Synthesis and metal ion uptake studies of chelating polyurethane resin containing donor atoms: Experimental optimization and temperature studies

Novel polyurethane (PU) bearing metal binding sites was synthesized by poly-condensation. Synthesized polyurethane was characterized by using Fourier transformation IR spectrometry (FTIR), nuclear magnetic resonance (H-1-NMR), and thermo-gravimetric analysis (TGA) techniques. The structural morphology of polyurethane was analyzed with scanning electron microscopy (SEM) and the polymer was used as an adsorbent for metal extraction using batch adsorption studies in aqueous media. Upon observation, it was found that maximum adsorption was obtained at pH = 6 with the adsorbent dose of 20 mg/L at 60 min of contact time for 100 mg/L of Pb(II) and Cu(II) as initial metal ion concentration. In comparison with 2-parameter and 3-parameter non-linear isotherm modelling, Redlich-Peterson adsorption model (3-P) fits well supporting Langmuir (2-P) compared with other sorption isotherms. From the Langmuir isotherm, maximum monolayer adsorption capacity of 496 mg/g and 481.8 mg/g for Pb(II) and Cu(II) ions were obtained, respectively. From the pseudo-second order equation, the R-2 values of Pb(II) and Cu(II) were found to be 0.9984 and 0.9958. Based on tan, the exothermic nature of adsorption is evidenced. PU was found to be stable after 5 cycles with 0.1 N H2SO4, suggesting that the synthesized polyurethane resin was chemically stable and could act as a potential adsorbent for heavy metal extractions in the aqueous media.