By using poly(propylene glycol)bis(2-aminopropyl ether) (D230) as curing agent, we have prepared color-stable hydrogenated Bisphenol A (HBA) epoxy polymers, containing TiO2 nanoparticles. The loading and size of TiO2 nanoparticles (5 ~ 10, 21, 200 ~ 400 nm) are changed in order to investigate their photocatalytic effect on removing pollutants deposited on the surface of stone. HBA/D230 polymers containing different amounts of TiO2 nanomaterials were applied to methyl orange (MeO) on the limestone with exposure to the dry and wet environment, respectively. The results showed that the modification of HBA by addition of titanium dioxide particles substantially not only enhanced its protective efficiency but also rendered the treated stone surface self-cleaning ability. The photocatalytic degradation effect of MeO at the concentration of 0.001 M was the best when the size of TiO2 nanoparticles was between 200 ~ 400 nm. Compared to those in dry environment, the decrease of the content of MeO in samples exposed to wet environment was due to humidity on the surface of limestone.

Xerogels’ formation in the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) was studied by varying pH through adopting three different type basic catalysts (n-octylamine, dodecylamine and tetradecylamine), respectively. The effect of different templates to the formation of xerogels was investigated and characterized by FTIR, N2 physisorption, TG-DSC and SEM analysis. The results showed that the morphology and textural characteristics of the xerogels prepared in three kinds of organic amine solutions were quite different. The texture of xerogels became more compact after addition of hydroxyl-terminated polydimethylsiloxane (PDMS-OH). Comparing with dodecylamine and tetradecylamine, n-octylamine is more suitable as catalyst to TEOS/PDMS for stone consolidation.

•Preparation of epoxy–SiO2–PDMS-OH polymer.•Structural properties of epoxy–SiO2–PDMS-OH polymer were characterized.•Protective ability of epoxy–SiO2–PDMS-OH agents for limestone was evaluated.Epoxy–SiO2 polymers modified by poly(dimethylsiloxane) hydroxyl terminated (PDMS-OH) were presented in this paper in order to evaluate their potential use as protective agents for stone surface. No volatile organic components were employed in this synthesis route which was environmentally friendly. FTIR, TG-DSC, SEM and AFM techniques were used to investigate the effect of adding PDMS-OH to (3-glycidyloxypropyl)-methyldiethoxysilane (GPTMS) and (3-aminopropyl)triethoxysilane (ATS), which leaded to epoxy–SiO2–PDMS-OH materials. The addition of PDMS-OH into GPTMS and ATS accelerated the curing process and increased the viscosity of sol. It was found that PDMS-OH was chemically incorporated into the polymer matrix via SiOSi bonds by FTIR analysis. Furthermore, an appreciable reduction of microcracks was obtained for epoxy–SiO2–PDMS-OH polymers when adding 30% w/w of PDMS-OH. The effectiveness of the epoxy–SiO2–PDMS-OH polymers synthesized as stone protective agents was evaluated.

A tetraethoxyorthosilicate (TEOS)-based stone protective coating containing functional 3-glycidoxypropyltrimethoxysilane (GPTMS) has been prepared in order to reduce gel crack formation during the drying phase using n-octylamine as a catalyst. The effect of gel time and viscosity on GPTMS concentration were studied. We have demonstrated that the addition of GPTMS accelerated the gel process and improve viscosity of sol. It was found that GPTMS was chemically incorporated into the gel matrix via Si–O bonds by Fourier transform infrared spectroscopy (FTIR) analysis. Nitrogen adsorption–desorption isotherms of xerogels were measured, they showed that the pore size of xerogels decreased with the addition of GPTMS. Atomic force microscopy (AFM) showed the surface roughness increased as content of GPTMS was higher. The Scotch Tape test and the hardness values showed improvement of cohesion and consolidation ability of hybrid sol. The protective performance evaluation of the treated stones with hybrid sol indicated its acid rain resistance.

•Use of coupling agents for increasing passivants and cohesion ability.•Structural properties of calcite-coupling agents were characterized.•Passivation property of calcite-coupling agents was evaluated.Deterioration of monuments constructed of limestone could be potentially arrested by applying a combination of coupling agents with consolidants, which can prevent acid attack and mechanical weakening. Two different coupling agents including N-(2-aminoethyl)-3-aminopropyl methyl dimethoxysilane (AE-APMDMS) and diethyl phosphatoethyl triethoxysilane(DEPETES) were used to link calcite. Calcite was impregnated with these coupling agents and studied by FTIR, TG-DSC and contact angle measurement. According to these techniques, new bands, a two stage decomposition pattern appeared and a slight increase in surface hydrophobicity for AE-APMDMS and DEPETES that indicated interactions between the coupling agents and calcite. The Scotch Tape test and compressive strength test showed that the cohesion between consolidant and limestone powder improved, while the ability of consolidation decreased, which were resulted by coupling agents. Resist acid test on limestone powder coated with the coupling agents resulted in a decreased deterioration rate. Limestone treated with combined consolidant plus AE-APMDMS or DEPETES showed a significant decrease in capillarity water absorption.

