High specific surface area MMT/NO2 intercalated modified MgAl-LDH core–shell composites: effective inhibition for steel in Cl− contaminated saturated Ca(OH)2 solution

This study developed nitrate-intercalated layered double hydroxides (NO₂-LDHs) and their core-shell composites (NO₂-LDHs@MMT) through an in situ co-precipitation method with montmorillonite (MMT). The corrosion inhibition performance for Q235 steel in simulated concrete pore solutions (saturated Ca(OH)₂ + 3.5 wt% NaCl) was systematically investigated. Comprehensive characterization via scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR) confirmed the successful construction of core-shell architecture and effective intercalation of nitrite anions between LDH layers. Nitrogen physisorption analysis revealed that the NO₂-LDHs@MMT composite possesses a specific surface area of 84.74 m² g^-1 with a pore volume of 0.284 cm³ g^-1, forming a hierarchical pore structure conducive to chloride ion entrapment. Electrochemical assessments including electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization demonstrated that both materials significantly improved the corrosion resistance of steel substrates, with NO₂-LDHs@MMT exhibiting superior performance (98.9% inhibition efficiency). The enhanced anticorrosion mechanism originates from: (1) the MMT core providing enlarged surface area for LDH growth, increasing active sites for Cl^- adsorption; (2) sustained release of NO₂ ^- from LDH galleries enabling stable passivation layer formation. These findings suggest that NO₂-LDHs@MMT composites hold promise as high-efficiency, durable corrosion inhibitors for steel reinforcement in chloride-contaminated alkaline environments.