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.

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.

The aim of the present work was to prepare a binary MO–Nd ₂ O ₃ system by the sol–gel method and to characterise a series of mixed oxides belonging to the binary MO–Nd ₂ O ₃ system (M = alkaline earth metal = Mg, Ca, Sr) to obtain suitable materials with catalytic properties. The molar ratio between the two oxides was MO/Nd ₂ O ₃ = 95/5. Different precursors as alkaline earth metal oxide source (MO), various starting solution compositions expressed in various molar ratios between reactants and different synthesis parameters (pH, temperature and time of reaction) have been used. The structural study by X-ray diffraction analysis was accomplished based on the X-ray 5.0 program, which has established the presence of the mixtures of crystalline polyphases. The lattice constants, the average size of the crystallites, the average lattice strains and the mass of unit cell variation have been calculated. The program also allowed the calculus of the anisotropy factor, which can give the image of the structural disorder. The surface defects are a consequence of structural changes inside of the crystalline lattice of the solid solutions and are quite important for catalytic properties. Some catalytic activity measurements have established the potential of the prepared sol–gel mixed oxides to be used in the oxidative dehydrogenation process of light alkanes (C ₁ C ₄ ). Sample 3SrNd was shown to present the best catalytic activity and selectivity in olefins in propane conversion ( C 2 = & C 3 = ) compared with 4Ca-Nd and 1Mg-Nd samples, which was interpreted as due to a better solid solution formation of Nd ³⁺ in SrO, favoured by the close ionic radius of Sr ²⁺ and Nd ³⁺ , as well as by the high basicity of Sr and the presence of a greater number of point defects.