Fungal growth in damp surfaces of water-damaged buildings is an increasing problem around the world, which has adverse effects on both people's health and buildings. By bio-deterioration, fungi can growth in indoor environments and generate materials losses in addition to health problems. Therefore, antifungal coatings must be developed to avoid these problems. Silica is used as supporting additive in coatings, such as the waterborne paints and, on the other hand, the addition of Ag nanoparticles into different materials is being widely studied for its effective antimicrobial properties. The aim of this work was to evaluate the bio-resistance to fungal growth on waterborne coatings containing siliceous additives, by accelerated four-week agar plate assay. The additives were synthesized by the sol-gel method and characterized by potentiometric titration and transmission electron microscopy (TEM). In addition, the paints were observed by scanning electron microscopy (SEM) at the end of the test. To carry out the bioresistance assay, Chaetomium globosum and Alternaria alternata fungi were used. After 4 weeks of assay, paints prepared with the silver-additives were the most efficient inhibiting the growth of both fungi. These paints, after their exposure for 6 months, in an internal environment with sunlight incidence, kept the antifungal activity against Chaetomium globosum and showed a higher activity against Alternaria alternata.
Zirconia is a widely used multifunctional material. Its interesting properties, such as high chemical resistance, thermal stability and high mechanical toughness, have turned this material into object of study within fields such as optics, electronics, and magnetism, among others. In recent years, the chemical properties of zirconium oxide have been used, mixed with silicon, in order to obtain more stable and robust mixed oxides, with the final application of toughening ceramics. These properties are related to the degree of mixing of the components at molecular level, therefore, the linking between Si-O-Zr. Considering the effective antimicrobial capacity of silver nanoparticles, their incorporation into different materials is very interesting, acting as biocides. The objective of this work is to obtain zirconium oxides by the sol-gel technique, using zirconium n-propoxide as precursor, and also to study the effect of different solvents (water, ethanol) and the use of various acid catalysts in the synthesis [acetic acid and a heteropolyacid (HPA), as the phosphomolybdic acid (H 3 PMo 12 O 40 )] on the physicochemical properties of the obtained solids. Finally, the addition of a silver salt was carried out into the sample with acetic acid and heteropolyacid as catalyst, in order to incorporate it as antimicrobial filler in paints. The obtained materials were characterized by SEM, XRD, FT-IR, textural properties through the absorption of N 2 (S BET ) and potentiometric titration with n-butylamine. Homogeneous solids were obtained in all the synthesis with acetic acid as catalysts. In addition, x-ray diffraction diagrams of amorphous solids were observed. The values obtained of surface areas are influenced by the variables of synthesis. The characteristic bands of zirconia were observed by FTIR in the solids synthesized. The results show that the solids environmentally synthesized are promising additives for use in paints.
A B S T R A C TThe addition of silver (Ag) into the chemical synthesis of materials, transform them into materials technologically relevant to be used as antimicrobial additives. In this work, the sol-gel method was used to obtain materials based on silica and zirconia, with the inclusion of Ag. The solids were characterized by potentiometric titration, specific surface area (S BET ), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and, the antifungal activity of the additives was assessed by agar plate inhibition against Chaetomium globosum and Alternaria alternata. In addition, the resistance to fungal growth on waterborne coatings was evaluated after the incorporation of the solids into paint formulation.Amorphous materials with different acidic and textural properties were obtained. Most of the tested solids showed antifungal activity at the highest concentration used, and the presence of Ag increased the percentage of inhibition. The mixed oxides Ag-additives improved the antifungal activity compare with the pure Ag-oxides (silica or zirconia). In this sense, a synergic effect between zirconia/silica and silver would be a promising result that would reduce the amount of silver in these bioactive materials. This work was performed as a preliminary study, in order to guide the selection of a suitable additive from a list of possible antifungal agents.
Recebido em 25/10/11; aceito em 18/6/12; publicado na web em 28/9/12The objective of this work was to synthesize nanosilicas with different degree of hydrophobicity by the sol-gel method, using tetraethyl orthosilicate as a precursor. For this purpose, 3-aminopropyl triethoxysilane (APS) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS), were added during synthesis as modifiers. A commercial biopolymer (Hexamoll Dinch, BASF) intended for packaging of apples, was added to the new nanosilicas. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, potentiometric titration, porosity, specific surface area and hydrophobicity/ hydrophilicity by wetting test. Colorimetry was used to evaluate change in apple pulp color after contact with the different silicas.
Antimicrobial coatings are used to avoid the proliferation of fungi and bacteria inside urban buildings by incorporating low concentrations of antimicrobial agents (biocides). This study is focused on evaluating the antifungal activity of copper (II) supported on a silica matrix, and as counter-cation of a heteropolyacid, obtained from the sol-gel method using various catalysts, against two fungal isolates. The fungi used in this evaluation were Alternaria alternata and Chaetomium globosum isolated by routine microbiological techniques from biodeteriorated paints films. In all cases, fungi were selected due to their ability to grow on the paint films and their negative impact on human health. First, silicas were prepared using tetraethylorthosilicate and methyl trimethoxysilane as precursors and acetic acid, hydrochloric acid as catalysts of the hydrolysis reaction of the alkoxide. The effect of addition of copper (II) in the form of copper nitrate was studied. With respect to the morphology of the silica, most of them are similar, between pure and modified silica, in all cases. Once the stage of the synthesis and characterization of the prepared materials was performed, six of them were selected to evaluate their antifungal activity by agar plate inhibition test against both fungi of interest (A. alternata and C. globosum), and the percent inhibition was determined in each case. Tested Cu-based solids were shown to have a higher antifungal activity because they completely inhibit the growth of both fungi with lower concentrations relative to its control. This work was performed as a preliminary study, in order to guide the selection of a suitable organic biocide from a list of possible antifungal agents. Graphical Abstract
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