A New and Original Method to Produce Ca(OH)2 Nanoparticles by Using an Anion Exchange Resin

Ca(OH)2 nanoparticles in hydro-alcoholic dispersion (nanolime) were successfully employed in Cultural Heritage conservation, thanks to the ability to overcome the limiting aspects of traditional lime treatments. Nanolime were currently produced by chemical precipitation process, at high temperature, with long times of synthesis, and after several purification steps to remove undesired secondary phases. In this paper, an innovative, simple and original method for nanolime production was described. The method was based on an ion exchange process between an anionic resin and a calcium chloride aqueous solution, operating at room temperature. A pure Ca(OH)2 nanoparticles suspension can be rapidly obtained after separating the resin from suspension, and any purification step was necessary. The exhausted resins can be regenerated and reused for a cyclic nanolime production. Structural and morphological features of the produced nanolime were preliminarily characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Moreover, XRD measurements allowed estimating nanoparticles reactivity by following their carbonatation process in air, in relation to different water/alcohol ratios and medium or high relative humidity conditions. The produced Ca(OH)2 nanoparticles appeared hexagonally plated, with dimension less than 100 nm and, compared with those obtained by typical wet precipitation method, they proved to be more reactive.