Natal Plum leaf extract as sustainable corrosion inhibitor for Brass in HNO3 medium: Integrated experimental analysis and computational electronic/atomic-scale simulation

Abstract

Background Metal corrosion and its protection remain critical areas of research due to the economic and environmental implications of material degradation. Corrosion inhibitors play a vital role in mitigating corrosion and extending the lifespan of metals. In this study, Natal Plum leaves extract (NPLE) was utilized as a green inhibitor for brass corrosion in HNO₃ solution. The eco-friendly nature of NPLE makes it a promising candidate for sustainable corrosion protection.

Methods The composition of extract phytochemicals was analyzed using gas chromatography mass spectrometry (GCMS–). The inhibition effect of NPLE on the corrosion of brass (Cu_63%-Zn_37%) in HNO₃ solution was evaluated through a combination of experimental and theoretical methods. Gravimetric analysis, electrochemical impedance spectroscopy (EIS), and polarization tests were used to quantify the degree of inhibition and assess the electrochemical behavior. The surface morphology and chemical composition of treated brass were analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Molecular adsorption mechanisms were explored using density functional theory (DFT) calculations, highlighting the interaction between extracted molecules and the brass surface.

Significant Findings The results demonstrated that NPLE achieved an inhibition efficiency of ∼98 % at 2.5 g/L after 72 h of exposure, as shown by EIS, which revealed a substantial increase in charge transfer resistance. Polarization tests indicated mixed inhibition effects with slight cathodic prevalence, reducing the corrosion current density from 145.612 μA/cm² (uninhibited) to 10.829 μA/cm² (inhibited). SEM and EDX analyses confirmed the formation of a stable protective film on the brass surface, with improved film stability attributed to the synergy between extracted molecules. DFT calculations revealed that NPLE molecules formed strong bonds with copper atoms, while interactions with zinc were primarily physical, highlighting the extract's efficiency in protecting brass from corrosion.