OPTIMIZATION AND THERMODYNAMIC CHARACTERISTICS OF COPPER CORROSION INHIBITION BY EXPIRED TOPLEX SYRUP IN SULFURIC ACID

Abstract

This study investigates the effectiveness of expired Toplex syrup as a sustainable and eco-friendly corrosion inhibitor for copper in 0.5 M sulfuric acid (H₂SO₄), using weight loss measurements to assess its performance. The influence of critical parameters inhibitor concentration (0.1 - 0.4 % v/v), temperature (293 - 323 K), and immersion time (0.5 - 1.5 h)-on corrosion rate and inhibition efficiency were comprehensively examined. Experimental results revealed a direct correlation between inhibition efficiency and both Toplex concentration and temperature, with peak efficiency (95.55 %) was achieved at 0.385 % v/v, 322.5 K, and 1 h of immersion. Optimization using Response Surface Methodology (RSM) with a central composite design yielded a statistically robust and predictive model (R2 = 0.994, Q² = 0.946). Adsorption behaviour followed both the Langmuir and Temkin isotherms, while thermodynamic analysis confirmed a spontaneous physisorption mechanism, as evidenced by negative Gibbs free energy values (ΔGads = - 11.69 to - 17.46 kJ mol⁻¹). Activation energy calculations indicated an endothermic corrosion process, with significantly higher energy barriers observed in the presence of the inhibitor supporting a predominantly physical adsorption mechanism. Furthermore, Scanning Electron Microscopy (SEM) revealed the formation of a uniform and protective film on the copper surface, confirming the role of Toplex syrup in mitigating
acid-induced degradation. These findings highlight the potential of expired Toplex syrup as an effective, low-cost, and environmentally benign corrosion inhibitor for copper in acidic environments, with promising implications for industrial applications.