One-stage synthesis and characterisation of supramolecular silica systems incorporating corrosion inhibitors for gradual release applications

Supramolecular silica systems, incorporating two different corrosion inhibitors (1H-Benzotriazole, BTA and 5-Phenyl-1H-tetrazole, PT), are successfully obtained via one-stage syntheses by self-assembly and characterised with a multi-analytical approach. Two different surfactants, namely cetyltrimethylammonium bromide (CTAB) or dodecylamine (DDA), are used both as templates and to promote synergistic corrosion inhibition in future application in smart and eco-sustainable coatings for metal substrates. The effect of the two different soft templates and the influence of a co-solvent (ethanol or methanol) on the morphology and the hierarchical porosity structure of the silica systems are investigated by electron microscopy techniques (SEM and TEM) and by nitrogen physisorption (BET/BJH). The confinement of both BTA and PT in mesoporous silica nanoparticles is qualitatively and quantitatively characterised by micro-Raman spectroscopy and thermal analyses. All synthesised composite samples show monodispersed nanoparticles (size in the range 50-500 nm). In the presence of CTAB soft template, spherical nanoparticle with non-intersecting longitudinal porosity is obtained and sphere-to-rod transition with chiral growth of particles is observed after the inhibitor encapsulation. On the contrary, by using DDA soft template, the symmetrical spherical shape of nanoparticles is retained when inhibitor is encapsulated, although with different diameter sizes. Radiant cylindrical-to-conical porosity is observed, depending on the solvent/co-solvent total volume and not influenced by the inhibitor. All supramolecular silica systems are characterised by a high loading capacity (30-40%) including both surfactants and azole compounds.