Photocatalytic and antifungal activity of CaZn2(OH)6•2H2O mixed with Ca(OH)2 for its application in cultural heritage

Abstract

The antifungal and photocatalytic activity of mixed compounds of double hydroxide [CaZn2(OH)6•2H2O] with portlandite [Ca(OH)2] synthesized via sol-gel were evaluated. The compound was tested by in vitro assay to determine its antifungal activity using the agar diffusion and broth microdilution assays, applied to the fungal models: Aspergillus niger and Penicillium oxalicum. Also, these compounds were characterized by X-ray diffraction, infrared spectroscopy, dynamic light scattering, and its morphological structure was identified by HR-SEM and TEM-SAED which shows agglomerated particles formed by nanoparticle sizes between 100−500 nm, which are correlated whit hydrodynamic radio around 155 nm. Additionally, in the relation of microbiological assays, the outstanding minimum inhibitory concentration of unmixed calcium zincate hydroxide dihydrate (CZ) correspond to 156 μg/mL, however, when is mixed with 10 % of Ca(OH)2 diminishes up to 78 μg/mL, indistinctively of the evaluated fungus. Likewise, a photocatalytic degradation test was carried out with methylene blue dye as a model organic pollutant, reaching an efficiency of ∼92 %. Our results suggest that low concentrations of Ca(OH)2 improve the antifungal activity of CZ, without altering the solution stability, the photocatalytic and chemical properties of the compounds. Therefore, the compatibility with the limestone of both materials can be proposed as an excellent product to avoid fungal biodeterioration.