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.
