Resumo

PENA, L. et al. Absorbancia y reflectancia de hojas de Ficus contaminadas con nanopartículas de plata. Rev. mex. fis. [online]. 2019, vol.65, n.1, pp.95-105.  Epub 09-Nov-2019. ISSN 0035-001X.

In this document, it is reported the preparation of spherical silver nanoparticles dispersed in water with bimodal size distribution (average diameter of 1.8 and 44 nm), which are deposited on the surface of Ficus benjamina leaves by the immersion method. The effect of nanoparticles on absorbance and reflectance on the adaxial surface of the leaves is investigated with regards to the leaves without contamination, in the region from 200 to 2000 nm. The absorbance of the contaminated leaf decreased with respect to the absorbance of the control leaf in the UV region, where absorptions of peptides, quinines and flavonoids predominate. The absorbance related to photosynthetic pigments was practically constant in the visible region (<700 nm). In the region from 730 to 780 nm, a small increase in óptical absorption appears related to a weak browning of the stressed leaf. For near-infrared wavelengths, óptical absorptions due to water (maximum at 970, 1194, 1458 and 1940) were increased, suggesting an infiltration process of this molecule in the internal structure of the leaf. On the other hand, the leaves reflect very little light in the UV-Vis region because their pigments absorb light in this region. A weak decrease in reflectance in green (554 nm) comes from polyphenols oxidation. The damage caused to the leaves by the induced stress was confirmed by an evident decrease of the reflectance for wavelengths in the near-infrared between 730 and 820 nm. While in the range from 840 to 1070 nm, the reflectance reached values as high as 96% in the contaminated leaf. The low reflectance observed in the region from 1190 to 2000 nm was related with the absorption of radiation by water. Additionally, damage on the surface of contaminated leaves and with water deficit was showed by using infrared spectroscopy. Regarding the morphology of the silver nanoparticles, it was observed that these tend to form aggregates on the adaxial surface of the Ficus leaf. The proposed methodology could explain how the nanoparticulate material existing in the atmospheric or terrestrial environment, is deposited on the leaves of the plants and could infer the effects of nanoparticles-stress on the transpiration processes, thermal balance and photosynthesis.

Palavras-chave : Optical properties; Ficus leaves; nanoparticulate material; aggregated shapes; 78.40.-q; 78.68.+m.