Macroestruturas porosas de óxido de grafeno reduzido decoradas com partículas de prata: um estudo teórico-experimental

Abstract

Porous macrostructures based on graphene species have excellent characteristics, such as high porosity, low density, large specific surface area, and excellent mechanical properties, allowing these materials a wide range of applications. These macrostructures can also be decorated with metallic particles that provide new characteristics, such as catalytic activity and better electrochemical performance. To achieve these characteristics as much as possible, it is essential to properly establish the synthesis route for these materials, as the preparation methodology directly influences their structure, properties, and, consequently, their applicability. In this sense, the present work aimed at the one-step synthesis and characterization of porous macrostructures based on graphene and decorated with silver particles, evaluating experimentally and theoretically the effect of synthetic variables, such as quantity and order of addition of reagents, on the structure, properties, and applicability. The macrostructures were obtained from the thermochemical reduction of graphene oxide (GO) in the metal precursor, silver nitrate, and without the cetyltrimethylammonium bromide surfactant (CTBA), and varying the order of addition of the reagents. The materials were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, Xray diffraction (XRD), and thermogravimetric analysis (TGA). Computational studies were performed using molecular dynamics simulations, using Coarse-Grained (CG) models, with the hydrophobic effect represented implicitly. The potential for application as a sensor was evaluated by adding the macrostructures in carbon paste electrodes, and cyclic voltammetry and chronoamperometry were performed to detect furosemide. SEM images showed that the synthesis methodology used provided the formation of well-defined porous macrostructures of reduced graphene oxide (rGO), decorated with silver particles. Variations in the presence or absence of surfactant, the order of the reagent's addition promoted changes in morphology. Also, a massive amount of silver particles on the 3D-rGO, with different shapes (wires, spheres, and cubes) and a wide dispersion of sizes, moldable according to the synthetic variables. These particles are preferentially located on the edges and folds of the rGO sheets, especially in the presence of surfactants during synthesis. Computer simulation studies demonstrate that the preferential formation of silver particles at the edges of graphene sheets is due to the edge's geometric effect. The XRD data indicate the formation of silver particles and possibly silver oxide, where the proportion of each species in the different samples varies according to the synthesis employed. The TGA curves indicate that the most thermally stable materials are synthesized in the absence of CTAB and with higher amounts of silver. Such results suggest that the rGO three-dimensional network provided excellent conditions for the nucleation and silver particles' growth. Simple changes in the synthesis route used for the production of porous GO-based macrostructures, such as quantity and order of addition of reagents, allows you to design materials with desired characteristics and properties, improving their performance in specific applications and can present potentialities for application as an electrochemical sensor, according to the synthesis route used.