Characterization of cement mortars with regional organic and inorganic additives.

The present investigation establishes the basis for future studies in the southeast of México for the improvement of building materials by combining regional organic and inorganic nanoparticles in admixtures to formulate cement mortars with durability potential in structures of concrete. The characterization of the organic extract of Albzia tomentosa by nuclear magnetic resonance (NMR) revealed the presence of epicatechin (tannin related) and sucrose. Calcium zinc hydroxide dihydrate nanoparticles (CZ NPs) showed the highest surface area of 60.7 m2 g-1. The electrical resistivity, propagation of ultrasound velocity and water absorption by capillarity properties were individually evaluated for the organic extract, the inorganic nanoparticles and their admixtures in cement mortars, at a curing time of 7, 28 and 96 days with and optimal concentration of 5 mg mL-1 of the added additives. The best results were obtained at 96 days showing slightly but clear improvement of the electrical resistivity (23.40 ± 0.022 kΩ cm, 22.40 ± 0.004 kΩ cm and 22.29 ± 0.013 kΩ cm), propagation of ultrasound velocity (1370 ± 10 m s-1, 1345 m s-1 ± 6, 1310 ± 9 m s-1) and capillary coefficient (0.0044 kg m-2s-1/2, 0.0045 kg m-2s-1/2 and 0.0049 kg m-2s-1/2) properties of the cement mortars with CZ NPs, extraction Albizia solution (EAS) and CZ NPs + EAS respectively when compared to the mortar control (19.91 ± 0.036 kΩ cm, 1266 ± 15 m s-1 and 0.0082 kg m-2s-1/2).

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.

Antifungal coatings based on Ca(OH)2 mixed with ZnO/TiO2 nanomaterials for protection of limestone monuments.

The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.