To achieve efficient and durable consolidation of weathered sandstone, the selection of a suitable consolidant is essential. To reasonably assess the suitability of different formulations, it is fundamental to compare their performance as a consolidant within a substrate, which reliably models the properties of deteriorated material. As a test substrate, the sandstone from quarries in Mšené in central Bohemia was selected, for its developed porosity and relatively low mechanical strength. To obtain relevant comparison of their application potential, both commercial (Remmers KSE OH and Surfapore) and self-developed consolidants were included. To test the long-term stability of each consolidant, the stone was subjected to accelerated weathering. The characterization of texture properties was based on the physical sorption of nitrogen and krypton, mercury intrusion porosimetry and water uptake. While the mechanical properties in microscale were determined by nanoindentation, the mechanical strength in macroscale before and after consolidation was measured by drilling resistance. Both commercial exhibited good mechanical performance with reasonable durability. The performance of our developed samples was comparable or, in some cases, superior. Very interesting were the consolidants containing TiO2 and ZnO nanoparticles, the former exhibiting comparable degree of consolidation and durability as commercial ones, with additional photocatalytic function, the latter unusually high increase in the mechanical strength, even after the weathering test. The diammonium hydrogen phosphate based consolidant showed exceptional durability in the weathering test, which makes it a promising product not only for carbonate but also sandstone materials.

Even if silicon alkoxides (especially ethylsilicates) have long been used as consolidants of weathered stone monuments, their physical properties are not ideal. In this study, an innovative procedure for the consolidation of sedimentary rocks was developed that combines the use of organometallic and alkylamine catalysts with the addition of well-defined nanoparticles exhibiting a narrow size distribution centered at ca 10 nm. As a suitable test material, the Pietra di Lecce limestone was selected because of its color and problematic physico-chemical properties, such as rather low hardness. Using the developed procedure, the mechanical and surface properties of the limestone were improved without the unwanted over-consolidation of the surface layers of the stone, and any significant deterioration in the pore size distribution, water vapor permeability or the stone’s appearance. The developed modified ethylsilicates penetrated deeper into the pore structure of the stone than the unmodified ones and increased the hardness of the treated material. The formed xerogels within the stone pores did not crack. Importantly, they did not significantly alter the natural characteristics of the stone.

The preparation of immobilized graphene–based photocatalyst layers is highly desired for environmental applications. In this study, the preparation of an immobilized reduced graphene oxide (rGO)/TiO₂ composite by electrophoretic deposition (EPD) was optimized. It enabled quantitative deposition without sintering and without the use of any dispersive additive. The presence of rGO had beneficial effects on the photocatalytic degradation of 4-chlorophenol in an aqueous solution. A marked increase in the photocatalytic degradation rate was observed, even at very low concentrations of rGO. Compared with the TiO₂ and GO/TiO₂ reference layers, use of the rGO/TiO₂ composite (0.5 wt% of rGO) increased the first-order reaction rate constant by about 70%. This enhanced performance was due to the increased formation of hydroxyl radicals that attacked the 4-chlorophenol molecules. The direct charge transfer mechanism had only limited effect on the degradation. Thus, EPD-prepared rGO/TiO₂ layers appear to be suitable for environmental application.

Rapid progress in the development of highly efficient nanoparticle-based construction technologies has not always been accompanied by a corresponding understanding of their effects on human health and ecosystems. Here, we compare toxicological effects of pristine TiO₂, ZnO and SiO₂, and coated SiO₂ nanoparticles and evaluate their suitability as additives to consolidants of weathered construction materials. First, WST-1 and LDH assays were used to determine the viability of human alveolar A549 cells at various nanoparticle concentrations (0–250 μg mL⁻¹). While the pristine TiO₂ and coated SiO₂ nanoparticles did not exhibit any cytotoxic effect up to the highest tested concentration, the pristine SiO₂ and ZnO nanoparticles significantly reduced cell viability. Second, as all the developed nanoparticle-modified consolidants increased the mechanical strength of weathered sandstone, the decisive criterion for the selection of the most suitable nanoparticle additive was as low toxicity as possible. We believe that this approach will be of high importance for industry to identify materials representing top functional properties and low toxicity at an early stage of the product development.