Comparative study of tea varieties for green synthesis of tellurium-based nanoparticles

Green chemistry approach for synthesizing nanoparticles using tea extracts has gained considerable attention due to its simplicity, cost-effective and the usage of environmentally friendly reagents. However, differences on the amount of phenolic compounds and caffeine depending on tea varieties could lead to nanoparticles with different morphology, structure or composition. Therefore, in the present study, black, decaffeinated black, green, decaffeinated green, oolong, pu-erh and yellow tea have been evaluated for the synthesis of tellurium-based nanoparticles (TeNPs) as a feasible and green alternative to overcoming the main limitations of traditional approaches for nanomaterial producing. In order to establish correlation between tea varieties and the feature of the resulting TeNPs, total polyphenol and flavonoid content, antioxidant activities and individual phenolic chromatographic profile of tea varieties were firstly determined by employing spectrophotometric and chromatographic methods. Regarding to TeNPs synthesis procedure, polyphenol standard solutions first and then water infusions from tea varieties were tested as reagents for performing the synthesis. Other parameters such as polyphenol or tea amount, addition of stabilizing agents or reaction time were also evaluated. The resulting nanoparticles were characterized in terms of morphology, structure and composition by Transmission Electron Microscopy (TEM), X-Ray Powder Diffraction (XRPD), Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) and UV–Vis spectroscopy. The developed methodology allowed us the production of Te and TeO2 nanoparticles of spherical morphology and different diameter sizes (10–100 nm). However, TeNPs were not obtained using decaffeinated green tea, suggesting an important effect of both the tea variety and caffeine content. Moreover, principal component analysis (PCA) was applied to elucidate patterns and differences among tea infusions which enabled to explain some features of the nanoparticles produced. Finally, TeNPs also showed antioxidative properties thorough the DPPH• free radical scavenging assay preserving the antioxidant capacity attributed to the different varieties of tea considered.