Design of an efficient and selective adsorbent of cationic dye through activated carbon - graphene oxide nanocomposite: Study on mechanism and synergy

Highlights: • Composite used as adsorbent involving graphene oxide (GO) and activated charcoal (AC). • Adsorption takes place through both the surface pores of AC and by electrostatic attraction from functional groups of GO. • Synergistic effects cause an increase in the adsorption capacity to 1000 mg/gm as compared to 180 mg/gm for AC. • Can adsorb cationic pollutants from a mixture of different components (neutral, anionic) and acts as a selective adsorbent. A nanocomposite of activated carbon (AC) and graphene oxide (GO) has been used as adsorbent of methylene blue (MB) dye from solution. FTIR spectroscopy, XRD, SEM imaging, size and zeta potential analysis of the nanocomposite material indicate retention of the essential features of both the components responsible for adsorption. Parameters like pH, temperature, adsorbent and salt concentrations, etc. were varied to optimize the adsorption. A very significant increase in adsorption by this nanocomposite, compared to those arising from the individual components, could be observed, resulting in an adsorption capacity of up to 1000 mg/gm. Fit of the data to kinetic equations gave rate constants for the process. Good fits to both Langmuir and Freundlisch isotherms indicated that the contribution of electrostatic attraction between the charged groups present in the composite and dye molecules, as well as the adsorption through AC surface pores both play significant roles. The synergy of these two different mechanisms yields the extraordinarily large adsorption capacity. This factor, together with the cheapness of the material, and its selectivity towards cationic dyes suggest its practical importance for water decontamination.