High capacity removal of silver(I) and lead(II) ions by modified polyacrylonitrile from aqueous solutions

Abstract

Different polymeric materials carrying synthetic adsorbents have been reported in literature for heavy metal removal. We have developed a simple method for functionalizing of polyacrylonitrile (PAN) with two volume percent (50 and 100) of triethylenetetramine (PAN–TETA 50 and 100). For the first time, PAN–TETA was used as an absorbent of silver and lead ions from aqueous solutions. PAN–TETA and their metal complexes have been studied by FT-IR and scanning electron microscope. The analysis method confirmed the presence of metal in PAN–TETA complexes. The prepared functionalized PAN were applied to remove heavy metal ions, such as Pb(II) and Ag(I) from aqueous solutions. The optimization of experimental conditions and parameters including initial pH, contact time, adsorbent dose, initial metal and ions concentration, and temperature for the removal of heavy metals were investigated. The adsorption increased with increasing metal ions concentration, initial pH, and temperature. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were considered to evaluate the rate parameters. The adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.997. Attempts were made to fit the isothermal data using Langmuir, Freundlich, and Temkin equations. The maximum sorption capacity of 108.14 mg g⁻¹ and 99.01 mg g⁻¹ for silver and lead ions were achieved at pH = 6, respectively. The values of thermodynamic parameters of ΔG°, ΔH,° and ΔS° indicated that the adsorption process was spontaneous and endothermic. The selectivity of two PAN–TETA for the adsorption of Ag(I) and Pb(II) were studied. The competitive adsorption tests verified that these functionalized polymers have good adsorption selectivity for Ag(I) with the coexistence of two ions. Desorption of the metal ions from PAN–TETA was studied in 0.5 M HCl and very high desorption rates, greater than 91%, were achieved in all cases. Based on adsorption/desorption data, PAN–TETA is a promising adsorbent for heavy metals removal from the aqueous medium.

Keywords:

• Polyacrylonitrile
• Triethylenetetramine
• Adsorption
• Kinetic model
• Thermodynamic parameter
• Heavy metal ions