Synthesis and Characterization of a Calcium Oxalate-Silica Nanocomposite for Stone Conservation

Abstract

A novel biomimetic nanocomposite, comprised of amorphous silica and calcium oxalate, has been efficiently synthesized by incorporating materials of low toxicity and cost, imitating a stable binary system occurring in well-preserved areas of monuments, plant biomineralization 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; the latter, mixed with tetraethoxysilane produced a crack-free mesoporous xerogel with pore radius of approximately 15 nm. FTIR, XRD, DTA-TG and SEM studies demonstrated that the nano-calcium oxalate was embedded into the silica matrix resulting in a crack free nanocomposite, which was deeply penetrated and homogeneously distributed within the treated porous medium. The hygric properties and the tensile strength of treated samples were improved, without affecting the microstructural characteristics. The physico-chemical stability and compatibility of the nanocomposite with stone create a potential strengthening and protective agent for inorganic porous materials.