Synthesis and Electrochemical Evaluation of MSNs-PbAE Nanocontainers for the Controlled Release of Caffeine as a Corrosion Inhibitor.

In this paper, a controlled-release system of caffeine as a corrosion inhibitor was obtained by encapsulating it in MCM-41 silica nanoparticles coated with a poly(ß-amino ester) (PbAE), a pH-sensible polymer. Encapsulation was verified using Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). The release of caffeine from the nanocontainers was analyzed in electrolytes with pH values of 4, 5, and 7 using UV-Vis, showing a 21% higher release in acidic electrolytes than in neutral electrolytes, corroborating its pH sensitivity. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to determine the inhibition mode and efficiency of the encapsulated and free caffeine. The caffeine released from the nanocontainers showed the highest efficiency, which was 85.19%. These results indicate that these nanocontainers could have potential use in smart anticorrosion coating applications.

Improvement in the Carbonation Resistance of Construction Mortar with Cane Bagasse Fiber Added.

In this work, sugarcane bagasse fiber, a waste product of agroindustry, was added to mortar mixes at different proportions looking to seal porosities so as to improve the resistance of concrete to carbonation and to improve its mechanical properties. To evaluate the behavior of bagasse fibers in the alkaline media typical of mortars, bagasse fibers were subjected to solutions with alkaline pH values, and their chemical structure and morphological behavior was evaluated using FTIR (Fourier transform infrared spectroscopy) and SEM (Scanning Electron Microscopy). Using mortar cylinders in an accelerated carbonation chamber to obtain results in short lapses, the compressive strength and the carbonation were evaluated. The FTIR analysis results indicate that pH values of 11 and 12 causes a delignification, while at pH 9 and 10, a swelling of the molecule occurs because of the addition of hydroxyl ions, behavior that is confirmed with SEM images. A clear effect of the fiber addition on the performance of concrete was observed as the carbonation front of 35 mm for the sample without fibers was reduced to 2 mm for the sample with 2% fiber addition, resulting in an increase of 5 MPa in compressive strength. These results indicate that in the range of mortar pH, chemical changes occured over the sugarcane surface that could cause the growth of fibers and could partially seal the porosity in the mortars, thus enhancing its performance.