Environmentally Sustainable Approach of Corrosion Inhibition of Mild Steel in 1 N HCl and 1 N H2SO4 via Antihistamine Loratadine (LT) and Its Amine Derivatives: Computational and Experimental Analysis

Abstract

The efficacy of pharmaceuticals in mitigating corrosion on metallic substrates has led to the development of a new class of inhibitors that are economically efficient and offer significant environmental benefits. In the present study, for the anticorrosion action of loratadine (LT), 4-(8-chloro-5,6-dihydro-11H-benzo [5,6] cyclohepta[1,2-b] pyridin-11-ylidene)-1-piperidinecarboxylic acid ethyl ester and its amine derivatives (LT1, LT2, and LT3), a theoretical study using DFT was conducted to elucidate the molecular interactions and complex formation mechanisms between these inhibitors and mild steel. The ΔE values for the studied inhibitors-2.17 eV (LT), 3.904 eV (LT1), 3.906 eV (LT2), and 3.85 eV (LT3)-indicate that the LT inhibitor shows greater reactivity compared to the other LT amine derivatives, particularly in terms of electron donation to the metal substrate. After that, the corrosion inhibitory efficacy of parent molecule LT was examined on steel substrate in a medium 1 N hydrochloric and 1 N sulfuric acid and was found to have an efficiency of 98.52 and 80.58%, respectively, (308 K for 100 ppm concentration) deliberated through the electrochemical techniques (PDP and EIS) and gravimetric technique. The reduction in Cdl values from 684.06 to 43.15 μF/cm² in 1 N HCl and from 693.41 to 83.91 μF/cm² in 1 N H₂SO₄ indicates an adsorption process in which inhibitor molecules displace water adsorbed on the metallic substrate, creating a barrier that prevents the metallic substrate from corrosive damage. The surface adsorption aligned with the Langmuir adsorption isotherm with Gibbs-free energy -51 kJ/mol in 1 N HCl and -49.23 kJ/mol in 1 N H₂SO₄. The AFM analysis with an average roughness of 16.29 nm in HCl and 49.23 nm in H₂SO₄ validated LT to form a barrier on mild steel, opposing corrosion. The decelerative effect of LT inferred from theoretical and experimental data comply, making them credible corrosion inhibitors.

Figure 1

Categories of drugs.

Figure 2

Structure of LT and its amine derivatives.

Figure 3

FT-IR Spectrum of LT.

Figure 4

Optimized structures of the studied LT molecule and its amine derivatives.

Figure 5

HOMO and LUMO structures with their energy difference of LT molecules and its amine derivatives.

Figure 6

ESP mapping of the LT molecule and its amine derivatives.

Figure 7

Fukui indices on the atoms of (a) LT, (b) LT1, (c) LT2, and (d) LT3.

Figure 8

Dual-reactivity descriptors on the atoms of (a) LT, (b) LT1, (c) LT2, and (d) LT3.

Figure 9

OCP curves of LT molecule in 1 N HCl and 1 N H₂SO₄.

Figure 10

Tafel plots drawn in 1 N HCl and 1 N H₂SO₄ solution without/with LT molecules.

Figure 11

Randle circuit schematic utilized for modeling EIS data is depicted for (a) the uninhibited system and (b) the inhibited system.

Figure 12

Nyquist (a,b), phase angle, and Bode plots (c,d) drawn in 1 N HCl and 1 N H₂SO₄ corrosive media without/with varied LT molecules.

Figure 13

Variation of corrosion rate and inhibition efficiency for LT molecule against 20–100 ppm concentration after 3 h of immersion in 1 N HCl and 1 N H₂SO₄ at 308–338 K.c

Figure 14

Langmuir isotherm plots of examined inhibitor at 308–338 K temperatures.

Figure 15

Two-dimensional and three-dimensional AFM micrographs of the polished metallic surface with and without the presence of LT molecules under varying conditions.

Figure 16

Mechanistic elucidation of the inhibitory mechanism of the LT molecule.