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Self-Assembly and Anticorrosive Property of <i>N</i>‑Alkyl-4-[2-(methoxycarbonyl)vinyl]pyridinium Bromides on X70 Steel in an Acid Medium: an Experimental and Theoretical Probe
A new
type of self-assembly inhibitors, <i>N</i>-alkyl-4-[2-(methoxycarbonyl)Âvinyl]Âpyridinium
bromide surfactants (designated as PPA-<i>n</i>, <i>n</i> = 8, 10, 12, and 14), has been synthesized and characterized
by various spectrum methodologies. The anticorrosive performance of
PPA-<i>n</i> on X70 steel in 5 M HCl was evaluated via weight
loss and electrochemical methods as well as theoretical calculation.
Scanning electron microscopy, energy-dispersive spectroscopy, and
X-ray photoelectron spectroscopy evidenced that PPA-<i>n</i> molecules self-assembled and formed a compact monolayer on the X70
surface, which blocked the active sites and elevated the energy barrier
of the corrosion reaction of X70 steel. The inhibitory efficiency
of PPA-<i>n</i> was up to 98% at 75 μM PPA-14. The
inhibition capacity as well as resistance to corrosion at higher temperature
increased with prolonged alkyl chain in PPA-<i>n</i>. Density
functional theory calculation suggested that the ester group and pyridinium
ring might be the most active sites for PPA-<i>n</i> adsorbing
on the X70 steel surface via the π* orbital of the pyridinium
accepting the 4s electrons of iron and empty 3d orbital of iron taking
up the nonpair electrons of the O atom in PPA-<i>n</i>.
The energy gap of the frontier orbitals of PPA-<i>n</i> are
in the order of PPA-8 > PPA-10 > PPA-12 > PPA-14, inferring
a contrary
order in the inhibition efficiency