Pore-engineered mesoporous silica nanocarriers for sustainable, stimuli-responsive corrosion-inhibitor release

Abstract

Corrosion of metallic materials, particularly in heritage structures and concrete-based infrastructures, remains a persistent challenge, necessitating protection strategies that are effective, long-lasting, environmentally sustainable, and compatible with heterogeneous substrates. In this work, mesoporous silica nanoparticles (MSNs) were developed as pH-responsive nanocarriers, for controlled corrosion-inhibitor release. Two MSN architectures were synthesised: hexagonally ordered mesopores (MSNs-hex) and centre–radial hierarchical porosity (MSNs-CR), providing tunable loading capacity and release kinetics. Polyacrylic acid (PAA) and polyethylenimine (PEI) were employed pH-responsive polymer gatekeepers under acidic-to-neutral and alkaline conditions, respectively. Benzotriazole (BTA), used as a conventional corrosion inhibitor, and caffeine (CAFF; 1,3,7-trimethylxanthine), selected as an environmentally more benign alternative, were loaded into the nanocarriers, and their release behaviour was systematically investigated. MSNs-CR architectures achieved higher inhibitor loading than MSNs-hex, approximately 6.5 and 1.3 wt%, respectively, confirming the enhanced cargo capacity of the hierarchical architecture. Functionalisation with PAA or PEI enabled pH-dependent release under neutral and alkaline conditions, respectively, with PEI-gated MSNs-CR releasing nearly 90% of both inhibitors over 48 h at pH 11. BTA and CAFF displayed comparable normalised release profiles, although a lower absolute amount of CAFF was incorporated and retained. Preliminary ageing tests on bronze showed a stronger protective effect for BTA, while CAFF still reduced surface oxidation relative to the uncoated aged substrate. Overall, this study establishes a versatile, stimuli-responsive platform integrating hierarchical pore engineering and polymer gating to control inhibitor loading and release, with promising potential for sustainable corrosion-protection applications.