SnO2 quantum dots decorated reduced graphene oxide nanocomposites for efficient water remediation

An adsorbent, SnO2 quantum dots (QDs) decorated reduced graphene oxide (RGO) nanocomposite, is used for removal of different organic dyes (methylene blue (MB), methyl orange (MO) and rhodamine B (RhB)), toxic metal ions (Co2+, Ni2+, Cu2+, Cd2+, Cr3+, Pb2+, Hg2+ and As3+), and pathogenic bacteria (Escherichia coli) from wastewater. It exhibits good removal capacity and fast adsorption rate for cationic dye MB. In binary solution the nanocomposite registered an excellent separation efficiency of 94% for MB/MO mixtures, whereas the same is 76% for MB/RhB mixture. The effect on removal process by different influencing parameters such as dosage of adsorbent (0.1-0.6 g/L), initial solution pH (3-11), initial dye concentration (10-50 ppm), contact time (0-60 min) and temperature (303-333 K) is investigated in order to find the optimum adsorption conditions. Adsorption isotherm data are extensively investigated using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms; it is found to fit well in Freundlich model. Adsorption kinetics is described by pseudo-second order kinetics. Thermodynamic study suggested that the MB adsorption on QDs-RGO is a spontaneous and exothermic process. QDs-RGO also shows good removal efficiency for lead (II) from individual as well as mixed solution. Adsorption kinetics and isotherm data are extensively investigated for adsorption of lead (II) and found to be better described by pseudo-second order kinetics and Freundlich model. Furthermore, QDs-RGO showed higher antibacterial activity towards E. coli than the individual constitute materials. It is essentially established from the results that QDs-RGO is an ideal aspirant for removal of positively charged organic dyes, toxic heavy metal ions and bacteria pathogen from wastewater. (C) 2016 Elsevier B.V. All rights reserved.