Antifungal wall coating based on Ca(OH) ₂ mixed with MgO and TIO ₂ nanoparticles

Abstract

Slaked lime (mainly composed of calcium hydroxide) is a commonly used building material applied on wall surfaces. This lime layer can be subjected to bio-deterioration due to the colonisation of different micro-organisms, with fungi being the main one. In this work, TiO₂ and MgO nanoparticles with sizes of 60 nm and 40 nm, respectively, were prepared using a hydrothermal method. They were mixed with Ca(OH)₂ particles in different proportions to form a series of suspensions. Powder X-ray diffraction analysis showed that MgO nanoparticles existed in the cubic phase while TiO₂ nanoparticles belonged to the anatase phase. The antifungal activities of these suspensions were tested in two different methods against Aspergillus niger, isolated from deteriorated wall surfaces. First, a preliminary assay was conducted by incorporating the nanoparticles mixture in the Potato Dextrose Agar medium with a fungal inoculum. In the second method, the suspensions were coated on glass Petri dishes. Then an inoculum of A. niger was introduced to the surface of this coating. Fungal growth on the coatings was observed under a natural photoperiod cycle and relative humidity of 80%. The study revealed that the Ca(OH)₂-MgO, Ca(OH)₂-TiO₂ and Ca(OH)₂-MgO-TiO₂ systems inhibited the germination and mycelial growth of A. niger. In contrast, the pure Ca(OH)2 system was readily colonised. However, pure MgO based coatings showed the highest antifungal activity, and pure TiO2 based coatings showed the lowest. MgO-TiO₂ mixtures exhibited an intermediate performance that gradually increased with the percentage (w/w) of MgO added. These nanoparticles can be used in pure or mixed form with Ca(OH)₂ to prepare an antifungal coating.