Elucidating the protective mechanism of self-healing pd-z@msn coating on microbial influenced corrosion of aluminium surface / Yasin M. Y. Albarqouni

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang Al Sultan Abdullah - 2026

Include bibliographical reference

Microbial-influenced corrosion (MIC) remains a critical challenge in marine and industrial applications, where traditional protective coatings lack the dual functionality needed to simultaneously inhibit corrosion and bacterial proliferation. Existing solutions often fail to provide controlled, stimuli-responsive release of inhibitors, leading to inefficient protection and premature coating failure. This research bridges that gap by developing an innovative, pH and temperature-responsive nanocomposite (PD-Z@MSN) for use in a smart epoxy coating. The study involved the synthesis of zinc oxide (ZnO) nanoparticles via Sol-gel, their encapsulation within mesoporous silica nanoparticles (MSN) synthesized by a modified Stöber method, and subsequent functionalization with polydopamine (PDA) to form the final PD-Z@MSN composite. Comprehensive characterization using FT-IR, XRD, XPS, FESEM, and Hr-TEM confirmed the composite’s spherical morphology (43–120 nm), high crystallinity, and successful integration of components, with PDA acting as a stimuli-responsive gatekeeper. Antibacterial testing against Escherichia coli and Bacillus cereus demonstrated strong efficacy, with inhibition zones of 11.80 mm and 11.56 mm, respectively, even at low concentrations. Density functional theory (DFT) analysis provided a molecular-level explanation, revealing the high electrophilicity and strong binding affinity of the composite, which facilitates interactions with bacterial cells and enhances reactive oxygen species (ROS) generation, leading to oxidative stress and apoptosis. Electrochemical corrosion evaluations revealed outstanding performance, with the optimized PD-Z@MSN/epoxy coating achieving a corrosion rate of only 0.0002 mm·y⁻¹ and a polarization resistance of 1.18 × 105 Ω·cm2 after 120 hours in 3.5% NaCl, corresponding to 98.7% inhibition efficiency, performance that meets and exceeds relevant ASTM standards for protective coatings. These results are directly linked to the composite’s proposed dual-action mechanism. For corrosion, the PDA shell responds to environmental stimuli, releasing Zn2+ ions that react with chlorides and hydroxides to form a protective layer of Zn(OH)2 on the aluminum substrate, effectively blocking anodic and cathodic sites. For antibacterial action, the same controlled release delivers ZnO, which generates bactericidal ROS, while PDA itself disrupts bacterial membranes and proteins. In conclusion, this research successfully designed and validated a dual-functional PD-Z@MSN/epoxy coating. Its intelligent, controlled-release mechanism provides a synergistic defense, combining potent, DFT-supported antibacterial action with superior, electrochemically-verified corrosion resistance. This offers a promising and advanced solution for combating MIC in demanding environments.