Unique preparation and characterization of graphene nano-materials

Abstract

Graphene and its nano-composites have extraordinary structure and exhibits excellent electrical, optical, mechanical, thermal and adsorptive properties. One of the important applications of the materials is the adsorption of environmental pollutants. Considering their high specific surface area many graphene based nano-materials have been used as removing heavy metal ions and organic pollutants from aqueous solutions. To reduce the concentration in permissible level by adsorption or degradation to less toxic molecules transition metal, metal oxide and their hybrid materials with graphene are in the focusing point of scientific communities. Hence, in our present work, graphene in the form of reduce graphene oxide (rGO) based binary and ternary metal composites in nanoscale have been synthesized by a in situ chemical method. GO was first synthesized from graphite flakes following Hummers method. Whereas the target metal ions were deposited on rGO by a in situ chemical reduction method of GO and metal salts. Sn/rGO, Ag/rGO and Ag+Sn/rGO nanocomposites were synthesized and were subjected to chemical characterization by FTIR, structural characterization by XRD. The surface areas of rGO, Sn/rGO and Ag+Sn/rGO composites were measured by BET analysis. The thermal stability all of those synthesize materials were studied by TGA analysis. The active surface areas rGO and Sn/rGO nanocomposite were measured by adsorption studies using methylene blue (MB) as a model dye. rGO and Sn/rGO nanocomposite were characterized for surface morphology and active surface and kinetics of adsorption by FESEM and adsorption of MB dye respectively. Adsorption of MB was studies in terms of contact time, concentration of MB and pH of the solution. The adsorption equilibrium of rGO and Sn/rGO reached within 5 h for MB concentration of 30-60 mg/L. The sorption was analyzed using pseudo-first-order and pseudo-second order kinetics models and was found to follow a pseudo-second order kinetic model. The extent of the dye adsorption increased with increasing initial dye concentration for Sn/rGO composite but reverses for only rGO. The equilibrium data in aqueous solutions were well represented by the Langmuir isotherm model. An adsorption-desorption study was examined resulting the mechanism of adsorption was reversible and ion-exchange. The adsorption capacity of MB onto Sn/rGO was found to be as high as 215.21 mg/g, which is several folds higher than the adsorption capacity of rGO that was found to be 119.84 mg/g. The active surface areas of crumpled 3-dimensional structure of Sn/rGO nanocomposite appears as a several folds higher than the partial overlapping and coalescing rGO, due to potential adsorption capacity for the adsorption of MB from aqueous solution. After MB adsorption, the possible change of the surface morphology and functionality and elemental composition of adsorbent was observed and examined by the FTIR technique, EDX data analysis and FESEM image.