Biossíntese e caracterização de nanopartículas de óxido de cobre (CuO) e óxido de zinco (ZnO) mediada por extratos foliares de Eucalyptus sp

Abstract

The Eucalyptus genus is widely distributed throughout Brazil, corresponding to approximately 70% of the area of planted forests. This is due to questions of adaptation to the climate and the quality of wood from species of this genus. However, several parts that make up these trees, such as leafs, have restricted uses, dificulting to use them, except for the species that allow the extraction of essential oils. Therefore, the objective of this study was to obtain the highest yield of phenolic compounds through the aqueous extraction of Eucalyptus dunnii Maiden and Eucalyptus grandis Hill leafs and then to use these extracts for the biosynthesis of copper oxide (CuO) and oxide zinc (ZnO) nanoparticles (NPs). The best phenolic extraction parameters obtained through Rotational Central Compound Design (RCCD) were 80 ºC and 75 min for E. dunnii and 72.7 ºC and 45 min for E. grandis. Two methods of synthesis were used to obtain the NPs. In Method I in which the synthesis occurred at room temperature for 24 h the particles were only dried at 100 ° C, where were not obtained X-ray diffraction peaks, having thus behavior of amorphous material for the two oxides. Verified this, was carried out thermal treatment in a muffle furnace at 700 ºC for CuO and 500 ºC for ZnO, which presented crystallinity and particle diameters of 19.88 and 26.47 nm respectively. In Method II, which was used higher concentration of precursor salt, temperature of 80 ºC for 20 min with vigorous magnetic agitation and later burning at 500 ºC, the NPs presented behavior of crystalline materials. The diameters were 24.72 and 25.28 nm for CuO synthesized with E. dunnii and E. grandis, respectively, and 32.24 nm for ZnO synthesized with E. dunnii. Through Fourier Transform Infrared Spectroscopy (FTIR) analyzes it was determined that the possible compounds involved in the synthesis and stabilization of NPs are phenolic, carboxylic acids, alcohols and proteins. The nanoparticles synthesized by Method II with E. dunnii extract were tested against the xylophagous fungi of the white rot Trametes versicolor and Phanerochaete chrysosporium. The CuO NPs inhibited between 98-100% of P. chrysosporium fungus growth at all concentrations tested, however the T. versicolor showed some resistance to the NPs in which the highest concentration inhibited 72.7% and the lowest concentration only 10.87%. The ZnO NPs inhibited 100% P. chrysosporium in all concentrations, in addition to being more efficient against the T. versicolor, inhibiting between 81 and 93% its growth. Thus, it is concluded that the nanoparticles of oxides biosynthesized through Eucalyptus leafs phenolic extracts are efficient antifungal agents, may be used in the future on preservation of wood.