RESUMO
Magnesium oxide (MgO) was synthesized by three different methods: the sol-gel (SG), microwave-assisted sol-gel (MW), and hydrothermal (HT) methods for comparing the influence of the preparation conditions on the properties of the products. The powders were annealed at 450 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM/HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), BET specific surface area and porosity, photoluminescence, and UV-Vis spectroscopy. The samples consisted mainly of periclase as a crystalline phase, and the MW and HT preparation methods generated particles with higher specific surface areas. The powders had less-defined morphologies and high levels of aggregation. The optical band gaps of the samples were determined from UV DRS, and the photocatalytic activities of the magnesium oxides obtained by the three methods towards the degradation of methyl orange (MO) under UV light irradiation was evaluated.
RESUMO
Multifunctional composite coatings composed of metal oxide nanoparticles dispersed in polymer matrices are an advanced solution to solve the problem of stone heritage deterioration. Their innovative design is meant to be stable, durable, transparent, easy to apply and remove, non-toxic, hydrophobic, and permeable. Coating formulations for the protection of buildings and monuments have been intensively researched lately. Such formulations are based on multifunctional composite coatings incorporating metal oxides. The present work aims to combine the hydrophobic properties of sodium polyacrylate (NaPAC16) with the antimicrobial effectiveness, with promising antimicrobial results even in the absence of light, and good compatibility of MgO (a safe to use, low cost and environmentally friendly material) and TiO2 (with antibacterial and antifungal properties), in order to develop coatings for stone materials protection. MgO (pure phase periclase) and TiO2 (pure phase anatase) nanopowders were prepared through sol-gel method, specifically routes. Aqueous dispersions of hydrophobically modified polymer (NaPAC16, polyacrylic acid sodium salt) and MgO/TiO2 nanopowders were deposited through layer-by-layer dip coating technique on glass slides and through immersion on stone fragments closely resembling the mosaic stone from the fourth century AD Roman Mosaic Edifice, from Constanta, Romania. The oxide nanopowders were characterized by: Thermal analysis (TG/DTA), scanning electron microscopy (SEM), X-ray diffraction (XRD), BET specific surface area and porosity, and UV-Vis spectroscopy for band gap determination. An aqueous dispersion of modified polyacrylate polymer and oxide nanopowders was deposited on different substrates (glass slides, red bricks, gypsum mortars). Film hydrophobicity was verified by contact angle measurements. The colour parameters were evaluated. Photocatalytic and antimicrobial activity of the powders and composite coatings were tested.
RESUMO
The essential oils (EOs) possess amazing properties explaining the interest for their applications in many essential domains. They also present the disadvantage of their chemical instability in the presence of air, light, moisture, and high temperatures. The paper focuses on two of the most known and used EOs, lavender and mint, respectively. The idea of the study was to protect them using the encapsulated systems. The originality of the work consists in the combination between the advantages of the molecular encapsulation of the EOs by cyclodextrins (CD) with the advantages offered by the sol-gel process. Original formulations have been processed by entrapping these essential oils in silica matrices obtained from a colloidal silica sol by the aqueous route of the sol-gel method. Another non-toxic ingredient, ß-cyclodextrin, able to form inclusion complexes (ICs) with the essential oils has been used. The characterization methods (chromatography, UV-vis, IR, and NMR spectroscopies) have evidenced the presence of the mentioned inclusion complexes. Due to their formation, which modifies the water solubility of the EOs, the chromatographic analysis was possible using water as solvent, which is a novelty in EOs determinations. Protected from both the cyclodextrin and silica matrix, the essential oils became more resistant versus the effects of the environment factors. Thus, the resulted powders can find applications in domains as agriculture, food industries, cosmetics, pharmaceutical, and medicine.
