Sonocatalysis: Eco-design strategy for developing novel inorganic sonogels for the conservation of stone heritage

Abstract

Products designed to form continuous inorganic networks from alkoxysilanes frequently include organic solvents because of the necessity to turning the precursors miscible with water and because dilution is required for certain applications. Thus, there is a demand for efficient mixtures employing eco-design strategies. This study explores the feasibility of sonocatalysis to prepare homogeneous mixtures with water to initiate sol-gel reactions and as the dilution agent. The approach allowed to design and prepare viable mixtures with unique tetraethoxysilane(TEOS):H2O ratios (1:4 to 1:32). By managing the ultrasonic irradiation parameters, it was possible to formulate mixtures with high degree of hydrolysis, appropriate condensation ratios, and capable to create sonogel materials containing other desired features for stone conservation. The water content manages the gelling times and gel deposition rates through a dilution effect, which might be useful to minimize undesirable side effects of conservation treatments, such as excessive pore occlusion. For instance, a TEOS:H2O ratio of 1:32 results in a very low gel deposition rate.Furthermore, the applicability and efficacy of successful mixtures was preliminary assessed, and it was demonstrated that the resulting inorganic networks, primarily composed of SiOSi bonds, can enhance the hardness and surface resistance of soft stones. This potential strengthening effect improves gradually with increasing TEOS:H2O ratios. The mixtures deserve further studies aimed at enhancing understanding of their consolidation characteristics.The advances achieved also opens the door for producing innovative dual-role hybrid inorganic-organic sonogels that can be used for materials protection and surface consolidation.