Protective Performance of Bromocresol Purple Dye for Aluminum in 1 M HCl: Experimental and Theoretical Investigation

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Document Type : Original Article

Authors

1 M. Utemisov West Kazakhstan University

2 Faculty of Natural and Geographical sciences M. Utemisov West Kazakhstan university, Uralsk, Kazakhstan

3 Faculty of Natural and Geographical sciences, M. Utemisov West Kazakhstan university, Uralsk, Kazakhstan

Abstract

Bromocresol purple (BCP) was investigated as a corrosion inhibitor for D16T aluminum alloy in 1.0 M HCl using experimental and quantum-chemical methods. It was found that the inhibition efficiency increased with inhibitor concentration and temperature, reaching 93.16% at 0.30 g·dm-3 and 313 K. Adsorption was best described by the Langmuir model (R2 > 0.996), while the Frumkin model indicated weak lateral interactions between adsorbed species. The negative ΔG0ads values (−24.83 to −29.58 kJ·mol-1), together with positive ΔH0ads and ΔS0ads, demonstrated spontaneous, endothermic, and temperature-favored adsorption. Polarization measurements revealed a decrease in jcorr from 1.16·10-4 to 1.48·10-5 A·cm-2, confirming mixed-type inhibition, while the contact angle increased from 53.57° to 93.96°. UV–Vis and FTIR analyses confirmed interfacial retention of BCP and the involvement of oxygen-containing groups and the conjugated π-system in adsorption. Quantum-chemical calculations at the DFT/B3LYP/6-311G(d,p) level showed that the quinonoid form had a lower HOMO–LUMO gap (7.30 vs. 9.51 eV), higher softness (0.274 vs. 0.210 eV-1), and higher electrophilicity (5.31 vs. 3.37 eV) than the lactone form, indicating enhanced charge-transfer capability. The results support a mixed physisorption–chemisorption mechanism leading to the formation of a compact protective layer that limits access of aggressive species to active dissolution sites.

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Progress in Color, Colorants and Coatings

Articles in Press, Accepted Manuscript
Available Online from 02 August 2026

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