization of melamine, 1,3,5-triazine-2,4,6-triamine, has been investigated here in aqueous solutions in a very wide pH range, which formerly was believed to be confined only in an acidic medium. We report here for the first time the polymerization can take place in neutral and alkaline besides acidic solution in presence of Cl⁻ ions. The key effects of the acidity of solution, potential window and concentration of Cl⁻ ions and melamine monomer on the polymelamine (pMel) deposition have been further confirmed one by one, respectively. We proved that presence of Cl⁻ ions is the necessary condition rather than H⁺. The electropolymerization of melamine is very sensitive to Cl⁻ (even in 1 mM), and in situ electrogeneration of active chlorine effectively promote the growth of pMel film in separate solutions with different pH. Based on the relevant reactions during the process of electropolymerization, a tentative mechanism is given here. With this knowledge, a better control of the electrochemical synthesis can be envisioned, thus making pMel film suitable for the construction of multifunctional platforms.