Utilization of Surfactant Encapsulated Keggin Polyanion Based Nanoparticles for Removal of Cr(VI) from Aqueous Medium: Adsorption Isotherms, Kinetics and Regeneration Studies

Surfactant encapsulated Keggin polyanion (SEK) based nanoparticles (NPs) were synthesized under ambient conditions upon mixing aqueous acidic solution of molybdate precursor with cationic surfactant. The resultant reaction mixture when left undisturbed for a definite period of time (aging) resulted in the formation of SEK NPs. Further, the influence of reaction parameters viz. aging period and nature of surfactant in the formation of SEK based solids and their effect in the removal of Cr(VI) ions from water was investigated. The chromium removal efficiency could be increased from 80.3% to 98.2% upon replacing aromatic with aliphatic cationic surfactant during the synthesis of SEK NPs. Similarly, aging period had a significant influence on Cr(VI) removal efficiency. Elimination of Cr(VI) could be enhanced from 33.8% (without aging), 75.7% (24 h aging) to 98.2% (48 h aging). Based on the results obtained, a plausible mechanism for the adsorption of Cr(VI) ions onto the surface of SEK NPs was envisaged. The adsorption process followed Langmuir adsorption isotherm and pseudo first order kinetics model. Under optimized conditions, 98.2% Cr(VI) removal efficiency was obtained in 60 min. Moreover, Cr(VI) loaded NPs could be regenerated and used up to 13 cycles.