Conservation of Monuments by a Three-Layered Compatible Treatment of TEOS-Nano-Calcium Oxalate Consolidant and TEOS-PDMS-TiO2 Hydrophobic/Photoactive Hybrid Nanomaterials

Abstract

In the conservation of monuments, research on innovative nanocomposites with strengthening, hydrophobic and self-cleaning properties have attracted the interest of the scientific community and promising results have been obtained as a result. In this study, stemming from the need for the compatibility of treatments in terms of nanocomposite/substrate, a three-layered compatible treatment providing strengthening, hydrophobic, and self-cleaning properties is proposed. This conservation approach was implemented treating lithotypes and mortars of different porosity and petrographic characteristics with a three-layered treatment comprising: (a) a consolidant, tetraethoxysilane (TEOS)-nano-Calcium Oxalate; (b) a hydrophobic layer of TEOS-polydimethylsiloxane (PDMS); and (c) a self-cleaning layer of TiO2 nanoparticles from titanium tetra-isopropoxide with oxalic acid as hole-scavenger. After the three-layered treatment, the surface hydrophobicity was improved due to PDMS and nano-TiO2 in the interface substrate/atmosphere, as proven by the homogeneity and the Si–O–Ti hetero-linkages of the blend protective/self-cleaning layers observed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Fourier-Transform Infrared Spectroscopy (FTIR). The aesthetic, microstructural, mechanical and permeabile compatibility of the majority of treated substrates ranged within acceptability limits. The improved photocatalytic activity, as proven by the total discoloration of methylene blue in the majority of cases, was attributed to the anchorage of TiO2, through the Si–O–Ti bonds to SiO2, in the interface with the atmosphere, thus enhancing photoactivation.

Efficiently texturing hierarchical superhydrophobic fluoride-free translucent films by AACVD with excellent durability and self-cleaning ability

“…Three obvious peaks were observed at 1072 cm À1 , 945 cm À1 , and 800 cm À1 and assigned to the Si-O stretching, Si-OH band and Si-O-Si symmetric stretching vibration of the TEOS precursor, respectively, indicating that hydrolysis and polymerization of TEOS occurred. 42,43 The bands observed at 2961 cm À1 and 1262 cm À1 were attributed to the asymmetric CH 3 stretching and CH 3 deformation in Si-CH 3 of PDMS. 44 The peaks at 864 cm À1 and 790 cm À1 were determined as the Si-(CH 3 ) 2 stretching vibration of PDMS.…”

Selected Aspects Regarding the Restoration/Conservation of Traditional Wood and Masonry Building Materials: A Short Overview of the Last Decade Findings

“…Generally speaking, the organic products (as well as many of the organic/inorganic composites) used as consolidants also possess very good hydrophobicity, which also makes them very good protective compounds. A particularly interesting study was recently published by Kapridaki et al [108]. In a three-layer treatment, the authors offered a complex conservation solution for stone monuments, incorporating a self-cleaning (based on TiO 2 nanoparticles), consolidation (based on calcium oxalate nanoparticles) and a protective hydrophobic layer.…”

Recent Advances in Protective Coatings for Cultural Heritage–An Overview

“…In fact, it has been shown that the weathering can induce the deactivation of its photocatalytic properties because of the formation of intermediate products, which reduce or block the positive action of TiO 2 against fouling accumulation. One proposed solution considers the implementation of three-layered surface treatment, which includes one layer of consolidant, a second hydrophobic layer, and a third self-cleaning layer made of TiO 2 nanoparticles [121]. This structure has been demonstrated as being more resistant to UV ageing and ensures a higher water vapour permeability.…”