Synthesis and Characterization of Hollow Mesoporous Silica Nanoparticles for Smart Corrosion Protection

Different approaches have been considered for the development of smart anticorrosive coatings by the incorporation of nanocontainers loaded with corrosion inhibitors into the protective layer. Nanocontainers are designed to allow a controlled release of the inhibitor in response to an external stimulus, thus, achieving more efficient and more economical use of the active component. In this case, a pH change is a very interesting stimulus to trigger the release because corrosion processes cause local pH changes. To this end, a special focus has been placed on the use of mesoporous silica nanoparticles (MSN) as nanocontainers due to their interesting characteristics, such as larger surface area, versatile functionalisation, stability, etc. However, the use of hollow mesoporous silica nanoparticles (HMSN), with a large central hole combined with an external mesoporous silica shell, offers an additional advantage due to the higher loading capacity. In the present work, HMSN have been efficiently synthesised, loaded with sodium phosphomolybdate, as a non-toxic alternative to the use of chromates, and encapsulated by a layer of an oppositely charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA). The morphology and textural properties of the produced nanocapsules have been studied by different techniques (SEM/EDS, TEM/EDS, Brunauer–Emmett–Teller (BET) analysis method, ζ-potential). Finally, the releasing capacity and corrosion protection at different pH values have been studied, confirming the smart behaviour of the encapsulated loaded HMSN.