A biomimetic approach to strengthen and protect construction materials with a novel calcium-oxalate–silica nanocomposite

• Nano-calcium oxalate monohydrate colloidal solution was synthesised in alcohol (CaOx).
• Incorporation of CaOx in TEOS yields a crack-free, stable nanocomposite (SilOxal).
• Mesoporous microstructure of SilOxal has physico-chemical compatibility with stone.
• SilOxal does not alter the microstructure of the treated stone.
• SilOxal improves the hygric properties and the tensile strength of stone.

A novel biomimetic nanocomposite composed of amorphous silica and calcium oxalate has been efficiently synthesised by incorporating materials of low toxicity and cost, imitating a stable binary system occurring in well-preserved areas of monuments, plant biomineralisation and the industrial processing of sugar. A simple two-step and cost-effective reaction route involving calcium hydroxide and oxalic acid dihydrate in isopropanol as precursors yielded a colloidal solution of nano-calcium oxalate; this solution was mixed with tetraethoxysilane to produce a crack-free mesoporous xerogel with pore radius of approximately 15 nm. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential thermal-thermogravimetric analysis (DTA-TG) and scanning electron microscopy (SEM) studies demonstrated that the nano-calcium oxalate embodiment into the silica matrix resulted in a crack-free nanocomposite. This nanocomposite penetrated deeply and was distributed homogeneously within the treated porous medium. The hygric properties and tensile strength of treated samples were improved without affecting the microstructural characteristics. The colour and water vapour permeability changes were ranged within acceptable limits. The physico-chemical stability and compatibility of the nanocomposite with stone created a potential strengthening agent with a partial protective effect for inorganic porous building materials.

Figure optionsDownload as PowerPoint slide