More
recently, the biological colonization of stone heritage and consequently
its biodeterioration has become the focus of numerous studies. Among
all microorganisms, fungi are considered to be one of the most important
colonizers and biodegraders on stone materials. This is why the development
of new antifungal materials requires immediate action. ZnMgO nanoparticles
(NPs) have several exciting applications in different areas, highlighting
as an efficient antimicrobial agent for medical application. In this
research, the application of Zn-doped MgO (Mg1–x
Zn
x
O, x = 0.096) NPs obtained by sol–gel method as antifungal coatings
on dolomitic and calcitic stones has been explored as a means to develop
effective protective coatings for stone heritage. Moreover, the photocatalytic
and antifungal activity of Mg1–x
Zn
x
O NPs were comparatively studied with
single ZnO and MgO NPs. Thus, compared to the MgO and ZnO nanomaterials,
the Mg1–x
Zn
x
O NPs exhibited an enhanced photocatalytic activity. After
UV irradiation for 60 min, 87% methylene blue was degraded over Zn-doped
MgO NPs, whereas only 58% and 38% of MB was degraded over ZnO and
MgO NPs, respectively. These nanoparticles also displayed a better
antifungal activity than that of single pure MgO or ZnO NPs, inhibiting
the growth of fungi Aspergillus niger, Penicillium
oxalicum, Paraconiothyrium sp., and Pestalotiopsis maculans, which are especially active in
the bioweathering of stone. The improved photocatalytic and antifungal
properties detected in the Mg1–x
Zn
x
O NPs was attributed to the formation
of crystal defects by the incorporation of Zn into MgO. The application
of the MgO- and Zn-doped MgO NPs as protective coatings on calcareous
stones showed important antifungal properties, inhibiting successfully
the epilithic and endolithic colonization of A. niger and P. oxalicum in both lithotypes, and indicating
a greater antifungal effectiveness on Zn-doped MgO NPs. The use of
Zn-doped MgO NPs may thus represent a highly efficient antifungal
protection for calcareous stone heritage.
Climatic changes and the increased air pollution intensify the atmospheric degradation of stone, affecting the aspect and integrity of valuable historical buildings constructed using limestone and located in tropical coastal sites. This paper analyzes limestone degradation process due to air pollution and humidity in tropical humid conditions in historical buildings located in the cities of Havana, Cuba and San Francisco de Campeche, Mexico. Havana shows higher pollution level than San Francisco de Campeche, which presents pollution levels as a consequence of a multipollutant situation along with the presence of airborne salinity. Temperature and humidity data were recorded from the walls of historical buildings in the city of Havana: the Minor Basilica and the convent of San Francisco. Changes in dry/wet cycles due to the absence of direct sun radiation as well as a high level of SO 2 allow the formation of a black crust (mainly composed of gypsum) in the lower part of the surface of the facade of the Basilica Minor in Havana; however, crusts formed in historical buildings located in San Francisco de Campeche City are mainly composed of calcium carbonate, indicating the importance of natural degradation mechanisms mainly due to dissolution in water. In the last case, the influence of water plays an important role in the development of biodegradation, which induces the formation of calcium oxalates. Caves and cracks were found in the walls of military buildings caused by water infiltration. The influence of air contamination, humidity, and construction materials determine the type of degradation that historical buildings undergo.
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