The aim of this work was to synthesize silver nanoparticles (NPs) through a green synthesis method using starch as a capping agent. The influence of the glucose content, temperature, and pH on the size of the NPs was evaluated by means of a response surface methodology. The obtained nanomaterials were characterized by UV-Vis spectroscopy, XRD, and TEM, and the crystalline structure of the silver was determined by XRD. The optimum synthesis time was after 3 h of reaction time the colloidal solution, did not show any further significant variation in the optical absorption peak (l max ). Response surface results indicate that the reducing agent (glucose) concentration was the most important factor influencing the NPs size, which ranged from 2 to 24 nm. TEM images show that NPs had predominantly spherical shapes, but also polyhedral shapes were present in smaller quantities. Analysis of Raman spectra infers that the glucose initially reduces silver ions to elemental silver. Then the starch undergoes hydrolysis providing primary hydroxyl that contributes to the reduction of silver. The carboxyl and hydroxyl groups of glucose and hydrolyzed starch stabilize the silver NPs by passivating their surface, so that they do not aggregate and remain uniformly distributed.
The glass transition temperature (T g ) and melting temperature (T m ) of gelatin-starch films were determined using differential scanning calorimetry. Also, the microstructure was observed using scanning electron microscopy (SEM) and the crystalline structure by means of X-ray diffraction (XRD). The effect of starch and glycerol concentrations in films on the thermal properties was evaluated through response surface methodology (RSM). The highest values of T m were obtained at starch concentration intervals of (0.26 to 0.54) %w/w and glycerol concentrations lower than 0.5 (%w/w). On the other hand, the T g values diminished as the glycerol concentration increased. Mathematical models for both transitions were fitted to the experimental data. The micrographs obtained by SEM show the influence of glycerol in the microstructure of the films, being more "gummy" as the content of the plasticizer increased. The XRD patterns of the films demonstrate the existence of some pseudo-crystalline regions in the biodegradable materials.
Green chemistry and a central composite design, to evaluate the effect of reducing agent, temperature and pH of the reaction, were employed to produce controlled cuprous oxide (Cu2O) nanoparticles. Response surface method of the ultraviolet-visible spectroscopy is allowed to determine the most relevant factors for the size distribution of the nanoCu2O. X-ray diffraction reflections correspond to a cubic structure, with sizes from 31.9 to 104.3 nm. High-resolution transmission electron microscopy reveals that the different shapes depend strongly on the conditions of the green synthesis.
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