A Novel Solid Platform–Based Ag Nanoparticles Chemically Impregnated Activated Carbon for Selective Separation of Tungstate Species in Water: Kinetics and Thermodynamic Study

Abstract

The level of tungstate in freshwater is disturbing due to its toxicity and its impact to human health. Thus, the current study explores the use of Ag nanoparticle (AgNP)-treated activated carbon (AgNPs/ AC) nanocomposite as solid phase extractor (SPE) for removal of trace levels of tungstate ions in water. The AgNPs/AC was synthesized by chemical binding of Ag nanoparticles onto AC. The microstructure image indicated that the AgNPs were uniformly dispersed on AC surface and thus maintaining high surface area. Scanning electron micrographs of AgNPs/AC revealed a three-dimensional structure which is suitable as SPE. The AgNPs/AC nanocomposite was used as a lowcost and effective SPE for tungstate removal from water. Adsorption of tungstate from aqueous media reached maximum at pH ≈ 4 and reached equilibrium in < 20 min. Tungstate sorption followed pseudo-secondorder kinetic with an overall rate constant (k) of 0.72 min. −1 The negative values of ΔH and ΔG are interpreted as exothermic and spontaneous reaction of tungstate sorption by the adsorbent, respectively. The positive value of ΔS (R 2 = 0.999) reflected good absorption and/or adsorption of the oxyanion [WO 4 ] 2− as an ion associate with the bulky cations and the surface area available in the nanocomposite. The sorbent A g N P s / A C w a s a l s o p a c k e d c o l u m n f o r preconcentration of trace levels of tungstate in tap water samples. Tungstate species were satisfactorily recovered with NaOH (1.0 mol L −1 ) and subsequently ICP-OES analyzed.