We have investigated the effect of solvent(ethanol, acetone, isopropanol) on the sol–gel process of tetraethylorthosilicate (TEOS) in which case, n-octylamine is used as polycondensation catalyst. Two sets of materials were prepared in the laboratory by using ethanol, acetone and isopropanol as solvents respectively: (1) xerogels from TEOS/n-octylamine, and (2) composites from TEOS/polyhedral oligomeric silsesquioxanes /n-octylamine. The chemical structure of xerogels was studied by FTIR, TG–DSC, scanning electronic microscope and nitrogen adsorption–desorption isotherms techniques. The results have shown that the solvents directly influence the gel time. Gel time is longer for acetone than that of ethanol and isopropanol. In the case of TEOS xerogels, the materials are essentially mesoporous when n-octylamine is used as a catalyst. Silica, when ethanol is used as a solvent, exhibits a more narrow pore size showing textures with a microstructure uniformly distributed with different porosity levels. However, when the aged-isopropanol gel is used, silica shows textures with a microstructure nonuniformly distributed.

Inorganic–organic hybrid crack-free xerogels were obtained by using a surfactant n-octylamine as a catalyst containing tetraethoxyorthosilicate (TEOS) and hydroxyl-terminated polydimethylsiloxane as an additive. We studied the effect of gelling time and viscosity on PDMS–OH concentration. We have demonstrated that the addition of poly(dimethylsiloxane) (PDMS) to a silica oligomer associated with a neutral catalyst, in the presence of a surfactant, accelerated the gelling process; this reduction of the time needed for the product to gel in carbonate stones helped to achieve effective stone protection. It was found that PDMS–OH was chemically incorporated into the gel matrix via Si–O–Si bonds by FTIR analysis and an appreciable reduction of gel fracture for hybrids prepared from 3 % w/w of PDMS. Nitrogen adsorption–desorption isotherms of xerogels were measured, it showed the pore size of xerogels decrease with the addition of PDMS when concentration of PDMS was below 6 %, while xerogels showed pores in the macroporous range when adding 12 % w/w of PDMS. The protective performance evaluated by its ability to resist acid rain reveals that the protective effects were satisfying.

Protective agents based on tetraethoxysilane (TEOS) have been widely used for the protection of stone heritages. However, TEOS-based protective agents suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developed capillary force, which is typical for TEOS-based protective agents. In this paper, we have prepared new TEOS-based protective agent containing flexible hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and colloidal silica particles (167 nm) using n-octylamine as a catalyst in order to reduce capillary force development and increase hydrophobicity, and have characterized them for the application of stone protective agent. The extent of surface hydrophobization depends on concentration of colloidal silica particles and reaches a maximum value of 123° at 0.2% (w/v) of colloidal silica particles for the case of treated with the modified composition. The presence of n-octylamine is a key factor which promotes the increase of the gel pore size. The protective performances were also evaluated by its ability to resist acid corrosion. The results reveal that the protective effects are satisfying.Highlights► Preparation of TEOS–SiO2–PDMS-OH hybrid gels using n-octylamine as a catalyst. ► Textural properties of TEOS–SiO2–PDMS-OH hybrid gels were characterized. ► Acid rain resistance property of hybrid agents for carbonate stone were evaluated.

Inorganic–organic hybrid crack-free xerogels were obtained by using a surfactant n-octylamine as a catalyst containing tetraethoxyorthosilicate (TEOS) and hexadecyltrimethoxysilane as an additive. We studied the effect of gelling time and sol pH on n-octylamine concentration. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the coating was tested by the contact angle measurements. The stone surface morphology of sample treated with hybrid sol was characterized. The results show the hybrid gel network exhibits a larger pore size than the gel containing exclusively the silica from TEOS. After the limestone’s surface was modified by hybrid sol, the contact angle of limestone increased from 58° to 123°. The protective performance evaluated by its ability to resist acid rain reveals that the protective effects are satisfied.