Sulfide-Ion-Responsive Mesoporous Silica/ZIF-8 Nanocapsules to Inhibit Microbiologically Influenced Corrosion

Microbiologically influenced corrosion (MIC) accounts for a large proportion of industrial steel corrosion, among which the most representative microorganism is sulfate-reducing bacteria (SRB). The direct application of the fungicides may cause high utilization dosage, increased bacterial resistance, and environmental pollution and cannot realize the effective long-lasting antimicrobial and corrosion inhibition performance. Herein, a novel kind of nanocapsule with both bactericidal and corrosion inhibition functions is developed. The hollow mesoporous silica (HMSNs) is used as the carrier and encapsulated with benzotriazole (BTA) inhibitors; their surface microchannels are sealed with the bactericide metronidazole (MNZ)-loaded ZIF-8 nanovalve. The high-performance liquid chromatography results confirm that the encapsulation amounts of MNZ and BTA in the nanocapsules are 7.67% and 4.20%, respectively. Moreover, the as-prepared BTA-HMSN/ZIF-8-MNZ nanocapsules exhibit a typical sulfide ion-responsive characteristic. The release rate of the encapsulated MNZ and BTA rises with the increased sulfide-ion concentrations, and the cumulative release amount reaches 80% after 24 h when the sulfide-ion concentration attains 2 mM. Furthermore, the antimicrobial performance of BTA-HMSN/ZIF-8-MNZ nanocapsules is evaluated in SRB solutions. The survival SRB amounts decrease evidently with the increased nanocapsule concentration, and the antibacterial efficiency is nearly 100% at a concentration of 250 μg·mL^-1. The weight loss test and surface analysis also confirm the excellent corrosion inhibition ability of the BTA-HMSN/ZIF-8-MNZ nanocapsules to Q235 steels, whose inhibition efficiency is up to 89.23% after 8 h of immersion in a corrosive environment after the addition of 12 mg·mL^-1 of BTA-HMSN/ZIF-8-MNZ nanocapsules. Meanwhile, the Q235 steel maintains a smooth and uniform surface with the protection of BTA-HMSN/ZIF-8-MNZ nanocapsules. Overall, the combination of MNZ bactericides and BTA corrosion inhibitors greatly strengthens the antimicrobial and corrosion inhibition performance of the nanocapsules, and this kind of intelligent sulfide ion-responsive protective system also provides insights for retarding MIC in a complex corrosive environment.