pH-responsive nanocapsules enabling synergistic inhibition and chloride trapping for active protection of epoxy coatings

Achieving durable corrosion protection in epoxy coatings remains challenging because barrier degradation, chloride penetration, and insufficient inhibitor utilization occur simultaneously during long-term exposure. Herein, mesoporous silica nanocapsules (MSN-BC) co-encapsulating benzotriazole (BTA) and cetyltrimethylammonium bromide (CTAB) were synthesized via a one-pot method, where CTAB functioned dually as a pore-forming agent and a corrosion inhibitor. Magnesium‑aluminum layered double hydroxide (LDH) nanosheets were subsequently grown in situ on the nanocapsule surfaces. The nanocapsules showed pH-responsive inhibitor release and strong Cl − adsorption. A key finding from electrochemical impedance spectroscopy (EIS) was that the dual-inhibitor (MSN-BC) system exhibited superior corrosion protection compared with nanocapsules containing only CTAB or BTA, indicating an enhanced combined inhibition effect. This interpretation was further supported by density functional theory (DFT) calculations, which suggested favorable co-adsorption of BTA and CTAB on the Q235 steel surface. At an optimal loading of 1 wt% in epoxy, MSN-BC-LDH dispersed uniformly, reduced coating porosity, and improved barrier performance. After 60 days in 3.5 wt% NaCl solution, the coating maintained an impedance modulus of 8.2 × 10 8  Ω·cm 2 at 0.01 Hz, one order of magnitude higher than pure epoxy. The enhanced protection arises from coating densification, LDH-enabled Cl − trapping, and synergistic dual-inhibitor action.