Adsorption of Pb(II) ion by pyromellitic dianhydride-modified polyvinylamine under programmed-temperature

Pyromellitic dianhydride-modified polyvinylamine gel (PAPVAM) as absorbent for Pb(II) ion was prepared. Pyromellitic dianhydride acted as cross-linking agent for polyvinylamine and chelating agent for Pb(II) ion. The structure of PAPVAM was confirmed by Fourier transform infrared spectroscopy and solid-state 13 C nuclear magnetic resonance. Plenty of pores existed in freeze-drying PAPVAM. The energy-dispersive X-ray mapping and X-ray photoelectron spectroscopy of PAPVAM with Pb(II) showed that Pb(II) was complexed with amino groups and carboxylic groups in PAPVAM. The adsorption of Pb(II) by PAPVAM was consistent with the pseudo-second-order kinetic model. The differential scanning calorimetry showed that the adsorption of Pb(II) by PAPVAM was an exothermal process. The adsorption process was also fitted with the Freundlich isotherm equation. Pb(II) penetrated into PAPVAM. Programmed-temperature was designed to improve the adsorption capacity of Pb(II). More precisely, Pb(II) was absorbed by PAPVAM at 50 °C for 2 h and then at 30 °C for 2 h. The adsorption of Pb(II) at 50 °C contributed to its penetration into PAPVAM gel, and its adsorption at 30 °C contributed to the improvement of the adsorption capacity in thermodynamics. Finally, the adsorption capacity of Pb(II) by PAPVAM was 140.42 mg g −1 under programmed-temperature above mentioned.