Adsorption kinetics, isotherm and thermodynamics studies for the removal of cationic dyes from environmental wastewater by reduced graphene oxide adsorbent synthesized via greener way

Abstract

Synthetic dyes emerging from wastewater effluents result in a hazardous environment to our society, hence removal of these dye molecules from the water bodies is necessary due to their toxic nature for living beings. In our study, a straightforward one pot synthetic process is conducted to synthesize reduced graphene oxide (RGO) using Averrhoa carambola fruit extract. To confirm the formation of RGO, different characterization techniques such as Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and X-Ray Diffraction (XRD) are investigated. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to understand the morphology of RGO. Adsorption kinetics for pseudo-first order and pseudo-second order has been carried out for both dyes. Freundlich and Langmuir adsorption isotherm models were confirmed to describe each of the adsorption ability responses with high correlation coefficients. Maximum adsorption capacities of methylene blue (MB) and crystal violet (CV) on RGO were 52.308 mg g−1 and 31.466 mg g−1 respectively. The adsorption ability of this adsorbent is monitored by recyclability in five subsequent cycles and it is observed that up to 5 cycles, there is no significant decrease in adsorption capability. The present study showed that RGO is highly efficient in removing MB and CV dyes from environmental water bodies. The thermodynamics study for the adsorption phenomena of MB and CV dyes on RGO sheet has been investigated.