pH-dependent release of environmentally friendly corrosion inhibitor from mesoporous silica nanoreservoirs

Coatings for corrosion protection usually contain pigments that constantly release substances actively inhibiting corrosion. However, this constant leaching places an important limitation on the protection lifetime of the coating. An intelligent release system may improve the long-term function of a coating, as uncontrolled loss by leaching is inhibited. This ensures that high amounts of inhibitors are still present when needed. Furthermore, this is also favourable for the environment, as no inhibitor is unnecessarily released into it. In this sense, smart mesoporous systems are excellent candidates thanks to their ability to provide more efficient and longer lasting anticorrosive protection by responding quickly to external stimuli such as local environmental changes (temperature, pH, local defects, humidity, etc.). A change in pH is a particularly interesting stimulus since, as is well known, corrosion activity leads to local pH changes in cathodic and anodic areas. In the present paper an environmentally friendly corrosion inhibitor, sodium phosphomolybdate, has been loaded into mesoporous silica nanoparticles. One of the main goals has been to study whether this corrosion inhibitor compound can offer controlled release as a function of pH, even in the absence of encapsulation. The results have shown that the polymerisation processes experienced by molybdenum species, as well as the different phosphate ions present as a function of pH, prevent their release into the environment in the absence of an outer capsule within the pH 3-9 range, thus avoiding the need to carry out an encapsulation stage. (c) 2017 Elsevier Inc. All rights reserved.